Learning Forum

[Atul Malge]

1. I am doing Moving Reference frame analysis of Savonius Turbine to get a steady state solution to get an initial solution to start with transient analysis. I am in dilemma whether MRF is like the rotor is placed stationary it's not rotating and we are getting a solution and using this as a startup calculation for transient analysis using the Sliding Mesh Motion Technique. It is like on the rotor I am sitting and observing the flow...in a steady state does it mean that the rotor is completely frozen and only the mathematical values are adultered, due to a change in the velocity term in the governing equation from u to ur (relative) ?. Also, in unsteady what could be the scenario, is it similar to Sliding mesh?

2. Now, the number of iteration, what shall be specified and how to know whether the no. of iteartions specified for MRF are enough to get a solution for the further analysis. Refer the image below for reference of the question.

[Rob]

MRF (Moving/Multiple Reference Frame) means we mimic motion but the mesh is static, and the solution can be steady state. Sliding mesh means the zone rotatates at a given speed and must be transient. 

[Atul Malge]

Still unclear about 1st Question Rob....please go through my question again...shall I reframe my question?

 

Also, 2nd question please

[Rob]

MRF (frame motion) - mesh is NOT moving. Sliding mesh (mesh motion) - mesh is moving. The options/terms changed at some point but everyone still refers to the "old" Fluent labels. 

OK. Iterations per timestep is the maximum iterations the solver can do to converge a time step. I generally aim for convergence in 10-15 iterations but set a maximum of 50. You then adjust the time step size until you reach the convergence aim (10-15 iterations). In terms of "how long", you need enough solved time for the flow to reach an equilibrium, which may be a constant value or some repeatable cycle. 

[Atul Malge]

Got it, Thanks Rob