Hi, For analysis types such as incompressible, you must delete the solid parts after creating the flow region: https://www.simscale.com/knowledge-base/flow-volume-extraction/#:~:text=In%20addition%2C%20delete%20the%20solid%20parts%20to%20be%20able%20to%20use%20the%20model%20in%20an%20analysis%20type%20that%20requires%20a%20single%20fluid%20region Cheers