So essentially, I have a hollowed out blade and I want porous medium inside it. I managed to do it, but when I try to solve for airflow through the porous medium and over the blade’s surfaces, it throws this error:
“Multiple bodies with material assignments were detected. Because this is a single region simulation, only a single body may be assigned a material. Please review your material assignments and leave only the flow volume with a material.”
Hi @vijayarvindr, thanks for posting on the forum and welcome to the SimScale Community 
Usually when this issue happens there is more than one solid body in the domain for a single region analysis type (such as incompressible). Make sure you delete all the solids apart from the Flow region/advanced concepts. Maybe this tutorial is helpful in ilustrating the workflow:
If you’d like to take a closer look at your project, please share the URL (here’s a guide teaching you how: Guide to Clear and Understandable Forum Posting).
Cheers
Igor