# Drag force acting on a disk in a 2D system

I have a 2-dimensional system with behavior governed by Langevin dynamics in which disks (circles) move through a fluid. In the Langevin equation, there is a velocity-dependent term that accounts for a frictional force. What expression would give me the frictional force acting on a disk?

I have only seen solutions of Stokes law for spheres; what is the two-dimensional analog?

I suggest using the general drag relation: $$F_d=0.5C_d\rho_lv^2D$$ where $F_d$ is the drag force per unit length, $D$ is the diameter of the cylinder and $v$ is the relative velocity norm between fluid and cylinder. The drag coefficient depends on the regime, for $Re<0.1$, $C_d\propto Re^-1$, for $Re>>1$, $C_d\approx1$