So I would like to simulate the solar radiation on a simple box. I created a fluid domain (smaller box) inside another fluid domain (larger box). I would like to know the solar radiation flux on the top surface of the small box. The solar vector is (0,0,1), so that only the top surface receives solar radiation. After several attempts, the solar flux remained at zero and I could not figure out what went wrong. Does anyone know what exactly is happening? Is my boundary conditions incorrect or something else is causing this?
I also attached the case file, data file and geometry file in this thread.
Any help is greatly appreciated.