hi, I am a beginner in sliding mesh simulation for stirred tank. I have done MRF and getting satisfactory results. My impeller rotation peed is 270 rpm.(tip speed 1.41 m/s). The problem I am facing is in selecting the time step size. can any one suggest me in getting through this problem. Thanks in advance. Randheer

What is the numerical Scheme you are using. The step size depends on if the scheme is implicit or explicit. If you use an explicit scheme a rough time size would be dt=0.5 dx/C where C is the courant number for the flow. For implicit scheme you can keep much higher time steps. Also since the rotation is 270 rpms try to keep t close to time period of oscillation so that you do not introduce artificial fluctations in the domain.

Dear debs I am using coupled explicit scheme. Please tell me what is dx(is it grid spacing?)and does the period of oscillation is same as the time required for one impeller rotation? thanks Randheer

dx refers to the smallest grid spacing. Period of oscillation is T=2*pi/omega .To ensure stability of your scheme use a lower time step . Google for explicit schemes and you might find literature materials about the neumann analysis for stability of schemes