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10.8.1 Gradual Increase of the Rotational Speed to Improve Solution Stability

Because the rotation of the reference frame and the rotation defined via boundary conditions can lead to large complex forces in the flow, your FLUENT calculations may be less stable as the speed of rotation (and hence the magnitude of these forces) increases. One of the most effective controls you can exert on the solution is to start with a low rotational speed and then slowly increase the rotation up to the desired level. The procedure you use to accomplish this is as follows:

1.   Set up the problem using a low rotational speed in your inputs for boundary conditions and for the angular velocity of the reference frame. The rotational speed in this first attempt might be selected as 10% of the actual operating condition.

2.   Solve the problem at these conditions.

3.   Save this initial solution data.

4.   Modify your inputs (i.e., boundary conditions and angular velocity of the reference frame). Increase the speed of rotation, perhaps doubling it.

5.   Restart or continue the calculation using the solution data saved in Step 3 as the initial guess for the new calculation. Save the new data.

6.   Continue to increment the rotational speed, following Steps 4 and 5, until you reach the desired operating condition.

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