极低雷诺数下，PIMPLE迭代初始残差保持为1，降不下来
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@李东岳 感谢老师回复！动量预测是关掉了的。
打开试了试，步长极小，残差也一直保持在一个值不下降，cumulative则很大，如下：
Courant Number mean: 7.953414508e-05 max: 0.4993036972 deltaT = 4.979675437e-35 Time = 6.00001e-05 PIMPLE: iteration 1 DICPCG: Solving for pcorr, Initial residual = 1, Final residual = 0.04941709914, No Iterations 29 DICPCG: Solving for pcorr, Initial residual = 0.03122316034, Final residual = 0.001556737496, No Iterations 121 DICPCG: Solving for pcorr, Initial residual = 0.006804280077, Final residual = 0.0003314734696, No Iterations 359 DICPCG: Solving for pcorr, Initial residual = 0.002308369425, Final residual = 9.709852492e-11, No Iterations 911 time step continuity errors : sum local = 1.793718362e-20, global = 1.178518414e-23, cumulative = 1.037419916e+19 smoothSolver: Solving for Ux, Initial residual = 3.985498772e-05, Final residual = 2.227155701e-11, No Iterations 1 smoothSolver: Solving for Uy, Initial residual = 6.302253167e-05, Final residual = 2.385619185e-11, No Iterations 1 GAMG: Solving for p, Initial residual = 0.004038713667, Final residual = 0.0001722133227, No Iterations 18 GAMG: Solving for p, Initial residual = 0.0005583071565, Final residual = 2.673668049e-05, No Iterations 34 GAMG: Solving for p, Initial residual = 9.485975434e-05, Final residual = 4.53317788e-06, No Iterations 33 GAMG: Solving for p, Initial residual = 2.596708738e-05, Final residual = 1.231466526e-06, No Iterations 38 time step continuity errors : sum local = 7.929103562e-15, global = -8.302368146e-16, cumulative = 1.037419916e+19 GAMG: Solving for p, Initial residual = 0.003717218882, Final residual = 0.000164557501, No Iterations 17 GAMG: Solving for p, Initial residual = 0.0005378364039, Final residual = 2.53035408e-05, No Iterations 34 GAMG: Solving for p, Initial residual = 9.265726415e-05, Final residual = 4.535601234e-06, No Iterations 36 GAMG: Solving for p, Initial residual = 2.556961887e-05, Final residual = 9.918214454e-11, No Iterations 548 time step continuity errors : sum local = 6.482264028e-19, global = 6.603865839e-20, cumulative = 1.037419916e+19 PIMPLE: iteration 2 ... PIMPLE: iteration 50 smoothSolver: Solving for Ux, Initial residual = 1.226945138e-10, Final residual = 6.6691269e-16, No Iterations 1 smoothSolver: Solving for Uy, Initial residual = 1.651845516e-10, Final residual = 3.177048458e-16, No Iterations 1 GAMG: Solving for p, Initial residual = 0.000949721577, Final residual = 4.516299707e-05, No Iterations 41 GAMG: Solving for p, Initial residual = 0.0004457930337, Final residual = 2.206483819e-05, No Iterations 23 GAMG: Solving for p, Initial residual = 7.977007558e-05, Final residual = 3.747481321e-06, No Iterations 36 GAMG: Solving for p, Initial residual = 2.418915618e-05, Final residual = 1.162060008e-06, No Iterations 48 time step continuity errors : sum local = 7.482194647e-15, global = -7.221446192e-16, cumulative = 1.037419916e+19 GAMG: Solving for p, Initial residual = 0.003705959955, Final residual = 0.0001646823634, No Iterations 17 GAMG: Solving for p, Initial residual = 0.0005377574684, Final residual = 2.535476181e-05, No Iterations 34 GAMG: Solving for p, Initial residual = 9.241219827e-05, Final residual = 4.525895839e-06, No Iterations 36 GAMG: Solving for p, Initial residual = 2.542969083e-05, Final residual = 9.774400044e-11, No Iterations 548 time step continuity errors : sum local = 6.388632178e-19, global = 6.502735317e-20, cumulative = 1.037419916e+19 PIMPLE: not converged within 50 iterations ExecutionTime = 21923.2 s ClockTime = 21963 s Courant Number mean: 7.964991508e-05 max: 0.4989139005 deltaT = 4.99051583e-35 Time = 6.00001e-05看到站内其它的帖子，试了试有量纲/无量纲计算（此前圆柱直径0.05，nu=50；改为圆柱直径0.0005，nu=0.5），也无法收敛。
走投无路试了一下StarCCM，多低雷诺数都能算，和OpenFOAM那些能收敛的算例比得还贼好
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@lwjetmann 在 极低雷诺数下，PIMPLE迭代初始残差保持为1，降不下来 中说：
@李东岳 感觉这个问题挺有意义的，肯定可以从原理上说清楚为啥发散。给的是一个极大的单块网格平动（入口速度零，零法向压力梯度；出口压力零，零速度梯度），一直调不出来就放弃了，可能雷诺数低到某个程度，就不能靠放大计算域来使边界条件匹配了。
祝李老师上课愉快！
老哥，这个问题最后解决了吗
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没有
做了一个能复现问题的干净算例，感兴趣的同学可以试试（网格量57万，需要算一段时间才发散，我保留了发散后的log.pimpleFoam文件，可以用文件里的plot_residual脚本来查看残差。使用的OpenFOAM版本为v2006或v2406）。
通过网盘分享的文件：2D_21cylinders.zip
链接: https://pan.baidu.com/s/1lHExA2yRnUzXFxYYtAc6rw?pwd=8888 提取码: 8888
