Journal of Fluids Engineering
ISSN / EISSN : 0098-2202 / 1528-901X
Published by: ASME International (10.1115)
Total articles ≅ 7,254
Latest articles in this journal
Journal of Fluids Engineering; https://doi.org/10.1115/1.4052826
The flow resulting from the rotation of a series of thin plates that initially separate two gases of different densities is analysed using Direct Numerical Simulations. The ninety degrees plates' rotation forms a vorticity shear layer and a density interface in between the tips of two neighbouring plates. Results of this study show that the shape of these layers strongly depends on the plate tip-based Reynolds number that can be varied thanks to a parametrisation of the plates' opening law. Different regimes are identified corresponding to single- or multi-mode initial interfaces, with or without the occurrence of starting vortices during the formation of the shear layer. The density interfaces resulting from this procedure are particularly well-suited to serve as initial conditions for the study of the Richtmyer-Meshkov instability-induced mixing. Results of this study also provide a description of vortex formation in stratified flows.
Journal of Fluids Engineering; https://doi.org/10.1115/1.4052817
The propulsion and vortical flow of a pre-swirl pump-jet propulsor (PJP) under effective wake conditions are numerically investigated by improved delayed detached eddy simulation. The numerical results agree well with the experiments. The effects of the interaction between the hull and PJP on the propulsion performance and flow characteristics are discussed in detail, particularly the effects on the flows around the duct and stator. Results show that the PJP performance changes noticeably owing to the hull retarded flow. The rotor forces are mainly changed due to the effective velocity magnitude of the PJP oncoming flow, while the flow direction does not show notable effects as the duct and stator notably improve the rotor oncoming flow. The appendage wake notably increases the thrust fluctuation of the rotor, causing dominant fluctuation components at low frequencies. The thrusts on the duct and stator are sensitive to the direction of the PJP oncoming flow, as the flows around them change considerably when the flow direction changes. The flow direction affects the velocity and pressure distribution of the duct and the generation and evolution of vortices in the stator region. The forward stagnation point on the duct plays a crucial role in duct thrust, around flow, and in the flow into the duct. The stator improves the uniformity of the rotor inflow during pre-swirling of the flow under effective wake conditions, which is very important for a submarine-applied PJP. The interaction between the hull and PJP is very complex.
Journal of Fluids Engineering; https://doi.org/10.1115/1.4052770
Gas entrainment may cause pressurization deterioration and even failure of pumps under conditions of high inlet gas volume fraction (GVF). When the inlet GVF increases to a critical value, an obvious deterioration performance of pump occurs. Air-water pressurization performance and inlet critical GVFs of a centrifugal multiphase pump are investigated experimentally under different inlet pressures and gas-liquid flow rates. To determine the first and second critical GVFs, a new method is proposed by computing the local extreme points of the second derivative of performance curves. New prediction correlations for two critical GVFs are established with relative errors lower than ±10% and ±8%. Boundaries of three different flow patterns and the transition flow rates are determined and presented by critical GVFs on the flow pattern diagram. Moreover, boundaries of maximum pressurization are determined by performance curve clusters and a power function correlation of gas-liquid flow rates when reaching the maximum pressurization is established. With the increase of inlet pressure from 1MPa to 5MPa, two-phase pressurization performance is significantly increased; occurrences of pressurization deterioration are obviously delayed with the first and second critical GVFs increasing by maximums of 8.2% and 7.1%.
Journal of Fluids Engineering; https://doi.org/10.1115/1.4052769
In order to improve the aerodynamic performance of the airfoil, the airfoil shape and the angle of attack (AOA) are optimized at the same time by the Multi-island Genetic Algorithm in this paper. The goal of the optimization is to maximize the lift-to-drag ratio which is calculated by computational fluid dynamics method. The airfoil is parameterized by the Bézier curve. The thickness and the camber of airfoil are no longer restricted to ensure a wide range of airfoil generation. The airfoil is optimized under different Reynolds numbers. The optimized airfoils obtained by the unconstrained AOA method are compared with several standard airfoils. The results show that the maximum lift-to-drag ratio of the optimized airfoil is much greater than the compared airfoils, and the optimized airfoils have good aerodynamic characteristics in a wide range of angle of attack. By comparing with the optimized airfoils obtained by the constrained AOA method, it shows that the constrained AOA method can't guarantee that the pre-constrained angle of attack is the optimal angle of attack of the airfoil, nor can obtain the maximum lift-to-drag ratio airfoil of all angles of attack and all airfoils. However, by using the angle of attack as one of the optimization variables, these problems can be solved well.
Journal of Fluids Engineering, Volume 144; https://doi.org/10.1115/1.4052050
Cyclone separators are an integral part of many industrial processes. A good understanding of the flow features is paramount to efficiently use them. The turbulent fluid flow characteristics are modeled using unsteady Reynolds-averaged Navier–Stokes (URANS), large eddy simulations (LES), and hybrid LES/Reynolds–averaged Navier–Stokes (RANS) turbulent models. The hybrid LES/RANS approaches, namely, detached eddy simulation (DES), delayed detached eddy simulation (DDES), and improved delayed detached eddy simulation (IDDES) based on the k−ω SST RANS approaches are explored. The study is carried out for three different inlet velocities (v = 8, 16.1, and 32 m/s). The results from hybrid LES/RANS models are shown to be in good agreement with the experimental data available in the literature. Reduction in computational time and mesh size are the two main benefits of using hybrid LES/RANS models over the traditional LES methods. The Reynolds stresses are observed in order to understand the redistribution of turbulent energy in the flow field. The velocity profiles and vorticity quantities are explored to obtain a better understanding of the behavior of fluid flow in cyclone separators.
Journal of Fluids Engineering, Volume 144; https://doi.org/10.1115/1.4052546
This study investigates the fluid dynamics and performance characteristics in micronozzle flows with changes in various geometric parameters using Navier–Stokes simulation based on slip wall boundary conditions. The various geometric parameters considered for the study are (1) area ratio with fixed throat dimension and (2) the semidivergence angle variation with no change in area ratio. The simulation results show that the flow choking for micronozzle happens not at the geometric throat; rather pushed downstream to the divergent channel of the nozzle. This is due to the thick boundary layer growth, which reduces the effective flow area and shifts the minimum allowable flow area downstream to the throat. The distance to which the choking point shifts downstream to the throat reduces with Maxwell's slip wall conditions compared to the conventional no-slip wall condition. The downstream movement of the choking point from the throat reduces with an increase in area ratio and with increase in divergence angle with fixed area ratio. This is due to the fact that the increase in area ratio and divergence angle increases the nozzle height at any particular section in the divergent portion of the nozzle. As a result of this, the boundary layer profile also moves upward and the restriction of potential core by the thick boundary layer reduces, which in turn leads to an increase in the effective minimum flow area downstream to the throat.
Journal of Fluids Engineering; https://doi.org/10.1115/1.4052744
The surface tension of a self-rewetting fluid (SRF) has a parabolic shape with the increase of temperature, implying potential applications in many industrial fields. In this paper, flow patterns and stability analysis are numerically performed for a gravity driven self-rewetting fluid film flowing down a heated vertical plane with wall slip. Using the thin film theory, the evolution equation for the interfacial thickness is derived. The discussion is given considering two cases in the review of the temperature difference between the interfacial temperature and the temperature corresponding to the minimum surface tension. The base state of the two-dimensional flow is firstly obtained and the influence of the Marangoni effect and slippery effect is analyzed. Then linear stability analysis and related numerical verification are displayed, showing good consistency with each other. For a low interfacial temperature, the Marangoni promotes the fingering instability and for a high interfacial temperature, the inverse Marangoni impedes the surface instability. The wall slip is found to influence the free surface in a complex way because it can either destabilize or stabilize the flow of the free surface.
Journal of Fluids Engineering, Volume 144; https://doi.org/10.1115/1.4052471
The freestream flow around a bluff object shows steady symmetric nature in the low Reynolds number laminar regime. However, when the Reynolds number increases to a critical value, the flow shows unsteadiness with alternate shedding of vortices. We show here numerically that the vortex shedding could be initiated for flow of a nanofluid over a bluff object even when the Reynolds number is lying in the steady regime (10≤Re≤30). Cu–H2O and Ag–H2O nanofluids are used and the volume fractions of Cu and Ag nanoparticles are gradually increased. At some critical values of the volume fractions, the flow shows unsteadiness with vortex shedding. The critical solid volume fraction is estimated from the convective stability analysis following the extended Landau model. The shedding phenomenon is established through contour plots, phase diagrams, and analysis of the time signals of lift coefficient. The critical volume fractions for the two different nanofluids for transition of steady to unsteady flow over circular and square-shaped bluff objects are observed to decrease with increasing Reynolds number.
Journal of Fluids Engineering, Volume 144; https://doi.org/10.1115/1.4052418
In this study, skin friction around a ½-scale Ahmed body was measured experimentally at a Reynolds number of Re = 2 × 105. The slant angle of the Ahmed body was 25 deg, and the yaw angles ranged from 0 deg to 8 deg. This study focused on the flow structure on the slant surface under different cross-wind conditions. A force balance system was applied to measure the aerodynamic drag of the model. The global skin-friction topology was measured by applying a luminescent oil layer with a subgrid data processing algorithm. The method used to measure the skin friction was conducted for the first time on the Ahmed body. The results indicated that the technique is highly capable of extracting the skin-friction topology. For a yaw angle below 3 deg, the flow on the slant surface was not significantly affected by the cross-wind condition, and the drag of the model was nearly constant. However, at yaw angles above 3 deg, the flow on the slant surface was highly affected by the roof longitudinal vortexes on the windward side, leading to a dramatic increase in the drag of the model. High consistency in the drag and skin-friction fields was observed. The detailed skin-friction structure at different yaw angles will be discussed in this study.
Journal of Fluids Engineering; https://doi.org/10.1115/1.4052745
Wire-wrapped hexagonal fuel bundles have been extensively investigated due to their enhanced heat transfer and flow characteristics. Experimental measurements are important to study the thermal-hydraulic behavior of such assemblies and to validate and improve the predicting capabilities of specialized correlations and computational tools. Presently, very limited experimental data is available on the local subchannel pressure drop. Experimental measurements of subchannel pressure drop were conducted in a 61-pin wire-wrapped rod bundle replica, for Reynolds numbers between 190 and 22,000. Specialized instrumented rods were utilized to measure the local pressure drop and estimate the subchannels' friction factor. Three interior subchannels, one edge subchannel and one corner subchannel were selected to study the effects of location and flow regimes on the friction factor and hydraulic behavior. The transition boundaries from laminar to transitions regimes, and from transition to turbulent regimes were estimated for the subchannels analyzed. The results were found in agreement with the predictions of the Upgraded Cheng and Todreas Detailed Correlation (UCTD). The results of the experimental campaign provided a better understanding of hydraulic behavior of the subchannels of wire-wrapped bundles, in relation to its geometrical features