Fluent - Shear stress divergence UDF
I'm trying to create a UDF which analyses the shear stress gradients (and hence contribution to the X and Y momentum) for steady, compressible turbulent (SA) flow.
This can be done easily by rearranging the navier stokes such that the X term would look like
Grad(P)+ rho(q . nabla)q 
where q is velocity. We have all these properties which can be easy to implement in a UDF and visualised using a user defined scalar.
However, I want to do this using the shear stress alone where we have tau xx + tau xy for the X momentum term which should then be equal or close to equal to the other method. However, I have been unsuccessful in doing so, my stress components are given as follows (note some over expansion etc for data analysis purposes). Instead of this longwinded way is there a shear stress variable available or do I need to calculate this. Is there a clear problem with my implementation process?
C_UDSI(c,t,0) = (-2/3)*(C_MU_L(c,t))*(C_DUDX(c,t) + C_DVDY(c,t)) + 2*(C_MU_L(c,t) + C_MU_T(c,t))*C_DUDX(c,t);
C_UDSI(c,t,1) = (C_MU_L(c,t) + C_MU_T(c,t))*(C_DVDX(c,t) + C_DUDY(c,t));
C_UDSI(c,t,2) = (-2/3)*(C_MU_L(c,t))*(C_DUDX(c,t) + C_DVDY(c,t)) + 2*(C_MU_L(c,t) + C_MU_T(c,t))*C_DVDY(c,t);