Problem with calculation of k
I am using modified simpleFoam (including temperature equation) solver in OF 2.1.1 to simulate film cooling problem. I use k-epsilon model. My boundary conditions are shown below.
I know in kEpsilon setting the k=0 is incorrect and leads to physically invalid terms as i read in an article before.set it a low number like 1e-5 or zerogradient is better.
Need to find this
HI Ehsan and others,
Thank you very much for your reply. It seems like I need to know this perfect. Now the biggest question that I faced using k-epsilon method is this. I have heard 3 main possibilities for the BC of k at the wall. Here are they.
1. k=0 : This said to be used in low Reynolds number flows.
What are the limit of low Re number?
2.Then I found from the OpenFoam 2.1.1 User's guide that we need to use specific wall functions to model the flow closer to the boundary.
And in an earlier version of the OpenFoam user's manual says we can use k=0 BC at the wall.
3.Finally some members in the forum has suggested to use zeroGradient condition for walls.
These are the three options we have and I need to know which one out of these would give us a better result.
And my other concern is that the DNS and experimental data tell that the value of k should be zero at the wall. I have seen this in almost every book.
Please give your comments. I need your expertise on this. Please help me to figure this our.
I suggest that you set k a low number, like 1e-10 or a more lower number.
Now I want to konw how have you modified the simpleFoam solver? I'm also simulating a film cooling case with a modified pisoFoam solver. However I didn't get a good result in temperature.
See this thread. It might help you. please let me know if this works for you. I am also doing a film cooling problem. We can collaborate more in the future.
I just translate what I see in my books:
If the first node is in the viscous sub layer which is near enough to the wall.you can set the k is zero.but when you are using wall functions,this node should not be set in the viscous sublayer,so in this control volumn,the production and dissipation is larger than the diffusion.so you should set the B.C. is zerogradient.
Wish this would help.
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