how to calculate the drag force of a sphere in axisymmetry
I have a rather basic simulation that I would like to preform that can be compared to reference values.
What I want to do is to simulate the drag force of a sphere in axisymmetry setup.
I have manage build the model and run the simulation and the velocity plot looks reasonable.
My question is how I should define the correct equation for drag force in the Boundary Integration box (for axisymmetry)?
My thanks for help in advance!
you would need to derive and integrate the (axisymmetric) expression for the Total-stress tensor in the z-direction, which should be something like
fz = r*(nz*p+miu*(-nr*(wr+uz)-2*nz*wz))
cd = 2*fz/(rho*umean^2*diam)
That said, the solution in the attached image does not look converged as fluctuates a lot between grid cells. Depending on the flow regime you might need to increase the mesh density, use artificial (numerical) stabilization, and/or a turbulence model.