Calculation and analysis of thermal flow field in hydrodynamic torque converter with a new developed stress-blended eddy simulation

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Konghua Yang ◽  
Chunbao Liu ◽  
Jing Li ◽  
Jiawei Xiong
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Performance Prediction ◽  
Vortex Structure ◽  
Viscosity Coefficient ◽  
Torque Converter ◽  
Physical Field ◽  
Content Type ◽  
Multi Scale ◽  
Eddy Simulation

Purpose The flow phenomenon of particle image velocimetry has revealed the transition process of the complex multi-scale vortex between the boundary layer and mainstream region. Nonetheless, present computational fluid dynamics methods inadequately distinguish the discernable flows in detail. A multi-physical field coupling model, which was applied in rotor-stator fluid machinery (Umavathi, 2015; Syawitri et al., 2020), was put forward to ensure the identification of multi-scale vortexes and the improvement of performance prediction in torque converter. Design/methodology/approach A newly-developed multi-physical field simulation framework that coupled the scale-resolving simulation method with a dynamic modified viscosity coefficient was proposed to comparatively investigate the influence of energy exchange on thermal and flow characteristics and the description of the flow field in detail. Findings Regardless of whether quantitative or qualitative, its description ability on turbulence statistics, pressure-streamline, vortex structure and eddy viscosity ratio were visually experimentally and numerically analyzed. The results revealed that the modification of transmission medium viscous can identify flows more exactly between the viscous sublayer and outer boundary layer. Compared with RANS and large eddy simulation, a stress-blended eddy simulation model with a dynamic modified viscosity coefficient, which was further used to achieve blending on the stress level, can effectively solve the calculating problem of the transition region between the near-wall boundary layer and mainstream region. Research limitations/implications This indeed provides an excellent description of the transient flow field and vortex structure in different physical flow states. Furthermore, the experimental data has proven that the maximum error of the external performance prediction was less than 4%. Originality/value An improved model was applied to simulate and analyze the flow mechanism through the evolution of vortex structures in a working chamber, to deepen the designer with a fundamental understanding on how to reduce flow losses and flow non-uniformity in manufacturing.

Liquid drop breakup in homogeneous isotropic turbulence

2019 ◽  
Vol 29 (7) ◽  
pp. 2407-2433
Author(s):  
Cheng Zhong ◽  
Alexandra Komrakova
Keyword(s):  
Flow Field ◽  
Turbulent Flow ◽  
Numerical Simulations ◽  
Energy Input ◽  
Drop Size ◽  
Second Phase ◽  
Drop Breakup ◽  
Content Type ◽  
Multi Scale ◽  
Turbulent Flow Field

Purpose This paper aims to demonstrate the capabilities of a diffuse interface free energy lattice Boltzmann method to perform direct numerical simulations of liquid–liquid dispersions in a well-controlled turbulent environment. The goal of this research study is to develop numerical techniques that can visualize and quantify drop interaction with the turbulent vortices. The obtained information will be used for the development of sub-models of drop breakup for multi-scale simulations. Design/methodology/approach A pure binary liquid system is considered that is subject to fully developed statistically stationary turbulent flow field in a cubic fully periodic box with the edge size of 300 lattice units. Three turbulent flow fields with varying energy input are examined and their coherent structures are visualized using a normalized Q-criterion. The evolution of the liquid–liquid interface is tracked as a function of time. The detailed explanation of the numerical method is provided with a highlight on a choice of the numerical parameters. Findings Drop breakup mechanisms differ depending on energy input. Drops break due to interaction with the vortices. Quantification of turbulent structures shows that the size of vortices increases with the decrease of energy input. Drop interacts simultaneously with multiple vortices of the size comparable to or smaller than the drop size. Vortices of the size smaller than the drop size disturb drop interface and pinch off the satellites. Vortices of the size comparable to the drop size tend to elongate the drop and tear it apart producing daughter drops and satellites. Addition of the second phase enhances turbulent dissipation at the high wavenumbers. To obtain physically realistic two-phase energy spectra, the multiple-relaxation-time collision operator should be used. Originality/value Detailed information of drop breakup in the turbulent flow field is crucial for the development of drop breakup sub-models that are necessary for multi-scale numerical simulations. The improvement of numerical methods that can provide these data and produce reliable results is important. This work made one step towards a better understanding of how drops interact with the turbulent vortices.

Performance Prediction for High Turning Low Aspect Ratio Stator Cascades in the Transonic Regime

1970 ◽  
Vol 92 (4) ◽  
pp. 390-398
Author(s):  
H. F. L. Griepentrog
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
Flow Field ◽  
Performance Prediction ◽  
Transonic Flow ◽  
Secondary Flows ◽  
Compressor Stage ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Boundary Layer Interaction

This paper describes a method for the prediction of the transonic flow field in a high solidity, high turning cascade, suitable for use as stator of a shock-in-rotor supersonic compressor stage. Effects of shock boundary layer interaction is taken into account by empirical correlation, valid for blade aspect ratios below unity. Use of partial slots for reduction of the secondary flows is briefly discussed and a correlation on slot efficiency is presented.

scholarly journals Numerical Investigation of Fluid Flow and Performance Prediction in a Fluid Coupling Using Large Eddy Simulation

2017 ◽  
Vol 2017 ◽  
pp. 1-11
Author(s):  
Wei Cai ◽  
Yuan Li ◽  
Xingzhong Li ◽  
Chunbao Liu
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Performance Prediction ◽  
Subgrid Scale ◽  
Eddy Simulation ◽  
Comparison Results ◽  
Large Eddy ◽  
Hydraulic Coupling ◽  
And Performance

Large eddy simulation (LES) with various subgrid-scale (SGS) models was introduced to numerically calculate the transient flow of the hydraulic coupling. By using LES, the study aimed to advance description ability of internal flow and performance prediction. The CFD results were verified by experimental data. For the purpose of the description of the flow field, six subgrid-scale models for LES were employed to depict the flow field; the distribution structure of flow field was legible. Moreover, the flow mechanism was analyzed using 3D vortex structures, and those showed that DSL and KET captured abundant vortex structures and provided a relatively moderate eddy viscosity in the chamber. The predicted values of the braking torque for hydraulic coupling were compared with experimental data. The comparison results were compared with several simulation models, such as SAS and RKE, and SSTKW models. Those comparison results showed that the SGS models, especially DSL and KET, were applicable to obtain the more accurate predicted results than SAS and RKE, and SSTKW models. Clearly, the predicted results of LES with DSL and KET were far more accurate than the previous studies. The performance prediction was significantly improved.

Asymmetric characteristics of the shock bifurcation in the reflected shock/boundary layer interaction

2018 ◽  
Vol 28 (10) ◽  
pp. 2357-2377 ◽  
Author(s):  
Yang Zhang ◽  
Jianfeng Zou ◽  
Jiahua Xie ◽  
Xiaoyue Li ◽  
Zhenhai Ma ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Vortex Shedding ◽  
Gradient Field ◽  
Reflected Shock Wave ◽  
Content Type ◽  
Layer Interaction ◽  
Reflected Shock ◽  
Shock Boundary Layer Interaction ◽  
Boundary Layer Interaction

Purpose When a reflected shock interacts with the boundary layer in a shock tube, the shock bifurcation occurs near the walls. Although the study of the shock bifurcation has been carried out by many researchers for several decades, little attention has been devoted to investigate the instability pattern of the bifurcation. This research work aims to successfully capture the asymmetry of the whole flow field, and attempt to achieve the instability mechanism of the shock bifurcation by a direct numerical simulation of the reflected shock wave/boundary layer interaction at Ma = 1.9. In addition, the reason for the formation of the bifurcated structure is also explored. Design/methodology/approach The spatial and temporal evolution of the shock bifurcation is obtained by solving the two-dimensional compressible Navier–Stokes equations using a seventh-order accurate weighted essentially non-oscillatory (WENO) scheme and a three-step Runge–Kutta time advancing approach. Findings The results show that the formation of shock bifurcation is mainly because of the shock/gradient field interaction, and the height of the bifurcated foot increases with the growth of the shock intensity and the gradient field. The unsteady asymmetry of the upper and bottom shock bifurcated structures is because of the vortex shedding with high frequency in the rear recirculation zone, which leads to the fluctuation of the recirculation area. The vortex shedding process behind the bifurcated structure closely resembles the Karman vortex street formed by the flow around the cylinder. The dimensionless vortex shedding frequency varies between 0.01 and 0.02. In comparison to the scenario at Ma = 1.9, the occurring time of instability is delayed and the upper and bottom bifurcated feet intersect in a relatively short time at Ma = 3.5. The region behind the bifurcated shock is a transitional flow field containing obvious cell structures and “isolated islands.” Originality/value This paper discovers an unsteady flow pattern of the shock bifurcation, and the mechanism of this instability in the reflected shock/boundary layer interaction is revealed in detail.

The Effects of Periodic Wakes on Boundary Layer Separation of Low-Pressure Turbine Using Large Eddy Simulation

2016 ◽  
Author(s):  
Xiaodi Wu ◽  
Fu Chen ◽  
Yunfei Wang
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Layer Separation ◽  
Low Pressure Turbine ◽  
Eddy Simulation ◽  
Instantaneous Flow Field ◽  
Large Eddy ◽  
Scale Structures

For low-pressure turbine, the unsteady disturbances are dominated by relative motions between rotors and stators and the unsteady flow is closely associated with aerodynamic efficiency of low-pressure turbine and engine performance. One of its most important manifestations is the boundary layer separation on the turbine blades by the passing wakes produced by upstream rows of blades. Hence, accurate prediction of the flow physics at low Reynolds number conditions is required to effectively implement flow control techniques which can help mitigate separation induced losses. The present paper concentrates on simulations for boundary layer separation of low-pressure turbine cascade under periodic wakes. In this paper, a multiblock computational fluid dynamics (CFD) code of compressible N-S equations is developed for predicting the phenomenon of boundary layer separation, transition and reattachment using large eddy simulation (LES) in the field of turbomachinery. The large-scale structures can be directly obtained from the solution of the filtered Naiver-Strokes equations and the small-scale structures are modeled by dynamic subgrid-scale model of turbulence. Firstly, unsteady boundary layer separation on a flat plate with adverse pressure gradient is simulated under periodic inflow. The time-averaged field, the phase-averaged field and the instantaneous flow field are presented and analyzed. The separation bubble becomes unstable and the location of transition moves back and forth due to vortex shedding. Secondly, a stator of turbomachinery which is influenced by wakes periodically passing is simulated. The results of the numerical simulations are discussed and compared with experimental data. For the instantaneous flow field, it seems that the spanwise vortices induced by upstream wakes are the primary reason of the initial roll-up of the shear layer and the Kelvin-Helmholtz instability plays an important role in the transition to turbulence which is observed in the separated flow.

scholarly journals Research on heat transfer characteristics of fractal-generated turbulence based on large eddy simulation

2019 ◽  
Vol 23 (6 Part B) ◽  
pp. 3993-4004
Author(s):  
Chengdong Duan ◽  
Yuncong Jiang ◽  
Nannan Wu ◽  
Qiwen Xu ◽  
Lijun Wang
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Cross Section ◽  
Mesh Size ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Effective Mesh Size ◽  
Layer Region

Turbulence plays an important role in the fields of heat and mass transfer and enhanced chemical reaction. In order to explore the effect of grid-generated turbulence on flow heat transfer, in this paper, three different fractal grid structures with the same blocking ratio ?, effective mesh size Meff and thickness ratio tr= t max/t min (Case1: The grid cross-section is a triangle, Case2: the grid cross-section is an inverted triangle, Case3:the grid cross-section is square, Case4:no grid) and without the grid were simulated based on large eddy simulation. The aim of this simulation is to explain the evolution characteristics and heat transfer mechanism of turbulent flow field under the four cases. The results show that, in the same initial condition, Case 2 can generate the highest turbulence intensity and the feature of heat transfer on the cylindrical surface is more uniform. In Case 3, the boundary-layer in the flow field is separated earlier, and more vortices are excited to enhance the heat transfer than other cases in the boundary-layer region. The surface average Nusselt number is 1.3 times than that of Case 4.

Large-Eddy Simulation of Interacting Film Cooling Jets

2009 ◽  
Author(s):  
Peter Renze ◽  
Wolfgang Schro¨der ◽  
Matthias Meinke
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Film Cooling ◽  
Plate Thickness ◽  
Turbulent Heat Transfer ◽  
Numerical Dissipation ◽  
Turbulent Heat ◽  
Eddy Simulation ◽  
Large Eddy

In the present paper the flow field of a film cooling configuration with three staggered rows of holes is investigated using large-eddy simulations (LES). The numerical method uses the MILES approach (monotone-integrated large-eddy simulation) and the discretization of the governing equations is based on a mixed central-upwind AUSM (advective upstream splitting method) scheme with low numerical dissipation. The current investigations focus on full-coverage film cooling with finest drilling holes. The film cooling configuration consists of three staggered rows of holes with a lateral hole spacing of p/D = 3 and a streamwise row distance of l/D = 6. The inclination angle of the cooling holes is α = 30° and the flat plate thickness is h/D = 12. The cooling hole exit geometry is fanshaped with lateral and streamwise expansions. The results evidence the different nature of the mixing process between the jets and the crossflow after the first, second, and third row. The turbulent kinetic energy peaks at the interaction region of the undisturbed boundary layer with the first row. The low velocity ratio leads to reduced velocity gradients in the lower boundary layer downstream of the first row. Thus, the turbulence production is reduced at the interaction with the following rows. The adiabatic film cooling effectiveness is substantially improved after the second and third injection and the decay of effectiveness is reduced, respectively. The turbulent heat transfer is investigated and strong variations of the turbulent Prandtl number are evident in the flow field.

Grid sensitivity of flow field and noise of high-Reynolds-number jets computed by large-eddy simulation

2018 ◽  
Vol 17 (4-5) ◽  
pp. 399-424 ◽  
Author(s):  
Christophe Bogey
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Field ◽  
High Reynolds Number ◽  
Mean Velocity ◽  
Laminar Jet ◽  
Eddy Simulation ◽  
Large Eddy ◽  
High Reynolds ◽  
Jet Axis

Three isothermal round jets at a Mach number of 0.9 and a diameter-based Reynolds number of 105 are computed by large-eddy simulation using four different meshes in order to investigate the grid sensitivity of the jet flow field and noise. The jets correspond to two initially fully laminar jets and one initially strongly disturbed jet considered in previous numerical studies. At the exit of a pipe nozzle of radius r0, they exhibit laminar boundary-layer mean-velocity profiles of thickness [Formula: see text] and [Formula: see text], respectively. For the third jet, a peak turbulence intensity close to 9% is also imposed by forcing the boundary layer in the nozzle. The grids contain up to one billion points, and, compared to the grids used in previous simulations, they are finer in the axial direction downstream of the nozzle and in the radial direction on the jet axis and in the outer region of the mixing layers. The main flow field and noise characteristics given by the simulations, including the mixing-layer thickness, the centerline mean velocity, the turbulence intensities on the nozzle lip line and the jet axis, spectra of velocity and far-field pressure obtained from the jet near field by solving the isentropic linearized Euler equations, are presented. With respect to those from previous studies, the results are very similar for the initially laminar jet with thick boundary layers, but they differ significantly for the initially laminar jet with thin boundary layers and for the initially disturbed jet. For the latter two jets, using a finer grid leads to a faster flow development, to higher turbulence intensities in the shear layers and at the end of the potential core, to stronger large-scale structures, and to the generation of more low-frequency noise. Moreover, very small mesh spacings appear to be necessary all along the jet mixing layers, and in particular during their early stages of growth, to properly capture the formation and dynamics of the flow coherent structures and thus obtain results in good agreement with measurements available for high-Reynolds-number jets.

Large-Eddy Simulation of Film Cooling Flow Ejected in a Shallow Cavity

2008 ◽  
Author(s):  
Peter Renze ◽  
Wolfgang Schro¨der ◽  
Matthias Meinke
Keyword(s):  
Boundary Layer ◽  
Heat Exchange ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Film Cooling ◽  
Cooling Fluid ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Cylindrical Holes ◽  
Shallow Cavity

In the present paper the flow field of a film cooling configuration with cylindrical holes embedded in a shallow cavity is investigated using large-eddy simulation (LES). The cooling jet is injected through a single row of inclined holes from a transverse cavity into a turbulent flat plate boundary layer at a temperature ratio of TR = 0.44. The mixing of the cooling fluid and the crossflow within the cavity is a highly unsteady process generating complex vortical structures. The impact of the boundary layer separation at the upstream cavity edge on the jet-crossflow interaction is studied in detail. The driving mechanisms of the momentum and heat exchange between the jet and the crossflow are identified and discussed. The flow field and the adiabatic cooling efficiency is compared to a standard cylindrical film cooling configuration without a cavity. The development of the counter-rotating vortex pair (CVP) downstream of the jet injection is investigated. An analysis of the vortex dynamics shows an impinging behavior of the jet fluid in this area. The Reynolds stress shows a more two-dimensional distribution compared to the anisotropic nature of the jet-in-a-crossflow (JICF) at standard cylindrical holes. Since the heat exchange is closely connected to the transport of momentum in the mixed boundary layer, this observation explains the enhanced lateral spreading of the cooling fluid.

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