DNS of duct flow
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Hello everyone
I have successfully make a DNS of channel flow with the solver given here: http://www.cfd-online.com/Forums/ope...s-2-1-0-a.html The result is good. But when I use the solver(ico—DNS)to simulate a duct flow(all the boundarys I set as wall except the inlet and outlet which I set as periodic boundary).And the value of dp/dx is 2 times of the value of channel flow case. I have changed the scheme of ddt to Euler/CN/backward.All the results are not good compared to results of Gavrilakis(1992,Direct numerical simulation of turbulent flow in a square duct). I also have refined my mesh but still failed getting a good result. Can you give me some advice? Thank you very much! I have attached my case here. regards! andersn |
Hi, andersn! I'm working in a duct of 1mm X 1mm, maybe there are some difference from yours . I found that the boundary condition of U in your dictionary of 0 is set as cyclic. should it be wall? i.e. fixedvalue? I have another question, How did you get the initial condition of p and U when your simulation parameters such as geometry size, and gradP changes?
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hello Niu
To my case,the flow direction I set as periodic boundary condition.As for the initial condition of p and U,I set it according http://www.cfd-online.com/Forums/ope...s-2-1-0-a.html using the tool perturbU.what kind of your case?Are you working on duct DNS also? I have update my meshes. Code:
Domain size:6.4X1X1 Can anyone give me some suggestion? regards! andersn |
Hello, anderson, in a duct flow , the boundary layer of wall of normal and that of wall of spanwise is superposed at the four corner, maybe the character of turbulence here don't agree the character of channel flow, not duct flow. How much is your duct flow and men velocity streamwise?
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is the flow direction the only homogenous direction in the duct flow?As in channel flow, the homogenous directions are streamwise and spanwise
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Thank you for your suggestion.what do you mean by that"only homogenous direction".In my case,the duct flow direction is along x-axis, while the other four boundaries are wall(no-slip).
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yes,The flow direction is the only homogenous direction which I use periodic boundary condition.
I have try some numerical scheme,but the rms of velocity in the flow direction is not good either(the attached files).Is it the problem of fvScheme or PISO method? why are DNS of channel flow and duct flow so different? I have been confused by it for a few weeks. regards! andersn |
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Are you sure your simulation reached fully developed? |
yes.this scheme is quite different from the channel one.
But at first I use the same scheme as the channel flow.I didn't change anything except the boundary condition of spanwise which I modified to wall.And I have refined my grid also.The flow time is so long and I am sure it has reached fully developed. I have simulated the channel flow case also. And the result is good enough. |
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In my simulation, the steady state was reached after about 160000s while the deltaT=0.5s, so it's quite long |
what kind of problem of yours? a duct flow or a channel flow?Can you share it with us.which solver did you use?Maybe the problem exist in fvSheme or polyMesh or something else.
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Hello Xianbei,
There are not homogenous in the two direction in duct flow(spanwise and normal wall). |
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Did you initialize your U filed with perturbU or other ways when simulating channel flow? Best Regards! Z.Q. Niu |
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Code:
ddtSchemes Code:
convertToMeters 1; |
I have just got to know that the fvm used in DNS is not as accurate as spectral method. So if a fvm is used in DNS ,the mesh should be much finer. I got this from a doctor, and I want to confirm the message, if you know something about the accuracy of the two methods, please show to me:)
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Is that helpful? I am using OpenFOAM for DNS pipe flow. I am also interested in this topic. |
Hi,
why everybody use ico-DNS instead of pisoFoam, pimpleFoam or icoFoam for DNS in channel-flow?? These solvers should give the same results and their are still implemented in OF. kind regards Florian |
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