micro scale calculation problem
Dear all,
Now my simulation model is that 10mm cyclinder with 20µm little radial clearance. I want to calculate the fluid is through the clearance condition. -which turbulent model and wall function is suitable to use? - how can i check mesh size in layer position with y plus in a reasonable range? hope someone can help me. thank you in advance |
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In the radial clearance, the velocity is 30m/s, which is turbulent structure. now my main issue is how to adapt the mesh size in reasonable range to assure the calculation accurate. have a nice day guava |
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Hi, I am not an expert about microfluidic, I just see from some estimation, velocity and lenght of 20µm turn out to produce a small Re number. What about the axial velocity? I doubt that the energy production can balance the energy dissipation to substain turbulent structures and produce inertial range in the energy spectra... but I could be in error |
What kind of fluid are you simulating? How high is the viscosity?
Estimating Re with an approximate value of air (1.5 e-5 m^2 s^-1) yields Re=40. So your flow is definitely laminar (assuming the fluid you use doesn't have a lower viscosity than air) since the critical Re is in the range of 2300 for a circular pipe. |
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viscosity is 2.24e-07 m^2 s^-1, and i have check the Re number, which is larger than 2300 in the clearance. I can't upload the model as a picture, maybe the problem didn't give a clear description. my proposal for this case is to know the leakage with piston through the clearance 20 µm. have a nice day guava |
Ok sorry for the detour, now lets get back to your initial question.
Since Re is still pretty low, the computational cost of fully resolving the boundary layer without a wall-function should not be too high. Try to get the Y+ values below 1 to achieve this with a small growth factor (1.05-1.1) in wall-normal direction. Thanks to the low Re again, the choice of the turbulence model will not be too important in this simulation. Any of the basic k-epsilon formulations should yield reasonable results. |
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I agree...what's more, your Re_tau is quite low such as a DNS is realizable |
thanks. finally i adapt K-E model with scalable wall function, that can give good result.
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