fluent用户手册摘要.docx

1、fluent用户手册摘要To make the most appropriate choice of model for your application, you need to understand the capabilities and limitations of the various options. Due to the strong interaction of the mean flow and turbulence, the numerical result for the turbulent flows tend to be more susceptible to me

2、sh dependency than those for laminar flows. Recommended that resolve ,with sufficiently fine meshes, regions where the mean flow undergoes rapid changes and the shear with large strain rates. Check the near-wall mesh by displaying or plotting y which is available in the postprocessing dialog boxes.

3、Fluent后处理1，建模及网格生成：gambit或者分离的CAD系统产生几何结构模型机网格；也可用Tgrid从已有的面网格中产生体网格；也可以从相关CAD软件包生成体网格，然后读入Tgrid或者fluent。初始化的时间注意：fluent有一个格式转换器允许从其他程序读入结构网格。计算花费数值耗散Create a line for plotting the centerline velocity distribution: link/rake surface-输入中心线的两点坐标，new surface name 命名为center line，-solution XY plot，curve设

4、置中心线格式-设置plot direction为某一轴线，例如设置x轴为plot direction，y轴为速度大小，surface选择中心线Create a line for plotting the velocity profile at the outlet.有旋与旋转流动问题有旋流动在一些燃烧器里用来增加流体滞留时间和驻涡，从而稳定燃烧。Segregated solver only:对四边形和六面体网格，选用presto；为求解大压力梯度和轴向速度梯度，网格必须足够精密；三维有旋流动：定义速度进口需要用柱坐标，求解时要渐渐增加旋转速度；轴对称旋转，旋转轴必须是x轴，网格必须在y=0以上

5、。旋转流动中，边界层很薄，fluent需要在靠近旋转边界的地方网格比较细；轴向速度比较陡，近中心线为典型的自由涡流动，因此为保证好的求解效果，网格要求比较密。RNG k-_ ModelThe effect of swirl on turbulence is included in the RNG k-_ model, enhancing accuracy for swirling flowsRNG turbulence model, the differential viscosity model :use a differential formula for the effective vi

6、scosity eff to account for the low-Reynolds-number effectsOnce you chose the RNG model, the swirl modification takes effect, by default, for allthree-dimensional flows and axisymmetric flows with swirl. The default swirl constant is set to 0.07, which works well for weakly to moderately swirling flo

7、ws. However, for strongly swirling flows, you may need to use a larger swirl constant._s is a swirl constant that assumes different values depending on whether the flow is swirl-dominated or only mildly温和的，和善的，适度的 swirling. This swirl modification always takes effect for axisymmetric, swirling flows

8、 and three-dimensional flows when the RNG model is selected. For mildly swirling flows _s is set to 0.07. For strongly swirling flows, however, a higher value of _s can be used.Differential viscosity model 考虑边界层的低雷诺数的影响。The RNG turbulence model in ANSYS FLUENT has an option of using a dierential for

9、mula for the eective viscosity e to account for the low-Reynolds-number eects.Differential Viscosity Model specifies whether or not the low-Reynolds-number RNG modifications to turbulent viscosity should be included. By default, this option is turned off. It is likely to have an effect only when the

10、 near-wall regions in the domain are well resolved已解决的 in terms of依据，按照 mesh density. Swirl Dominated Flow specifies whether or not the RNG modification to turbulent viscosity for swirling flows should be included. This option is available only in 3D and 2D axisymmetric swirl solvers, and it can yie

11、ld improved predictions when solving flows with significant swirl.The standard wall functions work reasonably well for a broad range of wall bounded flows. However, they tend to become less reliable when the flow situations depart from the ideal conditions that are assumed in their derivation. Among

12、 others, the constant-shear and local equilibrium assumptions are the ones that most restrict the universality of the standard wall functions. Accordingly, when the near-wall flows are subjected to屈服，受制 severe pressure gradients, and when the flows are in strong non-equilibrium, the quality of the p

13、redictions is likely to be compromisedThe non-equilibrium wall functions offered as an additional option that can potentially improve the results in such situations。Reattachment回帖，重附着，再附impingement冲击，碰撞viscous sublayer黏性底层identical一致的，相同的coarse粗糙的Standard Wall Functions vs. Non-Equilibrium Wall Func

14、tionsBecause of the capability to partly account for the effects of pressure gradients, the none-quilibrium wall functions are recommended for use in complex flows involving separation, reattachment, and impingement where the mean flow and turbulence are subjected to pressure gradients and rapid cha

15、nges. In such flows, improvements can be obtained, particularly in the prediction of wall shear (skin-friction coefficient) and heat transfer (Nusselt or Stanton number).For triangular and tetrahedral meshes, since the flow is never aligned with the mesh, you will generally obtain more accurate resu

16、lts by using the second-order discretization. For quad/hex meshes, you will also obtain better results using the second-order discretization, especially for complex flows.While the higher-order scheme may result in greater accuracy, it can also result in convergence diculties and instabilities at ce

17、rtain flow conditions. On the other hand, using a first-order scheme may not provide the desired accuracy. One approach to achieving improved accuracy while maintaining good stability is to use a discretization blending factor. A blending factor of less than 1 (typically 0.75 or 0.5) will make the c

18、onvective fluxes more diusive, which in some flow conditions can stabilize a solution that is otherwise unstable when the full higher-orderdiscretization scheme is employed. Note that in order to use this feature eectively, make sure that one of the allowed higher order discretization schemes is sel

19、ected for the desiredvariables in the Solution Methods task page.The QUICK scheme is applicable to quadrilateral or hexahedral meshes, If QUICK is used for hybrid meshes, it will be used only for quadrilateral and hexahedral cells. Second-order upwind discretization will be applied to all other cell

20、s.Note that SIMPLE, SIMPLEC, PISO, and Fractional Step use the pressure-based segregated algorithm, while Coupled uses the pressure-based coupled solver.The SIMPLE algorithm uses a relationship between velocity and pressure corrections to enforce mass conservation and to obtain the pressure field.If

21、 you choose SIMPLEC under Pressure-Velocity Coupling, you must also set the SkewnessCorrection, whose default value is 0.If you choose Coupled, you will have to specify the Courant number in the Solution Controlstask page, which is set at 200 by default. You will also specify the Explicit Relaxation

22、Factors for Momentum and Pressure, which are set at 0.75 by default.If high-order momentum discretization is used, you may need to decrease the explicit明确的，显式 relaxation to 0.5. For cases with very skewed meshes, the run can be stabilized by further reduction of the explicit relaxation factor to 0.2

23、5.It is good practice to begin a calculation using the default under-relaxation factors. If the residuals continue to increase after the first 4 or 5 iterations, you should reduce the under-relaxation factors.A cautious approach is to save a data file before making any changes to the under-relaxatio

24、n factors, and to give the solution algorithm a few iterations to adjust to the new parameters. Typically, an increase in the under-relaxation factors brings about a slight increase in the residuals, but these increases usually disappear as the solution progresses. If the residuals jump by a feworde

25、rs of magnitude, you should consider halting the calculation and returning to the last good data file saved.For most flows, the default under-relaxation factors do not usually require modification. If unstable or divergent behavior is observed, however, you need to reduce the under- relaxation facto

26、rs for pressure, momentum, k, and from their default values to about 0.2, 0.5, 0.5, and 0.5. (It is usually not necessary to reduce the pressure under-relaxation for SIMPLEC.) In problems where density is strongly coupled with temperature, as in very-high-Rayleigh-number natural- or mixed-convection

27、 flows, it is wise to also under- relax the temperature equation and/or density (i.e., use an under-relaxation factor less than 1.0). Conversely, when temperature is not coupled with the momentum equations (or when it is weakly coupled), as in flows with constant density, the under-relaxation factor

28、 for temperature can be set to 1.0.For other scalar 标量，数量equations the default under-relaxation may be too aggressive for some problems, especially at the start of the calculation. You may wish to reduce the factors to 0.8 to facilitate convergence.Note that with optimal 最佳的，理想的，优化的settings, the con

29、vergence of the coupled pressure-velocity algo-rithm will be limited by the segregated solution of other scalar equations, e.g., turbulence. For optimum solver performance, you will need to increase the relaxation factors for these equations to a value greater than the default values.here are two me

30、thods for initializing the solution: Initialize the entire flow field (in all cells). Patch values or functions for selected flow variables in selected cell zones or “registers” of cells. (Registers are created with the same functions that are used to markcells for adaption.)Before patching initial

31、values in selected cells, you must first initialize the entire flow field. You can then patch the new values over the initialized values for selected variables.Console控制台，主控台，；安慰，慰藉；graphics图形，图像integrate集成，结合，求积分manully手动的，用手。Monitoring surface integrals can be used to check for both iteration conv

32、ergence and meshindependence. For example, you can monitor the average value of a certain variable ona surface. When this value stops changing, you can stop iterating. You can then adaptthe mesh and reconverge the solution. The solution can be considered mesh-independentwhen the average value on the surface stops changing between adaptions.For most problems, the default convergence criterion in ANSYS FLUENT is sucient.This criterion requires that the scaled residuals decrease to 10*-3 for all equations except the energy and P-1 e