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.

Assessment of Turbulence Models on Bridge-Pier Scour Using Flow-3D

The main purpose of this paper is to analyze the influence of different turbulence flow models on scouring pit of bridge-pier. Flow-3D software is applied in line with the purpose. The key motivation for this study is to contribute to the Flow-3D software by means of some modification and adjustment in the sediment scour model and shallow water model. An assessment of turbulence model adopted with the parameters of the Melville experiment to estimate the maximum scour-depth was performed. In the simulation results, the alternate eddy formation and shedding were repeated while the Karman vortex street formed behind the pier for the large eddy simulation LES turbulence model is more realistic in the flow phenomenon. The results of the scour development of large eddy simulation (LES) turbulence model were found to be more satisfied than the Renormalized group (RNG) turbulence model and close to the prior experiment results. The simulated scour results were significantly different with the observed data collected from previous literature in the reason of some unsuitability of meshing method in Flow-3D software.

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.

应用RNG k-ε湍流模式数值模拟90°弯曲槽道内的湍流流动

本文将Yakhot与Orszag提出的RNGk-ε湍流模式与壁面律相结合,应用于90°弯曲槽道湍流流动的数值模拟.计算在任意非正交曲线坐标系下进行.并采用非交错网格有限体积方法求解三维不可压N-S方程.文中给出了详细的计算结果,并与实验结果进行了比较,结果表明,RNG k-ε湍流模式能够有效地模拟有曲率影响的湍流流动.

基于RNG k-ε湍流模型钝体绕流的数值模拟

采用RNGk ε湍流模型对钝体绕流流场进行了数值模拟.计算采用非交错网格的有限体积法求解二维不可压N S方程.计算结果表明,RNGk ε湍流模型可以成功地模拟绕钝体的不稳定、非定常和剧烈分离流动.

用RNGk-ε模型计算内燃机缸内湍流流动

应用快速畸变假设对 RNG k-ε湍流模型进行压缩性修正后 ,将其应用于内燃机缸内湍流流动的数值模拟 ,计算采用任意拉格朗日 -欧拉法。给出了用 RNG k-ε模型算得的结果 ,并与标准的 k-ε模型算得的结果和实验结果进行了对比。结果表明 ,用 RNG k-ε湍流模型算得的结果比 k-ε模型算得的结果有所改进 。

RNG k-ε模型在内燃机缸内湍流数值模拟中的应用

在内燃机整个工作循环中 ,其缸内流体始终进行着极其复杂而又强烈瞬变的湍流运动 ,要正确地分析内燃机的燃烧和排放 ,离不开对缸内湍流运动的正确描述和模拟。通过快速畸变分析对由重整化群理论得到的RNGk -ε湍流模型进行了压缩性修正 ,把经压缩修正后的RNGk -ε湍流模型应用于内燃机缸内湍流流动的数值模拟 ,计算采用任意拉格朗日欧拉法。给出了用RNGk -ε模型计算得到的结果 ,并与标准的k -ε模型算得的结果和实验结果进行了比较。结果表明 ,RNGk -ε湍流模型得到的结果比k -ε模型算得结果的精度有所提高 ,其计算程序编制的难易程度和计算成本与k-ε模型相当 。

基于修正RNG k-ε模型的叶片泵非设计工况数值模拟

对于非设计工况下流体机械的流场计算,由于其偏离设计工况,分离流动严重等特点,使得用普通的湍流模型数值模拟精度不高。本文采用一种将涡粘性系数Cμ与湍流脉动动能和湍流耗散率的变化相关联的方法,对RNG k-ε湍流模型进行修正。为验证其对非设计工况下叶片泵的预测精度,分别采用修正模型和原始RNG模型,数值模拟了一比转速为439的叶片泵的内部流场,得到了其扬程、效率曲线及在典型工况下的内部流场流线分布。通过比较改进前后RNG湍流模型的数值计算结果,并与实验结果对比,得出修正RNG模型更能准确预测出非设计工况下叶片泵的流场特性。

RNG k-ε湍流模型在三维弯曲河流中的应用

本文采用非正交曲线坐标下的三维RNG k-ε双方程湍流数学模型,该模型在水平方向采用非正交曲线坐标,在垂直方向采用等分网格的全坐标变换,采用由二维深度平均方程演化而来的2-D泊松方程计算三维自由水面,应用SIMPLEC程式求解方程。通过两个180°弯曲渠道和天然河流Fall River部分河段对本文的数学模型进行验证,给出水位、流速及二次流的分布图等。对比分析,本模型的计算结果和实测值吻合很好,表明采用2-D泊松方程法计算三维自由水面是可行的,RNG k-ε湍流数学模型可以应用到天然河道的计算中去。

RNG k-ε模型数值模拟油雾燃烧流场

采用RNG(R enorm alization G roup)k-ε紊流模型对某环形燃烧室火焰筒内三维两相燃烧流场进行数值模拟。运用偏微分方程法和区域法生成贴体网格,EBU-A rrhen ius紊流燃烧模型估算化学反应速率,六通量热辐射模型估算辐射通量。在非交错网格下求解气相采用S IM PLE算法,液相采用颗粒轨道模型和PS IC算法。近壁区处理分别采用两层和三层壁面函数。计算数据与试验值比较表明,采用三层壁面函数的RNG k-ε模型更适用于模拟三维两相燃烧流场。

基于RNGk-ε模型的大曲率弯管的软性磨粒流加工仿真与实验

针对微小尺寸、大曲率弯管结构化内表面难以使用工具进行接触式光整加工的问题。该项目提出了一种使用软性磨粒流加工此种类型弯管内表面的方法。为了验证理论分析的正确性,基于RNG k-ε湍流模型对加工过程中整个流道内部进行仿真实验。并搭建了实验平台进行加工实验,以验证仿真结果的可靠性。仿真的结果表明,磨粒在弯管内处于无规则的运动状态,并且弯管内部的内、外两侧壁面存在着明显的速度差和压力差,并且随着入口压力从2.0MPa增大至3.0MPa,内部压力与速度也随之增大。在加工实验中,对工件进行加工前,工件内表面各点粗糙度都相对较大,因此平均粗糙度也相应较大,大约为1.072μm。工件加工一段时间后,整个内表面的光整度变好,而且伴随着入口压力的增大,加工效果变好,表面粗糙的均匀程度提高,光整性也逐渐提高,可达0.450μm。加工实验结果证明磨粒在近壁区的切削痕迹确实呈无序化的运动形态,与前期的数值仿真结果相吻合。理论分析,仿真实验与加工实验共同为软性磨粒流实现微小尺寸、大曲率弯管的无工具精密加工提供了理论和现实依据。

用RNG k-ε紊流模型对截止阀三维紊流流动的数值模拟

采用了RNG k-ε紊流模型和贴体坐标对截止阀对称面和三维流场进行了模拟,同时用粒子成像流速仪(PIV)对弯型截止阀对称面模型的测试结果和数值模拟结果进行了验证。数值模拟结果与实验结果吻合较好。实验和计算结果揭示了截止阀的流场特性,并说明截止阀水流产生的涡旋、分离流、二次流和强烈的紊动是截止阀水头损失的主要因素。计算结果表明斜进口截止阀流态好于弯型进口截止阀的流态,RNG k-ε紊流模型对具有分离和二次流的紊流流动具有较好的模拟性。

基于RNGk-ε湍流模型的直接空冷岛数值模拟研究

空冷电厂中的直接空冷岛易受到环境风的影响,因而计算直接空冷岛周边流场和温度场对于设计和优化空冷岛的体型和工况具有重要的意义。文章采用建立在非结构网格有限体积法上的RNGk-ε湍流模型对直接空冷岛进行了流场和温度场的计算,压力和速度耦合采用来SIMPLEC算法。数值模拟获得了直接空冷岛周围的流场和温度场,计算发现通过设置挡风墙未出现热风回流现象,计算结果表明采用的RNGk-ε湍流模型及相关参数设置合理。文章提出的计算方法适合于直接空冷岛的流场及温度场的计算。

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.