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• Robustness of floor system of steel modular structure is studied. • Three module-removal scenarios are considered. • Comparisons of the frame structure and modular structure are made. • The effects of connection, beam, and slab are studied. This paper numerically investigates the collapse performance of the floor system in a steel modular structure. The study includes the analysis of the load-deformation relationship and internal force evolution of the floor system under four interior module loss, two edge module loss, and one corner module loss. The collapse resistance of the floor system in the modular structure is compared with that of the frame structure. Additionally, the study investigates the effects of critical variables such as the axial resistance of horizontal connections, floor slab thickness, and module beam dimensions on the collapse performance of the modular structure. The findings reveal that the floor system demonstrates the highest robustness in four interior module loss, while its weakest performance is observed in the scenario of one corner module removal. The final displacement of the floor system in two edge module loss and one corner module loss is 1.4 times and 2.5 times respectively, compared to that of the four interior module loss scenario. Moreover, when the material consumptions of the modular structure and frame structure are the same, the robustness of the floor system in the steel modular structure is significantly lower than that of the steel frame structure. It should be noted that under certain circumstances, increasing the axial resistance of the horizontal connections may not have a remarkable impact on the robustness of the floor system in the modular structure. In situations of two edge module losses, reducing the slab thickness and beam depth leads to an increase in the axial force in the horizontal connections of the floor system. [ABSTRACT FROM AUTHOR]

• The integration of central synthetic jet shows the overall heat transfer enhancement. • A significant heat transfer augment occurs at the central zone of array-jet unit. • The spatially-averaged Nusselt number had increased by 100% at H / d ≥ 6 under Re =3000. • The Nusselt number presents a monotonous increasing trend along with the impinging distance. • At Re> 10,000, the case of X / d = Y / d = 6 behaves the benefit of the central synthetic jet integration. An experimental investigation is performed to illustrate the heat transfer characteristics for a specific hybrid-jet impingement configuration that is comprised of a square-layout continuous-jet array and a center-positioned loudspeaker-driven synthetic-jet actuator. Herein four continuous-jet Reynolds numbers (ranging from Re =3000 to Re =10,000), three hole-to-hole pitches (X / d = Y / d = 4. 5 and 6), and a series of impinging distances (H / d = 2–10) are considered while the central synthetic jet is operated at f = 250 Hz with a characteristic Reynolds number of about Re 0 =4500. It is identified that the integration of central synthetic jet in the array-jet unit is indeed an effective means to enhance the overall heat transfer performance, which is more suitable for the practical applications wherein the synthetic jet Reynolds number is greater than or equivalent to the array-jet Reynolds number. By the integration of central synthetic jet, a significant localized heat transfer augment is achieved at the central zone of array-jet unit, especially under small and moderate array-jet Reynolds numbers. In terms of the spatially-averaged Nusselt number, an increase of more than 100% could be achieved by the central synthetic jet integration at H / d ≥ 6 under Re =3000. The benefit of the central synthetic jet integration is also clearly demonstrated under Re =5000, wherein the spatially-averaged Nusselt number could be increased by 30%-60%, taking a monotonous increasing trend along with the impinging distance generally. Under Re =7000, a relative increase among 10%-30% still remains. When the array-jet Reynolds number is increased up to 10,000, only in the sparse continuous-jet array (X / d = Y / d = 6) the benefit of the central synthetic jet integration could behave, with a limited relative increase of less than 20%. [ABSTRACT FROM AUTHOR]

Steel frames with concrete floor systems have been widely used in buildings due to their high constructional efficiency and excellent seismic performance. Currently, limited analytical studies focused on the effect of boundary conditions on collapse mechanisms of steel frames with concrete slabs. This article presents a revised energy-based method to determine the collapse resistance of steel frames with concrete slabs due to a penultimate-side column loss. The detailed models of main structural members are taken into account, including reinforced concrete slabs, steel beams, and steel columns. The reasonability and reliability of the analytical method are verified against validated numerical analyses using various slab aspect ratios, slab thicknesses, rebar ratios, beam section heights, and column heights. It is found that the analytical method can be used to accurately predict the collapse resistance of steel frames due to a penultimate-side column loss with errors less than 10%. A comparison of collapse resistance of substructures subjected to penultimate-side and intermediate-side column loss shows that boundary conditions have limited effects on the plastic bearing capacity of substructures. However, the ultimate bearing capacity of substructures due to a penultimate-side column loss decreases by about 20% due to the insufficient development of tensile catenary action in steel beams. [ABSTRACT FROM AUTHOR]

A series of experimental tests are performed for the pulsating jet impingement heat transfer by varying the Reynolds number (5000 ≤ Re ≤ 15000), operation frequency (5 Hz ≤ f ≤ 40 Hz) and dimensionless nozzle-to-surface distance (2 ≤ H/d ≤ 10) while fixing the duty cycle as DC = 0.5. The maximum uncertainty in the measurement of Nusselt number is estimated to be about ±7%. Meanwhile, numerical simulations are performed to demonstrate the instantaneous flow field of the pulsating jet impingement. Particular attention is paid to examine the influence of transmission chamber on the pulsating jet impingement heat transfer. The results show that by using an additional transmission chamber, the pulsating jet impingement heat transfer is enhanced. For example, the circumferentially-averaged Nusselt number around the stagnation point (x/d ≤ 2) is increased up 8%~16% by the adding of a transmission chamber in related to the baseline case under Re = 10000 and H/d = 6. Due to the presence of transmission chamber, the exiting jet velocity profile at the orifice outlet is varied. In related to the baseline case, the transmission chamber makes the time-averaged ejecting velocity in the central zone increase but decrease in the edge zone. As the peak velocity in the central zone of orifice outlet is effectively increased by the use of transmission chamber, the jet impinging velocity approaching to the target surface is also strengthened, resulting in a stronger jet impingement in the vicinity of the stagnation point. [ABSTRACT FROM AUTHOR]

This paper analytically deals with the collapse resistance of composite framed-structures considering effects of slab boundary restraints. The collapse resistance of composite framed-structures due to different interior-edge (IE) column losses are investigated. The IE columns refer to the interior columns directly adjacent to the exterior columns, among which those nearest to corner columns are defined as interior-edge-corner (IEC) columns and the rests are interior-edge-intermediate (IEI) columns. The responses of main structural members including reinforced concrete slabs, steel beams and steel columns at large deflections are fully accounted for. The collapse resistance of composite framed-structures for a general interior (GI) column loss scenario has been previously studied. Three contributions to internal energy dissipations were considered, including the elongations of rebar and steel beams, the tensile force-induced additional bending moments, and the bending moments along yield lines of the slab. For IE column loss scenarios, however, besides the original three energy dissipations, contributions due to the deformation of the peripheral beams and edge columns are included. The detrimental effect of the lateral displacement at the top of edge columns on the energy dissipations due to the elongation of rebar and steel beams is also accounted for. The reasonability and reliability of the analytical method are verified against validated numerical analyses. The resistance-displacement curves of structures due to IEI and IEC column losses are compared. It is confirmed that for the IEC column loss scenario, a structure has the least progressive collapse resistance due to its weakest boundary conditions. Due to the existence of the concrete slab, the differences between the progressive collapse resistance of structures for IEI and IEC column loss scenarios are mitigated. • The effect of slab boundary restraints on collapse resistance of composite framed-structures is analytically determined. • Removals of an interior-edge-intermediate and interior-edge-corner column scenarios are considered. • Parametric studies are conducted to study the differences of resistance-displacement curves for the two scenarios. [ABSTRACT FROM AUTHOR]

This paper proposes an energy-based method to theoretically determine the collapse resistance of reinforced-concrete (RC) beam–slab subassemblies subject to a middle column loss at large deflection. It considers the contributions to internal energy dissipation due to extension of rebar in the slab and beams, the additional resultant bending moment from membrane forces in the slab and catenary tensile forces in beams, and the sectional bending moment at plastic hinges of beams and along yield lines of slabs. Furthermore, the effect of tensile forces on the sectional bending moment of the slab and beams is also accounted for. The effectiveness and accuracy of the proposed method are validated against available test results. The proposed method is found to produce accurate predictions on the collapse resistance of the subassemblies, as well as capture the main feature of mechanism of the subassembly at large deflections. It is concluded that the energy dissipation due to the extension of rebar and additional resultant bending moment significantly contribute to the resistance of subassemblies at large deflections. The interaction between membrane forces and bending moment of the beam and slab sections has a detrimental effect on the collapse resistance. Neglecting this effect will overestimate the collapse resistance for the subassembly. [ABSTRACT FROM AUTHOR]

Highlights • Illustrating influence of transmission pipe on piston-driven synthetic jet impingement. • Revealing chevron-nozzle role on heat transfer enhancement of synthetic jet impingement. • Transmission pipe shows different effects, dependent on l / d , H/d and f. • Transmission pipe with small l / d leads to heat transfer increase at high f and small H/d. • Integrating of chevron-jet role into pulsating feature of synthetic jet is confirmed benefit. Abstract An experimental research is performed to illustrate the effects of the transmission pipe and nozzle exit shape on the synthetic jet impingement heat transfer, by using a piston-driven actuator. Three transmission pipes (namely short pipe, moderate pipe and long pipe) and two nozzle exit shapes (round and chevron) are taken into considerations. The experimental tests are conducted at five operational frequencies (f = 5 Hz, 10 Hz, 15 Hz, 20 Hz and 25 Hz) and four dimensionless jet-to-surface distances (H / d = 2, 4, 6 and 8). The results show that the heat transfer around the jet stagnation is generally decreased by the long-pipe nozzle in comparison with the orifice-nozzle case, especially at higher operational frequencies. However, at a high operational frequency and a small jet-to-surface distance, of particular interest is that the short-pipe nozzle could improve the synthetic jet impingement heat transfer when compared to the orifice-nozzle case. The chevron nozzle is confirmed to be benefit for the synthetic jet heat transfer enhancement. Its role behaves distinctly at different jet-to-surface distances and operational frequencies. At low operational frequencies, the favorable jet-to-surface distance for the synthetic jet impingement heat transfer is altered due to the presence of the chevron exit when compared to the round-exit nozzle. While at larger operational frequencies, the relationships of the circumferentially-averaged Nusselt number varying with the jet-to-surface distance in the round synthetic jet impingement remain in the chevron synthetic jet impingement. [ABSTRACT FROM AUTHOR]

A CFD-based multi-objective optimization is performed for improving the film cooling performance of the laidback fan-shaped holes on the suction surface of a turbine guide vane under a typical blowing ratio of M = 1.5. Among the main geometric parameters, the inclination angle (α), lateral expansion angle (β) and forward expansion angle (γ) are selected as the design variables, with respective lower and upper bounds of (25°, 55°), (10°, 20°) and (3°, 15°) in turns. Two independent objective functions that are simultaneously optimized are selected as the spatially-averaged adiabatic film cooling effectiveness (ranging from s/d = 0 to s/d = 12) and the discharge coefficient. By using a variant of non-dominated sorting genetic algorithm (NSGA-II) coupled with the RBFNN-based surrogate model, the Pareto front of optimal solutions is obtained, providing a variety of options for seeking the maximum spatially-averaged adiabatic film cooling effectiveness, the maximum discharge coefficient, or the compromise of both aspects. The optimized results show that the optimal geometers of (α, β, γ) are (50.3°, 19.5°, 9.8°), (25°, 18.7°, 11.8°) and (27.3°, 19°, 5.1°) for achieving the most maximum film cooling effectiveness, the most maximum discharge coefficient and the compromise of both aspects, respectively. In general, a large lateral expansion angle of the laidback fan-shaped film-cooling hole is necessary in the shape optimization for all of the optimal options. However, with regard to the other design variables, their selections are very distinct following the optimal option. Further, the influence role of optimal fan-shaped geometry on the film cooling performance is illustrated according to the detailed flow and thermal behaviors. [ABSTRACT FROM AUTHOR]

Abstract Numerical simulations are carried out to address further insights into the effects of round-to-slot film cooling holes on a multi-row film-cooled turbine blade under representative engine-simulated conditions by adopting both adiabatic and conjugate heat transfer CFD models. In the current study, only the alteration of film-hole shape at suction and pressure sides is concerned while the showerhead film cooling holes at the leading edge remain cylindrical or baseline shape. Four film-hole shapes are taken into consideration, including converging round-to-slot hole (RTSH-1), equivalent-area round-to-slot hole (RTSH-2), diffusing round-to-slot hole (RTSH-3) and fan-shaped hole (FSH). Beside, a series of computations are also performed to the individual single-row film cooling by setting the coolant-feeding condition as its corresponding one in the multi-row film cooling situation. Viewed from the comprehensive influence of film-hole shape on film cooling performance, such as coolant feeding usage amount, enthalpy loss coefficient and cooling effectiveness, it is suggested that RTSH-2 should be the most favourable shape. RTSH-1 leads to the smallest coolant usage and enthalpy loss coefficient but its cooling effectiveness is low. Although RTSH-3 could present the highest cooling effectiveness, it produces the largest coolant usage and cascade enthalpy loss coefficient. [ABSTRACT FROM AUTHOR]

Highlights • Further exploring convective heat transfer of piezoelectric fan in channel flow. • At small velocity ratios, impingement role dominated and channel flow is effectively pulsated. • At large velocity ratios, impingement role of fan streaming flow is seriously weakened. • Presenting vortical structures visualized by the use of λ 2 criterion. Abstract An experimental and numerical investigation is performed in the current study to further explore the convective heat transfer performance by a vertically-oriented piezoelectric fan in the presence of channel flow. The effects of velocity ratio and fan tip-to-heated surface clearance are taken into considerations. It is illustrated that the presence of channel flow has an innegligible influence on the vibration amplitudes of the piezoelectric fan under large channel flow velocities. In the presence of channel flow, the vortical structures at the edges of vibrating fan are certainly suppressed, especially under large velocity ratios. On the other hand, the vortical streaming flow mixes with the channel flow to form a long stripe of vortical structure downstream of the fan vibration envelope. Under small velocity ratios, the impingement role of streaming flow along fan tip is still dominated and simultaneously the channel flow passing through the vibration envelope is effectively pulsated. Therefore, combined flows generally produce heat transfer enhancement around the fan vibration envelope related to the pure vibrating fan, especially at a small non-dimensional tip-to-surface gap. While under large velocity ratios, the impingement role of streaming flow induced by a vibrating fan is seriously weakened by the strong channel flow. The convective heat transfer produced by combined flows in the fan vibration envelope is generally reduced in comparison with pure piezoelectric fan. Related to the pure channel flow, the combined flows effectively improve the convective heat transfer, especially downstream of the fan vibration envelope. [ABSTRACT FROM AUTHOR]

An experimental and numerical investigation is performed to explore the effects of blade shape on the convective heat transfer performance induced by piezoelectric fans. Five blade types are taken into consideration corresponding to the ones presented by Lin et al. [28], including one baseline type with a rectangular shape (Type-A), two rectangular shapes with wider widths (Type-B and Type-C), and two trapezoidal shapes in divergent (Type-D) and convergent (Type-E). All the blades are attached to the same piezoelectric patch and have the same exposed length. The vibration tests show that the blade shape has a significant influence on the vibrating characteristics of piezoelectric fan. Related to the baseline Type-A, Type-B and Type-C make the first-order resonance frequency a little descent. Type-D makes its first-order resonance frequency far less than the baseline type but Type-E is opposite. From the numerical simulations, the vortical structures induced by different blades vibrating at their respective resonance frequencies are illustrated. It is found that Type-B and Type-C produce stronger vortical flow although they have a little less vibrating frequency than the baseline Type-A. For Type-E, as its vibration frequency is obviously larger than Type-A, the scale of vortex shedding from the vibrating fan seems much stronger. In comparison with baseline type of piezoelectric fan, the location of highly local heat transfer zone moves from the center to both edges of fan-tip vibration envelope of fan-tip vibration envelope with the increase of blade width. In general, the blade types like Type-C and Type-E are suggested to be the favorable shapes for achieving better convective heat transfer performance. However, a little larger power consumption for actuating the piezoelectric fan is paid in relative to the baseline blade shape. [ABSTRACT FROM AUTHOR]

A special issue concerned in the current study is the supersonic ejector-based cooling system in an oil radiator air-cooled passage. To match the geometric feature of mixing chamber (variable sectional configuration with a big aspect ratio of cross section), a novel piccolo-tube multi-nozzles supersonic ejector is designed and numerically assessed. In the current 3-D numerical simulations, a simplified approach by utilizing an isotropic porous medium model is adopted for modeling the flow through a compact oil radiator. Simultaneously, a scaled-model experimental test is conducted for the purpose of validation. From a scaled-model test, it is suggested that the CFD simulation based on the porous medium approach is generally acceptable. In the presence of porous matrix, approximately 20%–40% decrease of the ejector pumping ratio is produced in relative to the situation without oil radiator, due to the flow resistance across the porous matrix. A conjunctive parameter considering the nozzle numbers, nozzle throat diameter, and piccolo-tube length is proposed. Either from the CFD-based analysis or from the scaled-model test, it is confirmed that there is an optimal conjunctive parameter for achieving the best ejector performance. [ABSTRACT FROM AUTHOR]

This paper proposes an energy-based method to determine the structural responses of steel beam-concrete slab composite substructures under side column removal scenarios. A tri-linear resistance-displacement curve is proposed. Three factors contributing to the internal energy dissipation are accounted for, including the extension of reinforcing bars and steel beams, the additional bending moment induced from membrane forces in the slab and tensile forces in beams, and sectional bending moment along yield lines of the slab. Parametric studies are conducted based on validated finite element models to investigate the effect of slab planar aspect ratio, slab thickness, slab reinforcement ratio and beam section height on the behavior of composite beam-slab substructures subjected to side column loss. The numerical results show that these four parameters have limited effects on the yield displacement of the substructure. The accuracy and effectiveness of the proposed method are verified against numerical results with errors less than 15%. It is found that the first two factors considerably contributed to the collapse resistance of the substructures at large deflections, by accounting for more than 70% of the total energy dissipation capacity. The contribution from the slab at the collapse limit state is mainly influenced by its reinforcement ratio. [ABSTRACT FROM AUTHOR]

Single-objective optimization for improving adiabatic film cooling effectiveness is performed for single row of round-to-slot film cooling holes on a flat surface by using CFD analysis and surrogate approximation methods. Among the main geometric parameters, dimensionless hole-to-hole pitch (P/d) and slot length-to-diameter (l/d) are fixed as 2.4 and 2 respectively, and the other parameters (hole height-to-diameter ratio, slot width-to-diameter and inclination angle) are chosen as the design variables. Given a wide range of possible geometric variables, the geometric optimization of round-to-slot holes is carried out under two typical blowing ratios of M = 0.5 and M = 1.5 by selecting a spatially-averaged adiabatic film cooling effectiveness between x/d = 2 and x/d = 12 as the objective function to be maximized. Radial basis function neural network is applied for constructing the surrogate model and then the optimal design point is searched by a genetic algorithm. It is revealed that the optimal round-to-slot hole is of converging feature under a low blowing ratio but of diffusing feature under a high blowing ratio. Further, the influence principle of optimal round-to-slot geometry on film cooling performance is illustrated according to the detailed flow and thermal behaviors. [ABSTRACT FROM AUTHOR]

An energy-based method is proposed to determine the structural responses of composite beam-slab substructures under middle column removal scenarios. A tri-linear resistance-displacement curve is proposed. Three factors contributing to the internal energy dissipation are accounted for, including the extension of reinforcing bars and steel beams, the additional bending moment induced from membrane forces in the slab and tensile forces in beams, and sectional bending moment along yield lines of the slab. Parametric studies are conducted based on validated finite element models to investigate the effect of slab planar aspect ratio, slab thickness, slab reinforcement ratio and beam section height on the behavior of composite beam-slab substructures subjected to middle column loss. The numerical results show that these four parameters have limited effects on the yield displacement of the substructure. The accuracy and effectiveness of the proposed method are verified against numerical results with errors less than 15%. It is found that the first two factors considerably contributed to the collapse resistance of the substructures at large deflections, by accounting for more than 65% of the total energy dissipation capacity. At the collapse limit state, the contribution from the slab is mainly influenced by its reinforcement ratio. The beam height has little effect on the beam contribution to the collapse resistance of the substructure. [ABSTRACT FROM AUTHOR]

This article proposes an energy-based method to determine the collapse resistance of beam–slab substructures subject to side-column removal scenarios. These include the removal of intermediate columns along the edge or those at corner. Four contributions to the internal energy dissipation are taken into account, including extension of reinforcing bars in the slab and beams, sectional bending moment at plastic hinges of beams, sectional bending moment along yield lines of the slab, and additional resultant bending moment from membrane forces in the slab and tensile forces in beams. The performance of the proposed method is validated against existing experimental results. A comparison of collapse mechanism of substructures subject to these two side-column removal scenarios is made in detail. It is found that no tensile catenary action developed in the beam for the removal of a corner column. The energy dissipation due to the extension of reinforcing bars and additional resultant bending moment contributes most to the resistance of substructures at large deflections. The proposed method can accurately capture the main collapse mechanisms of beam–slab substructures at large deflections, thus providing an accurate prediction of its progressive collapse resistance. [ABSTRACT FROM AUTHOR]

Due to the lack of studies on the thermal and hydraulic performances of roughed surfaces subjected to the piezoelectric fan in the presence of forced channel flow, an experimental investigation is performed for a micro pin-finned heat sink integrated with a specific piezoelectric fan in the current study. Some influence factors, such as characteristic Reynolds number of vibrating fan, fan tip-to-heated surface clearance and channel flow Reynolds number, are taken into considerations for two specific micro pin-fin configurations having the same pin-fin height. Particular attention is focused on evaluating the role of piezoelectric fan in the design of an active heat sink. It is confirmed that the micro pin-fin surface with a larger pin diameter (H250D400) provides a stronger heat transfer enhancement but greater additional flow losses than H250D250. The integration of piezoelectric fan into micro pin-fin heat sink is a highly efficient means for improving thermal performance. Its role on heat transfer enhancement behaves more significantly under a higher characteristic Reynolds number of vibrating fan and smaller fan tip-to-surface distance. With the presence of piezoelectric fan, the overall thermal performance parameter is generally bigger than the corresponding one without the piezoelectric fan except for the micro pin-fin type H250D400 under high channel flow Reynolds numbers. The linear relationships of heat transfer coefficient and overall thermal performance parameter are derived with respect to the total Reynolds number combining the channel flow and piezoelectric fan. It is demonstrated that the influence weighting of piezoelectric fan on the overall thermal performance parameter is weaker than that on the pure thermal performance of micro pin-fin heat sink. [ABSTRACT FROM AUTHOR]

An experimental investigation is performed to study the effect of film-hole configurations on the blade tip film cooling performance in a five-blade linear cascade. Six film-hole configurations are taken into consideration under four typical blowing ratios. In Type-A, Type-B and Type-C, the film holes are arranged in a single row along the middle-camber line with different hole-to-hole pitches. Type-D, Type-E and Type-F have the same film-hole number of 13 as Type-B. For Type-D, the film holes are also arranged in a row, but they are located close to the suction-side squealer. For Type-E, the film holes are arranged in two rows. For Type-F, two rows of 8 holes are concentrated at the leading edge, and the rest 5 holes are arranged in a line at the middle chord region of the blade tip. Besides, some numerical simulations are conducted to provide detailed coolant jet trajectory. The results show that film-hole arrangement has a great impact on the tip film-cooling effectiveness. The coolant issuing from middle-camber holes are suctioned by the vortex structures inside squealer cavity to flow towards the pressure side, producing good film coverage at the local zone between the middle-camber line and pressure-side squealer for Type-A, Type-B and Type-C. For Type-F, as more film holes are concentrated at the leading edge, the film coverage on the front tip surface is well improved compared to the other film-hole arrangements. Under the same coolant usage, Type-F obtains the most favorable film cooling performance except for the trailing edge, and Type-C produces wider film coverage extending to trailing edge. [ABSTRACT FROM AUTHOR]

A new scheme of center-satellite hot-jet orifices was proposed for improving the conjugated heat transfer performance in the vicinity of a conical concave leading edge. To illustrate the role of this scheme, a typical 6-satellite orifice configuration was designed having the same nominal diameter ( d ) or ejection area of impinging jets as that of the baseline single-orifice, and a series of experimental tests was performed to determine the hot-jet heating effectiveness under non-dimensional jet-to-leading edge distance ( H / d ) of 2–4 and nominal jet Reynolds number ( Re j ) of 7800–39,400. Four non-dimensional axial distances of satellite-orifice location ( H s / d = 0.15, 0.5, 1.0 and 1.5), three non-dimensional center-orifice diameters ( d c / d = 0.6875, 0.812 and 0.9375) were taken into consideration. Besides, numerical simulations were also performed to illustrate the effect of center-satellite orifices on the flow and heat transfer features inside the conical concave cavity. The results confirm that the center-satellite scheme has a significant impact on improving the conjugated heat transfer performance in the vicinity of conical wall leading edge due to more intensive jet impingement. In the current research conditions, the satellite-orifice arrangement with a larger non-dimensional axial distance ( H s / d ) or a smaller non-dimensional center-orifice diameter ( d c / d ) is suggested to be more favorable for the conjugated heat transfer improvement. However, the center-satellite scheme results in a higher pressure drop related to the baseline single-orifice. It is also noted that the pressure drop of center-satellite scheme is nearly unaffected by the center-orifice diameter and axial distance between center-orifice outlet and satellite-orifice location. [ABSTRACT FROM AUTHOR]

Experimental tests are carried out to investigate the convective heat transfer performances on a flat surface around the vibration envelope of a vertically-oriented piezoelectric fan in the presence of cross flow. Distinct behaviors of convective heat transfer are illustrated under the present conditions of piezoelectric-fan excitation voltage ( U = 50, 150, 250 V) or characteristic velocity ( u = 0.83, 1.67, 2.34 m/s) fan tip-to-heated surface gap ( G = 3, 5, 7 mm) and cross flow velocity ( u = 0.94, 1.56 m/s). In addition, three-dimensional flow field simulations are conducted to illustrate the instantaneous flow fields around the vibrating fan. By comparing with the pure piezoelectric fan, the vortex induced by the vibrating fan is pushed downward by the cross flow and a series of vortices are displayed down the vibrating fan. It is confirmed that the presence of cross flow is contributive to the improvement of convective heat transfer in the rear zone downstream fan vibration envelope. The impingement role of streaming flow induced by piezoelectric fan is reduced by the presence of cross flow in the fan vibration envelope. On the other hand, the oscillating movement of the piezoelectric fan promotes the disturbance intensity of cross flow passing through the fan vibration envelope. These two aspects make the conjugated convective heat transfer in the vicinity of fan vibration envelope complicated. In general, the convective heat transfer in the vicinity of fan vibration envelope is mostly improved by the combined action of fan-excited steaming flow and cross flow in the situation where the piezoelectric fan is placed very close to the heated surface. [ABSTRACT FROM AUTHOR]

A series of numerical computations are conducted to investigate the film cooling from a row of round-to-slot holes on a flat surface. Particular attention is paid to explore effect of slot width (0.2 ≤ s/d ≤ 0.5) on the film cooling performances of round-to-slot holes with a fixed slot length of l/d = 2.0 under typical blowing ratios ranged from 1.0 to 2.0. Besides, several experimental tests are also performed to obtain the film cooling effectiveness and discharge coefficient of the round-to-slot holes with specific geometries. The results show that the coolant flow turning towards both lateral sides due to the transitional flow passage of film-hole is dominated inside the round-to-slot hole. Owing to the specific interaction mechanism between the coolant jet issued from round-to-slot holes and the primary flow, the hot primary flow is mainly entrained into the coolant layer from the film-hole centerline. In general, the diffusing round-to-slot hole shows its favorable feature on the film cooling enhancement near the film hole. However, beyond a certain distance, the converging round-to-slot hole achieves a little higher laterally-averaged film cooling effectiveness than the diffusing round-to-slot hole. The converging round-to-slot hole with s/d = 0.2 produces higher laterally-averaged heat transfer coefficient than the cylindrical hole. While the diffusing round-to-slot hole produces less laterally-averaged convective heat transfer coefficient than the cylindrical hole beyond x / d = 10. The discharge coefficient decreases significantly as the slot width reduces. [ABSTRACT FROM AUTHOR]

Experimental investigations were carried out to study the conjugated convective heat transfer on the leading edge of a conical wall subjected to external cold flow and internal hot jet impingement by a single chevron nozzle. The geometric effects, including the chevron penetration depth ( p/d ranging from 0.1 to 0.2) and chevron length ( l/d ranging from 0.1 to 0.3) on the conjugated convective heat transfer performances were experimentally analyzed for a typical 6-chevrons nozzle under non-dimensional jet-to-leading edge distance ( H/d ) of 2–4 and jet Reynolds number ( Re j ) of 7800–39,400. The results show that the chevron jet is proved to be capable of improving the heating effectiveness in the vicinity of the conical surface leading edge, especially under a small jet Reynolds number. For the specified zone with a chordwise length of 5 d apart from the leading edge, the area-averaged heat effectiveness could be increased approximately 20% by the chevron nozzle in relative to the conventional nozzle. The heat transfer enhancement is improved with the increase of chevron penetration length for a fixed chevron length or the decrease of chevron length for a fixed chevron penetration length. The influence of chevron penetration depth or the chevron length on the specified area-averaged heating effectiveness becomes weaker gradually as the jet Reynolds number increases. For the current conditions, the non-dimensional jet-to-leading edge distance seems to have little influence on the specified area-averaged heating effectiveness. [ABSTRACT FROM AUTHOR]

Numerical investigations are performed to study the conjugated convective heat transfer on the leading edge of a conical wall subjected to external cold flow and internal hot jet impingement by a single chevron nozzle. The effects of the chevron length ( l / d = 0.1, 0.2, 0.3) and chevron penetration depth ( p / d = 0.1, 0.15, 0.2) on the hot-jet impingement heat transfer performance are analyzed for a 6-chevrons nozzle. In the current study, non-dimensional jet-to-leading edge distance ( H / d ) is varied from 2 to 4 and the jet Reynolds number ( Re j ) is varied from 7800 to 39,400. In relative to the conventional nozzle, the presence of chevrons increases the jet core velocity and produces more intensive jet fluctuation, thereby improves the heat transfer in the vicinity of the conical surface leading edge, particularly under a small jet Reynolds number or a smaller jet-to-leading edge distance. In general, the local circumferentially-averaged heating effectiveness is improved with the increase of chevron penetration depth ratio for a fixed chevron length ratio or decrease of chevron length ratio for a fixed chevron penetration depth ratio. Due to a large curvature of conical surface, the circumferentially-averaged heating effectiveness under H / d = 4 is greater than that under H / d = 2 at the same chordwise location once s / d is beyond 6. [ABSTRACT FROM AUTHOR]

• Explicit formulae are established to compute the maximum displacement of floor. • The effects of impactor mass, impact height, floor span, slab thickness, rebar diameter, and beam depth are studied. • Coefficient of restitution in impact is considered. • Practical recommendations for the maximum displacement of floor are proposed. Analytical and numerical investigations on the maximum displacement of the steel-concrete composite floor system subjected to falling impact are presented in this paper. Explicit formulae are established to compute the floor maximum displacement under impacts with different kinetic energy transfer ratios. Parametric analyses are conducted to study the influence of impactor mass, impact height, floor longitudinal span, floor thickness, rebar diameter, beam depth, and coefficient of restitution on the maximum displacement of floor. Associated practical recommendations are also proposed for determining the maximum displacement of floor under falling impact. It is found that in fully elastic impact, the maximum displacement is highly sensitive to the impact height, whereas in fully plastic impact, the value is significantly affected by the impactor mass. The upper-bound estimation of the displacement can be achieved by using fully elastic impact model. However, fully plastic impact model should be adopted when the impactor mass increases to more than 30 % of the total mass of the floor. [ABSTRACT FROM AUTHOR]

• A bionic heat sink with micro barchan-dune-shaped humps is proposed. • The micro dune can reinitialize the boundary layer by inducing a secondary flow. • The micro dune generally outperforms traditional fins in overall heat transfer performance. This paper proposes an innovative bionic heat sink with micro barchan-dune-shaped humps for improving the flow and heat transfer performance of the smooth narrow channel. The effects of the Reynolds number of the main flow (Re) and pitch distance of the dune array (P) on the thermal-hydraulic performance are investigated. In this work, the air is the working flow. The Reynolds number range is considered to cover the regimes of laminar, transitional, and turbulent, Re = 860–6,050, and the pitch distance (P) equals 8, 12, and 16 mm. The results show that the micro barchan-dune-shaped hump can induce a secondary flow downstream of the slip face and enhance the local heat transfer performance. For the multi-dune models, the case with P = 16 mm provides the highest overall thermal performance parameter (η). The η value decreases monotonically with decreasing P in the considered range. In addition, compared with other micro pin fin shapes (including the hexagonal cylinder, square cylinder, and triangular cylinder), the η of the barchan dune shape is almost identical to that of the hexagonal cylinder and exceeds the other two shapes by more than 20%. [Display omitted] [ABSTRACT FROM AUTHOR]

• 3D flow and heat transfer simulations for a piezoelectric fan on concave surface are implemented. • Different relative curvature and moving-orientation of the piezo-fan are investigated. • The heat transfer with transverse fan arrangement is better than the longitudinal counterpart. The present work aims at numerically investigating on the flow and heat transfer performances induced by vibrating piezoelectric fan for cooling heated concave surfaces. Two main relevant parameters, relative curvature (K) of concave surface and moving-orientation of the piezoelectric fan, are taken into consideration. The relative curvature (K) is varied from 0.01 to 0.25. The moving-orientations of the piezoelectric fan include transverse oscillation and axial oscillation. The influence mechanism of these parameters are analyzed in terms of the time-averaged heat transfer coefficient, instantaneous streamlines and isosurface of λ 2. The heat transfer results indicate that the axial oscillation is more favorable for improving the heat transfer performance than the transverse oscillation, especially in the zone near the fan vibration envelope. Meanwhile, the flow field reveals that the relative curvature of the concave surfaces influences the flow feature under longitudinal configuration substantially. [ABSTRACT FROM AUTHOR]

• The flexural buckling, lateral-torsional buckling and axial-torsional buckling are studied. • Random nature of corrosion is captured by Monte Carlo simulation. • Non-uniform pitting corrosion is considered. • The effects of corrosion ratio, depth and location on the buckling strength are studied. This paper developed an efficient algorithm to study the elastic buckling strengths of non-uniformly corroded steel members. The algorithm is derived based on the authors' previous work on buckling strength assessment for the steel members by further introducing random non-uniform corrosion damage to the cross-section along member. In the algorithm, the random nature of the corrosion is captured by the Monte Carlo simulations. Moreover, the non-symmetric section effects, including the noncoincidence of section shear center and centroid and Wagner effects, caused by the non-uniform corrosion are considered in the algorithm. The proposed algorithm permits more than ten million times of Monte Carlo simulations being completed efficiently, which greatly reduces the computational expense compared with the existing finite element analysis algorithms. The effects of corrosion depth, corrosion ratio, and corrosion location on the flexural buckling (FB), lateral-torsional buckling (LTB), and axial-torsional buckling (ATB) strengths of the steel member are studied. It is found that corrosion has the most adverse effect on ATB than LTB and FB strengths of the member. When the corrosion distributes more compactly through the section, its adverse effect on the buckling strength of the member could be more significant. Even for the same corrosion ratio, corrosion depth, and total corrosion region number, the reduction factor of the buckling strength can be varied by up to more than 20% due to the difference of the corrosion locations. The reduction factor of the FB strength is generally linear against the corrosion depth. While for the LTB and ATB strength, the reduction factors show nonlinear as per the corrosion depth. [ABSTRACT FROM AUTHOR]

• Convergent piezo-fan behaves more favorable than the divergent one in channel flow. • The perturbation effect by fan is not obvious under large inlet turbulence intensity. • Beam shape has a significant effect on the development of thermal boundary layer. The beam shape of a piezo-fan and the inlet turbulence intensity (TI) of channel flow are important parameters that affect the heat transfer enhancement of a heated surface in an airflow channel with a vibrating piezo-fan. In this study, 3D numerical channel models of different piezo-fans are considered when investigating the influence of beam shapes and inlet turbulence intensity on the heat transfer performance of channel flow, within a range of 4000–30,000 Reynolds numbers (Re CF) and 5% to 20% inlet turbulent intensity (TI). The influence of these parameters is analyzed in terms of the distributions of the flow field, time-averaged heat transfer coefficient, and overall thermal performance. The results show that the piezo-fans with the widest rectangular shape and a convergent shape behave better in terms of overall thermal performance in the channel. However, as the turbulence intensity increases to 20%, the difference in heat transfer caused by the beam shape becomes negligible. The maximum overall thermal performance parameter (η) = 1.47 is obtained at Re CF = 13,000 and TI =20% for the convergent beam shape (Beam-E). [Display omitted] [ABSTRACT FROM AUTHOR]

A Computational study was conducted to investigate the convective heat transfer characteristics by a row of tab-excited air jets impingement on a wedge-shaped concave surface having larger curvature than semi-circular concave surface. The geometric effects, including the tab number and tab penetration ratio, as well as the offset-jets arrangement, on the impinging jet flow and heat transfer behaviors are analyzed under several non-dimensional jet-to-leading edge distances (6, 9, 12) and the jet Reynolds numbers ranging from 6900 to 26,100. The results show that both the jet offset-arrangement and tab-excitation are proved to be capable of improving the convective heat transfer in the vicinity of jet impingement region. Either for the conventional round jet or tab-excited jet, it appears that an optimum non-dimensional jet-offset distance is about 1.5. The heat transfer enhancement is improved as the increase of tab number (ranging from 4 to 8), as well as tab penetration ratio (ranging from 0.13 to 0.25). The influence intensity of non-dimensional jet-offset distance on the convective heat transfer inside a concave cavity is more significant for the tab-excited jet impingement than that for the conventional round jet impingement. In general, the effects of jet offset-arrangement and tab-excitation on the jet impingement heat transfer enhancement behave more significant under larger jet Reynolds number as well as smaller impingement distance. [ABSTRACT FROM AUTHOR]

The convective heat transfer characteristics under a normally synthetic jet impingement driven by a piston actuator are investigated experimentally in the present study. Particular attentions are paid to present the detailed local and laterally-averaged heat transfer comparison between synthetic jet and continuous jet, as well as the effect of orifice shape on the synthetic jet impingement. Three jet orifices including single-round, single-square, and single-rectangular are designed to have the approximately same exit area. In additional, heat transfer regimes for the synthetic jet impingement in the situation of large stroke length to jet-to-surface spacing are further identified. In the present, the equivalent convective heat transfer coefficient is defined in terms of the difference between target temperature and ambient temperature. The results show that continuous jet exhibits stronger local heat transfer than the synthetic jet in the vicinity of stagnation point. However, the synthetic jet produces much flatter and more uniform local heat transfer coefficient distributions over the surface, showing its advantage over the continuous jet on laterally-averaged convective heat transfer enhancement at a larger jet-to-surface spacing. For the piston-driven synthetic jet featured by low excitation frequency and large stroke length, there is evidence for a power law relationship between stagnation Nusselt number and jet Reynolds number with an exponent of approximately 0.32. Two kinds of heat transfer regimes are observed and a critical ratio of stroke length to jet-to-surface spacing is identified as 18 approximately regardless of orifice shape. The orifice shape has a moderate effect on the convective heat transfer. The single-rectangular synthetic jet produces a slightly better stagnation point heat transfer than the other orifices. The synthetic jet originated from the round-hole orifice seems to introduce favorable overall convective heat transfer achievement. The advantage of synthetic jet impingement in comparison to the corresponding continuous jet is relatively degraded for the square-hole orifice. [ABSTRACT FROM AUTHOR]

This paper numerically studies the anti-collapse behavior of the modular steel building (MSB) in the scenario of interior module removal and corner module removal. The vertical displacement, lateral displacement and internal force of a six-storey MSB in a sudden module loss are studied. The reasonability by using rigid body assumption in collapse analysis of the MSB is examined. A refined fracture model of the steel is incorporated into ABAQUS via user subroutine, in which the effects of both stress triaxiality and Lode angle on the fracture ductility of the steel are considered. In the pushover analyses, the effects of the horizontal connection, opening of the wall panel and thickness of the wall panel on the collapse resistance and failure mode of the MSB are studied. The dynamic amplification factor (DAF) of the MSB at the collapse limit state is also obtained. It is found that the rigid body assumption may significantly underestimate the displacement and maximum shear force in the horizontal connection of the MSB. Two types of failure modes of the structure are observed, namely, connection failure-induced collapse and module unit failure-induced collapse. Among the studied parameters, the effect of the opening size of the wall panel on the behavior of the structure is the most significant. In the scenario of the interior module removal and corner module removal, the DAFs of the structure at the collapse limit state range from 1.20–1.29 and 1.27–1.50, respectively. • Anti-collapse behavior of modular steel building (MSB) was studied. • The reasonability of rigid body assumption in collapse analysis of MSB was studied. • Effects of connection and wall panel on collapse resistance of MSB were studied. • Dynamic amplification factor of the MSB at the collapse limit state was obtained. [ABSTRACT FROM AUTHOR]

Computational and experimental studies were conducted to investigate the conjugated convective heat transfer produced by single row of impinging jets inside a confined channel with non-uniform initial crossflow issued from discrete holes. The effects of the crossflow-to-jet Reynolds number ratio and crossflow holes arrangement (inline or staggered in relative to the impinging jet holes) on the jet impingement behaviors were studied providing the same total cooling air mass flowrate. Particular attention was paid to examine the tab-excited jet impingement behaviors in a confined channel with non-uniform crossflow. The results show that the tabbed excitation on the improvement of convective heat transfer in the vicinity of impingement region is not as well as the situation where no initial crossflow is present. For the inline arrangement of crossflow holes, the location corresponding to the peak laterally-averaged Nusselt number is moved downstream and the peak laterally-averaged Nusselt number is decreased significantly under larger crossflow-to-jet Reynolds number ratios. While for the staggered arrangement of crossflow holes, the location corresponding to the peak laterally-averaged Nusselt number is not affected by the crossflow but the peak laterally-averaged Nusselt number is decreased monotonously with the increase of crossflow-to-jet Reynolds number ratio. Under small crossflow-to-jet Reynolds number ratio, the initial crossflow arrangement has little influence on the laterally-averaged Nusselt number distribution. Among three crossflow-to-jet Reynolds number ratios ranged from 0.5 to 2, the maximum relative difference of peak laterally-averaged Nusselt numbers between two different crossflow arrangements is occurred under crossflow-to-jet Reynolds number ratio of 1. [ABSTRACT FROM AUTHOR]

Convective heat transfer on the rib-roughened wall impinged by a row of air jets inside semi-confined channel was experimentally investigated. Four rows of transverse ribs were arranged in the wall-jet zone downstream from the impinging jet stagnation to enhance heat transfer. Three typical rib configurations, including orthogonal ribs, V-shaped ribs and inverted V-shaped ribs, were considered under different non-dimensional jet-to-target distances ranging from 1 to 3 diameters and impinging jet Reynolds numbers ranging from 6000 to 30,000. The results show that the rib-roughened wall enhances the convective heat transfer up to 30% in the ribbed region by comparison with the smooth wall under the same jet Reynolds number. Among three rib configurations, the inverted V-shaped rib seems to be advantageous on the convective heat transfer enhancement, especially at lower jet-to-target spacing. The ribs on the impinging target do provide stronger convective heat transfer in the wall-jet region, but at greater expense of pressure drop inside the channel. At the jet-to-target spacing ratio of 1, the flow coefficient of the rib-roughened channel is decreased 5%–10% in related to the smooth channel. [ABSTRACT FROM AUTHOR]

Numerical investigation is performed to further address the effects of geometric parameters and excitation frequency of the actuator on the synthetic jet fluidic characteristics by utilizing a two-dimensional unsteady Reynolds-averaged Navier–Stokes model. The vibrating diaphragm is modeled as a movable wall varying in sinusoidal mode. Computations are carried out by using FLUENT software with the coupled user definition function (UDF) describing the diaphragm movement. The results show that the geometric parameters of the actuator, such as the cavity depth and diameter, as well as orifice thickness and diameter, have important influences on the synthetic jet fluidic characteristics. The velocity output could be maximized if the geometric parameters of the synthetic jet actuator are designed to ensure that the cavity acoustic Helmholtz resonance frequency is coincided with the diaphragm excitation frequency. For a fixed actuator cavity, when the diaphragm excitation frequency is consistent with the Helmholtz resonance frequency of actuator cavity, the relative pressure insides the cavity is obviously great during the ejection stroke while low during the suction stroke. In the presented actuator parameters, the synthetic jet is enhanced as the decrease of cavity depth for the fixed orifice. The change of cavity diameter in the vicinity of corresponding cavity acoustic resonance diameter has relatively weaker influence on the synthetic jet. When the diaphragm is excited at high frequency, small orifice diameter will restrict the ejection and suction capacity of the synthetic jet actuator. [ABSTRACT FROM AUTHOR]

Abstract: Experimental study was conducted to investigate the heat transfer produced by single row of impinging jets inside a confined channel with different tab orientations of the triangular tabs at the jet exits. The effects of the tab number, tab orientation angle and tab penetration length on the jet impingement heat transfer behaviors were experimentally tested under nozzle-to-plate spacing of 1–3 diameters and jet Reynolds number of 10,000–20,000. A numerical computation was also carried out on the simulation of impinging jet flow fields to reveal the trends and differences observed in the heat transfer measurements. The results show that the presence of tabs increases the jet core velocity and induces array pairs of vortices, and hence enhances the heat transfer in the impingement region over the no-tab case. The tabs oriented upwards or downwards at 45° can better improve the heat transfer than the normal inclination case. The heat transfer enhancement produced by the tabs increases with the tab penetration length for the given range of 0.12–0.23 diameter. For the arrays of 4–12 triangular tabs, the array of 8 tabs seems to produce more effective heat transfer enhancement. [Copyright &y& Elsevier]

Abstract: A numerical research on the film cooling performance of a single row of converging slot-holes (console) on the blade suction side in an engine-simulated environment was carried out, in which the Reynolds number was arranged from 400,000 to 600,000 and the blowing ratio was arranged from 0.5 to 3. A comparison in contrast to a cylindrical hole was made and the effects of major factors on the film cooling effectiveness and aerodynamic loss were explored, including the film hole location, blowing ratio and primary flow Reynolds number. For the console cooling geometry, the interaction between the coolant jet from inclined console and the mainstream flow results in secondary vortices with a sense of rotation opposite to the kidney pair, which makes the coolant jet from the console be of the flow mechanism for suppressing normal penetration. Additional corner vortices are also observed in the intersection of two consoles on the convex surface. When the film holes are located upstream of the channel throat, the level of aerodynamic loss for the console is obviously less than the cylindrical holes. At higher blowing ratios, more coolant jet momentum is transferred to the tangent and lateral flow of the coolant jet issued from the consoles, resulting in a film cooling enhancement. The console row shows great potential in the blade film cooling application, especially favorable when it is located upstream of the channel throat. [Copyright &y& Elsevier]

A three-dimensional numerical study on the flow and heat transfer characteristics over a rotating disk surface with discrete pins was conducted by the use of RNG k-ε turbulent model. And some experiments were also made for validation. The effects of rotating angular speed and pin configuration on the temperature maps and convective heat transfer characteristics on the rotating surface were analyzed. As the increase of rotating velocity, the impingement of pumping jet on the centre of rotating disk becomes stronger and the transition from laminar to turbulent occurs at the outer radius of rotating disk, which resulting in heat transfer enhancement. The pins on the disk make the pumping action of a rotating disk weaker. Simultaneously, they also act as perturbing elements to the cyclone flow near the rotating disk surface, making the overall heat transfer to be enhanced. The needle pins have higher convective heat transfer capacity than the discrete ring pins with the same extend pin areas. [ABSTRACT FROM AUTHOR]

A simplified physical model is built up to study the swirl flow effect induced by a rotating disk on the jet impingement behaviors, which is adopted to simulate the grinding process. To solve the definition problem of the interface between a rotating disk and a stationary plate in the computational simulation, a tiny gap is set between the rotating disk and the stationary plate. The results show that the rotating disk suspended above the surface adds more complexity to the flow field of jet impingement on a stationary plate. The swirling flow around the rotating disk obstructs the impinging jet flow to penetrate into the interfacial contact zone and forces the wall jet across the rotating disk to flow along transverse directions. For the given jet impinging velocity and nozzle orientation, as the disk rotational speed increases, the effect of the rotating disk on the impinging jet flow behaves more significantly. The impinging jet with small inject velocity is difficult to penetrate through the interfacial contact zone to follow by the disk swirl flows. For smaller jet impinging distance or larger oblique angle, the flow recirculation away from the interfacial contact zone becomes stronger. [ABSTRACT FROM AUTHOR]

Three-dimensional numerical calculation was performed to investigate the effects of partial blockage inside cylindrical film holes on the film cooling effectiveness over a flat plate. Five blockage ratios ranged from 0.1 to 0.5 and a series of blockage positions were considered under the blowing ratios of 0.3-1.5. It is found that the blockage position has a significant influence on mainstream-coolant jet interaction. The partial blockage located at the leading edge of coolant-hole exit mitigates the primary vortices due to mainstream-coolant jet interaction. The coolant jet penetration along vertical direction is suppressed and the peak velocity along streamwise direction is augmented under the action of partial blockage at the upstream side of film holes, providing an increment of film cooling effectiveness, especially under high blowing ratio. While the partial blockages located at the trailing or lateral edges of coolant-hole exit weaken the film cooling effectiveness. In relation to the partial blockage located in the vicinity of coolant-hole exit, the partial blockage located in the vicinity of coolant-hole inlet or middle has less impaction on the film cooling effectiveness under low blowing ratio. [ABSTRACT FROM AUTHOR]

Abstract: Synthetic jet is a novel flow technique which synthesizes stagnant air to form a jet, and is potentially useful for cooling applications. An experimental measurement utilizing particle image velocimetry (PIV), hot-wire anemometer and infrared camera on the synthetic jet impingement cooling driven by piezoelectric actuator was carried out in the present investigation. The flow and heat transfer characteristics of impinging synthetic jets formed from a single cavity but with different orifices, such as single-slot, single-hole, three-slots and three-holes, were explored. The synthetic jet output from the piezoelectric actuator reaches a peak value when it is excited at its optimum frequency. The synthetic jet output from the piezoelectric actuator reaches a peak value when it is excited at its optimum frequency. For single-hole synthetic jet, the optimum frequency is nearly the same as that of single-slot orifice given the same orifice exit area. But the optimum frequency for the multi-orifices is lower than that of single-orifice synthetic jet. In general, the synthetic jet originated from the single-slot orifice introduces a stronger entrainment and more vigorous penetration in relative to that from the single-hole orifice, performing better than the single-hole synthetic jet orifice. And the multiple synthetic jets exhibit complex influence on the heat transfer by comparison to single synthetic jet for a given actuator cavity and a single actuator. Only when the multi-slots or multi-holes are arranged in their optical mode, the multiple synthetic jets could achieve competitive heat transfer capacity with the single synthetic jet. [Copyright &y& Elsevier]

Abstract: A new concept of film cooling central body for the exhaust system of turbofan engine was brought out to suppress the infrared radiation of engine in this paper. The ability of infrared suppression was estimated by experiments and numerical calculations. The numerical method, which use forward–backward ray tracing and narrow band model, had been validated by the experimental results. The aerodynamic characteristics and infrared radiation distribution of exhaust system with/without film cooling central body were investigated for several different configurations. The experimental results reveal that the bypass flow can be used to cooling the central body and suppress the infrared radiation at the rear aspect of the engine. The inlet area of lugs in the bypass passage determined the mass flow rate into the central body. To obtain the effects of the film cooling holes configuration on the surface temperature and infrared radiation intensity of the exhaust system, a series of computations on full scale exhaust system have been performed. The numerical simulation results indicate that the film cooling central body can suppress the infrared radiation of the inside enclosure by 40–70% comparing to the central body without the film cooling at zero degree aspect (normal to nozzle outlet). The film cooling central body for exhaust system of turbofan engine has remarkable ability to suppress the infrared radiation from the inside enclosure of nozzle. [Copyright &y& Elsevier]

Abstract: Experimental investigation was conducted in the current study to investigate the film cooling performance of a single row of consoles on a large-scale curved-plate model simulating the blade suction side, and an aided numerical study was also made to reveal the detailed film cooling features of consoles on the curved surface. A comparison in contrast to cylindrical hole was made. For the console cooling geometry, the interaction between coolant jet from inclined console and the mainstream flow results in reasonable vortices configuration to reduce mainstream–coolant interaction. And additional corner vortices are observed in the intersection of two consoles on the convex surface. The console row shows great potential in the blade film cooling application to produce high cooling effectiveness, especially at large blowing ratios. But this is at the expense of greater pressure drop. And the heat transfer coefficient ratio for the console is a little bigger than conventional cylindrical hole. Furthermore, the effects of major factors on the film cooling effectiveness, heat transfer coefficient and discharge coefficient were explored, including film hole location, blowing ratio and primary flow Reynolds number. [Copyright &y& Elsevier]

Abstract: The conjugate heat transfer characteristics under a normally synthetic jet driven by piston actuator and horizontally forced flow were investigated experimentally. The effects of excitation frequency and orifice shape on the flow and heat transfer characteristics are explored. The piston-driven actuator produces fairly big velocity at higher operating frequency and the time-averaged orifice velocity is almost proportional to the frequency when the piston reciprocates at relatively low frequency (from 8Hz to 24Hz). The orifice shape shows very weaker effect on the exit velocity of synthetic jet, given the same orifice exit area, but has an important influence on the interaction between the normally synthetic jet and horizontally forced flow. The convective heat transfer capacity is enhanced under the conjugate action of a synthetic jet and forced flow, especially significant at higher excitation frequency of the synthetic jet. For all the orifice shapes, the peak laterally-averaged convective heat transfer coefficient is increased up to 100% in relative to individual action of the forced flow when the piston reciprocates at 24Hz. Such detailed heat transfer results about the conjugate heat transfer characteristics have not been reported earlier and are expected to be useful for understanding the effects of excitation frequency and orifice shape on the conjugated heat transfer characteristics. [Copyright &y& Elsevier]

Abstract: Experimental study was conducted to investigate the enhanced cooling performance caused by ridge-shaped tabs located along the upstream edge of the film cooling holes. Three covering ratios of ridge-shaped tab on film hole and four blowing ratios were considered in the present. The results show that the presence of ridge-shaped tabs in the nearby region of the primary film cooling holes mitigates the primary vortices due to mainstream–coolant jet interaction in the downstream region. The lower penetration of coolant jet provides an increment in the film cooling effectiveness and also enhance heat transfer coefficient over the baseline case. The ridge-shaped tabs provide enhancements in cooling effectiveness, but this is at the expense of larger pressure drop, especially for ridge-shaped tabs with bigger covering ratio. [Copyright &y& Elsevier]

A numerical investigation is performed to study the serrated trenched-hole film cooling performance on the convex and the concave surfaces, with the use of a plenum coolant-fed mode. In current study, the relevant curvature of curved surface is varied as 2r 1 /d = 30, 60 and 90 at the convex side, 2r 2 /d = 90, 120 and 180 at the concave side. In addition, three coolant injection angles (such as θ = 30°, 35° and 45°) are considered in a specific curved channel. The blowing ratio defined in terms of the local primary flow velocity is ranged from 0.25 to 1.5. From the present study, a critical parameter (I 0), in the form of I cos2 θ , is preliminarily identified to be around 0.5 for the serrated trenched-hole film cooling. When I cos2 θ < I 0 , the film cooling effectiveness on the convex surface is better than that on the flat surface and concave surfaces. The situation is opposite when I cos2 θ > I 0. In particular, this critical value for the serrated trenched-hole film cooling is obviously less than the unity that previously identified in the cylindrical-hole film cooling situation. The relevant curvature shows nearly rare influence on the film cooling effectiveness under small blowing ratios, either on the convex surface or the concave surface. However, under high blowing ratios, it has a pronounced impact on the film cooling effectiveness, in particular at the concave side. Under M = 1.5, the area-averaged adiabatic film cooling effectiveness in the region between s/d = 10 and s/d = 20 is increased up to 33% by the smallest relevant curvature case with respect to the biggest relevant curvature case. The coolant injection angle plays an important role on the mutual interaction of jet-in-corssflow of the serrated trenched-hole film cooling. The reduction in the coolant injection angle leads to an obvious film cooling enhancement, either on the convex surface or the concave surface. Moreover, the enhancing effect led by the reduction of coolant injection angle behaves more pronouncedly as the blowing ratio increases. [ABSTRACT FROM AUTHOR]

• Identifying SJ impingement enhancement with the use of planar-lobed orifices. • Illustrating confinement effect of concave target on lobed-orifice SJ impingement. • A maximum increase of 26% in Nu s-av is achieved by proper lobed orifice on flat target. • At the most Nu s-av is reduced up to 25% on concave target with respect the flat target. • Relationship between petal- and arch-shaped orifices is contrary on different targets. The heat transfer characteristics of a single synthetic jet (SJ) issuing from planar lobed orifice are investigated experimentally in current study. Two specific planar-lobed orifices (petal-shaped orifice and arch-shaped orifice) and two typical targets (flat target and semi-cylindrical concave target) are taken into consideration. For each lobed orifice, three configurations are included. In the petal-shaped orifices, the lobe numbers are chosen as N =4, 6 and 8 in turns. While in the arch-shaped orifices, the lobe number is fixed as N =6 but the lobe aspect ratios are altered as AR =1, 2 and 3 respectively. All lobed orifices have the same exit area with the baseline round orifice. The experimental tests are performed under a series of operational frequencies (ranging from 10Hz to 25Hz) and dimensionless jet-to-target distances (ranging from 2 to 14 for flat target, and from 6 to 14 for concave target). Under the present conditions, SJ impingement heat transfer enhancement is mostly achieved by the planar lobed orifices when compared to the baseline round orifice, which depends tightly on the lobe shape and target shape. Among current petal-shaped orifices, the N =6 petal-shaped orifice is demonstrated to be a most promising orifice configuration. With regard to current arch-shaped orifices, a moderate lobe aspect ratio is demonstrated to be the superior. When compared to the flat target, SJ impingement heat transfer on the concave target is seriously reduced, regardless of orifice shapes. Interestingly, the relationship of SJ impingement heat transfer on the concave target, between the N =6 petal-shaped orifice and AR =2 arch-shaped orifice, is found contrary to that on the flat target. On the concave target, the N =6 petal-shaped orifice does not show its advantages on SJ heat transfer enhancement as appeared on the flat target. However, the AR =2 arch-shaped orifice still shows its positive role on SJ heat transfer enhancement obviously in comparison to the baseline round orifice. [ABSTRACT FROM AUTHOR]

This paper provides a design-based framework in collapse assessment of multi-storey steel framed-structures. A simple approach for different column-removal scenarios of the structure is proposed, wherein the three-dimensional effects of the floor system, boundary restraints of the affected substructure and potential vierendeel actions in multi-storey framed-structures are incorporated. The effectiveness of the approach proposed is verified against numerical analyses on a full-scale steel frame with six-storey. Extensive discussions are also made from the comparisons between the results from the simplified approach and numerical simulations with finite element method (FEM). The proposed approach is found to sometimes give conservative evaluations for the column destabilizing-induced collapse of the structure, which ensures sufficient security in the robustness assessment of the structure. For the beam/connection failure-induced collapse, the proposed approach can obtain more reliable assessment conclusions. Unlabelled Image • A design-based framework in collapse assessment of multi-storey steel framed-structures is provided. • Six single column-removal scenarios are considered. • 3-D effects of the floor system, boundary restraints and vierendeel actions are incorporated. • The beam/connection failure-induced collapse of the structure is accurately predicted. • The column destabilizing-induced collapse of the structure is predicted with a certain degree of safety. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study on the performance of the multi-storey steel frame in sudden multi-column-removal (MCR) scenarios. The reliability of the numerical analyses are initially validated against experimental results. The effects of the removed column number, column location and magnitude of the applied load on the robustness of the frame are discussed. Results from numerical analyses can provide references to the collapse-resistant design of steel frames in the following two aspects. The one is the allowable maximum number of failure columns in robustness assessment of the steel frame. The other is the typical column-removal scenarios which should be particularly considered in practical design. It is found that for steel moment frame with design loads, it will collapse in some four-column-removal scenarios. Hence four-column-removal scenarios should be avoided by taking certain construction measurements in practical design. Two and three-column-removal scenarios should be particularly considered when assessing the robustness of the frame. For steel moment frame with twice design loads, the frame will collapse in any two-column-removal scenarios. Moreover, in small load case, the frame has the greatest robustness due to corner-column-related losses. While in large load case, the robustness of the frame is the strongest in interior column losses. The linearly consecutive column losses have less adverse effects on the robustness of the frame than the rectangular-shaped column-removal scenarios. Unlabelled Image • The performances of the multi-storey steel frame in multi-column-removal scenarios are studied. • The effects of the removed column number, location and magnitude of the load are discussed. • A maximum allowable number of failure columns is recommended for the steel frame. [ABSTRACT FROM AUTHOR]

The aircrafts face the serious issue of particle deposition on blade surface when inevitably working in the dust environment. A simplified C3X turbine blade within film holes is selected to investigate the particle deposition characteristics on blade surface. The EI-Batsh deposition model is applied to observe the particle deposition process and the dynamic grid method is used to rebuild the surface morphology of deposit layer. It is found that the particle deposition rate rises with the increasing particle size due to the increasing impacting frequency of particles. But the deposition rate gradually decreased when the particle diameter increasing to the constant value (15 μm). The particle density has a little influence on particle deposition in comparison to the particle size, especially when particle density increases to 1700 kg/m3, density no longer affects the deposition rate. Besides, the deposit layer on blade surface leads to the increase of particle deposition rate due to the increasing roughness when St < 1. Morphology changes of blade surface at three characteristic positions under different particle sizes. [Display omitted] • The EI-Batsh deposition model is applied to observe the particle deposition process. • The dynamic grid method is used to rebuild the surface morphology of deposit layer. • The effects of particle size and density on particle deposition are studied. • The particle deposition and the surface morphology variation are discussed. • The Stokes number is applied to show the particle deposition characteristics. [ABSTRACT FROM AUTHOR]

This paper describes a multi-objective optimization method for round-to-slot shaped film-holes (RTSH) using computational fluid dynamic analysis and surrogate model approximation. The physical model is a single-row of film cooling holes on a flat surface. Three design variables relating to the main RTSH geometric parameters are investigated: the film-hole inclination angle (θ), slot width (s), and film-hole height (t). The slot length (l) and hole-to-hole pitch (P) are fixed as 2 d and 2.4 d , respectively, where d is the film-hole diameter. The optimal model is constructed by selecting the discharge coefficient (C d) and spatially-averaged adiabatic film cooling effectiveness (η ad,av) as independent objective functions. From the Pareto front of optimal solutions, the optimized round-to-slot holes are obtained under blowing ratios of M = 0.5 and 1.5. Numerical assessments corresponding to the maximum η ad,av (Opt-A), maximum C d (Opt-B), and a compromise between the two objective functions (Opt-C) are performed, and the mechanisms influencing the optimal film-hole shapes in terms of film cooling performance are analyzed in depth. [ABSTRACT FROM AUTHOR]