Hi, I want to calculate the drag force on a sphere moving through the fluid. I am using "laminar flow" with axisymmetry. Normally, my code is working perfectly fine and giving me the correct value of the drag force, same as predicted by theory, 6pietarv. Now I want to learn to use "volume force" with the help of this code thus I added extra volume force F=Div.(2ppeta(strain rate)), where pp is some input constant, Div stands for divergence and strain rate is 2X2 tensor. Due to this term, the effective viscosity should (1+pp)eta as 2ppeta(strain rate) is just like viscous stress and the drag force on the sphere should be 6pi(1+pp)etarv. But I am getting the wrong value. Am I making any mistake?
PS: comsol file and a pdf file (for more details) are attached herewith.
Thanks and regards Harsh Soni