turbo machinery problem
 

if my rotating domain's rpm is more than 100k rpm means why recommended to solve with 2 or 3 low rpms (ex: 10k, 30k & 70k rpm) and then to solve 100k rpm?
what's is the physics or logic beyond this?

The fluid flow will likely be simpler at lower RPM. If the solution diverges at 10k RPM, then it definitely won't converge at 100k RPM. This allows you to analyze individual components (e.g., mesh, timestepping scheme, boundary conditions) with a simpler problem rather than diving right into the complex problem without verifying your model works.