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The effects of an immersed tube on slugging fluidization and particle behaviors in slugging fluidized beds were investigated using computational fluid dynamics. Both shallow and deep slugging fluidized beds with and without an immersed tube were simulated using the two-fluid model. The presence of an immersed tube gave rise to regions of high voidage below the tube and regions of low voidage above the tube. Formation of the high voidage region occurred by particle deflection away from the immersed tube, while that of the low voidage region resulted from particle vortices above the tube. The presence of an immersed tube was observed to facilitate bubble formation and bubble coalescence in both shallow and deep slugging fluidized beds. In shallow beds, an immersed tube regularized pressure fluctuations but increased the amplitude of fluctuations. In deep beds, an immersed tube reduced the frequency of pressure fluctuations by facilitating wall slug formation. Based on random sampling and statistical testing (Z-test) of mean slug lengths, it was concluded that mean slug lengths increased when U was increased from 0.90 m/s to 1.0 m/s in the deep free column (p-value = 0.0422). Based on an F-test of the slug length variance, it was concluded that there was larger variability of slug lengths for U of 1.0 m/s than for U of 0.90 m/s in the deep free column (p-value = 0.0202). However, the results of these statistical tests on mean slug lengths and slug length variance for the deep single tube column showed that U had no significant effect on mean slug length or slug length variance at the 5% significance level. Thus, one of the effects of an immersed tube in a deep slugging fluidized bed was regulation of the size of slugs formed and prevention of any significant increase in mean slug size or slug size variability. [ABSTRACT FROM AUTHOR]

This study involves an optimization procedure for the factors affecting the performance of the parallel connected vortex tube system using the Taguchi method. The effect of vortex tube inlet pressure, working fluid, nozzle material and nozzle number parameters on vortex tube performance were obtained as a percentage using experimental design and analysis. Experimental studies were carried out at inlet pressures (150, 300 and 450 kPa) with brass and polyamide nozzles having 3, 4 and 5 nozzle numbers using air, oxygen and carbon dioxide as working fluids. These parameters were selected as control parameters and Taguchi L18 orthogonal array was used to design of experiments. According to the optimization study performed with Taguchi method for the ΔT value, which is the performance indicator of the vortex tube, the most important control factor was found to be working pressure (79.50%). The order of importance of other control factors on ΔT was determined as working fluid, number of nozzles and nozzle material, respectively following of inlet pressure. Furthermore, the validity of the optimization was verified with the confirmation experiment. [ABSTRACT FROM AUTHOR]

Conventional machining of nickel-titanium shape-memory alloys (NiTi SMAs) faces significant challenges as a result of high thermal and mechanical distortions. The phase transformation temperatures of NiTi SMAs are primarily affected by the rise in temperature during the cutting process, which causes poor machinability under the conventional coolant approach. This research explored the effects of hybrid cooling-lubricating of minimal quantity nano-lubricants with compressible-chilled air generated from a vortex tube during the turning of the NiTi alloys. The experimental procedure involved measurement of induced-cutting force components under variable cutting conditions utilising various coolant approaches. A depth of cut, 0.5 mm with cutting speeds of 12.5, 25, and 50 m/min and feed rates of 0.05 and 0.1 rev/min were utilised. The hybrid cooling approach of minimum quantity nano-lubricants with vortex cooling, can increase tool life for most of the tested conditions and has a considerable influence in reducing the inducedcutting force. In contrast, only marginal improvement was observed for the surface roughness when using the same coolant-lubricant strategy. [ABSTRACT FROM AUTHOR]

In this manuscript, both experimental and numerical investigations have been carried out to study the mechanism of separation energy and flow phenomena in the counter flow vortex tube. This manuscript presents a complete comparison between the experimental investigation and CFD analysis. The experimental model was manufactured with (total length of 104 mm and the inner diameter of 8 mm, and made of cast iron) tested under different inlet pressures (4, 5, and 6 bar). The thermal performance has been studied for hot and cold outlet temperature as a function of mass fraction, α, (0.3-0.8). The 3-D numerical modeling using the k-ε model used with code (FLUENT 6.3.26). Two types of velocity components are studied (axial and swirl). The results show any increase in both cold mass fraction and inlet pressure caused to increase ΔTc, and the maximum ΔTc value occurs at P = 6 bar. The COP of two important factors in the vortex tube which are a heat pump and a refrigerator have been evaluated, which ranged from 0.25 to 0.74. A different axial location (Z/L = 0.2, 0.5, and 0.8) was modeled to evaluate swirl velocity and radial profiles, where the swirl velocity has the highest value. The maximum axial velocity is 93, where it occurs at the tube axis close to the inlet exit (Z/L = 0.2). The results showed a good agreement for experimental and numerical analysis. [ABSTRACT FROM AUTHOR]

The complex three-dimensional flow that develops around an inclined flat solar panel near the ground is investigated using Computational Fluid Dynamics. The early stage evolution of the flow and the interaction of the shear layers emanating from the sides of the panel, the large separation region behind the panel and the boundary layers on the panel and ground are captured using Delayed Detached-Eddy Simulation to model the turbulence. The mean analysis shows that a small clearance produces a wall-jet like flow in the gap region between the panel and the ground, which tends to elongate the wake region in the downstream direction. On the other hand, a strong upwash is observed for a larger gap, reducing the length of the wake. Transient three-dimensional flow structures are captured using vorticity contours and the λ2-criterion. The early stage development of flow around the panel shows inverted hairpin-like vortices that are shed from the leading edge, touch down on the ground, generate a counter-rotating sheared vortex and a pair of vertical vortex tubes that extend from the ground and curl up into the wake. This pair of vortex tubes appears to be the source of the meandering structures reported in the literature. When the flow reaches a quasi-steady state, there is an asymmetric distorted flow for the smaller gap, whereas there is a nearly symmetric wake pattern for the larger gap. [ABSTRACT FROM AUTHOR]

This paper discusses a study of air-temperature variation along the expansion chamber axis in zones of the nozzle inlet and flow swirler in direct-flow, counterflow, three-flow, and single-flow vortex tubes. It is established that, in all cases, air cooling in the vortex tube occurs in the zone of the swirling device, while its heating occurs in the zone of flow unwinding. The change in the air temperature in the axial zone along the expansion chamber appears due to heat exchange between the heating and cooling zones. [ABSTRACT FROM AUTHOR]

An experimental analysis has been carried out to investigate the thermal and friction factor characteristics of fluid flow in a tube with double strip helical screw tape (DS-HST) inserts with different values of twist ratio and compared with single strip helical screw tape inserts and plain tube. Water is used as a working fluid at different flow rates with constant heat flux conditions. CFD analysis is also carried out to visualize thermal and fluid flow characteristics of fluid flow in tube with inserts. Experimental results have showed that Nusselt number and friction factor have attained excellent enhancement with double strip helical screw tape inserts in the range of flow rates than single strip helical screw tape inserts at the value of twist ratio 1.5. Correlation is also developed for Nusselt number with a range of Reynolds number, twist ratio and number of strips. Moreover, the performance ratio has attained maximum value at twist ratio of 2.5 with high values of flow rate. It is concluded that DS-HST is able to attain enhancement in the efficiency of heat exchanger, causing a reduction in size for thermal applications. [ABSTRACT FROM AUTHOR]

The optimization of the wind energy conversion is one of the most important domains which was widely interested researchers. The i istabilities in the wind turbine wake are one of the sources of energy loss which strongly influenced the helical lube vortex structure and are generally difficult to be quantified using experimental facilities. This paper presents a numerical investigation on the wake downstream of a horizontal axis wind turbine (HAWT) model using the Fluent software. Results were validated using experimental measurements conducted in the CRTEn wind tunnel. The Kelvin wave's theory was, also, used to analyze the deformations acting on the zip vortices. The cartography of the velocity gradient tensor components of the first tip vortex and the different families of Kelvin wave's were studied and classified according to the azimuth wavenumber. The obtained results confirm that the tip vortices meandering correspond to the helical mode of Kelvin wave's and the stretching-compression phenomenon is the most important deformation acting on the tip vortex tubes during the development of HAWT wake. [ABSTRACT FROM AUTHOR]

AISI 52100 hardened bearing steel is popular in many industrial applications due to its excellent wear resistance and high strength. Therefore, a high level of surface integrity of the same is the utmost important requirement to enhance fatigue life. Machining of hardened AISI 52100 steel is difficult because severe plastic deformation and generation of high temperature alter the surface metallurgy of the machined component and hamper the tool life. The present investigation includes a comparative analysis of surface integrity of AISI 52100 bearing steel during hard turning under different near-dry environments, namely, dry, Minimum Quantity Cooling and Lubrication (MQCL), Compressed Chilled Air by Vortex Tube (CCAVT), and Hybrid Nanofluid Minimum Quantity Cooling and Lubrication (Hybrid NF-MQCL). Soyabean (a vegetable) oil is used as cutting fluid in MQCL and base fluid in Hybrid NF-MQCL environments. To prepare hybrid nanofluid, two different nanoparticles Al2O3 and MWCNT, are used. The chilled air is generated through a vortex tube. The surface integrity of AISI 52100 steel was studied in terms of microhardness, the thickness of the white layer, surface roughness (Ra), and residual stresses. Higher cutting speed and feed show positive and negative correlation on surface integrity of AISI 52100 steel, respectively. Hybrid nanofluid MQCL exhibits the lowest surface roughness (0.34 μm), microhardness (625 Hv0.1), compressive residual stresses (−168 MPa), and thin white layer (0.9 μm) in contrast, and dry machining shows higher surface roughness, microhardness, tensile residual stress, and thick white layer. In comparison, MQCL and CCAVT are found to be intermediate. It is found that hybrid nanofluid MQCL enhances the overall performance of the machined surface as compared to other near-dry techniques. [ABSTRACT FROM AUTHOR]

In this work, a state-of-the-art vortex detection method, Instantaneous Vorticity Deviation, is applied to locate three-dimensional vortex tube boundaries in numerical simulations of solar photospheric magnetoconvection performed by the MURaM code. We detected three-dimensional vortices distributed along intergranular regions and displaying coned shapes that extend from the photosphere to the low chromosphere. Based on a well-defined vortex center and boundary, we were able to determine averaged radial profiles and thereby investigate the dynamics across the vortical flows at different height levels. The solar vortex tubes present nonuniform angular rotational velocity, and, at all height levels, there are eddy viscosity effects within the vortices, which slow down the plasma as it moves toward the center. The vortices impact the magnetic field as they help to intensify the magnetic field at the sinking points, and in turn, the magnetic field ends up playing an essential role in the vortex dynamics. The magnetic field was found to be especially important to the vorticity evolution. On the other hand, it is shown that, in general, kinematic vortices do not give rise to magnetic vortices unless their tangential velocities at different height levels are high enough to overcome the magnetic tension. [ABSTRACT FROM AUTHOR]

This numerical study focuses on the coherent structures and bypass transition mechanism of the Stokes boundary layer in the intermittently turbulent regime. In particular, the initial disturbance is produced by a temporary roughness element that is removed immediately after triggering a two-dimensional vortex tube under an inflection-point instability. The present study reveals a complete scenario of self-induced motion of a vortex tube after rollup from the boundary layer. The trajectory of the vortex tube is reasonably described based on the Helmholtz point-vortex equation. The three-dimensional transition of the vortex tube is attributed to the Crow instability, which leads to a sinusoidal disturbance that eventually evolves into a ring-like structure, especially for the weaker vortex. Further investigation demonstrates that three-dimensional or quasi-three-dimensional vortex perturbations in the free stream play a critical role in the boundary layer transition through a bypass mechanism, which is featured by the non-modal and explosive transient growth of the subsequent boundary layer instabilities. This transition scenario is found to be analogous to the oblique transition in the steady boundary layer, both of which are characterised by the formation of streaks, rollup of hairpin-like vortices and burst into turbulent spots. In addition, the streamwise propagation of turbulent spots is discussed in detail. To shed more light on the nature of the intermittently turbulent Stokes boundary layer, a conceptual model is proposed for the periodically self-sustaining mechanism of the turbulent spots based on the present numerical results and experimental evidence reported in the literature. [ABSTRACT FROM AUTHOR]

The vortex tube is one of the widely used cooling systems in the industry. Investigating the effect of all input variables on the outlet cold temperature difference in laboratory state is timeconsuming and costly. To this purpose, in the current study, attempts were made to model and predict the effect of all input variables on the outlet cold temperature difference of air and inlet air using adaptive neuro-fuzzy inference system (ANFIS) method. The ANFIS method was designed with three structures of fuzzy inference systems called subtractive clustering (SC) algorithm, fuzzy c-means (FCM), and grid partition (GP) with four types of input membership functions including trimf, gaussmf, gbellmf, and pimf. For model training and testing, 326 laboratory data were used. The developed models were compared using statistical parameters of correlation coefficient, mean absolute relative deviation, standard deviation, and root mean square error (RMSD) together with general desirability function. The results showed that GP algorithm with input pimf membership function with the greatest value of correlation coefficient (0.9975) and lowest value of RMSD for test data (0.4199) and general desirability function value of 0.71 is the best method to predict outlet cold temperature difference. Using the above-mentioned method, the most optimum state of vortex tube performance for industrial applications was found to be the use of 3 or 6 nozzels, at the pressure range of 0.55 to 0.6MPa and the nozzle angle of 20 to30 degrees, and for laboratory applications was obtained to be the use of 6 nozzles, at the pressure range of 0.55 to 0.6MPa, and the nozzle angle of 25 to 35 degrees. [ABSTRACT FROM AUTHOR]

The spinning behavior of flow-acoustic resonant fields inside an axisymmetric cavity configuration was numerically investigated in four flow conditions containing different resonances between vortex-shedding modes and diametral acoustic modes. Zonal large-eddy simulations (ZLESs) were conducted to determine the aeroacoustic and aerodynamic fields simultaneously. In the ZLESs, a shear stress transport turbulence model was used to model the relatively steady flow field inside the inlet and outlet sections. Simultaneously, the wall-modeled LES formulation was used in the cavity section to resolve the highly complex flow-acoustic resonant fields. The ZLES results were well validated by the experimental results in the literature in terms of the frequency, amplitude, and spatial features of the acoustic pressure pulsations. Subsequently, the spinning behavior and mechanism of the excited diametral acoustic modes and the resonant vortex-shedding modes were comprehensively illustrated. The results showed that the excited diametral acoustic mode span anticlockwise along the cavity circumference, resulting in intense acoustic-pressure fluctuations several times greater than at the inlet dynamic-pressure head, together with longitudinal pressure propagations. Using proper orthogonal decomposition analysis, the spinning mechanism was found to be closely related to the interaction between the α-mode and the β-mode, which had fixed temporal and spatial phase lags. Thereafter, the first vortex-shedding mode gave rise to a strong spinning motion of the resonant flow field, while the second vortex-shedding mode created a slight spinning motion. The corresponding phase-dependent flow fields at consecutive planes along the cavity circumference revealed the spatiotemporal evolution of the velocity variations, surface streamlines, and vorticity variations of the shedding vortices. Large-scale helical vortex tubes were formed within the cavity volume due to the strong spinning behavior. [ABSTRACT FROM AUTHOR]

High-resolution, pulse-to-pulse observation of the 2016 Vela glitch and its relaxation provided an opportunity to probe the neutron star internal structure and dynamics with unprecedented detail. We use the observations of this glitch to infer superfluid characteristics in the framework of the vortex creep model. The glitch rise time constraint of 12.6 s put stringent limits on the angular momentum exchange between the crustal superfluid and the observed crust. Together with the observed excess acceleration in the rotation rate as compared to the post-glitch equilibrium value, this discriminates crustal superfluid-crust lattice and core superfluid-crustal normal matter coupling time-scales. An evident decrease in the crustal rotation rate immediately before the glitch is consistent with the formation of a new vortex trap zone that initiates the large-scale vortex unpinning avalanche. Formation of vortex trap by a crust breaking quake induces short-lived magnetospheric changes. The long-term post-glitch spin-down rate evolution reveals the moments of inertia and recoupling time-scales of the superfluid layers participating in the glitch and leads to an estimation of the time to the next glitch that agrees with the time interval between the 2016 and 2019 glitches. Our results are consistent with theoretical estimates of effective neutron and proton masses in the superfluid. We also constrain the vortex line-flux tube pinning energy per intersection as 2 MeV. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the impingement of a two-dimensional (2-D) vortex pair translating downwards onto a horizontal wall with a wavy surface. A principal purpose is to compare the vortex dynamics with the complementary case of a wavy vortex pair (deformed by the long-wavelength Crow instability) impinging onto a flat surface. The simpler case of a 2-D vortex pair descending onto a flat horizontal ground plane leads to the well known 'rebound' effect, wherein the primary vortex pair approaches the wall but subsequently advects vertically upwards, due to the induced velocity of secondary vorticity. In contrast, a wavy vortex pair descending onto a flat plane leads to 'rebounding' vorticity in the form of vortex rings. A descending 2-D vortex pair, impinging on a wavy wall, also generates 'rebounding' vortex rings. In this case, we observe that the vortex pair interacts first with the 'hills' of the wavy wall before the 'valleys'. The resulting secondary vorticity rolls up into a concentrated vortex tube, ultimately forming a vortex loop along each valley. Each vortex loop pinches off to form a vortex ring, which advects upwards. Surprisingly, these rebounding vortex rings evolve without the strong axial flows fundamental to the wavy vortex case. The present research is relevant to wing tip trailing vortices interacting with a non-uniform ground plane. A non-flat wall is shown to accelerate the decay of the primary vortex pair. Such a passive, ground-based method to diminish the wake vortex hazard close to the ground is consistent with Stephan et al. (J. Aircraft, vol. 50 (4), 2013a, pp. 1250–1260; CEAS Aeronaut. J., vol. 5 (2), 2013b, pp. 109–125). [ABSTRACT FROM AUTHOR]

We show and explain how a long bead--spring chain, immersed in a homogeneous isotropic turbulent flow, preferentially samples vortical flow structures. We begin with an elastic, extensible chain which is stretched out by the flow, up to inertial-range scales. This filamentary object, which is known to preferentially sample the circular coherent vortices of two-dimensional (2D) turbulence, is shown here to also preferentially sample the intense, tubular, vortex filaments of three-dimensional (3D) turbulence. In the 2D case, the chain collapses into a tracer inside vortices. In the 3D case on the contrary, the chain is extended even in vortical regions, which suggests that the chain follows axially stretched tubular vortices by aligning with their axes. This physical picture is confirmed by examining the relative sampling behaviour of the individual beads, and by additional studies on an inextensible chain with adjustable bending-stiffness. A highly flexible, inextensible chain also shows preferential sampling in three dimensions, provided it is longer than the dissipation scale, but not much longer than the vortex tubes. This is true also for 2D turbulence, where a long inextensible chain can occupy vortices by coiling into them. When the chain is made inflexible, however, coiling is prevented and the extent of preferential sampling in two dimensions is considerably reduced. In three dimensions, on the contrary, bending stiffness has no effect, because the chain does not need to coil in order to thread a vortex tube and align with its axis. [ABSTRACT FROM AUTHOR]

The influence of a diametral acoustic mode on the flow dynamics was numerically investigated for an axisymmetric cavity system with vortex-excited acoustic resonances occurring at high Reynolds numbers and low Mach numbers. The zonal large eddy simulation (ZLES) was conducted to simulate the flow-acoustic coupling fields by the first three diametral acoustic modes at their maximum resonance intensities, respectively. First, the ZLES-simulated acoustic pressure pulsations were well validated by a preliminary acoustic modal analysis and acoustic pressure measurements in the literature. Subsequently, the acoustic-driven cavity flow dynamics were comprehensively demonstrated in terms of the time-averaged flow quantities, shear layer quantities, and high-order turbulence quantities. The results demonstrated that the shear layer momentum thickness, velocity fluctuations, and Reynolds shear stresses were remarkably intensified by the strong resonances with the first and second diametral acoustic modes. Simultaneously, large-scale helical vortex tubes were formed within the cavity, yielding an intensified flow three-dimensionality. Thereafter, the dominant flow modes behind the acoustic-driven cavity flow dynamics were extracted using the data-driven proper orthogonal decomposition from the highly noisy ZLES database. It was found that the first diametral acoustic mode significantly enhanced the dominant positions of the vertical flow-oscillation mode, yielding a large-scale flapping behavior of the mainstream flow, while the second diametral acoustic mode would modulate the cavities to synchronously absorb/release the flow streaks, resulting in the alternating expansion and compression behaviors of the mainstream flow. [ABSTRACT FROM AUTHOR]

Various schemes for pressure reduction of natural gas at gas separation stations using machineless devices are considered. Examples of gas-dynamic devices used for cold and heat generation and gas mixtures phases separation are given. The formula for determining temperature efficiency of vortex coolers operating on a quasi-ideal gas is obtained. The experimental characteristics of small-scale vortex tubes fed by high-pressure natural gas are presented. The influence of the Joule–Thompson effect on the temperatures of cold and hot flows is demonstrated. [ABSTRACT FROM AUTHOR]

Copyright of Natural Gas Industry is the property of Natural Gas Industry Journal Agency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Drainage & Irrigation Machinery Engineering / Paiguan Jixie Gongcheng Xuebao is the property of Editorial Department of Drainage & Irrigation Machinery Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Vortex tube (Ranque-Hilsch type/ RHVT) is a simple device used to obtain both cold and hot gas streams simultaneously from a compressed gas. The obtained cold gas is widely used in many low temperature commercial applications. In this work, the performance of the vortex tube was examined experimentally by studying the effects of inlet pressure variations, conical valve opening percentage, tube diameter and hot gas tube length on the thermal performance of the tube. Four tubes with diameters 14, 21, 25 and 32 mm with four hot exhaust gas lengths; 25, 50, 75 and 100 cm were tested experimentally and the obtained data were analyzed. It was observed that the 75 cm length of the hot side length, gives the maximum coefficient of performance for RHVT, as well as the maximum cold temperature reduction, either with or without insulation. Furthermore, the thermal performance of the RHVT was optimum for the two inner diameters; 14 and 21mm. This indicates that, when the ratio of hot side length to inner diameter (Lh/D) lies between 36 and 50, then the thermal performanmce of the RHVT is optimum and is highly recommended, which agrees with the results published in previous studies and invesitigations. [ABSTRACT FROM AUTHOR]

This paper presents a simple straight tube with different types of inserts in which there is a flow of water + Al2O3. The experimental and computational studies were performed for different inserts, such as simple insert, twisted‐I, twisted‐II, and simple straight tube. The coefficient of heat transfer and Nusselt number is computed for mass flow rate ranging between 0.06 and 0.20 m/s. The simple straight tube is used as a means of validating the experimental results with computational results. The work concluded that twisted‐II inserts provide enhanced thermal performance in comparison to all other process conditions. In this study, statistical analysis is performed by statistical software and by generating model equations. Furthermore, the effect of a twisted insert in heat pipe for two types of fluids, that is, water and nanofluid (Al203 + water) is experimentally and computationally designed using the Taguchi method and orthogonal array concept. Moreover, temperature and velocity contours are developed for all four types of insert designs in the tube. [ABSTRACT FROM AUTHOR]

Aviation turbulence is modelled as an interaction between an aircraft and a vortex tube. The vortex tube can have an arbitrary orientation/offset with respect to the aircraft. We compare modelling the aircraft (i) as a point and (ii) having a finite area (wing and fuselage). We consider both vertical and horizontal accelerations experienced by the aircraft. The baseline vortex tube has an area which is of the order of the aircraft area. [ABSTRACT FROM AUTHOR]

We investigate the occurrence of anomalous transport phenomena associated with tracer particles propagating through arrays of steady vortices. The mechanism responsible for the occurrence of anomalous transport is identified in the particle dynamic, which is characterized by long collision-less trajectories (Lévy flights) interrupted by chaotic interactions with vortices. The process is studied via stochastic molecular models that are able to capture the underlying non-local nature of the transport mechanism. These models, however, are not well suited for problems where computational efficiency is an enabling factor. We show that fractional-order continuum models provide an excellent alternative that is able to capture the nonlocal nature of anomalous transport processes in turbulent environments. The equivalence between stochastic molecular and fractional continuum models is demonstrated both theoretically and numerically. In particular, the onset and the temporal evolution of heavy-tailed diffused fields are shown to be accurately captured, from a macroscopic perspective, by a fractional diffusion equation. The resulting anomalous transport mechanism, for the selected ranges of density of the vortices, shows a superdiffusive nature. [ABSTRACT FROM AUTHOR]

Plasma control of forebody asymmetric vortices is mostly achieved by means of dielectric barrier discharge (DBD) plasma actuators. However, DBD actuators suffer from some disadvantages such as a weak induced body force, a single-direction induced jet, and an unclear control mechanism. We carry out wind tunnel experiments involving the forebody vortex control of a slender body at high angles of attack using an innovative extended DBD actuator, which has a stronger capacity to induce an electric wind than a DBD actuator. Through synchronous measurements of the pressure distribution and particle image velocimetry (PIV), the spatiotemporal evolution of the dynamic interactions between plasma-actuation-induced vortices and forebody asymmetric vortices is analyzed. The influence of plasma discharge on the boundary layer separation around a slender body and the spatial topological structures of asymmetric vortices are further surveyed, as the optimized actuation parameters. Extended DBD actuators are found to be more capable of controlling asymmetric vortices than DBD actuators, and a linear proportionality of the sectional lateral force versus the duty ratio is achieved. There exists an optimal normalized reduced frequency (f+ = 2πfpd/U∞ = 2.39) for asymmetric vortex control under the present experimental conditions. The research results can provide technical guidance for the control and reuse of forebody asymmetric vortices. [ABSTRACT FROM AUTHOR]

Two innovative kinds of sliding discharge plasma actuators based on different formation hypotheses of forebody asymmetric vortices are designed using a slender body model. Particle image velocimetry and surface pressure measurements are synchronously used to compare the control effect of antiflow and along-flow sliding discharge actuators for a forebody asymmetric vortex at high angles of attack. The experimental results show that the two kinds of sliding discharge plasma actuators can effectively change the random lateral force caused by the asymmetric vortices, and a better control effect is manifested using the along-flow sliding discharge plasma actuator, which contributes to the approximately linear proportional control of the lateral force. This finding suggests that the convective instability of the forebody vortex system in the leeward region of the slender body has a significant influence on the random lateral forces and moments. Through improving the spatial stability of forebody vortices, the flow control efficiency can be effectively improved. An optimal pulse frequency exists in each of the three actuation modes, but it may vary due to the different geometry configuration of the plasma actuator. In this regard, the research findings will potentially provide technical guidance for improving the efficiency of plasma actuators and understanding the formation mechanism of asymmetric vortices. [ABSTRACT FROM AUTHOR]

The flow in a Ranque tube with a square cross-section channel has been studied using the hydraulic concept of strongly swirling flow with a circulation zone. Based on experimental data, it has been found that for flow in a vortex tube, the hydraulic condition of flow crisis is satisfied: the longitudinal velocity becomes equal to the velocity of propagation of centrifugal waves at the boundary between the vortex and the circulation zone. It has been shown that the temperature variation along the flow occurs mainly in the region of the working channel in which the ratio of the longitudinal velocity at the vortex boundary to the propagation velocity of centrifugal waves fluctuates about unity. The existence of a previously unknown energy separation mechanism due to the presence of hydraulic jumps in the development of internal waves in a Ranque tube was assumed. [ABSTRACT FROM AUTHOR]

Turbulent flows at high Reynolds numbers are dominated by vortex filaments and/or sheets with sharp gradients in the vorticity field near the boundaries of the vortical structures. Numerical simulations of high Reynolds number flows are computationally demanding due to the fine grid required to accurately resolve these sharp gradient regions. In this paper, an alternative approach is proposed to improve the computational efficiency of Navier–Stokes solvers by reformulating the momentum equations as a set of equations for the time-dependent evolution of the flexion field. The flexion vector represents the curl of the vorticity field and is better able to resolve nonlinear effects in regions with large vorticity gradients. The improved resolution capabilities of the flexion-based approach are illustrated through the pseudospectral computations of the rollup of a perturbed 2D shear layer and the transition to a turbulence/viscous decay of the three-dimensional (3D) Taylor–Green vortex. The flexion-based formulation also provides further insight into the dynamics of turbulence through the evolution of the mean-square flexion or palinstrophy. Analysis of data from the Taylor–Green vortex simulations shows that the observed rapid growth of small-scale features and palinstrophy in 3D turbulent flows is primarily associated with flexion amplification by the curl of the vortex stretching vector. Consequently, we hypothesize that the primary physical mechanism responsible for energy cascade from large to small scales is the curl of the vortex stretching vector of interacting vortex tubes, as opposed to the stretching of individual vortex tubes. [ABSTRACT FROM AUTHOR]

When the cross-section is reduced, a vortex displays spiralling and elasticity, bursting when the external velocity drops. How are these properties affected near a free surface? To answer, a visualization experiment in water is considered where an oscillating obstruction is pitched orthogonally to a rolling oscillation expending minimum energy. We show that short aerated vortices in adverse pressure gradient and shear remain stable during stretching, bursting into bubbles when relaxed after maximum stretching. A vertical aerated double helix (DH) root vortex of contra-rotating vortex tubes is produced near a Rossby number of 0.20. The vortex approaches an inclination of $45^{\circ }$ to the vertical, where stretching intensifies the vorticity to the maximum extent. Vortex inclinations up to $45^{\circ }$ are stable and unstable thereafter. Vortex bursting commences only when the inclination crosses $45^{\circ }$ by the slightest amount. When relaxed, oscillations are produced, breaking the vortex into arrays of bubbles, sometimes precisely at $45^{\circ }$ inclination. The bubble diameter, modelled by equating the effects of the centrifugal force (CF) on the vortex core pressure, to surface tension scales with the inverse of the square of the rotational velocity. When a high CF is withdrawn, the bursting DH aerated vortex cone is crushed due to surface tension. A root vortex and a coiled-up trailing edge vortex together form a compact Hill's vortex when the highest CF is relieved, bursting into bubbles spectacularly scattered in the unstable sector. The DH vortex breakup is the connection point of vortices in proximity. At high CF, the DH has stacks of Taylor air tubes at $45^{\circ }$ to the external flow bursting when relaxed. Kelvin waves abound when bursting. [ABSTRACT FROM AUTHOR]

The dynamics of the structure of an infinite vortex tube in ideal gas under explosive external energy deposition near its axis is studied. With neglect of viscosity and heat conduction, it is discovered that the tube is destroyed under arbitrarily small power of energy release and the time of vortex destruction decreases as the total power of energy release increases. The physical model of the flow explaining the revealed relationships is constructed. The analytical relations assessing the problem parameters for the practical use of explosives in destruction of large-diameter vortices are obtained. The estimates show that the proposed method can be applied in practice. [ABSTRACT FROM AUTHOR]

Experimental results of wave-induced vortex generation around a slender, vertical cylinder are discussed. Coherent vortices appear in long waves (kR ∼ 0.1, where k is the wave number and R is the cylinder radius) during the timing of the secondary load cycle, a strongly nonlinear component of the wave force acting on the cylinder, which is also measured. However, the secondary load cycle is also present in moderately long wave cases (kR ∼ 0.3) where there is no vortex formation. The measurement of vortex generation is enabled by particle image velocimetry. The flow downstream the cylinder, in three horizontal planes at different depths, is measured. The vortex formation that occurs in the long waves is attached to the cylinder in the form of thin vortex tubes. These appear symmetrically at angles of 40°–45° off the wave propagation direction. In one weak long wave case, several very thin vortex tubes appear along the back side of the cylinder. Vortex diameters are 20% of the cylinder diameter in four cases and 50% of the cylinder diameter in one case. The measured vorticity emanates from the cylinder's boundary layer and is an order of magnitude stronger than the vorticity caused by wave breaking. Wave breaking reduces the vortex strength. The fact that the secondary load cycle appears without and with flow separation effects indicates that the load cycle is a gravity wave phenomenon that scales with the Froude number but that flow separation effects also contribute to the magnitude of such suction forces. [ABSTRACT FROM AUTHOR]

Experiments are conducted on a supersonic mixing layer with two lobed mixers, which are designed following the concept of a shock-eliminating combustor. Instantaneous images were obtained to examine the evolution process of large-scale vortices downstream of the lobed mixers. The results show that no streamwise vortices appeared downstream of the lobed mixer with a penetration angle of approximately 6.7° owing to the smaller pressure difference between the peak and trough regions of the lobed mixer compared with the rectangular lobed mixer (RLM). However, it provides a similar mixing enhancement as an RLM. Streamwise vortices appear downstream of the lobed mixer with a higher penetration angle of approximately 9.7°. Greater mixing enhancement is observed in the lobed mixer with a larger penetration angle. The lobed mixers have potential applications for mixing enhancement in air-breathing propulsion systems, such as scramjet engines. [ABSTRACT FROM AUTHOR]

It is of great importance to reveal the refrigeration mechanism at low-temperature around 4 K in pulse tube for improvement of the cooling performance in 4 K pulse tube crycoolers (PTCs). In this paper, the thermo-physical process in 4 K pulse tube was studied analytically from microscopic viewpoint using CFD simulation. The thermodynamic cycles of different gas parcels throughout the pulse tube were investigated. It was found that the real gas characteristics of the helium at the pulse tube cold end manifest more apparently from the central part nearer to the wall outside the boundary layer. Furthermore, it was revealed that boundary layer has the weakened heat loss or helpful effect on refrigeration in phase-shifting 4 K pulse tube operating at low frequency. This research newly provides intensified understanding of the inherent characteristics of 4 K GM-type pulse tube. [ABSTRACT FROM AUTHOR]

A gas-kinetic scheme (GKS) based on an unstructured grid is applied to simulate the evolution of the fluid motions in exponential variable cross-section resonators. The effects of the acoustic field intensity on the oscillatory pressure, velocity, temperature, and flow streaming structure were investigated numerically, and the model was validated. The results demonstrate that the geometry and driving strength are the main factors affecting the final performance of the system. For the quasi-linear and moderate non-linear cases in optimum exponential tube, the periodic generation, evolution, and shedding of vortices in flow fields are associated with the storage and release of energy, which is the transmission mode of the third type of direct current (DC) flow, and its driving mechanism is attributed to the asymmetrical pressure and temperature. Meanwhile, some new physical characteristics were also discovered for the highly non-linear case, e.g., the disorder and unsteadiness of the flow direction accomplished with turbulent flow streaming structures. The secondary flow is manifested as multiscale, irregular and unsteady vortices throughout the tube. The smallest increment of pressure and velocity amplitude occurs concurrently with the biggest increment of temperature amplitude. These evidences suggest that there is an optimal driving strength, even for a good configuration tube, with which the maximum efficiency can be obtained. [ABSTRACT FROM AUTHOR]

Three-dimensional CFD simulations carried to evaluate mixing performance of two designs of micromixers namely RB-TSAR and EB-TSAR. The results of flow physics analysis indicate that the interfacial area between the two flow fluids can be enhanced by creating a flow in transverse direction with the help of split and recombination of fluid streams by placing baffles in diffuser shaped mixing elements along the axial direction. Further, the simulation results indicate that at inlet Reynolds number below 1, the molecular diffusion is the most dominant mechanism of mixing, and the mixing index is almost the same for all cases. However at Re > 5, the secondary flow influencing the mixing process dramatically and thus mixing index is increased. The results also reveal that baffles can break the fluid streams, produce fluid convection and increase the contact area of the fluid by folding and deflecting which in turn helps to improve the mixing index. The split and recombination of the fluid streams and separation vortices play vital role in enhancing the mixing performance. The design configurations studied here showed mixing index higher than 0.85 for the Re in the range from 10 to 50. [ABSTRACT FROM AUTHOR]

Despite many advantages of cyclone-based particle separation, insufficient removal efficiency limits its use in fine particle removal. In this paper, we have developed an electric field-assisted cyclone capable of removing ultrafine particles (0.3 μm) with enhanced efficiency. Effects of several design parameters including flow rate, applied voltage, and the length of vortex tube have been experimentally evaluated for inertial and electrostatic separations of particles. With an optimization of the normalized vortex tube length, s/D = 1, the presented cyclone demonstrated the improved removal efficiency of 76% at the flow rate of 400 lpm and 25 kV voltage. [ABSTRACT FROM AUTHOR]

We present results from direct numerical simulations on laminar and turbulent non-canonical thermals with an initial rectangular density distribution at a Reynolds number of Re = 500 and Re = 5000, respectively. We find the non-canonical shape to induce strong azimuthal variations in the thermal for both the laminar and turbulent cases. These include noticeable differences in downward and horizontal propagation speeds as well as differences in the strength of the vortex tube. These differences persist over a significant period of time and help generate a cross-flow component that is otherwise not present in canonical cases. The cross-flow component is in the opposite direction to that observed in gravity currents with the same initial density distribution. This is counterintuitive seeing that both flows are solely driven by buoyancy. By extracting the three-dimensional streamlines, we find the descending vortex tube to force the dense fluid to follow a helical path. [ABSTRACT FROM AUTHOR]

The main objective of this research was to determine and verify friction coefficient using conical tube upsetting test for cold upsetting process with oil lubrication. Chosen material for conical tube is steel C45E. For experimental setup two types of conical tubes were used: conical tubes with cone angle of: 8° 30' and 15°. After the upsetting, change in height and outer diametar of specimens is measured. Required calibration curves for estimation of friction coefficient are provided by finite element (FE) simulation of the process. For the simulation of the process Simufact.forming 12 software is used. By comparison of experimental results and calibration curves it is concluded that the friction coefficient of µ = 0.095 agrees the most with both types of specimens. Estimated value of friction coefficient is verified by comparison of force - stroke (F-s) diagram and characteristic dimensions of specimens from numerical simulation for estimated coefficient and experimental results. [ABSTRACT FROM AUTHOR]

Vortex tube ejector is employed to extract sediments from canal. It consists of a duct laid across whole bed of the canal with a slit along its top edge and compared to the other alternative sediment-extraction devices, it is very efficient and economical. In this study, adaptive neuro-fuzzy inference system (ANFIS), artificial neural network (ANN) approaches were employed to predict the trapping efficiency of vortex tube ejector. Data-set as many as 144 was obtained by conducting experiments on vortex ejector. Out of 144 data-set, 100 data selected randomly were used for training whereas remaining 44 were used for testing the models. Input data-set consists of sediment size (mm), concentration of sediment (ppm), ratio of slit thickness and diameter of tube, (t/d) and extraction ratio (%) whereas trapping efficiency (%) was considered as output. Three membership's functions, i.e. triangular, generalized bell-shaped, and Gaussian were used with ANFIS. A comparison of results suggests that Gaussian membership function-based ANFIS model performs well in comparison to other membership functions-based ANFIS models, ANN and predictive equations proposed by previous researchers. Sensitivity analyses suggest that extraction ratio is the most important parameter in estimating trapping efficiency of vortex ejector. [ABSTRACT FROM AUTHOR]

Three-dimensional flow in a vortex tube with straight nozzle was investigated numerically. Four different turbulence models, Spalart-Allmaras, standard k − ε , SST k − ω and realizable k − ε were proposed to replicate the flow in the vortex tube. The simulation results of pressure, temperature and velocity field were compared with the experimental data based on dimensionless analysis. It was found that the sudden gas expansion in the vortex chamber causes a pressure drop. The secondary circulations phenomena were observed and identified. Furthermore, the friction between the gas and wall surface and the energy transfer between different laminar flows are the main factors of energy separation in the vortex tube. The realizable k − ε model predicts energy separation better than other models studied in this research. [ABSTRACT FROM AUTHOR]

In this investigation, experimental and computational fluid dynamics (CFD) technique is used to study a newly designed Ranque-Hilsch vortex tube (RHVT), such as a convergent-divergent one. The FLUENT code is used to solve the governing equations with three dimensional compressible and turbulent models using the standard k-ε turbulence model. In this study, based on obtained results by the CFD study, the investigation point of the minimum temperature of cold reversed flow is analyzed, and results show that the minimum cold temperature is not located exactly in the cold exit of the vortex tube. Finally, in order to attain more temperature separation in the vortex tube system, some suggestions and results are presented. Moreover, a comparison of a convergent-divergent vortex tube with the simple one and their influence on the maximum cooling point are some other results presented in this manuscript. There is an acceptable agreement between CFD and experimental results in the present paper. The obtained results show that reducing the throat diameter from 8 to 2.5 enhances the amount of cooling capacity in the vortex tube. [ABSTRACT FROM AUTHOR]

This study compares detailed regime maps in the case of operation using the air of two Ranque tubes with circular and square working channels with identical inlet guides and identical outlets. The degree of air expansion and the fraction of a flow rate through a cold outlet vary in ranges of 2–8 and 0.2–0.8, respectively. It is observed for both tubes that, as the degree of expansion increases, the dependences of a volumetric flow rate and a cooling ratio on the fraction of a cold flow rate become invariant. It is revealed that the cooling ratio in a circular tube is 1.5–2.0 times greater than that in a square channel, with the volumetric flow rate therein being approximately 10% lower. [ABSTRACT FROM AUTHOR]

This study provides analysis of a cooled Ranque–Hilsch vortex tube (RHVT) with various specifications. It shows how cooling influences energy conversion inside the RHVT and improves performance of the device in separation of hot gas from the cold stream within the fluid by presenting the temperature detachment (the temperature diminution of cold air (ΔTc = Ti − Tc), isentropic efficiency (ηis), and coefficient of performance (COP) of divergent, convergent, and straight VTs. Two key parameters including hot tube length and number of nozzles for cooling and insulated cases are investigated to find out how the performance of the VT is affected by different geometry configurations under cooling conditions. These influences were researched for straight, convergent, and divergent VT separators under different flow characteristics. The optimum geometrical conditions for the cooling cases were identified. Results are indicative of positive influence of cooling for energy separation inside a VT. The quantities of ΔTc, ηis, and COP for the cooled RHVT are greater than uncooled RHVT for various types of VTs. Cooling the VTs leads to an increase of 12.5% in ΔTc, 14.4% in ηis, and 15.1% in COP when the base case was an uncooled VT. [ABSTRACT FROM AUTHOR]

The present work represents a 3-D numerical investigation of forced convection heat transfer over circular and oval tube banks with longitudinal vortex generators (LVGs) for flow through a fin-and-tube heat exchanger. The thermo-hydraulic performance parameters are studied numerically using computational fluid dynamics (CFD) tool. It is found that within the range of Reynolds number (500-850) studied, the degree of heat transfer enhancement is greatly influenced by the tube shape. Heat transfer increases by 13 % when the angle of attack is varied from 15° to 25°, with a corresponding pressure drop of 40 % and 62 % for the oval tubes and circular tubes, respectively. The effect of the aspect ratio of the oval tubes is observed to be very significant. Several other performance parameters of the oval and circular tube banks with vortex generators under the same operating conditions are compared with a focus on finding an optimal configuration. [ABSTRACT FROM AUTHOR]

Phase transformation of nickel-titanium (NiTi) alloys due to temperature rise during machining process can deliberately deliver poor machinability. Hence, this study investigated the hybrid cooling and lubricating effects of nano-minimum quantity lubricant (NanoMQL) with vortex chilled air of NiTi machining. NanoMQL with vortex chilled air depicted a consistently low tool wear of 0.14 mm as compared to other conditions despite experiencing similar cutting duration, particularly for a lower speed of 12.5 m/min. Likewise, the hybrid cooling method had a profound effect towards tool wear resistant when cutting speed was doubled. A reduced cutting force of 108–185 N and a 15–18% improvement on surface roughness was also observed under the hybrid coolant and lubrication. Conclusively, a substantial improvement towards machinability of NiTi alloys was evidenced in this study. [ABSTRACT FROM AUTHOR]

A modern production strategy faces the increasing challenges of practicing green production without sacrificing machining performance. Thus, this paper compares emulsion cooling, minimum quantity lubrication without and with a Ranque-Hilsch vortex tube when turning martensitic stainless steel X20Cr13. Experimental tests were organized corresponding to Taguchi orthogonal array L27(34). The Taguchi based entropy weighted grey relational analysis was exploited to acquire the optimum combination of cutting speed, feed, depth of cut and cooling method that concurrently minimize surface roughness and tool life while maximizing material removal rate. The combination of minimum quantity lubrication with Ranque-Hilsch vortex tube confirmed to be the best cooling method. Hence, the use of classic metalworking fluids when turning martensitic stainless steels can be excluded, which is important for reducing environmental pollution and hence for machining sustainability. (Received in August 2019, accepted in November 2019. This paper was with the authors 1 month for 1 revision.) [ABSTRACT FROM AUTHOR]