[Iaroslav]

Hello everyone,

I am currently working on modeling a free, supersonic air jet (where the medium is air) where compressibility effects are very important. The issue I am having is that none of the turbulence models take into account compressibility.

My colleague and I are currently trying to implement changes to the standard k-e model in Fluent, but we are not getting good results. I am posting here to see if anyone has already made similar changes and see if they have any suggestions. Here is what I have so far in my UDF (note that so far I have only modified Cmu):

#include "udf.h"

DEFINE_TURBULENT_VISCOSITY(custom_mu_t, c, t)
{
real mu_t;
real s_11;
real s_12;
real s_22;
real s_g;
real div_vel;
real mach_g;
real l_g;
real alpha;
real c_mu;

real rho = C_R(c,t);
real k = C_K(c,t);
real d = C_D(c,t);
real temper = C_T(c,t);
real dudx = C_DUDX(c,t);
real dvdy = C_DVDY(c,t);
real dudy = C_DUDY(c,t);
real dvdx = C_DVDX(c,t);

s_11 = dudx;
s_22 = dvdy;
s_12 = 0.5*(dudy+dvdx);
div_vel = dudx+dvdy;

s_g = sqrt(2*((SQR(s_11)+2*SQR(s_12)+SQR(s_22))-1/3*SQR(div_vel)));

alpha = sqrt(1.4*287*temper);
l_g = 0.09*pow(k,1.5)/d;
mach_g = s_g*l_g/alpha;
c_mu = 0.07*exp(-0.4*mach_g);

mu_t = c_mu*rho*SQR(k)/d;

return mu_t;
}

I appreciate any comments or suggestions.
Thank you,
Iaroslav