Modeling of flows closer to Kolmogorov Scale
I am trying to simulate a leakage in a tank through an orifice in CCM+, the diameter of the orifice is 1um. I realize that the scale is smaller or almost closer to kolmogorov scale, as TKE would cease to exist, I am modeling using Spallart Allmaras Model which solves for viscosity alone. It would be quite helpful if someone has done similar work in the past. The literature on leakage rates in quite less.
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That type of problem is really a nano / micro channel flow problem. Navier-Stokes is not very appropriate description of those types of flows (and forget turbulence). Although small, the Kolmogorov scales are still much larger than the mean free path of the mean molecular motion. When your channels are 1 micron in diameter, you are restricting the microscopic and macroscopic motion to much smaller dimensions. Even the continuum assumption breaks down. Bottom line is, I wouldn't use CFD for those types of problems. |
My mistake, i shouldn't have used the term "doesn't exist". TKE would dissipate as heat and the remaining term would be viscosity. I am not sure if DNS would solve the problem. When i run using spallart allmaras model, I can see a huge rise in temperature within the orifice.
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You really need a nano-microscale fluid flow model to solve these problems, not Navier-Stokes. That's just my take, maybe someone else has tried it and it works. |
I was also coming down on that conclusion, but there is a bit of uncertainty as the little literature i've found mentions about choked flow in the orifice. DNS and turbulence models (rans, k-omega..etc) are two different things, for that reason i was thinking about DNS. The results however are still subject to experiment or previous work done by someone.
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