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June 26, 2020, 09:35 |
How STARCCM computes turbulent viscosity
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#1 |
Senior Member
MA
Join Date: Mar 2020
Posts: 163
Rep Power: 6 |
Hi everyone,
I was wondering to know how CCM+ computes the turbulent viscosity (to be specified in initial conditions before running a simulation); I have checked the link https://www.cfd-online.com/Wiki/Turb...ary_conditions where it requires to have epsilon and turbulence length scale but I only have the free-stream turbulence and free-stream velocity. However, I looked into CCM+ manual where it defines a model "Turbulent Viscosity User Scaling" I think it is mainly for scaling the already known turbulent viscosity. I need this turbulent viscosity to define the viscosity ratio and other boundary conditions as given in the above link. Thanks for your time. |
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June 26, 2020, 13:12 |
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#2 |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,675
Rep Power: 66 |
The turbulent viscosity ratio is in the initial conditions, not the turbulent viscosity. But what is actually needed as an initial condition and boundary conditions is the k and epsilon or k and omega. Turbulence intensity, length scale, and viscosity ratios are just convenience features provided to eventually calculate k and epsilon/omega.
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June 26, 2020, 14:04 |
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#3 | |
Senior Member
MA
Join Date: Mar 2020
Posts: 163
Rep Power: 6 |
Quote:
For instance, Re is the Reynold at full scale and turbulence intensity is 7%. Whereas, in my simulation I am using Re/10 and Turbulence Intensity = 1%. How should be my choice for Turbulent Velocity Scale and Turbulent Viscosity Ratio because STARCCM+ does not ask directly for k and omega values but viscosity ratio and turbulent velocity scale (using K-Omega SST model). Also, I have referred a paper on this - where Menter suggested to use following equations to calculate turbulent viscosity ratio, K and omega (see page no: 6): http://cfd.mace.manchester.ac.uk/twi...2554-CP.PS.pdf omega = constant*V/L Nu_t = 10^-3*Nu K = Nu_t*Omega I did the calculations as attached. Do you think I should specify these values for turbulent viscosity ratio and turbulence velocity scale as computed below? Thanks for your time. |
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