I am running a Lagrangian particle tracking case with and without the turbulence dispersion model activated. The particles don't disperse more when turbulence dispersion is activated.
There's practically no difference at all, even though analytically we know that the particles should be moving around all over the place. What is going on?
Turbulence dispersion turns itself off if the flow is not deemed to be sufficiently turbulent. In CFX 11.0, there is a check if the flow is locally turbulent (eddy viscosity ratio > 5).
If this is not the case, turbulence dispersion is turned off until this criterion is met.
This limit can be controlled by a CCL parameter:
Eddy Viscosity Ratio Limit = < real number larger than zero>
This is adjusted where the particle dispersion model is activated.