Use of STAR CD for viscoplastic flow

The results

IV.1 The first simulation

    At first, we tried to simulate a simple water flow which would permit us to recover the Poiseuille profile at the outlet of the domain. The profile obtained is a parabolic one as the theory plans.

The results obtained were the same than the theorical ones, so we validated the mesh and the limits conditions we had taken.

IV.2 Viscosity modifications

    To simulate a viscoplastic flow, we had to modify the expression of  the viscosity. The fluid must be taken as a non-Newtonien one and different expression for the viscosity could be used. The model used is the Bingham law coupled with the Herschel-Bulkley model which leads to a model with two viscosities: A very high viscosity for a low stress and an average viscosity for higher stress.


So, we had to create a user subroutine describing this phenomena in Fortran which can be integrated and compiled with STAR CD.
STAR CD offers the possibility to create his own viscosity model with the user subroutine named VISMOL.F.
We made the following code to simulate Bingham model:

IV.3 The simulations

We used, at first, the option of non-newtonien flow already coded in STAR CD. We made different simulation with m*jjd**n.
We took the following values:  n=3 and m=0.001 .
We obtained the following results:

We obtained the profile of a viscoplastic flow.

Now, we present the results obtained with the subroutine vismol.gif
We obtained the profile of a fluid which got a very high viscosity.
because the value of our stress limit was two important that impose a very large y0.