[mazhar16823]

Hi Everyone,


I am using K-Omega SST Model for an external aerodynamics (wind turbine) problem.


For the initial conditions, I want to calculate the turbulent velocity scale and viscosity ratio.


First, I used the reference: https://www.cfd-online.com/Wiki/Turb...ary_conditions


However, the equations I used are taken from STARCCM+ Manual. While calculating for Turbulent Velocity Scale, I see that for turbulent length scale I need turbulent time scale and for turbulent time scale I need specific dissipation rate (omega) and for omega, again I need turbulent length scale as shown in the picture. This is confusing, how can I evaluate turbulence length scale to get the turbulent velocity scale in the end?


Secondly, for turbulence viscosity ratio, I checked with above link it is "Mu_t/Mu" but I don't know how to get Mu_t and whether "Mu" in the denominator is dynamic viscosity?


Thanks for your time;

[mazhar16823]

Originally Posted by mazhar16823

Hi Everyone,


I am using K-Omega SST Model for an external aerodynamics (wind turbine) problem.


For the initial conditions, I want to calculate the turbulent velocity scale and viscosity ratio.


First, I used the reference: https://www.cfd-online.com/Wiki/Turb...ary_conditions


However, the equations I used are taken from STARCCM+ Manual. While calculating for Turbulent Velocity Scale, I see that for turbulent length scale I need turbulent time scale and for turbulent time scale I need specific dissipation rate (omega) and for omega, again I need turbulent length scale as shown in the picture. This is confusing, how can I evaluate turbulence length scale to get the turbulent velocity scale in the end?


Secondly, for turbulence viscosity ratio, I checked with above link it is "Mu_t/Mu" but I don't know how to get Mu_t and whether "Mu" in the deominator is dynamic viscosity?


Thanks for your time;

Sorry I forgot to attach the figure. Here it is: https://drive.google.com/drive/folde...VxIKHYJCwx7oI7

[magnetobli]

For velocity scale - you need to calc turb intensity (based on reynolds umber) , turb kinetic energy (based on intensity and bulk flow speed), dissipation rate (based on kinetic energy, intensity and Cu- assumed 0.09), take ratio of kinetic energy and dissipation gives time scale. Velocity scale is length scale (0.07 * duct width) / time scale. Equations are found after quick search online.