[mazhar16823]

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.

[LuckyTran]

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.

[mazhar16823]

Originally Posted by LuckyTran

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.

That's what causes a problem. I have to specify the turbulent viscosity ratio, and turbulent velocity scale for inlet/outlet boundary and initial conditions. I am unable to decide which values of both should be taken.

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.