Turbulent dispersion force with eddy viscosity models?
 

In the multiphase interaction term (often denoted as M), I want to add turbulent dispersion force along with viscous drag force for liquid-liquid rotating system. I am using eddy viscosity models(RANS-k-e realizable), which assumes isotropic turbulence in the system. I could use Reynolds stress model (RSM;7 equations) to take anisotropy into account, but that cost (sim. time) me more.

Thus, I want to use eddy viscosity model and want to enable turbulent dispersion model (Now, M = (F(drag)+F(turb.disp))).

Question: What it represents when I enable turbulent dispersion model without taking anistropy effect?