# DEFINE_DPM_DRAG - fluid phase velocity correction

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 March 20, 2021, 07:25 DEFINE_DPM_DRAG - fluid phase velocity correction #1 New Member   Join Date: Nov 2020 Posts: 3 Rep Power: 4 Hi! A Lagrangian (one-way) tracking is used to model submicron particle dispersion and deposition in a turbulent channel flow. The discrete random walk (DRW) model in Fluent gives bad results for submicron particles, so I want to implement a fluctuating correction to the fluid phase velocity in the DEFINE_DPM_DRAG macro: u = + u', Here: c->V[i] = // from the cell of the fluid simulation p->Vprime[i] = u' // modelled with the DRW I call the fluid phase velocity and change it like this: cphase_state_t *c = &(p->cphase[0]); for (i=0; iV[i] += p->Vprime[i] ; (Equation *) Based on this velocity a new particle Reynolds number is found, and 18*Cd*Re/24 is returned. Then to my question: In what way has equation* changed the cell velocity (u_cell = c->V[i]) and the velocity field? 1) Just for this timestep? In that case, u in the Lagrangian tracking equation includes the modeled fluctuating velocity: d/dt(v_p) = F_D (u-v_p) (Equation **) Here, F_D = mu/(rho_p*d_p^2)*(18*Cd*Re/24). 2) Only inside the DEFINE_DPM_DRAG drag? u, in equation **, is not affected by the velocity correction. 3) For the whole simulation? The velocity field is changing during the simulation because of fluctuating velocity corrections from all the particles. In other words, is this cell velocity (c->V[i]) called in the Lagrangian tracking equation?