CFD Online Discussion Forums - BrowninanMotionForce of particles in laminar flow

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BrowninanMotionForce of particles in laminar flow

Hello

In DPM model, Brownian force is one of the major forces, which act on a particles.

Look at the following link ( line 194-197 ):
https://github.com/OpenFOAM/OpenFOAM...nMotionForce.C

For laminar regime, the Brownian force is defined by :

Code:

const scalar rhoRatio = p.rho()/p.rhoc();

  const scalar s0 =

            216*muc*sigma*Tc/(sqr(mathematical::pi)*pow5(dp)*(rhoRatio)*cc);

  f = eta*sqrt(mathematical::pi*s0/dt);

For laminar regime, the correlation for this force is presented in the
following :
http://uploadgoogle.ir/uploads/145915541121.jpg

note:where subscripts "f" and "p" denote the fluid and particle,
respectively. Moreover, rho is for continuous phase.

As shown in this figure, the square of rho_p (particle density) shoud
appears at the equation of S0 but I had supposed that the power one of
rho_p hed been appeared in the (S0) of the code.

- Is this a bug in the code ?? ( If i don't mistake. )
- what is muc?? ( dynamic or kinematic viscosity of continuous phase )

Please kindly guide me.

Just to your second question:

mu is usually the dynamic viscosity and muc in this cas the dynamic viscosity of the continous phase.

Please kindly guide me.

I think that there are some mistakes in the code of BrownianMotionForce.C

a) dt in the code is not the time step (as the reference paper) of the simulation.

b) the Boltzmann constant is in eVK^-1 but the reference paper uses the constant in J/K !!!

The results from the simulation (with the values above) seems to be logical