Tagged: des, fluent, les, turbulence, turbulencemodel


March 11, 2022 at 9:19 amFoxCFDSubscriber
Hello everyone,
I'm doing simulations with WMLES SOmega and SBES  WMLES SOmega. According to the literature, to have a "good" LES simulation we should ensure that we're resolving 80% of the turbulent kinetic energy and 20% is being modeled by the subgridscale model.
Computing Turbulent Kinetic Energy in WMLES
This can be checked by computing the turbulent kinetic energy being resolved by the mesh and by the subgridscale model. Let's call k_res and k_sgs.
Assuming k_res = 0.5 * (U_RMSE ^2 + V_RMSE ^2 + W_RMSE ^2 )
Question 1: How do we compute k_sgs in the WMLES model ?
Is there a formula to compute easily k_sgs using the subgrid quantities available by Fluent like
 Subgrid Turbulent Viscosity
 Subgrid Effective Viscosity
 Subgrid Turbulent Viscosity Ratio
 Subgrid Filter Length (is this the length computed by the equation 4 in the referenced paper?)
After this, the total turbulent kinetic energy can be computed by k_total = k_res + k_sgs
Now to assess the quality of the simulation we could compute the ratio k_res / k_total and check if it is more than 80% or not.
Computing Turbulent Kinetic Energy in SBES
Furthermore I wish to do the same for the SBES simulation. However, here we're also dealing with turbulence quantities from RANS.
We have the turbulent kinetic energy directly available from it (let's call it k_RANS). I suspect this is from the areas where RANS is activated because k_RANS is very small compared to the k_res earlier computed.
Question 2: Therefore, after computing k_sgs can we compute k_total as k_total = k_res + k_sgs+ k_RANS ?
The referenced paper for the WMLES model is A hybrid RANSLES approach with delayedDES and wallmodelled LES capabilities
Thank you for reading 😀

March 11, 2022 at 9:48 amaitor.amatriainSubscriberThe calculation of the LES quality is a beta feature in the 2022R1 version:
10.1. Estimation of the LES Resolution Quality (ansys.com)
The characteristic length of the transition zones in SBES is negligible with respect to the characteristic length of the domain. In addition, these transition zones have no ┬¿physical┬¿ sense, so you can omit them. The LES part is treated in the same way as the pure LES.

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