Simulation Analysis of New Energy Vehicle Engine Cooling System Based on K-E Turbulent Flow Mathematical Model

New energy vehicles have better clean and environmental protection characteristics than traditional fuel vehicles.The new energy engine cooling technology is critical in the design of new energy vehicles.This paper used oneand three-way joint simulation methods to simulate the refrigeration system of new energy vehicles.Firstly,a k-εturbulent flow model for the cooling pump flow field is established based on the principle of computational fluid dynamics.Then,the CFD commercial fluid analysis software FLUENT is used to simulate the flow field of the cooling pump under different inlet flow conditions.This paper proposes an optimization scheme for new energy vehicle engines’“boiling”phenomenon under high temperatures and long-time climbing conditions.The simulation results show that changing the radiator’s structure and adjusting the thermostat’s parameters can solve the problem of a“boiling pot.”The optimized new energy vehicle engine can maintain a better operating temperature range.The algorithm model can reference each cryogenic system component hardware selection and control strategy in the new energy vehicle’s engine.

Numerical prediction of inner turbulent flow in conical diffuser by using a new five-point scheme and DLR k-ε turbulence model

The internal turbulent flow in conical diffuser is a very complicated adverse pressure gradient flow.DLR k-ε turbulence model was adopted to study it.The every terms of the Laplace operator in DLR k-ε turbulence model and pressure Poisson equation were discretized by upwind difference scheme.A new full implicit difference scheme of 5-point was constructed by using finite volume method and finite difference method.A large sparse matrix with five diagonals was formed and was stored by three arrays of one dimension in a compressed mode.General iterative methods do not work wel1 with large sparse matrix.With algebraic multigrid method(AMG),linear algebraic system of equations was solved and the precision was set at 10-6.The computation results were compared with the experimental results.The results show that the computation results have a good agreement with the experiment data.The precision of computational results and numerical simulation efficiency are greatly improved.

REVISED k-ε TURBULENCE MODEL IN ELECTROMAGNETIC CONTINUOUS CASTING OF MELT

The research is motivated by the ongoing the electromagnetic continuous casting of molten metal. The revised k-ε model considering the effect of magnetic field application was derived. The specific model equations for the electromagnetic braking were used to calculate the velocity distribution in the continuous casting mold of steel. The results show that the revised k-ε model considering the effect of magnetic field application tends to suppress the production of turbulence and difference between the conventional and revised k-e model is small.

A K-εTWO-EQUATION TURBULENCE MODEL FOR THE SOLID-LIQUID TWO-PHASE FLOWS

A two-equation turbulence model has been dereloped for predicting two-phase flow the two equations describe the conserration of turbulence kinetic energy and dissipation rate of that energy for the incompressible carrier fluid in a two-phase flow The continuity, the momentum, K and εequations are modeled. In this model,the solid-liquid slip veloeites, the particle-particte interactions and the interactions between two phases are considered,The sandy water pipe turbulent flows are sueeessfuly predicted by this turbulince model.

Multi-layer analytic solution for k-ωmodel equations via a symmetry approach

Despite being one of the oldest and most widely-used turbulence models in engineering computational fluid dynamics(CFD),the k-ωmodel has not been fully understood theoretically because of its high nonlinearity and complex model parameter setting.Here,a multi-layer analytic expression is postulated for two lengths(stress and kinetic energy lengths),yielding an analytic solution for the k-ωmodel equations in pipe flow.Approximate local balance equations are analyzed to determine the key parameters in the solution,which are shown to be rather close to the empirically-measured values from the numerical solution of the Wilcox k-ωmodel,and hence the analytic construction is fully validated.The results provide clear evidence that the k-ωmodel sets in it a multilayer structure,which is similar to but different,in some insignificant details,from the Navier-Stokes(N-S)turbulence.This finding explains why the k-ωmodel is so popular,especially in computing the near-wall flow.Finally,the analysis is extended to a newlyrefined k-ωmodel called the structural ensemble dynamics(SED)k-ωmodel,showing that the SED k-ωmodel has improved the multi-layer structure in the outer flow but preserved the setting of the k-ωmodel in the inner region.

Heat Transfer and Flow Characteristics Predictions with a Refined k-ε-f_u Turbulent Model in Impinging Jet

Local heat transfer and flow characteristics in a round turbulent impinging jet for Re≈23 000 is predicted numerically with the RANS approach and a k-ε-fu turbulence model. The heat transfer predictions and turbulence parameters are verified against the axis-symmetric free jet impingement measurements and compared with previous other turbulence models, and results show the k-ε-fu model has a good performance in predictions of the local wall heat transfer coefficient, and in agreement with measurements in mean velocity profiles at different radial positions as well. The numerical model is further used to examine the effect of the fully confined impingement jet on the local Nusselt number. Local Nusselt profiles in x and y-centerlines for the target plate over three separation distances are predicted. Compared with the experimental data, the numerical results are accurate in the central domain around the stagnation region and present a consistent structure distribution.

CURVAURE SENSITIVE NONLINEAR TURBULENCE MODEL

By modifying the Rodi assumption to take account of the influence of flow curvature, a new curvature modified algebraic stress model(CMASM) is de- veloped from the second moment closure in the generalized curvilinear coordinate system. And the explicit form of this ASM, a new curvature modified nonlinear k-ε model (CMNKE), is derived in the orthogonal curvilinear coordinate system. This new nonlinear k-ε model is further validated by a numerical simulation of a two- dimensional U-type turnaround duct flow. The results show that the CMNKE can effectively capture the main characteristic of this curvature flow and simulate the damping effect of the shear stress by a convex curvature and the enhancing effect by a concave curvature. So, this model is a rational and effective simplification to the second moment closure.

Solution of Self-similar Equations of the k-ε Model in the Shear Turbulent Mixing Problem and Its Numerical Simulation

The paper presents the k-ε model equations of turbulence with a single set of constants chosen by the authors, which is appropriate to simulate a wide range of turbulent flows. The model validation has been performed for a number of flows and its main results are given in the paper. The turbulent mixing of flow with shear in the tangential velocity component is discussed in details. An analytical solution to the system of ordinary differential equations of the k-ε model of turbulent mixing has been found for the self-similar regime of flow. The model coefficients were chosen using simulation results for some simplest turbulent flows. The solution can be used for the verification of codes. The numerical simulation of the problem has been performed by the 2D code EGAK using this model. A good agreement of the numerical simulation results with the self-similar solution, 3D DNS results and known experimental data has been achieved. This allows stating that the k-ε model constants chosen by the authors are acceptable for the considered flow.

Assessment of k–ε models using tetrahedral grids to describe the turbulent flow field of a PBT impeller and validation through the PIV technique

In turbulence modeling, the RNG and Realizable models have important improvements in the turbulent production and dissipation terms in comparison to the Standard. The selection of the appropriate turbulence model has an impact on the convergence and solution in STRs, and they are used in mixing, multiphase modeling or as starting solution of transient models as DES and LES. Although there are several studies with the pitched blade turbine(PBT) impeller, most of them used the Standard model as representative of all k–ε models, using structured hexahedral grids composed of low number of cells, and in some cases under axial symmetry assumptions.Accordingly, in this work the assessment of the Standard, RNG and Realizable models to describe the turbulent flow field of this impeller, using the Multiple Reference Frame(MRF) and Sliding Mesh(SM) approaches with tetrahedral domains in dense grids, is presented. This kind of cell elements is especially suitable to reproduce complex geometries. Flow velocities and turbulent parameters were verified experimentally by PIV and torque measurements. The three models were capable of predicting fairly the pumping number, the power number based on torque, and velocities. Although the RNG improved the predictions of the turbulent kinetic energy and dissipation rate, the Realizable model presented better performance for both approaches. All models failed in the prediction of the total dissipation rate, and a dependence of its value on the number of cells for the MRF was found.

Three-dimensional turbulent model of heat transfer and fluid flow in GTAW process

A two-equation K-ε turbulent fluid flow model is built to model the heat transfer and fluid flow in gas tungsten arc welding （GTAW） process of stainless steel S US310 and S US316. This model combines the buoyancy force, lorentz force and marangni force as the driving forces of thefluidflow in the weld pool. The material properties are functions of temperature in this model. The simulated results show that the molten metal flowing outward is mainly caused by the marangoni convection, which makes the weld pool become wider and shallower. The comparison of the weld pool shape of SUS310 and SUS316 shows that the slight differences of the value of thermal conductivity mainly attributes to the difference of the weld pool shape and the distinction of heat transport in laminar and turbulent model makes large diversity in the simulated results.

基于CFD的干法手套箱内气体流场的数值模拟研究

在乏燃料干法后处理中,将氧化物制备成金属时,可采用熔盐电解工艺技术,由于核燃料具有较高的毒性和放射性,为了确保操作过程的安全,整个工艺过程必须在干法手套箱内进行,干法手套箱是干法后处理熔盐电解工艺研究的必要保障。在以往的实际使用过程中,气量的设计理念是加大通风量,这就造成需要处理的废气量增加,能耗增多,运行成本提高。本文基于CFD以及统计学标准差的概念,研究了箱体内气体流场受到出入口位置、流速等因素的影响,建立了风机流量与箱体体积的函数关系式,为干法手套箱和热室的设计提供了重要的参数。

不可压湍流流动K-ε两方程模型参数辨识

本文提出了不可压湍流流动情况下标准 K -ε两方程模型的参数辨识方法 ,并对轴对称管道流动、二维后向台阶流动、轴对称突扩管道流动下的模型参数进行了参数辨识与分析 ,得到了一些初步结论 :( 1)参数辨识方法是确定湍流模型经验参数值的一种有效方法 ;( 2 )参数辨识结果受数值计算精度和流动特性影响很大 ;( 3)由于标准 K -ε两方程模型本身还有缺陷 。

基于标准K-ε模型与CFD的浮子流量传感器的研究

依据湍流模式理论中的标准 K- ε模型及 CFD(计算流体力学 )实现了对浮子流量传感器三维湍流流场的数值研究 ,利用物理概念清晰的“有限体积法”作为数值解法 ,并采用以压力为基本求解变量的 SIMPL E算法求解离散控制方程 ;提出“浮子受力平衡度误差分析法”控制计算精度 ,通过对传感器速度场、压力场的三维研究 ,获得传感器流场的关键信息 ,即浮子受力大小以及传感器流量值。数值计算结果 ,即针对 30 0 K水 ,粘度为 1.0 0 3× 10 - 3Pa· s流场的计算结论得到了物理实验验证。

基于k-ε模型模拟平衡态大气边界层的比较研究

平衡态大气边界层的准确模拟是计算风工程领域的基础性难题,也是研究热点问题之一。该文首先对近年来国内外针对这一问题的理论研究成果按入流边界条件、湍流模型参数、附加源项模型以及壁面函数模型等四个方面进行了全面梳理和系统总结,并建议了一组新的标准k-ε模型湍流模型参数和通用壁面函数模型表达式。接着,采用计算流体动力学方法,建立简单边界层流动数值风洞模型,按照以上四种类别采用递进的方法对这些理论成果进行了详细的数值模拟验证和比较分析。结果表明:基于湍动能k方程解析解的入流边界条件并不必然会生成平衡态边界层,它和湍动能剖面的数学模型表达形式关系很大;除入流湍流边界条件外,湍流模型参数取值及壁面函数对平衡态大气边界层的模拟亦有较大影响,而增加源项并不能有效改善速度和湍动能剖面在整个流域范围的自保持性。该文对这一类问题的研究具有一定参考价值。

TWO MODIFICATORY K-ε TURBULENCE MODELS FOR TURBULENT SWIRLING FLOWS

Since the standard K-ε model used to predict the strongly swirling flowleads to a large deviation from experimental results, it is necessary to introduce modification tothe standard K-ε model. Based on the algebraic Reynolds stress model and Bradshaw's turbulentlength scale modification conception, we present two modified K-ε models. To investigate thebehaviour of the modified turbulence models, they are used to predict two representative turbulentswirling flows. The computational results, after compared with the experimental data, show that themodified K-ε models substantially improve the prediction of the standard K-ε model for theturbulent swirling flows.

A k-ε Turbulence Model Considering Compressibility in Three-Dimensional Transonic Turbulent Flow Calculation

Based on the standard k-ε turbulence model, a new compressible k-ε model considering the pressure expansion influence due to the compressibility of fluid is developed and applied to the simulation of 3D transonic turbulent flows in a nozzle and a cascade. The Reynolds avenged N-S equations in generalized curvilinear coordinates are solved with implementation of the new model. The high resolution TVD scheme is used to discretize the convective terms. The numerical results show that the compressible k-ε model behaves well in the simulation of transonic internal turbulent flows.

Optimal convergence rates for three-dimensional turbulent flow equations

In this paper, the convergence turbulent flow equations are considered. By rates of solutions to the three-dimensional combining the LP-Lq estimate for the linearized equations and an elaborate energy method, the convergence rates are obtained in various norms for the solution to the equilibrium state in the whole space when the initial perturbation of the equilibrium state is small in the H3-framework. More precisely, the optimal convergence rates of the solutions and their first-order derivatives in the L2-norm are obtained when the LP-norm of the perturbation is bounded for some p ε [1, 6）.

COMPARISON OF K-ε AND K-ω TURBULENCE MODELS FOR SIMULATION OF SHALLOW RECIRCULATING FLOWS IN AN OPEN CHANNEL

The paper describes the comparison of commonly used k-ε and k-ω turbulence models for simulating the recirculating flows behind a sudden expansion in a straight open channel. The depth-average numerical model and the quasi three-dimensional multilayer model are presented respectively. The governing equations are split into three parts in the finite difference approach: advection, dispersion and propagation. Comparison of the results computed with the k-ε and k-ω models shows that the two turbulence models have strong robustness in simulating the reattachment length of the recirculating flows. The computed results are found in good agreement with the measured data.

Numerical simulation and experimental verification of plasma jet development in gas gap switch

Plasma jet triggered gas gap switch has obvious advantages in fast control switch.The development of the plasma in the ambient medium is the key factor affecting the triggering conduction of the gas switch.However,the plasma jet process and its characteristic parameters are complicated and the existing test methods cannot fully characterize its development laws.In this work,a two-dimensional transient fluid calculation model of the plasma jet process of the gas gap switch is established based on the renormalization-group k-εturbulence equation.The results show that the characteristic parameters and morphological evolution of the plasma jet are basically consistent with the experimental results,which verifies the accuracy of the simulation model calculation.The plasma jet is a long strip with an initial velocity of 1.0 km·s-1and develops in both axial and radial directions.The jet velocity fluctuates significantly with axial height.As the plasma jet enters the main gap,the pressure inside the trigger cavity drops by80%,resulting in a rapid drop in the jet velocity.When the plasma jet head interacts with the atmosphere,the two-phase fluid compresses each other,generating a forward-propelled pressure wave.The plasma jet heads flow at high velocity,a negative pressure zone is formed in the middle part of the jet,and the pressure peak decreases gradually with height.As the value of the inlet pressure increases,the characteristic parameters of the plasma jet increase.The entrainment phenomenon is evident,which leads to an increase in the pressure imbalance of the atmospheric gas medium,leading to a significant Coanda effect.Compared with air,the characteristic parameters of a plasma jet in SF6are lower,and the morphological evolution is significantly suppressed.The results of this study can provide some insight into the mechanism of action of the switch jet plasma development process.

EXPERIMENT ON THE FORECAST OF CHARACTERISTIC QUANTITIES OF ATMOSPHERIC TURBULENCE BY MESOSCALE MODEL MM5

In nested nonhydrostatic mesoscale model MM5,the characteristic quantities of atmospheric turbulence,i.e.,the standard deviations of the turbulent fluctuated speeds for three directions in PBL are computed by Mellor-Yamada's level 2.5 closure scheme.The magnitudes and the vertical profiles of these quantities computed from the model are closely connected with temperature and wind speed profiles as well as the type of the ground with a significant diurnal variation,and are in agreement with known magnitudes and regularities in different stratification conditions.Hence the method in this paper is reasonable and convincible.Their horizontal distribution depends on the horizontal distribution of the stratification.The method of predicted characteristic quantities of turbulence from mesoscale model in this paper can be used in the problem of atmospheric diffusion and atmospheric environment.