There are a few possible reasons why cloud map might be showing a granular distribution for the water film thickness when using a coupled DPM-EWF model:
Particle Size Discretization: In the DPM, you likely define a range of particle sizes to represent the water droplets. This discretization can lead to a blocky or granular appearance in the cloud map, especially if the range is large or the number of size classes is small.
Limited Resolution: Cloud maps often have a limited number of cells to represent the solution space. If the water film is thin or the cloud map resolution is coarse, you might see a patchy or granular distribution instead of a smooth film.
Turbulent Fluctuations: If you're simulating a turbulent flow, the water film thickness may fluctuate due to the turbulent eddies. These fluctuations can be captured by the DPM and reflected as a granular distribution in the cloud map.