请问为什么OpenFOAM会比Fluent计算快？

MrZZQi

@Samuel-Tu 编译层面的问题是没有的，不清楚计算的效率够不够高。但其实我的UDF做的事情不多，不套速度也没有显著提升。
@东岳额，之前Fluent跑了1个半月，最近OpenFOAM跑了2天吧...大概是这个比例...如果确实没有道理的话可能我要去重新看一遍“FluentXX天速成宝典”了...

李东岳

@MrZZQi 虽然我是OpenFOAM用户，并且希望大家用OpenFOAM。但也不得不承认好像你Fluent设置的有问题我不太懂Ansys的debug，希望有大佬评论评论

MrZZQi

刚发现提供的信息有点少，现在把改过的设置都放上来请大家参照一下@ @
Fluent:
求解器：
intelMPI, Pressure-Based, Transient, VOF(evaporation-condensation, 0.1)->(这里是用了UDF的地方，但是不用速度也差不多)
SST-k omega（默认） SIMPLE，二阶迎风，松弛因子压力和动量改成了0.2-0.4。变步长最大Co1.0。
物性：
气体： PengRobinSonRealGas,其他物性2-3阶多项式拟合；
液体：2-3阶多项式拟合；
边界：
全部都是定热流的wall。

OpenFOAM:
compressibleInterFoam（参照interCondensatingEvaporatingFoam和icoReactingMultiPhaseFoam做了蒸发冷凝的功能）
fvSolution和fvSchemes和教程中depthCharge3D中的基本一致
边界也都是定热流的wall

都是比较常规的设置，Fluent单步的步长比OpenFOAM要大，但是每一步计算的时间都长很多。

附单步迭代的信息：
OpenFOAM

PIMPLE: iteration 1
Tsat min/max: 80.181136, 80.247495
MULES: Solving for alpha.liquid
Phase-1 volume fraction = 0.51083031  Min(alpha.liquid) = -3.856554e-19  Max(alpha.liquid) = 1
Tsat min/max: 80.181136, 80.247495
MULES: Solving for alpha.liquid
Phase-1 volume fraction = 0.51083032  Min(alpha.liquid) = -3.8121024e-19  Max(alpha.liquid) = 1
Tsat min/max: 80.181136, 80.247495
dmdtNet Min/Max = -14.671404, 0.014690669
smoothSolver:  Solving for T, Initial residual = 2.1393496e-07, Final residual = 1.5003722e-10, No Iterations 1
min/max(T) = 77.605204, 205.25453
Tsat min/max: 80.181136, 80.247495
GAMG:  Solving for p_rgh, Initial residual = 0.00095227022, Final residual = 1.5511687e-06, No Iterations 2
Tsat min/max: 80.181149, 80.247508
GAMGPCG:  Solving for p_rgh, Initial residual = 3.5730969e-05, Final residual = 4.5624732e-08, No Iterations 2
smoothSolver:  Solving for epsilon, Initial residual = 0.00017132906, Final residual = 6.8634692e-10, No Iterations 2
smoothSolver:  Solving for k, Initial residual = 5.1282064e-05, Final residual = 5.9328133e-11, No Iterations 2
ExecutionTime = 38531.31 s  ClockTime = 38630 s

Courant Number mean: 0.0013264008 max: 0.093482513
Interface Courant Number mean: 0.00010650775 max: 0.086589298
deltaT = 0.0078032335
Time = 2371.64461

Fluent:

Global Courant Number [Variable Time Step Criteria] : 1.000000
Updating solution at time level N...
Global Courant Number [Explicit VOF Criteria] : 0.401506
 done.
 physical-dt  7.0533e-03

  iter  continuity  x-velocity  y-velocity  z-velocity      energy           k       omega       uds-0       uds-1       uds-2       uds-3     time/iter
 378845  3.4443e-03  7.4834e-08  1.7722e-07  8.4802e-08  2.7444e-11  3.5311e-09  3.4612e-09  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:00   50
 378846  1.7348e+01  6.9973e-03  1.2052e-02  6.9842e-03  9.9895e-06  4.4626e-03  4.0640e-03  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:49   49

 Interrupting at the end of timestep.
 378847  3.4815e+00  4.7497e-03  5.4942e-02  5.0623e-03  1.2069e-07  1.4736e-03  3.8117e-03  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:38   48
 378848  2.9977e+00  3.1421e-03  5.6644e-02  3.3267e-03  1.2558e-06  7.9539e-04  1.9987e-03  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:39   47
 378849  1.2080e+00  2.1748e-03  4.8020e-02  2.2187e-03  7.3282e-07  5.9542e-04  1.3687e-03  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:31   46
 378850  8.6966e-01  1.4942e-03  4.0897e-02  1.4858e-03  2.1947e-08  4.6336e-04  7.9309e-04  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:24   45
 378851  6.8811e-01  1.0188e-03  3.3542e-02  1.0270e-03  8.7177e-09  2.9763e-04  3.9274e-04  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:28   44
 378852  5.8073e-01  7.0182e-04  2.7173e-02  7.6750e-04  9.5772e-08  1.8172e-04  1.8759e-04  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:22   43
 378853  5.3692e-01  5.3621e-04  2.2038e-02  6.3227e-04  5.8170e-08  1.0728e-04  9.3101e-05  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:25   42
 378854  4.5448e-01  4.3891e-04  1.7867e-02  5.4102e-04  2.9606e-09  6.1895e-05  5.0058e-05  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:20   41
 378855  3.8447e-01  3.6896e-04  1.4415e-02  4.6896e-04  5.6247e-09  3.6698e-05  3.0128e-05  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:23   40

  iter  continuity  x-velocity  y-velocity  z-velocity      energy           k       omega       uds-0       uds-1       uds-2       uds-3     time/iter
 378856  3.3015e-01  3.1262e-04  1.1634e-02  4.0507e-04  4.9572e-09  2.3493e-05  2.0253e-05  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:18   39
 378857  2.7745e-01  2.6668e-04  9.4143e-03  3.4592e-04  1.0535e-09  1.6748e-05  1.4701e-05  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:14   38
 378858  2.3252e-01  2.2920e-04  7.6248e-03  2.9420e-04  1.1210e-09  1.2696e-05  1.1017e-05  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:19   37
 378859  1.9462e-01  1.9401e-04  6.1676e-03  2.4997e-04  1.0988e-09  9.6986e-06  8.2737e-06  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:14   36
 378860  1.6188e-01  1.6209e-04  4.9825e-03  2.0981e-04  4.9028e-10  7.3564e-06  6.2046e-06  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:18   35
 378861  1.3445e-01  1.3550e-04  4.0196e-03  1.7539e-04  4.0848e-10  5.5568e-06  4.6415e-06  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:14   34
 378862  1.1154e-01  1.1313e-04  3.2405e-03  1.4599e-04  4.1076e-10  4.1948e-06  3.4757e-06  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:18   33
 378863  9.2579e-02  9.3990e-05  2.6188e-03  1.2056e-04  5.7101e-10  3.1690e-06  2.6054e-06  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:14   32
 378864  7.6537e-02  7.7585e-05  2.1142e-03  9.9562e-05  2.8031e-10  2.3981e-06  1.9606e-06  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:17   31
 378865  6.3182e-02  6.3877e-05  1.7063e-03  8.2046e-05  2.2622e-10  1.8242e-06  1.4817e-06  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:13   30
 378866  5.2162e-02  5.2492e-05  1.3770e-03  6.7482e-05  2.2715e-10  1.3937e-06  1.1252e-06  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:16   29

  iter  continuity  x-velocity  y-velocity  z-velocity      energy           k       omega       uds-0       uds-1       uds-2       uds-3     time/iter
 378867  4.2969e-02  4.3074e-05  1.1112e-03  5.5418e-05  1.3508e-10  1.0696e-06  8.5871e-07  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:12   28
 378868  3.5363e-02  3.5306e-05  8.9661e-04  4.5449e-05  1.0888e-10  8.2461e-07  6.5957e-07  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:09   27
 378869  2.9082e-02  2.8907e-05  7.2347e-04  3.7235e-05  9.2262e-11  6.3807e-07  5.0846e-07  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:12   26
 378870  2.3971e-02  2.3705e-05  5.8154e-04  3.0525e-05  6.6142e-11  4.9811e-07  3.9486e-07  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:10   25
 378871  1.9709e-02  1.9380e-05  4.6905e-04  2.4966e-05  5.3191e-11  3.9020e-07  3.0861e-07  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:12   24
 378872  1.6191e-02  1.5819e-05  3.7877e-04  2.0392e-05  4.7621e-11  3.0595e-07  2.4215e-07  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:09   23
 378873  1.3332e-02  1.2936e-05  3.0475e-04  1.6673e-05  3.4573e-11  2.4177e-07  1.9115e-07  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:12   22
 378874  1.0955e-02  1.0553e-05  2.4611e-04  1.3608e-05  2.7992e-11  1.9173e-07  1.5171e-07  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:09   21
 378875  8.9954e-03  8.6002e-06  1.9901e-04  1.1098e-05  2.3739e-11  1.5253e-07  1.2082e-07  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:07   20
 378876  7.3847e-03  7.0089e-06  1.6101e-04  9.0497e-06  2.0773e-11  1.2127e-07  9.6339e-08  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:09   19
 378877  6.0787e-03  5.7267e-06  1.2972e-04  7.3914e-06  1.4919e-11  9.7050e-08  7.7220e-08  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:07   18

  iter  continuity  x-velocity  y-velocity  z-velocity      energy           k       omega       uds-0       uds-1       uds-2       uds-3     time/iter
 378878  4.9943e-03  4.6712e-06  1.0491e-04  6.0301e-06  1.2072e-11  7.7824e-08  6.2116e-08  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:08   17
 378879  4.1015e-03  3.8081e-06  8.4964e-05  4.9174e-06  1.0264e-11  6.2522e-08  5.0093e-08  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:06   16
 378880  3.3681e-03  3.1058e-06  6.8847e-05  4.0110e-06  9.0611e-12  5.0126e-08  4.0364e-08  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:08   15
 378881  2.7743e-03  2.5420e-06  5.5536e-05  3.2794e-06  6.4648e-12  4.0483e-08  3.2706e-08  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:06   14
 378882  2.2820e-03  2.0764e-06  4.4982e-05  2.6779e-06  5.2388e-12  3.2736e-08  2.6560e-08  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:04   13
 378883  1.8769e-03  1.6953e-06  3.6490e-05  2.1863e-06  4.4704e-12  2.6502e-08  2.1599e-08  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:06   12
 378884  1.5441e-03  1.3851e-06  2.9619e-05  1.7860e-06  3.9710e-12  2.1395e-08  1.7541e-08  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:04   11
 378885  1.2745e-03  1.1348e-06  2.3929e-05  1.4616e-06  2.8385e-12  1.7412e-08  1.4340e-08  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:05   10
 378886  1.0507e-03  9.2914e-07  1.9415e-05  1.1960e-06  2.2983e-12  1.4190e-08  1.1754e-08  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:04    9
 378887  8.6644e-04  7.6065e-07  1.5778e-05  9.7847e-07  1.9721e-12  1.1584e-08  9.6529e-09  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:04    8
 378888  7.1490e-04  6.2323e-07  1.2831e-05  8.0127e-07  1.6393e-12  9.4759e-09  7.9462e-09  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:03    7

  iter  continuity  x-velocity  y-velocity  z-velocity      energy           k       omega       uds-0       uds-1       uds-2       uds-3     time/iter
 378889  5.9033e-04  5.1121e-07  1.0437e-05  6.5658e-07  1.4488e-12  7.7358e-09  6.5362e-09  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:02    6
!378890 solution is converged
 378890  4.8934e-04  4.2061e-07  8.4459e-06  5.3920e-07  1.0344e-12  6.3703e-09  5.4173e-09  0.0000e+00  0.0000e+00  0.0000e+00  0.0000e+00  0:00:02    5
Flow time = 106.9029003888784s, time step = 8002

提前谢过各位大佬！

cccrrryyy

@MrZZQi FLUENT时间步长是不是太大了，还是说这个算例一般都这么大？100多秒用了8000个时间步，一步相当于0.0125s。另外加的uds残差一直都是0，相当于没有求解。FOAM那边时间步用的多少？每一个时间步的迭代步数呢？

MrZZQi

@cccrrryyy 因为整体速度都很小，所以步长设置的都偏大一些，OpenFOAM步长也在0.005-0.01之间。UDS都是0是因为我把UDF的功能都关了，这样方便对比一些

cccrrryyy

@MrZZQi 那这个感觉挺奇怪，怎么会快这么多。我看OpenFOAM好像外迭代就1步，FLUENT也是这样么？

MrZZQi

@cccrrryyy 对的，几何比较简单，网格质量还可以。我看计算也收敛了，所以就没有增加迭代次数。Fluent里单步大概迭代40-50次，所以慢很多。

我把结果整理一下，如果有什么发现甚至错误再在下面更新

李东岳

我不太懂商软的使用，下周把这个给你在CFD界推一下，帮你争取点关注。

MrZZQi

@东岳千万别现在还完全没有搞懂，甚至连什么问题都没弄清楚。您那个公众号我挺多同学关注的，到时候有疏漏就闹笑话了。

李东岳

也行也行

CFD中文网

请问为什么OpenFOAM会比Fluent计算快？