LES初始速度场设置和壁面函数设置

cccrrryyy

圆柱扰流之前在论坛看到也有人算，好像不太容易算准。大略看了一下你的设置，有以下几个问题，按我认为的重要性排列。
1、PIMPLE算法一般我会给至少20个nOuterCorrectors，然后2个nCorrectors。你的虽然是不可压的算例，不过nOuterCorrectors是不是也可以多给一些。现在每一个时间步都达到收敛要求了么？我觉得可以尝试pisoFoam，这样就不用管nOuterCorrectors，但相应的时间步可能需要小一点。
2、当前时间步你的CFL数是多少？
3、速度对流项的格式，LES还是尽量避免迎风吧。迎风总会有些数值耗散，会导致细节上有些地方不准确。中心差分最好，当然前提是网格质量要高，不然太容易发散。
你最好参考一下文献里面别人的设置，同样量级雷诺数下别人的入口条件、格式、网格等等，不然修改起来完全没有方向。

random_ran

看到有人讨论圆柱绕流就很激动。

可是我已经挖了太多坑还没填。关注中，加油。

hoversoar

@cccrrryyy 非常感谢您的建议!

附上现在1w雷诺数的光滑圆柱绕流的例子的某个时间步的截图，用of里头的monitor监控的residual，我也一直很困惑Uz的曲线不像稳定的样子。
我现在把2个nOuterCorrectors由2提高到5（从31秒开始），算个十秒左右看看结果。
目前的时间步库朗数是控制在1.5以下。
这个十秒计算过之后，我会把速度对流格式换成中心差分继续跑看看结果是否有改善，到时候再过来更新！

Screenshot from 2020-02-27 11-33-27.png

hoversoar

@random_ran 欢迎吃瓜

random_ran

前排小板凳，

附上现在1w雷诺数的光滑圆柱绕流的例子的某个时间步的截图，用of里头的monitor监控的residual，我也一直很困惑Uz的曲线不像稳定的样子。

为什么关注点再 U_z 不在残差最大的 p 上投入精力？

我现在把2个nOuterCorrectors由2提高到5（从31秒开始），算个十秒左右看看结果。

这样做的原因是？为什么是从2到5？而不是其他的数字，比如7?

目前的时间步库朗数是控制在1.5以下。

这个十秒计算过之后，我会把速度对流格式换成中心差分继续跑看看结果是否有改善，到时候再过来更新！

这个是 case 是机密么？如果能简单运行，我也想试试你的 case.

hoversoar

@random_ran
问得好！

Uz太抢眼了。我看了下之前算的几个例子，发现p的残差几乎都在0.001这个量级。不知道怎么才能继续降下去？
我一开始尝试增加到10个nOuterCorrectors, 发现第4~5个外循环开始残差下降不明显甚至开始上升，No Iteration也几乎为0。为了节省时间所以设定到5。

PIMPLE: iteration 1
smoothSolver:  Solving for Ux, Initial residual = 0.000154843, Final residual = 2.69652e-07, No Iterations 1
smoothSolver:  Solving for Uy, Initial residual = 0.00295664, Final residual = 4.75419e-06, No Iterations 1
smoothSolver:  Solving for Uz, Initial residual = 0.00438083, Final residual = 8.2538e-06, No Iterations 1
GAMG:  Solving for p, Initial residual = 0.00648663, Final residual = 8.19988e-05, No Iterations 4
GAMG:  Solving for p, Initial residual = 0.000125942, Final residual = 4.5224e-05, No Iterations 1
time step continuity errors : sum local = 3.53308e-10, global = -1.25279e-13, cumulative = -2.33184e-10
GAMG:  Solving for p, Initial residual = 0.000354817, Final residual = 8.87088e-05, No Iterations 1
GAMG:  Solving for p, Initial residual = 0.000110154, Final residual = 9.47584e-07, No Iterations 8
time step continuity errors : sum local = 7.40376e-12, global = -2.0947e-13, cumulative = -2.33394e-10
PIMPLE: iteration 2
smoothSolver:  Solving for Ux, Initial residual = 1.15813e-06, Final residual = 1.15813e-06, No Iterations 0
smoothSolver:  Solving for Uy, Initial residual = 1.59673e-05, Final residual = 4.28047e-08, No Iterations 1
smoothSolver:  Solving for Uz, Initial residual = 3.989e-05, Final residual = 1.15289e-07, No Iterations 1
GAMG:  Solving for p, Initial residual = 0.00371771, Final residual = 8.15447e-05, No Iterations 3
GAMG:  Solving for p, Initial residual = 0.000113078, Final residual = 4.60568e-05, No Iterations 1
time step continuity errors : sum local = 3.60026e-10, global = 4.84724e-15, cumulative = -2.33389e-10
GAMG:  Solving for p, Initial residual = 0.000230915, Final residual = 6.19172e-05, No Iterations 1
GAMG:  Solving for p, Initial residual = 8.10529e-05, Final residual = 8.7777e-07, No Iterations 8
time step continuity errors : sum local = 6.86178e-12, global = 1.42834e-14, cumulative = -2.33375e-10
PIMPLE: iteration 3
smoothSolver:  Solving for Ux, Initial residual = 2.91121e-08, Final residual = 2.91121e-08, No Iterations 0
smoothSolver:  Solving for Uy, Initial residual = 3.97728e-07, Final residual = 3.97728e-07, No Iterations 0
smoothSolver:  Solving for Uz, Initial residual = 8.90301e-07, Final residual = 8.90301e-07, No Iterations 0
GAMG:  Solving for p, Initial residual = 0.000168175, Final residual = 1.98109e-05, No Iterations 1
GAMG:  Solving for p, Initial residual = 3.82521e-05, Final residual = 3.82521e-05, No Iterations 0
time step continuity errors : sum local = 2.99032e-10, global = -2.47605e-14, cumulative = -2.33399e-10
GAMG:  Solving for p, Initial residual = 4.55083e-05, Final residual = 4.55083e-05, No Iterations 0
GAMG:  Solving for p, Initial residual = 4.55083e-05, Final residual = 9.29993e-07, No Iterations 3
time step continuity errors : sum local = 7.27013e-12, global = -1.36329e-15, cumulative = -2.33401e-10
PIMPLE: iteration 4
smoothSolver:  Solving for Ux, Initial residual = 1.71081e-09, Final residual = 1.71081e-09, No Iterations 0
smoothSolver:  Solving for Uy, Initial residual = 2.12255e-08, Final residual = 2.12255e-08, No Iterations 0
smoothSolver:  Solving for Uz, Initial residual = 4.28694e-08, Final residual = 4.28694e-08, No Iterations 0
GAMG:  Solving for p, Initial residual = 3.37196e-05, Final residual = 3.37196e-05, No Iterations 0
GAMG:  Solving for p, Initial residual = 3.37196e-05, Final residual = 3.37196e-05, No Iterations 0
time step continuity errors : sum local = 2.63599e-10, global = -1.96671e-15, cumulative = -2.33403e-10
GAMG:  Solving for p, Initial residual = 3.64374e-05, Final residual = 3.64374e-05, No Iterations 0
GAMG:  Solving for p, Initial residual = 3.64374e-05, Final residual = 6.46133e-07, No Iterations 2
time step continuity errors : sum local = 5.05107e-12, global = 3.57324e-16, cumulative = -2.33402e-10
PIMPLE: iteration 5
smoothSolver:  Solving for Ux, Initial residual = 3.81718e-10, Final residual = 3.81718e-10, No Iterations 0
smoothSolver:  Solving for Uy, Initial residual = 3.41675e-09, Final residual = 3.41675e-09, No Iterations 0
smoothSolver:  Solving for Uz, Initial residual = 5.30364e-09, Final residual = 5.30364e-09, No Iterations 0
GAMG:  Solving for p, Initial residual = 2.63333e-05, Final residual = 2.63333e-05, No Iterations 0
GAMG:  Solving for p, Initial residual = 2.63333e-05, Final residual = 2.63333e-05, No Iterations 0
time step continuity errors : sum local = 2.05857e-10, global = 4.08418e-16, cumulative = -2.33402e-10
GAMG:  Solving for p, Initial residual = 2.98151e-05, Final residual = 2.98151e-05, No Iterations 0
GAMG:  Solving for p, Initial residual = 2.98151e-05, Final residual = 9.1923e-07, No Iterations 1
time step continuity errors : sum local = 7.18597e-12, global = 1.67701e-15, cumulative = -2.334e-10
PIMPLE: iteration 6
smoothSolver:  Solving for Ux, Initial residual = 1.86276e-10, Final residual = 1.86276e-10, No Iterations 0
smoothSolver:  Solving for Uy, Initial residual = 2.12072e-09, Final residual = 2.12072e-09, No Iterations 0
smoothSolver:  Solving for Uz, Initial residual = 1.8065e-09, Final residual = 1.8065e-09, No Iterations 0
GAMG:  Solving for p, Initial residual = 2.79915e-05, Final residual = 2.79915e-05, No Iterations 0
GAMG:  Solving for p, Initial residual = 2.79915e-05, Final residual = 2.79915e-05, No Iterations 0
time step continuity errors : sum local = 2.1882e-10, global = 1.66412e-15, cumulative = -2.33398e-10
GAMG:  Solving for p, Initial residual = 3.20665e-05, Final residual = 3.20665e-05, No Iterations 0
GAMG:  Solving for p, Initial residual = 3.20665e-05, Final residual = 7.84955e-07, No Iterations 1
time step continuity errors : sum local = 6.13629e-12, global = 2.44261e-15, cumulative = -2.33396e-10
PIMPLE: iteration 7
smoothSolver:  Solving for Ux, Initial residual = 1.86182e-10, Final residual = 1.86182e-10, No Iterations 0
smoothSolver:  Solving for Uy, Initial residual = 1.67569e-09, Final residual = 1.67569e-09, No Iterations 0
smoothSolver:  Solving for Uz, Initial residual = 1.11517e-09, Final residual = 1.11517e-09, No Iterations 0
GAMG:  Solving for p, Initial residual = 3.13138e-05, Final residual = 3.13138e-05, No Iterations 0
GAMG:  Solving for p, Initial residual = 3.13138e-05, Final residual = 3.13138e-05, No Iterations 0
time step continuity errors : sum local = 2.44792e-10, global = 2.48318e-15, cumulative = -2.33394e-10
GAMG:  Solving for p, Initial residual = 3.63778e-05, Final residual = 3.63778e-05, No Iterations 0
GAMG:  Solving for p, Initial residual = 3.63778e-05, Final residual = 7.91691e-07, No Iterations 1
time step continuity errors : sum local = 6.18895e-12, global = 3.12078e-15, cumulative = -2.3339e-10
PIMPLE: iteration 8
smoothSolver:  Solving for Ux, Initial residual = 1.92788e-10, Final residual = 1.92788e-10, No Iterations 0
smoothSolver:  Solving for Uy, Initial residual = 2.05456e-09, Final residual = 2.05456e-09, No Iterations 0
smoothSolver:  Solving for Uz, Initial residual = 9.56459e-10, Final residual = 9.56459e-10, No Iterations 0
GAMG:  Solving for p, Initial residual = 3.49563e-05, Final residual = 3.49563e-05, No Iterations 0
GAMG:  Solving for p, Initial residual = 3.49563e-05, Final residual = 3.49563e-05, No Iterations 0
time step continuity errors : sum local = 2.73267e-10, global = 3.06099e-15, cumulative = -2.33387e-10
GAMG:  Solving for p, Initial residual = 4.11002e-05, Final residual = 4.11002e-05, No Iterations 0
GAMG:  Solving for p, Initial residual = 4.11002e-05, Final residual = 7.86332e-07, No Iterations 1
time step continuity errors : sum local = 6.14706e-12, global = 3.60325e-15, cumulative = -2.33384e-10
PIMPLE: iteration 9
smoothSolver:  Solving for Ux, Initial residual = 2.26526e-10, Final residual = 2.26526e-10, No Iterations 0
smoothSolver:  Solving for Uy, Initial residual = 2.22568e-09, Final residual = 2.22568e-09, No Iterations 0
smoothSolver:  Solving for Uz, Initial residual = 8.66044e-10, Final residual = 8.66044e-10, No Iterations 0
GAMG:  Solving for p, Initial residual = 3.87527e-05, Final residual = 3.87527e-05, No Iterations 0
GAMG:  Solving for p, Initial residual = 3.87527e-05, Final residual = 3.87527e-05, No Iterations 0
time step continuity errors : sum local = 3.02945e-10, global = 3.67155e-15, cumulative = -2.3338e-10
GAMG:  Solving for p, Initial residual = 4.62632e-05, Final residual = 4.62632e-05, No Iterations 0
GAMG:  Solving for p, Initial residual = 4.62632e-05, Final residual = 8.09623e-07, No Iterations 1
time step continuity errors : sum local = 6.32914e-12, global = 4.16309e-15, cumulative = -2.33376e-10
PIMPLE: iteration 10
smoothSolver:  Solving for Ux, Initial residual = 2.52859e-10, Final residual = 2.52859e-10, No Iterations 0
smoothSolver:  Solving for Uy, Initial residual = 2.63933e-09, Final residual = 2.63933e-09, No Iterations 0
smoothSolver:  Solving for Uz, Initial residual = 8.84599e-10, Final residual = 8.84599e-10, No Iterations 0
GAMG:  Solving for p, Initial residual = 4.41963e-05, Final residual = 4.41963e-05, No Iterations 0
GAMG:  Solving for p, Initial residual = 4.41963e-05, Final residual = 4.41963e-05, No Iterations 0
time step continuity errors : sum local = 3.455e-10, global = 4.12535e-15, cumulative = -2.33372e-10
GAMG:  Solving for p, Initial residual = 5.2893e-05, Final residual = 5.2893e-05, No Iterations 0
GAMG:  Solving for p, Initial residual = 5.2893e-05, Final residual = 8.16536e-07, No Iterations 1
time step continuity errors : sum local = 6.38319e-12, global = 4.56977e-15, cumulative = -2.33367e-10
smoothSolver:  Solving for k, Initial residual = 0.000235852, Final residual = 4.67513e-07, No Iterations 1

现在这边的例子是光滑圆柱，如果要算看看很高兴分享。（how）

random_ran

Uz太抢眼了。

不知道坐标系是如何定义？

我看了下之前算的几个例子，发现p的残差几乎都在0.001这个量级。

非常有意思的问题，我之前没怎么考虑过压力残差的取值问题。我也好好思考一下。

不知道怎么才能继续降下去？

减小时间步长？提高收敛准则？或者优化网格形态？...

我一开始尝试增加到10个nOuterCorrectors, 发现第4~5个外循环开始残差下降不明显甚至开始上升，No Iteration也几乎为0。为了节省时间所以设定到5。

我之前也一直在用 piso，不过是默认值，没有动，我得好好看看 piso 算法再来回答你的问题。

现在这边的例子是光滑圆柱，如果要算看看很高兴分享。（how）

我记得论坛里有人分享过 *.zip 包含算例和运行脚本，简单点的办法就是做相同的事情
稍微难一点的是可以把楼主的 case 文件，在层主的 compute 仓库下 caseIdoNotUnderstand

然后我们一起来 hack.

hoversoar

@random_ran
我上传了case在google drive , 点击链接！（github 文件太大，我放弃了...）
晚些我会更新一下最近算的这个case的结果。

hoversoar

更新一下。按照@cccrrryyy 的建议算了几天，虽然结果还是不尽如人意，还是贴上来和大家讨论下。

Step1，31-38s，把nOutercorrectors 从2改成5.

几点观察：

阻力系数，升力系数主要与Uy残差曲线有关
在34.5s处震荡减小，CdCl均明显下降。
Uz曲线不稳定

hoversoar

Step2. 38.5-51s, fvscheme中的速度对流项从upwind 改为 Gauss linear
图片21.jpg 图片3.jpg

残差相比迎风格式，有明显的量级上升。Uz 呈现出收敛的趋势，稳定了。
Uy同样的在47s处出现振幅下降，CdCl下降。
把40s处当成稳定，分为两个区段来考虑。CdClSt系数如下表。

看趋势50.5s处出现第二次Uy残差的振幅下降，51s之后会怎样？我打算继续算下去10s左右看看是不是周期性的。

random_ran

楼主 mesh 太大了,我把设置文件拷贝下来,打算用很小的脚本来生成圆柱网格.

这样的话,别人可以更方便地帮助你.

我们就可以一起讨论了.

仓库地址: https://github.com/randomwangran/chigua

hoversoar

@random_ran这个mesh是用ICEM生成的，我已经转化到openfoam了。
你真的太nice了！！！！

random_ran

@hoversoar 台兄过奖了。我只是好奇罢了。自己玩的很杂，可是遇到能一起玩的，实在不易，所以慢慢来。我在找 of 的脚本，自动生成。最好简单可控，小 mesh 大家可以互相交流，大 mesh 大家自己留着做研究就好。

李东岳

科研整的挺好老铁们 @random_ran 是这个领域的专家 hoversoar命中遇到天子

hoversoar

@东岳对，抱紧大腿！怎么加表情 - -

random_ran

今天才把case文件整理了一下,下一步找合适的网格.

@东岳岳兄过奖了.
@hoversoar 今天才整理了一下你的 case.

乃有新发现的话留言在这,大家都能看到,或者帮助你,我只能尽力,还是要靠氖自己的.

hoversoar

@random_ran 非常感谢！慢慢会成长的哈哈哈

hoversoar

上次算到step2的中心差分的50.5s处，说可能会阻力又下降。
那之后我把它继续算到了59.5s，然后速度对流项的linear换到了limitedLinear。把结果贴上来一下。
捕获.JPG

几个发现：

整体看起来的话，三个阶段的定量CdCl差距不是很大。和文献也对的比较上。初步认定是速度对流项选择了迎风格式造成的。
跟之前的猜想有关，在55s处残差的Uy震荡明显，造成了Cd上升，Cl振幅也增大。
换成limitedLinear 0.5 之后，可以发现残差有明显的下降。@random_ran 是否可以回答前面的问题，虽然P的量级并没有发生变化。但是Uz的曲线震荡明显（相比中心差分），猜想可能是由于TVD 里头那个0.5造成的，混入了一部分迎风格式，造成耗散？

一些疑问：

我这样中途切换差分格式是否ok？
这个网格是纯结构化的光滑圆柱，但是如果是非结构化质量并没有那么高的情况下，TVD的系数应该怎么取？可能要参考经验感觉来试？

下一步：
根据@cccrrryyy 的建议，和疑问中的1点。
我把这个case在limitedlinear 0.5的条件下，从头开始算。并且将pimple改为piso，步长缩小，并控制CFL小于0.8。

且看结果。
good night

hoversoar

Screenshot from 2020-03-05 17-49-39.png

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
    Point usage OK.
    Upper triangular ordering OK.
    Face vertices OK.
    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces...
    Patch            Faces    Points   Surface topology                  
    front            42924    43120    ok (non-closed singly connected)  
    back             42924    43120    ok (non-closed singly connected)  
    cylinderwalls    11564    11760    ok (non-closed singly connected)  
    inlet            5782     5940     ok (non-closed singly connected)  
    outlet           5782     5940     ok (non-closed singly connected)  

Checking geometry...
    Overall domain bounding box (-1.9999997 -1.9999999 -0.16500001) (1.9999997 1.9999999 0.16500001)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (1.6166424e-16 9.3817059e-18 -4.6447921e-15) OK.
    Max cell openness = 1.2635419e-15 OK.
    Max aspect ratio = 103.67801 OK.
    Minimum face area = 9.5109381e-08. Maximum face area = 0.0011336842.  Face area magnitudes OK.
    Min volume = 5.3196771e-10. Max volume = 6.3409456e-06.  Total volume = 4.1415295.  Cell volumes OK.
    Mesh non-orthogonality Max: 2.405209 average: 0.4164805
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 0.12001675 OK.
    Coupled point location match (average 0) OK.

Mesh OK.

贴一下现在这个mesh的check结果和样子。

cccrrryyy

辛苦了，做了这么多测试！关于对流项格式，建议看openfoam.com上的介绍，链接在这里。注意，严格意义上二阶格式一定要过（0.5 0.75）那个绿色的点。我自己用的最多的是Gauss linear和Gauss vanLeer（这个说实话我不懂，但是很好用）。
关于limitedLinear的系数，好像除了试没啥别的办法。不过这就是参考文献的价值了，如果有类似的算例，用它的格式最靠谱，这样能够快速缩小需要查验的问题的范围。

CFD中文网

LES初始速度场设置和壁面函数设置