Hello there, I am also interested in optical flow simulation. If it might help, I am actually using CARLA simulator which uses Unreal Engine, and you can find their implementation of optical flow here. And also, it seems like their visualization of optical flow works just fine, you can see their “ColorCodedFlow” function.
However, their optical flow suffers from some problems that are discussed in this issue. I actually have been struggling with this for a while now and I ended up trying to do the simulation of optical flow myself, instead of relying on their code.