湍流模型在肘形进水流道三维流场数值模拟中的适用性研究

为找到可准确模拟低扬程泵站肘形进水流道水流流动的湍流模型,在对肘形进水流道进行网格无关性分析的基础上,选用S-A、Standardκ-ε、RNGκ-ε、Realizableκ-ε、Standardκ-ω、SSTκ-ω和RSM等7种常用湍流模型分别对肘形进水流道三维湍流流动进行数值模拟,并从流道水头损失和流态两个方面与流道模型试验结果进行比较。结果表明,不同湍流模型满足网格无关性所需的网格数量不同,RNGκ-ε、Realizableκ-ε和S-A湍流模型数值模拟的水力损失与模型试验结果的相对误差分别为1.01%、7.07%、9.09%,RNGκ-ε与Realizableκ-ε湍流模型计算得到的流场几乎完全相同,建议在对肘形进水流道三维湍流流动进行数值模拟时优先考虑采用RNGκ-ε湍流模型。研究成果可为进水流道三维湍流流动数值模拟的模型选择提供依据。     

不同湍流模型对风力机叶片翼型气动性能参数计算结果的影响研究

为了比较不同湍流模型得到的风力机叶片翼型气动性能参数计算结果的区别,采用S-A、SST k-ω和RNG k-ω这3种湍流模型对风力机叶片NACA0018翼型进行数值计算,然后将得到的结果和文献给出的风洞实验值进行比较,最后分别讨论了一阶迎风、二阶迎风和QUICK这3种离散格式对计算精度的影响。结果表明:当翼型在未失速(攻角小于14°)状态时,RNG k-ω模型得到的升力系数值与实验值最为接近;当翼型处于失速状态(攻角大于等于14°)时,S-A模型得到的升力系数值与实验值最为接近,而SST k-ω模型得到的阻力系数值与实验值最为接近。     

不同湍流模型在斜流泵性能预测中的应用

为研究不同湍流模型在斜流泵性能模拟上的差异,以比转速为425的斜流泵为研究对象,选取κ-ε、κ-ω、SST、RNGκ-ε四种湍流模型,对斜流泵设计工况下的内部流动进行数值计算,并分析各湍流模型在斜流泵内流计算中的适用性。结果表明,SST模型预测的扬程偏差较大,为7.69%,其余模型扬程预测偏差均小于5%,其中RNGκ-ε模型扬程预测偏差最小,为3.76%;SST模型预测的效率偏差最大,为3.70%,κ-ε模型和κ-ω模型的效率偏差最小,均为3.00%;4种模型在吸入段及导叶处的轴向速度分布基本一致,κ-ω模型对叶轮轴向速度预测的高速域范围略优于其余三种模型;κ-ε模型和RNGκ-ε模型对斜流泵涡量预测结果较为相似,而κ-ω模型和SST模型的预测结果比较接近。研究结果可为预测斜流泵性能和内部流动特性提供参考。     

基于不同湍流模型的混流泵内部流动及性能研究

以低比转数混流泵为例,基于CFX软件,分别选取标准κ-ε模型、RNGκ-ε模型、剪切应力传输SSTκ-ω模型、BSLκ-ω模型4种湍流模型,模拟了该混流泵在设计工况和非设计工况下叶轮内流场的流动分布及叶片压力变化情况,并对比分析了外特性计算结果与试验结果。结果表明,基于4种湍流模型的计算结果与试验结果均基本一致,其中基于标准κ-ε模型的扬程、效率的预测结果与试验结果更为接近。     

基于两方程湍流模型的均匀流中湍流动能衰减规律研究

通过理论推导和数值模拟,从湍流模型封闭系数的确定过程、输运方程扩散项的影响因素、入口边界条件和网格尺度等方面分析标准k-ε模型、标准k-ω模型和SST k-ω湍流模型在计算均匀来流时湍流动能的衰减规律及其本质物理区别;通过数值模拟分析中性大气条件下湍流动能的衰减规律.结果表明,在均匀流中,采用标准k-ε湍流模型,入口湍...     

风剪切来流对风力机近尾迹流动特性影响

在风剪切来流风况下,对WindPACT 1.5MW风力机近尾迹流动特性进行了数值计算,同时研究了三种风剪切系数(0.1、0.2和0.3)对风力机近尾迹流动特性的影响。基于雷诺平均不可压N-S方程的计算流体力学方法数值模拟三维非定常的风力机流场,其中,湍流模型选取Shear Stress Transport k-ω湍流模型。研究结果表明:在近尾迹区域,来流空气的轴向诱导因子和切向诱导因子受到旋转叶片的强烈影响,并在风力机下游形成明显的轴向速度亏损。这种轴向速度亏损随空气向下游流动过程中,逐渐减弱。轴向诱导因子和切向诱导因子受风剪切影响,呈非周期性分布,并且风剪切系数增加,这种影响随之增强。     

三种κ-ε模型模拟混流式水轮机转轮叶片湍流场差异性比较

为比较Standardκ-ε模型、RNGκ-ε模型、Realizableκ-ε模型用于水轮机数值模拟时的异同,采用三种κ-ε模型对不同工况下带有副叶片的混流式水轮机转轮进行了三维定常湍流数值模拟,流场求解使用分离式解法,压力场求解使用SIMPLEC算法。结果表明,三种κ-ε模型用于水轮机的数值模拟具有一定的准确性和适用性,在相同模拟条件下都可得出与实际流态大致吻合的结果,但在计算量、捕捉流动细节及计算精度等方面存在差异,可为水轮机数值模拟研究中κ-ε模型的选择提供参考和依据。     

风力机翼型大攻角分离流的数值模拟

为了准确预测风力机翼型在大攻角下分离流动的气动性能,并且为风力机的设计与安全运行提供一种可靠的数值模拟手段,针对某风力机专用翼型,分别采用基于非定常不可压缩Navier-Stokes方程的大涡模拟(LES)模型、RNG k-ε模型和Standard k-ε模型对其气动性能进行数值模拟,并计算出翼型攻角为35～90°,雷诺数为2×106时的气动力参数。将不同湍流模型的计算结果与风洞试验数据进行比较,并分析流场结构。分析结果表明,LES模型能够准确地模拟出翼型表面的分离流动,计算结果与试验数据取得了很好的一致性,并且优于RNG k-ε模型和Standard k-ε模型的模拟结果。     

水平轴风力机三维旋转效应数值模拟研究

采用带转捩的k-ω SST湍流模型,求解RANS方程获得对风工况下风力机叶片周围的流场,使用inverse BEM方法后处理获取局部动压和局部迎角,并对叶片三维旋转流动进行详细分析。数值模拟结果在低速轴扭矩、剖面载荷系数、压力分布等方面都与实验值吻合得较好。为提供较深入的关于三维旋转效应物理机理的理解,与相似入流条件下二维流动进行比较,详细讨论三维旋转效应对剖面载荷和流场结构的影响极其成因,研究表明三维旋转效应在叶根分离区影响显著,对剖面延迟分离有明显作用。     

用RNG k-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,此模型适合于计算内燃机缸内湍流流动.     

基于CFX的混流泵内流场数值模拟

基于三维不可压缩流体的N-S方程和RNGκ-ε湍流模型,采用流体计算软件ANSYS-CFX计算了额定转速下190～300L/s流量范围内9个工况点的某混流泵内部流动,研究了小流量工况、最优工况和大流量工况等工况下叶片压力面、吸力面的静压分布及各断面翼型附近的相对流速分布;通过分析混流泵内部流动速度和叶片表面静压分布,揭示了其内部流动的主要特征。预测了泵的水力性能,并与泵模型性能试验结果进行了对比。结果表明,最优工况时数值模拟与试验结果吻合较理想,满足工程实际的需要。     

Evaluation of Turbulence Models in the Prediction of Heat Transfer Due to Slot Jet Impingement on Plane and Concave Surfaces

The performance of several turbulence models in the prediction of convective heat transfer due to slot jet impingement onto flat and concave cylindrical surfaces is evaluated against available experimental data. The candidate models for evaluation are (1) the standard k – ε model, (2) the RNG k – ε model, (3) the realizable k – ε model, (4) the SST k – ω model, and (5) the LRR Reynolds stress transport model. Various near-wall treatments such as equilibrium wall function and two-layer enhanced wall treatment are used in combination with these turbulence models. The computations are performed using the commercial computational fluid dynamics (CFD) code Fluent. From the validation exercises, it is found that when the impingement surface is outside the potential core of the jet, most of the turbulence models predict reasonably accurate thermal data (local Nusselt number variation along the impingement surface). When the impingement surface is within the potential core of the jet, the turbulence models grossly overpredict the Nusselt number in the impingement region, but in the wall jet region the Nusselt number prediction is fairly accurate. Overall, the RNG k – ε model with the enhanced wall treatment and the SST k – ω model predict the Nusselt number distribution better than the other models for the flat plate as well as for the concave surface impingement cases. However, the hydrodynamic data such as the mean velocity profiles are not accurately predicted by the SST k – ω model for the concave surface impingement case, whereas the RNG k – ε model predictions of the velocity profiles agree very well with the experiment. The Reynolds stress model does not show any distinctive advantage over the other eddy viscosity models.     

Numerical simulation of 3D turbulent isothermal flow in a vortex combustor

Numerical simulations of strongly swirling turbulent flows in a vortex combustor (VC) are conducted. A comprehensive investigation of a three-dimensional isothermal VC flow using three first-order turbulence models: the standard k–ε turbulence model, Renormalized Group (RNG) k–ε model and shear stress transport (SST) k–ω model; and a second-order turbulence model, Reynolds stress model (RSM) together with a second-order numerical differencing scheme is conducted in the present work. The computation indicates that the RSM is superior to the other turbulence models in capturing the swirl flow effect in comparison with measurements. The numerical results for the VC flow provide the characteristics of the flow in terms of relevant parameters for the VC design and operation, composed of axial and tangential velocities, pressure fields, and turbulence kinetic energy.     

Turbulence modelling for wall-bounded particle-laden flow with separation

The performance of different turbulence models and source-term models for the turbulent separated particle-laden flow is investigated. The accuracy of various turbulence models is firstly evaluated without any modification by the source-term model. The considered models are the k–ω SST model; the standard, the RNG and the realizable k–ε models with the standard, the non-equilibrium and the enhanced wall functions. The accuracy of various source-term models is then compared. The results are investigated and analyzed to find the best combination of the turbulence model and the source-term model in predicting the combined effects of turbulence, particles, viscous wall and flow separation. It is found that the RNG k–ε turbulence model with the non-equilibrium wall function using the source-term model of Tu and Fletcher is the most suitable combination for this type of flow.     

Numerical study on heat transfer of turbulent channel flow over periodic grooves

A numerical investigation of turbulent forced convection in a two-dimensional channel with periodic transverse grooves on the lower channel wall is conducted. The lower wall is subjected to a uniform heat flux condition while the upper wall is insulated. To investigate turbulence model effects, computations based on a finite volume method, are carried out by utilizing four turbulence models: the standard k − ε, the Renormalized Group (RNG) k − ε, the standard k − ω, and the shear stress transport (SST) k − ω turbulence models. Parametric runs are made for Reynolds numbers ranging from 6000 to 18,000 with the groove-width to channel-height ratio (B/H) of 0.5 to 1.75 while the groove pitch ratio of 2 and the depth ratio of 0.5 are fixed throughout. The predicted results from using several turbulence models reveal that the RNG and the k − ε turbulence models generally provide better agreement with available measurements than others. Therefore, the k − ε model is selected to use in prediction of this complex flow. In addition, the results of the heat transfer coefficient, friction factor, skin friction coefficient and thermal enhancement factor are also examined. It is found that the grooved channel provides a considerable increase in heat transfer at about 158% over the smooth channel and a maximum gain of 1.33 on thermal performance factor is obtained for the case of B/H = 0.75. This indicates that the reverse/re-circulation flow in a channel with transverse grooves can improve the heat transfer rate.     

特种发动机离心式水泵性能预测

采用MRF模型和κ-εRNG（重整化群）湍流模型对某特种车辆发动机用离心式水泵进行了模拟计算,获得了水泵内流场的压力和相对速度分布,并预测了水泵的性能,指出了水泵性能与发动机冷却系统需求之间的矛盾,为水泵优化设计、提升性能提供了理论依据。     

水平轴风力机风轮气动性能数值模拟

以某上风向定桨水平轴风力机风轮为研究对象进行数值模拟,采用不可压N—S方程和κ -ω SSTN方程湍流模型,数值模拟了不同风速下风力机风轮的流动特性。结果表明：随着风速的增大,靠近叶片中部截面最先发生失速。在此基础上,分析了叶片整体的压力与速度分布。     

The Effect of Conjugate Heat Transfer on Film Cooling Effectiveness

The film cooling effectiveness of a two-dimensional gas turbine endwall is compared for the cases of conjugate heat transfer and an adiabatic wall condition using five common turbulence models. The turbulence models employed in this study are: the RNG k–ε model, the realizable k–ε model, the standard k–ω model, the SST k–ω model, and the RSM model. The computed flow field and surface temperature profiles along with the film effectiveness for one and two cooling slots at different injection angles are presented. The results show the strong effect of conjugate heat transfer on the film effectiveness compared to the adiabatic case and also compared to the effectiveness values obtained from analytically solvable models.     

Prediction of convection from a finned cylinder in cross flow using direct simulation,turbulence modeling,and correlation-based methods

Direct numerical simulation (DNS), two shear-stress transport (SST) turbulence models, and three k-ε models are used to predict mixed convection associated with air in cross flow over an isothermal, finned cylinder. The DNS predictions reveal complex time-variation in the flow field. Convection heat transfer coefficients predicted by the SST models are in good agreement with those generated by DNS, whereas the k-ε models do not accurately predict heat fluxes. Correlation-based predictions of heat transfer coefficients are, in general, in poor agreement with the DNS and SST predictions. The impact of various geometrical modifications on convection coefficients is also presented.     

Turbulence models application on CFD simulation of hydrodynamics,heat and mass transfer in a structured packing

In this study, turbulence model applications on two-phase flow simulation in a structured packing are investigated using CFD application. Dry pressure drop, irrigated pressure drop, mass transfer and heat transfer are studied by k–ε, RNG k–ε, k–ω and BSL turbulence models. The best results obtained by k–ω and BSL models, but k–ω is recommended because it is more robust than BSL. The mean absolute relative error (MARE) between CFD prediction of k–ω model and experimental data for dry pressure drop, irrigated pressure drop, mass transfer and heat transfer are 16.9%, 10.7%, 8.1%, 0.9%, respectively.