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The pressure ratio of a compressor increases when the engine performance is improved, which leads to a higher air velocity in the combustion chamber. This aggravates the pressure loss in a conventional diffuser, which is proportional to the square of the inlet velocity. It is, therefore, an urgent need for a new diffuser technology. Regardless of whether high-temperature, or low-pollution, combustion chambers are being used, the significant difference when compared with other chambers is the notable increase in the combustion air and its entry through the dome of the flame tube. However, the increased amount of air in the dome causes a mismatch between the diffuser outlet and the dome intake of the flame tube. Therefore, to solve the problem of an excessive total pressure loss and a mismatch of the intake air in the combustor, a novel air-bleeding aerodynamic diffuser has here been proposed. The effects of various parameters (including the number of air-bleed holes, the position of the first row of holes, and the position of the second row of holes) and their interactions on the performance of this diffuser have then been investigated by using the experimental design presented by Taguchi. The maximum static pressure recovery was achieved by using a genetic algorithm combined with the CFD method. Among the three parameters, the results revealed that the position of the first row of holes had the largest impact on the performance of the diffuser. Also, the optimal values of the three parameters varied for the inlet Mach numbers 0.10, 0.15, and 0.20. The relative difference between the predicted values and the values obtained by the numerical simulations were all below 3%, which showed the reliability of the predictions. As compared with the reference case, the optimized results for the three working conditions increased by 19.16%, 21.38%, and 40.62%, respectively. [ABSTRACT FROM AUTHOR]

Concerning dual-carbon applications, establishing a new energy-dominated power system to achieve carbon peaking and carbon neutrality objectives is imperative. Pumped storage units excel in this context, owing to their unique advantages. During the load-shedding process of the pump turbine, the intricate flow patterns and cavitation phenomena substantially influence the flow field. This study introduces a cavitation model to perform numerical simulations of load rejection processes in pumped storage power plants, aiming to thoroughly investigate the impact of cavitation phenomena on the units. The results indicate that as the rotational speed increases, the dynamic and static interference within the no-blade region becomes notable, resulting in pressure pulsations within the guide vane region and exacerbating structural deformation and fatigue failures. Moreover, deviations from the designated operational point disrupt the symmetry of the flow field, leading to irregular changes in radial forces. Accounting for the mass disturbance and changes in wave velocity attributable to a cavitation phase transition, pressure fluctuation amplitude increases within the draft tube, consequently engendering complex flow phenomena. These findings offer indispensable guidance for the optimal design and safe operation of pump turbines within new power systems. [ABSTRACT FROM AUTHOR]

In order to study the flow characteristics of an integrated natural circulation reactor under inclined conditions, a typical three-dimensional analysis model of natural circulation was established. The natural circulation under inclined conditions was numerically simulated using the computational fluid dynamics method, and the velocity and temperature distribution characteristics of heat exchangers and mixed-flow channels with different inclined angles were analyzed. The results show that as the inclination angle of the heat exchanger flow rate increases, there is a spatial migration phenomenon corresponding to the direction of the average flow rate. A large inclination angle will lead to a serious deterioration of the natural circulation capacity in the lower channel. Under inclined conditions, there is a phenomenon of temperature stratification in the mixed-flow channel. [ABSTRACT FROM AUTHOR]

• The flow characteristics of vertical slot fishways at different slopes (1.5%, 3.0%, 4.5%, 6.0%) were systematically studied. • The turbulence and energy dissipation in a fishway increase with increasing slope. • The distribution of vorticity shows little variability with increasing slope but may interfere with the passage of fish through the vertical slot. • An increase in water depth has no significant effect on the flow characteristics in the pool. The effects of a vertical slot fishway slope (with slope values from 1.5% to 6%) on a flow field are numerically investigated, using a re-normalization group k – ε model. The distribution of the velocity, turbulence kinetic energy (TKE), average energy dissipation rate per unit volume (E), and vorticity for different slopes are systemically explored. The results indicate that, with an increase in slope, the appearance of downward flow in conjunction with an increase in vertical velocity results in three-dimensional flow characteristics. The recirculation region in H s , at a 6.0% slope, was 20.9% less than that at a 1.5% slope. Meanwhile, the flow velocity in the vertical slot region grew with increasing slope, which would limit the passage of fish with burst speed lower than the velocity in the vertical slot region. The TKE and E may locally exceed the threshold at larger slopes. Furthermore, vorticity distribution shows little variability with increasing slope, but may interfere with the equilibrium of the fish in the vertical slot region. In addition, the change in water level has little effect on the flow field, which is changed by the increase in slope. These findings can aid vertical slot fishway designs especially in terms of the efficiency of fish passage. [ABSTRACT FROM AUTHOR]

The Savonius hydrokinetic turbine (SHT) is widely used for generating electricity from running water. However, most optimization work has been carried out on conventional blades with similar concave and convex profiles. This study aims to enhance SHT performance by modifying the rotor blades' outer surface radius (0.079, 0.087 and 0.095 m) to create a semi-elliptical shape, thus reducing opposing forces. The tip speed ratio (TSR) varies from 0.5 to 1.3 with an interval of 0.1. A constant channel velocity of 0.8 m/s at Re = 2.25 x 105 is considered for the analysis. The flow field has been numerically investigated using the SST k - ω model. This study comprises the angular variation in the coefficients of power (Cp) and torque (Cm), performance curves of the rotor, and pressure distribution on the blade surface at different angular positions. It is observed that the rotor with a radius of 0.095 m has a maximum Cp value of 0.142, which is 7.57% and 18.33% higher than the Cp values of rotors with radii of 0.079 m and 0.087 m, respectively. The maximum power output of the rotor with a radius of 0.095 m is 2.32 W, whereas the power outputs of the rotors with radii of 0.087 m and 0.079 m are 2.16 W and 1.96 W, respectively. An increase in the instantaneous values of Cm between rotation angles 0° to 115° is observed, during which the returning blades mainly interact with the incoming stream. The pressure decreases as the radius of the semi-elliptical outer surface increases at rotor positions ranging from 0° to 225°, but it increases at rotor positions ranging from 270° to 315°. [ABSTRACT FROM AUTHOR]

The plunger valve has an important role in a large compressor system as its operating characteristics directly affect the aerodynamic boundary condition of the compressor equipment. In this study, dynamic modeling and analysis method of the plunger valve are proposed for an accurate control of the system. By considering the interaction between the dynamic flow in the valve and actuator action, a lumped parameter model for the fluid-structure interaction force and multibody dynamic model of the actuator are developed based on intrinsic correlation parameters. A combination analysis to simultaneously predict valve flow and actuator dynamic characteristics is proposed. The predicted results are in a good agreement with experimental data, which validates the proposed model and analysis method. The analysis results show that the coupling effect between the valve flow and actuator is significant and has an important role in valve control, particularly when the valve opening is smaller. Compared to the experimental data and computational fluid dynamics results, the presented methods are accurate for valve control and effective for prediction of flow rate. [ABSTRACT FROM AUTHOR]

The sleeve regulating valve is an important part of a pipeline system and is widely used in the fields of nuclear power and thermal power. In this study, a series of numerical and experimental studies are performed to understand the depressurized flow characteristics inside a new type of multi-layer sleeve regulating valve. In the calculations, the standard k-ԑ turbulence model and the mixture model combined with the Zwart-Gerber-Belamri cavitation model are used to clarify the internal flow and cavitation characteristics in the regulating valve. With the new valve, the results show that when the valve is fully opened, the pressure drop at all levels of the valve is comparatively average (approximately 2-3 MPa for each level) and the fluid velocity in the sleeves at all levels is comparatively uniform at 90 m/s--which can prevent the valve from being eroded by highly changing fluid flow rates, and also offers ideal pressure reduction performance. To reduce the degree of cavitation, it is recommended to adjust the outlet pressure of the valve to 0.7 MPa. [ABSTRACT FROM AUTHOR]

The study focuses on heat transfer performance and flow structure associated with swirling jet on a flat target surface. The analysis is carried out with helicoid inserts of swirl number S = 1.3 by varying the number of vanes with Reynolds number between 11200 and 35600. The comparison of swirling jet with circular jet is carried out on its heat transfer performance. The heat transfer and flow structure are visualized using thermo-chromic liquid crystal sheet and oil film technique respectively. The numerical simulation is also performed at Re = 24700 for H/D distance between 1 and 4 using computational fluid dynamics. The heat transfer results reveal that the presence of axial recirculation zone at Re = 29800 and 35600 for the triple helicoid affects the uniformity of heat transfer distribution at 0 < X/D < 1.5 at H/D = 3. The axial component of velocity with respect to swirling jet is less than zero in the stagnation area and it increases at 0.57 < r/D < 0.97 for single vane and 0.63 < r/D < 0.97 for double and triple vanes. While the steep increase in tangential velocity of the triple vane jet is apparent at 0 < r/D < 0.5 at H/D = 2 and 3, the maximum value of point radially shifts inward towards the jet. The location of maximum turbulent kinetic energy approaching the surface at about r/D = 0.9 - 1.2 which characterizes the swirling jet at H/D = 2. [ABSTRACT FROM AUTHOR]

This study proposes a new intermediate warehouse to prevent the problem that the ore in the vertical pipeline hydraulic lifting system blocks the nozzle during the process of being sucked into the lifting hard tube. A mathematical model and a finite element model of ore transport are established. Numerical simulation and experimental research are performed on the process of ore injection into the intermediate warehouse. Results show that the proposed intermediate warehouse has higher ore transmission efficiency, smaller pressure pulsation, and more stable transmission process compared with the traditional structure scheme. The larger the slurry conveying flow, the shorter the time required to convey the ore. In the process of slurry injection, the closer to the inlet, the more uneven the velocity distribution on the Z section, and the more concentrated the dynamic pressure. The closer to the lower end of the intermediate warehouse, the more dispersed the dynamic pressure, and the fluctuation of dynamic pressure in the intermediate warehouse is the main cause of unstable flow. The feed flow has a great influence on the stress state of the intermediate warehouse structure, the ore transfer time, and the stress decay period. The feed flow rate should be reasonably selected to meet the working requirements. [ABSTRACT FROM AUTHOR]

Several engineering equipment's and installations often operates under severe conditions such as elevated temperatures and high pressures in turbines, combustion furnaces and chambers, engines, generators, etc. This results in lessening the life time of such facilities. Hence, many efforts have been made to study the effects of such conditions with few focusing on the effects of surface injection on heat transfer (HT) characteristics. In this work, a test rig was developed to investigate the influence of blowing ratio (M), from 0 to 4, as well as injection angle Φ (from 30° to 150°) on the flow and HT characteristics. The velocity distribution was measured using particle image velocimetry (PIV) technique. A significant increase in both friction coefficient and heat transfer were obtained by increasing the Re for the case of Φ > 90° at constant M and a decrease for angles Φ < 90°. Results indicated that, the average Nusselt number (Nu) ratio increases with increasing the M for all injection angles, with minimum and maximum values occurring at the angles of 60° and 150°, respectively. General correlations for the Nu and friction factor have been proposed as functions of the flow, Φ, and M based on the results of this work. The correlations, were found to represent the experimental data with reasonable accuracy. Also, the experimental results were well compared with the previous work with highest deviation of about 6.42% for the ratio of heat coefficient. [ABSTRACT FROM AUTHOR]

Local exhaust ventilation is used to capture contaminants and maintain a comfortable atmosphere in premises. Exhaust hoods with extension units (canopy hoods) are commonly used in open-type local exhaust devices. The goal of this study was to use computational and experimental methods to determine the effect of adding an extension to a local exhaust hood on the separated-flow streamlines, vortex zones, exhaust velocity distribution, and local drag coefficient. We used the discrete vortex method together with computational fluid dynamics to investigate air flows near round and slotted extended exhaust hoods. We then compared the computed airflow velocity field, vortex zone outlines at the inlet of a local exhaust hood, and local drag coefficient factor with data from a field experiment. Outlines of vortex zones resulting from flow separation at the inlet of the hood were considered for a hood length of 5 times gauge (the radius of a round hood or half-width of a slotted exhaust hood), hood tilt angles of 90°, 75°, 60°, 45°, and 30°, and extension lengths of 0; 0.5; 1; and 2 times gauge. We found that longer extensions caused the first vortex zone to enlarge, and the contaminant capture velocity of the local exhaust hood to decrease. We identified the behavior of the local drag coefficient at various hood tilt angles, extension lengths (as listed above), and hood lengths (including 2, 3, and 5 times gauge), and translated them into equations for computing the local drag coefficient. • Algorithm for computing flow separation in extended exhaust hood has been developed. • Vortex zone outlines at inlet of a round extended exhaust hood have been determined. • Calculations of velocity to a hood with varying extension lengths have been performed. • Local drag coefficient has been determined numerically for extended exhaust hoods. • Expressions have been obtained enabling LDC computation for extended exhaust hoods. [ABSTRACT FROM AUTHOR]

In the square column attachment ventilation (S-CAV) mode, the introduction of multiple airflows attached to the column into the horizontal diffusion zone inevitably leads to various "airflow collision" phenomena. However, after the floor-attached airflow collides, the indoor air distribution may deviate from the design goal. In this paper, the layout of the axisymmetric and non-axisymmetric arrangement of double columns is summarized. The airflow collision mechanism and flow characteristics for different column layouts are analyzed via experiments and computational fluid dynamics (CFD) simulations, and a new partition form is proposed to more effectively control the indoor environment. A 1:2 scale model was employed for the velocity verification experiments and flow field visualization. The results indicated that the airflow collision area can be divided into impact, transition, and collision zones with axisymmetric double-column layouts. In the range of 1–3 m/s, any variation in the supply air velocity, irrespective of the occurrence of airflow collision, may be considered negligible with respect to its impact on the attenuation trend of the axial velocities. At the same absolute value of the air supply temperature difference, the cooling condition experiences a 3.1 times greater kinetic energy loss due to collision than does the heating condition. In a nonsymmetric arrangement of two columns, the curve formed by the stagnation point rotates, and the direction of rotation is biased toward the side of the column that is farther away. The findings provide a solid theoretical basis for the engineering application and optimal design of CAV modes. • Study the collision mechanism under S-CAV mode by CFD and visualization experiment. • The airflow collision area is categorized into impact, transition, and collision zone. • Air supply velocity showed a limited effect on the attenuation trend of the axial velocities. • Kinetic energy loss due to collision is 3.1 times greater in cooling than heating conditions. • The stagnation line will rotation when the column is arranged non-symmetric. [ABSTRACT FROM AUTHOR]

The cylindrical volute intake structure possesses some advantages including convenient processing, convenient installation & uninstallation and high machining efficiency. The helium turboexpander with this novel intake structure in a superconducting cryogenic device is investigated deeply in this study. Based on the established mathematical model and the corresponding numerical computation methods, the whole flow passage internal flow of the helium turboexpander is numerically simulated. And then the distribution characteristics of total pressure, static pressure, static temperature, relative velocity and total enthalpy in the cylindrical volute, nozzle, impeller and diffuser are explored, and loss mechanism of the internal flow is analyzed. The results indicate that the novel cylindrical volute intake structure has obvious pre-rotation effect on the inlet flow field of the nozzle, and this intake structure has little loss. In addition, the expansion effect in downstream components including nozzle and impeller is obvious, and the flow field changes uniformly. The overall efficiency of the turboexpander is up to 84.8%, which indicates that it is reasonable that the novel cylindrical volute is used as the intake structure of turboexpander. [ABSTRACT FROM AUTHOR]

Lighter weight, simpler structure and throat area controllable are the developing trends of aircraft engine exhaust system. To meet these challenges, a new concept of hybrid throat control (TC) nozzle was proposed to improve the control efficiency of throat area (η) by using a rotary valve with secondary injection. The flow mechanism of the hybrid TC nozzle and the effect of aerodynamic and geometric parameters on nozzle performance were investigated numerically. Then the approximate model characterizing the hybrid TC nozzle was established with design of experiment and response surface methodology. The approximate model was used to analysis the coupling effect between parameters and optimized the parameter combination. The results show that the flow area of the nozzle can be restricted effectively by the rotary valve and the secondary flow, and η is bigger than 5.24. Nozzle pressure ratio and secondary pressure ratio are the dominant factors for the nozzle throat area control performance. The optimization of the parameter combination was carried out with penalty function approach, with ratio of throat area control being 30 percent and corrected mass flow ratio of secondary flow being 5 percent The maximize error of the optimization result is 4.13 percent and it verifies the validity and feasibility of the approximate model. [ABSTRACT FROM AUTHOR]

Flow past wall-mounted cylindrical structures is commonly encountered in natural rivers where piers of bridge crossings or vegetation stalks are common within channels. In the current study, the influence of cylindrical structures on flow/bathymetric alterations for three different permeabilities is explored via two-dimensional numerical modeling. In model construction processes, the structure permeability is varied with the surface void ratio along the perimeter of the cylinder, i.e. the density of emergent and submerged solid elements is used to delineate the cylinder boundaries. The validation of this model is guaranteed through careful comparison with experimental data obtained for similar hydrodynamic conditions and cylinder properties. The validated model then is applied to investigate flow properties and scour and deposition patterns with structure permeabilities of 0.0, 0.38, and 0.62. Simulated results show that a permeable structure has less impeding effects on flow than a solid cylinder. The wake velocity reduction decreases 38% with a 63% increase in the structure permeability due to increasing intensity of the bleeding flow through surface voids, causing less flow contraction and diversion, lower turbulent kinetic energy, and lower lee-side scour around the permeable structure and less deposition downstream under live-bed conditions. [ABSTRACT FROM AUTHOR]

The flow structure and geomorphology of rivers are significantly affected by vegetation patterns. In the present study, the effect of vegetation in the form of discontinuous and vertically double layered patches particularly on the resulting flow turbulence was examined computationally in an open channel. A k-ɛ model was implemented in this research work which was developed using 3-D numerical code FLUENT (ANSYS). After the validation process of numerical model, the impact of discontinuous layered vegetation patches on the flow turbulence was investigated against varying vegetation density and patch length. The mean stream-wise velocities at specified positions showed larger spatial fluctuations directly upstream and downstream of vegetation elements, whereas sharp inflections in the profiles were witnessed at the top of smaller submerged elements i.e. z/hs= 1 (where z is the flow depth and hs is the smaller vegetation height). The reduction in flow velocity due to tall vegetation structure was more as compared with that of short vegetation. The mean velocity in the patch regions was visibly higher than that in the gap regions. The profiles of turbulent flow properties showed more rise and fall within the patches with a high vegetation density i.e. Ss/d= 4; and St/d= 8 (where Ss/d and St/d are the smaller and taller vegetation spacing, while d is the vegetation diameter) as compared with low vegetation density i.e. Ss/d= 8; and St/d= 16. The turbulent flow structure in the large patch and gap regions was found to be more stable than that in the small patches and gaps; whereas, due to the variation in distribution form of the patch, turbulence is relatively unaffected, and the flow structure variation is low. Turbulence was observed to be large, followed by a saw-tooth distribution within the patches; whereas, low turbulence is observed in the non-vegetation regions. The turbulent intensity acquired maximum of 13% turbulence for dense vegetation arrangement as compared to that of sparse arrangement having maximum of 9% turbulent intensity. A noteworthy rise in turbulent kinetic energy and turbulent intensity was witnessed as the flow passed through the vegetated regions. Hence, a non-uniform flow was observed through discontinuous and double layered vegetation patches. [ABSTRACT FROM AUTHOR]

Fish-bone type dividing dikes are river engineering structures used for river training and to protect a mid-channel bar from scour. The flow characteristics around fish-bone type dividing dikes are very complicated, especially near its fish-bone dam. To understand the flow and scour processes associated with fish-bone dams, this paper conducts a numerical simulation of flow characteristics for different fish-bone dam angles. Based on the Yudaizhou fish-bone type dividing dike of the Dongliu Waterway, a 3-D numerical model is established via Flow-3D to simulate the flow characteristics around a fish-bone type dividing dike, which is verified by flume experiments. Based on the results, the effects of different fish-bone dam angles on water level and velocity distribution are investigated. With increasing fish-bone dam angle, the longitudinal and lateral gradients of the water level gradually decreased, and the variation degree of the longitudinal velocity also decreased; however, the variation degree of the lateral velocity increased. Vortex areas formed around the fish-bone dam and the downstream zone of the dike. A large velocity gradient was found around the dike, and the downstream vortex area decreased with increasing fish-bone dam angle. [ABSTRACT FROM AUTHOR]

Higher vector efficiency of fluidic thrust vectoring (FTV) technology results in less requirement on secondary flow mass, which helps to reduce the influence of secondary flow on the performance of an aero-engine. In the paper, a new concept of FTV, named as a hybrid shock vector control (SVC) nozzle, was proposed to promote the vector efficiency of a SVC nozzle. It adopts a rotatable valve with a secondary flow injection to enhance the jet penetration, so as to improve the vector performance. The flow characteristics of a hybrid SVC nozzle were investigated numerically by solving 2D RANS equations. The influence of secondary pressure ratio (SPR) and rotatable valve angle on vector performance were conducted. Then, the coupling performance of a hybrid SVC nozzle and an aero-engine was estimated, by using the approximate model of a hybrid SVC nozzle and the performance simulation model of an aero-engine. Results show that, a desirable vector efficiency of 2.96 °/%-? (the vector angle achieved by using secondary flow of 1% of primary flow) of a hybrid SVC nozzle was obtained. In the coupling progress, when a secondary flow of 5.3% of primary flow was extracted from fan exit to a hybrid SVC nozzle, a vector angle of 14.1°, and a vector efficiency of 2.91°/%-? were achieved. Meanwhile the thrust of the aero-engine thrust decreased by 5.6% and the specific fuel consumption (SFC) increased by 0.5%. [ABSTRACT FROM AUTHOR]

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In this paper, a new method of dynamic mesh based on two functional controls is used in the continuous guide vane closure, and the three-dimensional numerical simulation is carried out to investigate the transient flow characteristics for a Francis-type reversible pump-turbine in the turbine mode in the load regulation scenario, with the detached eddy simulation (DES) turbulent model. The transient flow characteristics during the closure of the guide vanes are illustrated by analyzing the signals of the mass flow, the torque and the pressure fluctuations in the frequency and time-frequency domains. It is shown by the simulated results that a continuous assessment of the transient flow characteristics during the guide vane closure may be made by using the new method of the dynamic mesh. Furthermore, the flow field analysis involves both the onset and the development of the unsteady phenomena progressively based on an organized guide vane closure law. The flow pattern in the return channel maintains a relatively stable flow field before the last stage of the closure, as compared with the unstable flow field in other domains. To identify the unit variation under the fluid-dynamical conditions, the influence of the three-dimensional unsteady flow structures in the passage is analyzed and its evolution during this transient process is characterized by the fluid-dynamics and the spectral analysis. [ABSTRACT FROM AUTHOR]

Tall modern buildings are extremely sensitive to the wind. Thus, assessment of wind loads to design these buildings is essential. The purpose of this study is first to introduce a theoretical framework and simultaneously express basic aerodynamic studies. Furthermore, assessments are made to reduce drag coefficient performance of aerodynamic modification approaches including chamfered, rounded, and recessed corners as well as the performance of aerodynamic formations namely, set-back, taper, and 45-deg helical in a tall triangular building of about 120 m (40 stories). CFD simulation of this study is done by Autodesk Flow Design 2014. Building scales are presumed to be B = 1/6H. The results show that aerodynamic modification of rounded-corners, tapered are capable to cause a reduction in the drag coefficient of the building by 66% and 24%, respectively. Moreover, the technique of aerodynamic modification is approximately 74% more efficient to meet wind effect than aerodynamic form techniques. [ABSTRACT FROM AUTHOR]

The supercritical carbon dioxide (SC-CO2) jet has a wide application prospect for rock breaking and jet fracturing in the development of the unconventional shale energy, due to its special physicochemical properties. To investigate its jet flow characteristics, the high-speed photography is used in experiments and the simulations through a compressible numerical model are carried out. It is shown that the jet flow field can be divided into three typical regions, the mixing layer possesses the same characteristics as a gas/gas turbulent mixing layer, with the divergent angles evidently smaller than those of the incompressible jets. The predicted results by the numerical model are in a good agreement with those of the experimentations. Through the dimensionless analysis, the potential core shows a length of about 9d and an increasing trend with the increase of the inlet pressure while the decay rate shows a decreasing trend, and the radial profiles consistent well with the "Ue - η" normalized method. In addition, a significant temperature drop of the SC-CO2 is observed between the nozzle inlet and the exit. A simple and convenient semi-empirical equation for calculating this temperature variation is deduced. Finally, the flow characteristics suggest that the SC-CO2 jet should be treated as a compressible jet. [ABSTRACT FROM AUTHOR]

Abstract Blast furnace (BF) slag is regarded as a high-grade waste heat resource. Dry centrifugal granulation technology became an important method for its low-energy consumption, recovering waste heat, etc. In this paper, the analytic formulas of liquid film thickness and the average radial velocity were obtained by micro-element force analysis. The influence of various factors on liquid film was analyzed by computational fluid dynamics (CFD)simulation. It was revealed that liquid film produced a slip when the cup diameter was 50 mm and the rotary speed was 1500 rpm. The critical rotary speed of the slip increased with an increase in the cup diameter. The liquid film thickness changed almost linearly with the inlet mass flow rate. With the amount of slag constant, the influence of the slag inlet conditions on the liquid film at the edge of the cup was negligible. The surface tension mainly affected the initial spreading process of the liquid film. With the increase of the cup edge inclination angle, liquid film thickness increased. [ABSTRACT FROM AUTHOR]

The flow characteristics of methane hydrate slurry formed from an 100% water cut system at a flow rate (mean velocity) range from 0.62 to 3.84 m/s were experimentally investigated in a high-pressure flow loop. The effects of hydrate volume fraction, tube diameter and flow rate on the flow regimes, pressure drops and the coefficients of pipe friction were measured. The experimental results indicated that a turbulent flow took place easily at low hydrate volume fraction region with a relatively high flow rate, while it transformed into a laminar flow with the increase of the hydrate volume fraction. There existed a critical value of hydrate volume fraction where the transition occurred. In the turbulent flow regime, the coefficients of pipe friction were close to that of the continuous phase (water in this study) and the effects of hydrate volume fraction and flow rate could be neglected. In the laminar flow regime, methane hydrate slurry could be considered as a pseudoplastic fluid and presented shear-thinning behavior which got more obvious with the increase of the hydrate volume fraction. An empirical Herschel-Bulkley-type equation was established based on the experimental data and the flow characteristics of methane hydrate slurry could be estimated in pipes with different diameters based on the modified hydrate volume fraction. It was of great significance for hydrate slurry transportation not exceeding the critical value of hydrate volume fraction. [ABSTRACT FROM AUTHOR]

Fluid flow in a rock fracture bounded by two rock surfaces with surface asperities is a complex phenomenon to study. However, precise knowledge of the flow characteristics through a real rock fracture is essential in order to design and estimate the efficiency and production of unconventional oil and gas exploration and geothermal energy extraction projects. The aim of this numerical study, is therefore to incorporate a rock fracture in the modelling platform using a pre-processing procedure and to couple it with the flow parameters. 3-D scanning technology was used to obtain the rock fracture surfaces and to generate the fracture profile in a grid matrix form. In addition, the generated fracture profile was imported in to the COMSOL Multiphysics software package to simulate the flow characteristics of the rock fracture. The COMSOL model was validated using experimental permeability results conducted under triaxial conditions. According to the results, the COMSOL numerical model can simulate the flow characteristics through the rock fracture with more than 90% accuracy compared to the experimental data. The numerical results also reveal that the pressure gradient through a rock fracture is nonlinear and depends on the fracture profile. Furthermore, the nonlinearity of pressure gradient varies on different sections of the fracture, confirming the heterogeneity nature of the fracture. In addition, the results illustrate that the entire fracture width does not contribute to the final flowrate and that it is essential to consider the effective fracture width in flow calculations. [ABSTRACT FROM AUTHOR]

In order to analyze intake port flow characteristics of a four-valve direct injection (DI) diesel engine, steady-state flow bench experiments and numerical simulations method were coupled to investigate the following four combined intake ports: (1) helical port (left) and tangential port (right); (2) tangential port (left) and helical port (right); (3) helical port (left) port and helical (right); and (4) tangential port (left) and tangential (right) port. Results show that the simulation of port flow coefficients matches experimental findings very well, and the port coefficients of the above four combinations do not vary much, but their swirl ratios are very different. Specifically, when the valve lift is the maximum, the swirl ratio of the combination of "helical and tangential" is the greatest among the four combinations, and the swirl ratio of "tangential and tangential" is the minimum. And the3D fluid simulation method and steady-state experiment are important means to investigate the flow characteristics of the combined intake ports. [ABSTRACT FROM AUTHOR]

Subaqueous debris flow is one of the most important marine geological disasters. Understanding the subaqueous debris flow is related to the safety of marine engineering and the development of the national economy. In this paper, the subaqueous debris flow is taken as the research object. Through a comparative study of terrestrial debris flow, combined with existing research results, the characteristics, motion characteristics and motion dynamics of subaqueous debris flow are studied, and the future research direction of subaqueous debris flow is discussed. The study shows that the water pressure during the motion process of subaqueous debris flow can not be ignored. Physical model test and numerical simulation are the most important research methods at present. How to accurately measure the parameters of the motion process in the physical model test is a difficult problem. In the numerical simulation, the constitutive model and the coupling of multiphase medium need to be further studied. A large number of measured data, physical experiments and numerical simulation data remain to be accumulated. It is a direction to study the kinetic theory of subaqueous debris flow from the point of view of plastic fluid mechanics and energy conversion. [ABSTRACT FROM AUTHOR]

CO 2 geological storage in tight sandstone reservoirs is an effective method of CO 2 capture, utilization, and storage (CCUS). CO 2 migration and flow characteristics in sandstone during geological storage affect the physical and mechanical properties of rocks significantly. In this study, laboratory injection experiments combined with X-ray computed tomography (CT) scanning and scanning electron microscopy (SEM) tests, and computational fluid dynamics (CFD) numerical simulation have been conducted to investigate the effect of geological and engineering parameters on CO 2 migration and flow characteristics. The results show that: (1) The injection rate and injection pressure affect the Sc-CO 2 migration path. Moreover, the fluid velocity and fluid pressure affect the pressure distribution in pores significantly. Limiting the injection rate and pressure during the CO 2 geological storage is beneficial for the stability of the storage. (2) The pressure distribution of the fluid changes with orders of magnitude depending on the injection pressure. However, the overall transient relative pressure is almost consistent and the fluid pressure in the bending section of the bending pores exhibits a linearly decreasing trend. (3) SEM tests provide a connection between laboratory experiments and CFD simulation on microscopic scale. The injection pressure and the acoustic emission (AE) energy have a positive correlation to a certain extent. The Sc-CO 2 migration path could be forecasted preliminarily through the fluctuation of the injection pressure-time curves and AE response. The results enrich the theory of CO 2 migration and flow characteristics during CO 2 geological storage. • Geological and engineering factors on CO 2 migration and flow feature are conducted. • The injection rate and injection pressure affect the Sc-CO 2 migration path. • The fluid velocity and pressure affect the stress distribution significantly. • SEM provide a connection between laboratory experiments and CFD simulation. • Injection pressure and AE energy have a positive correlation. [ABSTRACT FROM AUTHOR]

During winters, the high-speed train travels in the northern of China is struck by to the snow, ice and coldness, massive snow accumulating on the bogies. To understand the cause of snow packing on the highspeed train's bogies clearly, the 3-D unsteady Reynolds-averaged Navier-Stokes equations with a RNG double-equations turbulence model and a DPM discrete phase model were used to investigate the flow field carried snow particles in a single high-speed train bogie region and monitor the movement of snow particles. And, the numerical simulation was verified by the wind tunnel test. The results show that when air flows into the region, the airflow will rise and impact on the wheels, brakes, electromotors and other parts of bogie regions. The snow particles will follow the air, while the air direction changes sharply the particles will keep the movement due to the inertia. Afterwards, the snow packs on the bogie. In front of the bogies the streamlines of the air and the particle path lines are basically the same. However, due to the inertia of mass particles, the following characteristics of the snow particles with the air are not obvious in the bogie leeward side. Different structures of the end plates will affect the snow accumulation in the bogie regions. [ABSTRACT FROM AUTHOR]

The opening unit is an important device in a rotor spinning unit to comb fibres and remove trash. In this paper, numerical simulation is carried out to study the flow structure in the rotor spinning channel and the trash removal process in the trash removal unit. Firstly the effect of the opening unit on the airflow field in the rotor channel is investigated by singlephase simulation. The result shows that the effective area for fibre conveyance enlarges as the absolute value of negative pressure at the outlet increases, while it decreases as the opening roller speed increases. However, the effect of the negative pressure and the opening roller speed on the length of the vortex in the axial direction is quite small. Secondly the trash separation process in the trash removal unit is simulated using the Discrete Phase Model (DPM). Suitable rotational speeds of particles of different diameters are acquired. These results could provide a valuable reference for parameter selection in the trash-removal process. [ABSTRACT FROM AUTHOR]

An optimum designed plate-type falling film heat exchanger is the key technique to scale down the size of a LiBr/H 2 O absorption heat pump. Flow characteristics have the largest impact on the performance of a plate-type falling film heat exchanger. However, there is no research on falling-film flow characteristics of LiBr solution on the corrugated plate in vacuum atmosphere. Numerical flow models based on a plate-type falling film heat exchanger were constructed with 2-D and full 3-D spatial and temporal resolution using the Volume of Fluid technique. Flow characteristics of horizontal columns with different degrees of arc were successfully modelled with 2-D spatial model and the optimum arc degree is found. The falling-film flow patterns under different Reynolds number are thoroughly analyzed with full 3-D spatial model. [ABSTRACT FROM AUTHOR]

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The large eddy simulation(LES) of the flow characteristics in an annular jet pump (AJP) is conducted, and the flow characteristics are systematically analyzed from both time-averaged and instantaneous aspects. The jet expansion, the velocity distribution and the energy are considered to analyze the time-averaged evolution of the flow field in the AJP. The transient flow characteristics can also be acquired from the analysis of the turbulence intensity and the Reynolds stress. The simulation demonstrates that in the time-averaged characteristics, the potential cores increase linearly with the increase of the flow ratio. With the flow development, the jet half-width gradually increases and the residual energy coefficient decreases. Compared with the distribution of the time-averaged axial velocity, that of the instantaneous velocity is more complex and disorderly. The high intensity of the axial turbulence mainly occurs in the mixing layer and the near-wall regions of the diffuser. The annular distribution of the Reynolds stress is mainly in the mixing layer and the recirculation region. There is a low-stress zone between the mixing layer and the high-stress region in the wall-boundary layer. The intensity of the spanwise vortexes is larger than that of the streamwise vortexes, and therefore, the former make greater contribution to the total vorticity. This research provides a better understanding of the flow characteristics in the AJP. [ABSTRACT FROM AUTHOR]

The structural parameters of an elastic porous material MR used for perspective rotary seals, are analyzed in this article. The porosity value range, also as the wire diameter and the thickness of the elastic sealing element were determinated. It is clearly justified the necessity of additional research of flow characteristics of porous elastic sealing elements made of MR-material. The results of experimental studies of characteristics of rotor seals made of an elastic porous MR- material are also given. [ABSTRACT FROM AUTHOR]

The pipe diffuser, an efficient kind of radial bladed diffuser, is widely used in centrifugal compressors for gas turbine engines. This paper investigates flow characteristics of a pipe diffuser for centrifugal compressors by solving three-dimensional Reynolds-averaged Navier-Stokes equations. The results show that the pipe diffuser is adaptable to high Mach number incoming flows, and its unique leading edge could uniform the flow distortion. Numerical analysis indicates that the choke in pipe diffuser occurs suddenly, which leads to the dramatically steep performance curves near choke condition. Besides, it is found that the first half flow passage is particularly important to the pipe diffuser performance as it influences the choking behavior, the static pressure distribution, and the matching, so more attention should be paid to this region when designing or optimizing a pipe diffuser. Two counter-rotating vortices generated in the diffuser inlet region are captured by numerical simulation, and they can exist in the downstream of the diffuser passage. More detailed analysis show that these two vortices dominate the flow structure in the whole diffuser passage by shifting flow to certain positions and forming high-momentum flow cells and wake flow cells. The leading edge formed by the intersection of adjacent diffuser passages significantly affects this pair of vortices. In addition, these two vortices also affect the flow separation in pipe diffuser flow passages, they suppress separation near the front wall and back wall while facilitate separation at center locations. Therefore, it is recommended to design the leading edge of the pipe diffuser carefully to control the vortices and obtain a better flow field. [ABSTRACT FROM AUTHOR]

Plenum chambers are commonly used to provide flow homogenization in ventilation and air conditioning systems. To reduce energy consumption and improve ventilation performance, the interior flow characteristics of a multi-path plenum chamber system were investigated through visualization experiments of flow field. As the flow distribution remained uneven after the primary structural parameters of the traditional chamber were optimized, a flow homogenization chamber was proposed by inserting a perforated plate to further improve flow uniformity. Taking the "one-inlet and two-outlet" chamber configuration as a case study, the proposed flow homogenization mechanism was analyzed in terms of flow control. The effects of the perforated plate geometry on flow uniformity and resistance performance were studied using two typical chambers with cross-sectional aspect ratio (W/H) of 1/1 and 5/1. The recommended dimensionless installation location of the perforated plate (y/L) in each chamber was determined to be 0.1 and 0.3 of the chamber length from the input, respectively, with an optimal aperture diameter (d) of 30 mm. In addition, the effectiveness of the flow homogenization chamber was verified using four commonly used air duct sizes, and different application scenarios were discussed for multi-path duct connections. The results show that the adjustment of perforated plate on flow field improved the flow distribution uniformity for chamber system with W/H = 1/1 and 5/1 by up to 87.50% and 56.71%, respectively, compared with the standard 90° T-junction connection. • Airflow movement inside chamber is analyzed through visualization experiments. • Inserting perforated plate can effectively improve the flow uniformity of chamber. • Conversion between axial and radial flows is the most critical step for flow homogenization. • The optimal installation location and aperture rate of perforated plate are obtained. [ABSTRACT FROM AUTHOR]

Many gas pre-drainage boreholes are generally constructed in coal seams to ensure safe underground operation. True triaxial experiments were conducted to study the mechanical response and gas flow characteristics of pre-drilled coal to reveal the in-situ behavior at pre-drilled regions in coal seams. The mechanical parameters, failure modes, and flow rate evolutions of pre-drilled coal samples were collected. The gas flow rate of pre-drilled coal samples showed an S-shaped trend with the increase of strain, and no obvious descending progress was found in the flow rate-strain curves. The typical failure mode for pre-drilled coal samples was shear-type during the true triaxial stress compression. V-shaped macro-fractures around the boreholes were observed when boreholes were perpendicular to bedding planes and parallel to face cleats. In contrast, single shear macro-fractures around the boreholes were observed when boreholes were parallel to butt cleats. The pre-drilled coal samples exhibited lower peak strength values when boreholes were parallel to butt cleats, induced by the relatively low cohesion parameter. Pre-drilled coal's initial flow rates perpendicular to bedding planes and parallel to butt cleats directions were only 33.33% and 41.67% of values measured along face cleats. More complex macro-fractures were formed, and up to a 39.30% decrease in strength was observed in pre-drilled coal samples under true triaxial unloading stress paths. The variations in volumetric strain level and the flow rate evolution were further discussed with an anisotropic conceptual failure model. These mechanical responses and flow characteristics of pre-drilled coal would guide the design of borehole layout and prevention of coal dynamic disasters. • Mechanical parameters and flow rate evolutions of pre-drilled coal were measured. • Failure mechanisms of pre-drilled coal were revealed under true triaxial stress. • The effects of anisotropy on the mechanical and flow characteristics were studied. [ABSTRACT FROM AUTHOR]

The braided river is a common river pattern, but the phenomena that occur when a stratified flow passes through a braided river are not well known. In the present study, flow characteristics under different temperature conditions were observed by combining laboratory experiments and numerical simulations. The results indicate that the positions of the hightemperature zone, the high-velocity zone and the secondary circulation varied significantly as the temperature difference between two layers varied. The transfer path of the high-velocity zone was reversed when going from isothermal to thermalstratified flow, which was caused by the reversal circulation structure in cross-section. In thermalstratified flow with a slight temperature difference of 1°C and 3°C, the high-temperature zone stayed very near the middle of the outside bank along the anabranch, with no shift to the inner bank, while with a little large temperature difference of 5°C, a shift of the high-temperature zone along the anabranch occurred. In addition, the turbulence kinetics also varied with the temperature difference. [ABSTRACT FROM AUTHOR]

The supersonic condensation process of methane-vapor-nonane mixture was investigated in a supersonic nozzle. First, the physical model of the ternary mixture of the supersonic condensation process in a nozzle was established. Second, the mathematical model of the ternary mixture of the supersonic condensation process in a nozzle was determined based on the simulation results from a binary mixture supersonic condensation process. This work developed the flow characteristics and condensation mechanism of the ternary mixture in supersonic flows. The results indicate that when spontaneous condensation occurs, the release of latent heat causes the pressure, temperature and the Mach number to change abruptly. Condensation is still an expansion process, and after the condensation shock, water vapor began to condense spontaneously at x = 4.0 mm. The water vapor droplets served as the external nuclei of the nonane, which decreased the energy barrier of the nonane vapor, allowing it to condense at a lower super-cooling (38.3 K) and super-saturation temperature (37.4 K). It was observed that the existence of water vapor accelerated the condensation of the nonane vapor. [ABSTRACT FROM AUTHOR]

It is known that more than 80% of global energy is produced by internal combustion engines. Therefore, the improvement of working cycles and modernization of systems and components of the piston and combined internal combustion engines with the aim of improving their technical and economic indicators is one of the urgent tasks in the global energy sector. Research studies in this area were carried out mainly by means of numerical simulations or experimentally under static conditions. Information about gas exchange processes in the unsteady gas dynamic conditions are quite limited and controversial. This work aims at obtaining of the additional clarifying information about the gas dynamics in the air-gas tract of the internal combustion engine and finding ways of improving the processes. The results of experimental studies of gas exchange processes in the intake and exhaust tracts piston engines were presented in the article. Experimental studies were conducted on full-scale models of a single-cylinder engine. The experimental dependencies of change of the instantaneous velocity and pressure of the gas flow in the gas paths from the crank angle were presented in the article. Improvement of gas exchange processes in the intake and exhaust pipes of internal combustion engines due to the transverse profiling of the channels was proposed in the paper. [ABSTRACT FROM AUTHOR]

In the paper it is theoretically proven that the topological structure of the airflow field in an airliner cabin is absolutely unstable. These are typical flow characteristics in the cabin. This also explains why in previous numerical simulations and experiments, discrepancies often arose in flow-direction results. Next, we used the fine LES with 22 million grid cells to reproduce the primary flow instability phenomenon in a symmetric cabin. However, the unsteady RANS (URANS) method with conventional turbulence models, such as the RNG k-ɛ turbulence mode, the Realizable k-ɛ turbulence model and the V2f turbulence model, cannot effectively simulate the instability of flow field in a symmetric cabin. So we developed an anisotropic model (BV2fAM) based on the idea of the V2f model. Three million grid cells are used in the BV2fAM simulation. The flow instability phenomenon is successfully reproduced in the numerical simulation of BV2fAM. [ABSTRACT FROM AUTHOR]

For understanding foam propagation behaviour in porous media, experimental investigations were carried out concerning lamellae foam flow characteristics in a vertical tube. Foam is treated as a two-phase fluid, and the governing non-dimensional parameters were obtained through theoretical analysis. Two types of foams, CO2 and N2 foams, were studied and clear linear relationships between non-dimensional parameters of Δ pd/ σ and (3 μU/ σ)2/3 were observed. With different threshold values, the experimentally obtained mechanistic models for both foams predict much higher flow resistance compared with present popular models. Experimental results reveal the fact that a startup pressure is necessarily needed for mobilising the foam lamellae, and therefore indicate that the Herschel-Bulkley model instead of the power-law model could be better in revealing the mechanism of flowing foams in porous media in large scale. [ABSTRACT FROM AUTHOR]

The gas flow characteristics in rectangular cross section converging-diverging micronozzles incorporating the effect of three-dimensional (3D) rough surface topography are investigated. The fractal geometry is utilized to describe the multiscale self-affine roughness. A first-order slip model suitable for rough walls is adopted to characterize the slip velocities. The flow field in micronozzles is analyzed by solving 3D Navier-Stokes (N-S) equation. The results show that the dependence of mass flow rate on the pressure difference has a good agreement with the reported results. The presence of surface topography obviously perturbs the gas flow near the wall. Moreover, as the surface roughness height increases, this perturbation induces the supersonic "multiwaves" phenomenon in the divergent region, in which the Mach number fluctuates. In addition, the effect of 3D surface topography on performance is also investigated. [ABSTRACT FROM AUTHOR]

Although gerotor pumps are used in a wide range of industrial applications, higher work pressure causes shock or collision among pump components, which leads to large stress fluctuations and shortened pump life expectancy. This paper therefore proposes a novel variable clearance design that diminishes such component collisions. After a geometric mathematical model is constructed of variable clearance rotors, a fluid analysis model is developed based on a relief groove design. Applying the model to two fixed clearance and three variable clearance designs demonstrates the effects of various fixed clearance sizes on gerotor pump peiformance and identifies the differences between fixed and variable clearance designs. The results support the feasibility of the proposed design: the appropriate variable clearance designs maintain robust flow characteristics and effectively reduce shock and collision among pump components, thereby reducing stress level, increasing stability, and extending the life expectancy of the gerotor pumps. [ABSTRACT FROM AUTHOR]

An experimental apparatus is developed for further study of flow characteristics in microchannels, compressible gas—air, is used as a workfluid.The experimental study were performed in copper micro tubes and plexiglass tubes with the diameters 0.2 mm, 0.3 mm, 0.4 mm,0.5 mm and 1.0 mm, and the roughness less than 3%. The results show that the material of micro-tubes does not affect the experimental results; transition from laminar to turbulent flow occurred at critical Reynolds number about 1100 in the tubes with diameter 0.2 mm, the critical Reynolds numbers are respectively about 1300,1600,1800 in the tubes with diameters 0.3 mm, 0.4 mm and 0.5 mm, so the conclusion show the descending direction of the critical Reynolds number with the decreasing tube diameters, and the phenomena of transition in advance from laminar to turbulent flow is apparently observed. At the same time, the larger the diameter, the Reynolds number increases, the pressure drop increases even faster. And the results do not change with the change of tube number. [ABSTRACT FROM AUTHOR]

As wind flows around a sharp-edged body, the resulting separated flow becomes complicated, with multiple separations and reattachments as well as vortex recirculation. This widespread and unpredictable phenomenon has long been studied academically as well as in engineering applications. In this study, the flow characteristics around rectangular prisms with five different aspect ratios were determined through wind tunnel experiments and a detached eddy simulation, that placed the objects in a simulated deep turbulent boundary layer at Re = 4.6 × 104. A series of rectangular prisms with the same height (h = 80 mm), different longitudinal lengths (/ = 0.5/î, h, and 2h), or different transverse widths (w = 0.5h, h, and 2li) were employed to observe the effects of the aspect ratio. Furthermore, five wind directions (0°, 10°, 20°, 30°, and 45°) were selected to observe the effects of the wind direction. The simulated results of the surface pressure were compared to the wind tunnel experiment results and die existing results of previous papers. The vortex and spectrum were also analyzed to determine the detailed flow structure around the body. The paper also highlights the pressure distribution around the rectangular prisms with respect to the different aspect ratios. With an increasing transverse width the surface suction pressure on the top and side surfaces becomes stronger. In addition, depending on the wind direction, the pressure coefficient experiences a large variation and can even change from a negative to a positive value on the side surface of the cube model. [ABSTRACT FROM AUTHOR]

Vortex amplifiers (VA) use fluidic phenomena to modify flow through a containment breach, when used to protect glove box workers from exposure to the contents. The influence of control port geometry on swirl, operating characteristics, global flow, and momentum characteristics is studied experimentally. Shape and size of the control flow channels and the pressure applied at the tangential ports are critical in determining the trajectory of the jet issuing from the tangential ports and deflection of radial flow and vortex strength. Dominance of control-to-exit area ratio is confirmed. A clear improvement in performance is noted for a practical geometry derived from shaped passages of the device. Flow and momentum characteristics provide additional design data. The relationship of swirl number to output flow is demonstrated. Global flow and momentum characteristics provide insight into design and operation that is useful when avoiding back diffusion. [ABSTRACT FROM AUTHOR]

Continuous extrusion forming technology has much excellence as high production efficiency, saving energy and so on, however the flowing uniformity of the billet is the key of affecting the product quality of brass alloy rod in continuous extrusion. The flow characteristics of the brass rod billet were obtained based on continuous extrusion process, and then two kinds of forming channel shapes were designed in this paper. The results show that the grain size of the brass alloy rod is fine and uniform after continuous extrusion. For the process of round-table shaped channel, the flow velocity of the billet is nonuniform, the product appears circular microstructure, which make the performance and microstructure of product uneven. For the process of table-cone shaped channel, the flow velocity is more uniform, and the circular microstructure disappears, which make the performance and microstructure of brass alloy rod more uniform. The research results show that the product of brass alloy rod with uniform grain and excellent properties is obtained based on the table-cone shaped channel during continuous extrusion. [ABSTRACT FROM AUTHOR]

This paper presents the simulation and the analysis of the transient process of a Francis turbine during the load rejection by employing a one-dimensional and three-dimensional (1-D-3-D) coupling approach. The coupling is realized by partly overlapping the 1-D and 3-D parts, the water hammer wave is modeled by defining the pressure dependent density, and the guide vane closure is treated by a dynamic mesh method. To verify the results of the coupling approach, the transient parameters for both typical models and a real power station are compared with the data obtained by the 1-D approach, and good agreements are found. To investigate the differences between the transient and steady states at the corresponding operating parameters, the flow characteristics inside a turbine of the real power station are simulated by both transient and steady methods, and the results are analyzed in details. Our analysis suggests that there are just a little differences in the turbine outer characteristics, thus the traditional 1-D method is in general acceptable. However, the flow patterns in the spiral casing, the draft tube, and the runner passages are quite different: the transient situation has obvious water hammer waves, the water inertia, and some other effects. These may be crucial for the draft tube pulsation and need further studies. [ABSTRACT FROM AUTHOR]