Numerical analysis of turbulent mixed convection air flow in inclined plane channel with k-εtype turbulence model

Numerical study on turbulent mixed convection in inclined plane channels,from 15° to 90° (vertical),was carried out to examine the effect of inclination on fluid flow and heat transfer distributions.The turbulent air flows upward or downward into the duct with one wall heated from bottom.Calculation results with several kinds of k-εtype turbulence models were used to compare the experimental data with those in literatures to determine suitable model.The dependents of Nusselt number on the inclination angle of both the buoyancy-aided and buoyancy-opposed flow are discussed.

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.

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.

PARAMETER ESTIMATION OF ENGINEERING TURBULENCE MODEL

A parameter estimation algorithm is introduced and used to determine the parameters in the standard k-epsilon two equation turbulence model (SKE). It can be found from the estimation results that although the parameter estimation method is an effective method to determine model parameters, it is. difficult to obtain a set of parameters for SKE to suit all kinds of separated flow and a modification of the turbulence model structure should be considered. So, a new nonlinear k-e two-equation model (NNKE) is put forward in this paper and the corresponding parameter estimation technique is applied to determine the model parameters. By implementing the NNKE to solve some engineering turbulent flows, it is shown that NNKE is more accurate and versatile than SKE. Thus, the success of NNKE implies that the parameter estimation technique may have a bright prospect in engineering turbulence model research.

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.

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.

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.

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.

用RNGK─ε模式数值模拟180°弯道内的湍流分离流动

将Ｙａｋｈｏｔ与Ｏｒｓｚａｇ新近提出的ＲＮＧＫ－ε湍流模式推广应用于１８０°强曲率弯道内的湍流分离流动的数值模拟，计算在任意曲线坐标下进行，并采用速度协变分量作为求解变量以保证计算的高度稳定性，控制方程的求解采用通常的控制容积法，文中给出了详细的数值计算结果，并与实验结果进行了比较，结果表明，ＲＮＧＫ－ε湍流模式能有效地模拟有强曲率影响的湍流分离流动。

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.

RNGk-ε模型在超空化流动计算中的应用评价

为深入了解两相共存超空化的非定常特性,分别采用标准RNGk-ε模型及其修正模型,计算了绕水翼的超空化流动,并通过与实验结果的对比对各个模型进行了评价。计算结果表明:标准RNGk-ε模型及其修正模型均可以模拟绕水翼的超空化流动状况,能比较准确地模拟两相共存超空化阶段汽相和水汽混合相界面的反向波动过程;模型常数的不同主要表现为对空穴内逆压梯度的影响,并由此导致了计算获得的最大空穴长度以及两相界面反向波动速度的差异;超空化区域内水汽两相的变化与压强分布均存在对应关系,压强的变化导致了水汽两相界面的反向波动。

基于组分输运模型和RNG k-ε模型的浑水异重流数学模型研究及其应用

基于组分质量守恒理论,将浑水异重流的运动过程看成是含沙浑水中的泥沙这一组分在水体中的传输过程,建立组分方程,与考虑了平均流动中的旋流流动情况的RNGk-ε方程组进行耦合求解,利用目前广泛使用的商用FLUENT软件进行数学模型计算,并采用室内模型试验进行论证。结果表明:该数学模型可以有效模拟浑水异重流的潜入和前锋运动过程,为深入研究水库、湖泊及河流入海口浑水异重流问题提供了新的途径。借助此模型模拟了水库内汛期浑水异重流运动情况。

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 。

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。

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。

基于RNG k-ε模型的聚结器油相体积浓度场数值模拟

为优化聚结器结构,应用计算流体力学(CFD)方法,选用RNG k-ε模型,以SIMPLE算法为基础,对旋流式和蛇形管式聚结器在湍流状态下的流体流动场进行数值模拟,得出2种结构聚结器的油相体积浓度分布云图.数值模拟结果表明,蛇形管式聚结器对油滴的兼并和聚结效果优于旋流式聚结器.