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.

Menter SST湍流模型系数在高速流动模拟中的不确定度量化研究

Menter SST湍流模型系数的不确定性会对高速流动数值模拟的结果产生显著影响。本文针对二维压缩拐角、二维圆柱和三维双椭球体3个典型高速模型,定量评估湍流模型封闭系数不确定性对数值模拟的影响。首先,采用非嵌入多项式混沌方法量化由Menter SST湍流模型封闭系数不确定性导致的气动力/热数值模拟的不确定度;然后,依据Sobol敏感性指标对封闭系数的敏感性进行排序,辨识导致不确定度的关键因素。研究结果表明气动热的不确定度普遍大于气动力。在考察的9个封闭系数中,σ_(ω1)、β^(*)、κ、a_(1)是对数值模拟结果不确定度贡献较大的关键模型参数,其敏感性大小与当地流动特征相关:在流动的大部分区域内,生成项系数σ_(ω1)和κ是导致数值模拟结果不确定度的主要因素;而在流动发生分离或出现激波后的区域,数值模拟结果受耗散项系数β^(*)与剪切应力限制器参数a_(1)的影响更显著。

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.

考虑旋转和曲率影响的SST k-ω湍流模型改进

分析了离心泵中常用湍流模型的优缺点,采用考虑旋转和曲率影响的RNG k-ε模型和Realizable k-ε模型分别对SST k-ω湍流模型进行了改进,生成了两种新的湍流模型。以开源代码库OpenFOAM作为平台对改进的湍流模型实现了程序化,应用新的湍流模型分别对一低、中、高比转数的离心泵进行数值计算,并将修改前后的数值计算结果与试验结果从能量性能的角度进行了详细对比。分析结果表明,改进后的湍流模型能成功用于离心泵内流计算中,且计算精度较修改前更接近于试验值。

k-ω SST两方程湍流模型中参数影响的初步分析

Menter的k-ωSST两方程湍流模型在流体力学计算中有良好表现。利用均匀试验设计方法对k-ωSST模型中八个参数在小攻角亚声速、跨声速和大攻角三种典型的翼型绕流流场计算中的影响规律进行了分析。分析结果表明在附着流中参数a1是对流场的影响最大的参数;而在分离流中,参数a1对流场的影响与湍流产生与耗散等项的作用相当,模型中的四个参数:σω2、β2、β*和a1的取值都会对计算结果有较大的影响。

提高k-ω SST模型对翼型失速特性的模拟能力

采用CFD软件fluent,k-ωSST模型对S825翼型进行了二维数值模拟.针对k-ωSST模型对翼型分离失速特性模拟不准的情况,对分离区域内湍流的强非平衡输运特性进行了分析.研究表明:原始模型由于不能准确模拟分离区内湍流的强非平衡输运特性,导致其对翼型失速特性模拟失效;提出了通过修正模型系数a1及β*∞,提高k-ωSST模型预测非平衡湍流输运特性的方法,从而提高对翼型失速特性的模拟精度.

应用SSTk-ω湍流模型计算Rushton搅拌釜流场

应用SSTkω-湍流模型对Rushton搅拌釜流场进行了计算,并与文献报道实验数据以及标准k-ε模型、RNGkω-模型预测结果进行了比较。结果表明SSTkω-模型所计算的排除流量准数与实验值相差较小,桨叶区速度场与实验数据吻合较好,略优于标准k-ε模型,同时也给出了近壁区的计算结果。在湍动动能的预报上,SSTk-ω模型值与标准k-ε模型比较接近,优于RNGkε-模型,但与实验值都还不同程度地存在着一些差异。

基于SST k-ω湍流模型的平衡大气边界层模拟

为实现SST k-ω湍流模型下空流场大气边界层的平衡,提出通过在湍动能输送方程与比耗散率输送方程中添加源项的方法使来流边界条件与湍流模型相协调,并通过相应的CFD数值算例分别考察了不考虑源项与考虑源项时沿流场不同位置处的平均速度、湍动能及比耗散率剖面的一致性。计算结果表明,当考虑源项时沿流场不同位置处的平均速度剖面、湍动能剖面及比耗散率剖面均有较高程度的一致性,较好地实现了大气边界层的平衡。研究结论为平衡大气边界层的研究提供了新的思路和研究方法,对结构风工程中CFD数值模拟有一定的理论及应用价值。

基于SST k-ω模型的汽车空调CFD仿真分析

以汽车空调为研究目标,利用SST k-ω两方程模型,在除霜模式下分别对带HVAC及不带HVAC的空调系统进行仿真计算,分析了HVAC系统对仿真计算结果产生的影响。此外,分析结果显示位于驾驶员侧的前挡玻璃表面速度满足要求,位于副驾驶侧的前挡风玻璃表面速度大于1.5 m/s的区域覆盖率仅为75%左右,不满足国标要求。侧窗玻璃表面速度均值不到1 m/s,也不满足国标,仿真结果与试验结果对比相一致。风道存在较大问题,导致除霜风道气体集中从中间风道吹出,两侧风道的气流极小。根据结果提出进一步的改进建议,即在除霜风道增加必要的隔板装置,为汽车空调的改进设计提供依据。

基于改进k-ω SST模型的风力机尾流数值模拟

基于双方程k-ω SST模型提出两种改进湍流模型,采用丹麦科技大学的自编求解器EllipSys3D结合致动盘方法,对单台风力机尾流流场进行数值模拟。该文将SST-sust模型引入到风力机尾流的数值研究中,为了更进一步增大预测到的湍流强度和提高尾流恢复速度,提出SST-Csust模型和SST-Dsust模型,它们是在SST-sust模型的基础上分别调整湍流模型的封闭常系数、修正ω方程的耗散项。通过与理论、实验以及LES模型进行对比分析,结果表明该文提出的改进模型在尾流区速度分布和湍流强度分布的预测方面可取得较好的应用效果。

SST k-ω-k_p两相湍流模型及其在湿蒸汽凝结流动数值模拟中的应用

首先,建立了湿蒸汽凝结流动的双流体模型,考虑了湿蒸汽两相流动中相间的速度滑移、耦合以及湍流扩散作用的影响．然后,针对蒸汽透平叶栅中流动的湍流特性,在单相湍流计算中数值模拟精度相对良好的两方程SST k-ω湍流模型基础上,参照颗粒湍能输运方程理论,推导建立了SST k-ω-k_p湿蒸汽两相流动湍流模型,模型中引入了液相黏性、导热及扩散系数等拟流体概念．对二维叶栅中存在自发凝结的湿蒸汽流动进行的数值模拟表明:建立的数值模型表现良好,明显优于单流体模型,特别是吸力面的压力分布模拟精度有很大提高,具有较高的精确性和可靠性．由于实验数据的匮乏,数值模拟中发现的汽液两相的动力特性以及液相的参数分布有待于进一步的实验来验证．

基于SST k-ω湍流模型的高层建筑体型系数数值研究

目的研究建筑物高度和宽度的变化对其表面绕流流场的影响,分析建筑物风荷载体型系数的变化,为结构设计人员在结构抗风设计方面提供参考.方法利用计算流体动力学软件STAR-CCM+,选用基于雷诺平均(RANS)的SST k-ω湍流模型,对不同高度和宽度的建筑物进行数值模拟,计算建筑物风荷载体型系数.结果在宽度相同的情况下,随着高度的增加,正面、侧面和背面的体型系数绝对值增加;随着宽度的增加,侧面和背面的体型系数绝对值增加,而正面影响不大.结论高层建筑的体型和体量对风荷载体型系数有一定的影响,在结构抗风设计中应该适当予以考虑.

基于SST k-ω湍流模型的二维圆柱涡激振动数值仿真计算

随着海洋工程逐渐向深海发展,广泛使用的柔性立管因为高频振动很容易受到严重的损伤。因此对于这类细长柔性结构的涡激振动(VIV)研究是当今的一个热点,同时随着计算机的快速发展,CFD(计算流体力学)技术成为研究涡激振动问题不可或缺的一种方法。本文采用雷诺平均纳维尔-斯托克斯(RANS)方程,并结合SST k-ω湍流模型,研究低质量比弹性支撑刚性圆柱体的涡激振动问题。从振幅响应、频率响应、3个响应分支的水动力性能、尾涡模式等方面和Williamson相关实验作对比。结果表明,SST k-ω湍流模型能够有效准确地模拟圆柱绕流的涡激振动。本文丰富了海洋工程的理论研究,为柔性立管的实际应用提供了一定的理论指导。

基于SST k-ω湍流模型与遗传算法的高速电梯井道风口优化设计

为了改善和提高电梯的气动特性和运行稳定性,基于SST k-ω湍流模型对电梯进行空气流体仿真,计算气动阻力、侧翻力矩、俯仰力矩,分析实验数据变化趋势。通过最小二乘拟合,建立电梯气动特性的一元数值模型。根据正交实验结果与一元数值模型,基于MATLAB回归分析,建立电梯气动特性的多元数值模型,并以此作为目标函数,以气动阻力、侧翻力矩和俯仰力矩最小作为优化目标,基于遗传算法进行电梯气动特性的多目标优化,仿真验证优化后电梯气动特性得到较大改善,为电梯气动特性的改善提供了一定的参考价值和意义。