Sliding Mesh CL Monitors Discrepancy Transient Simulation Fluent

Hi,

I’m trying to model a small 4 bladed rotor and have a query.  The model consists of a 360 mm diameter rotor with 4 NACA 0015 blades of 70mm chord. The rotor rotates at CCW with a chord based Reynold’s number of approx. 40,000. Each of the 4 blades pitches in a sinusoidal manner to +/-45 degrees as the rotor rotates, in one rotor rotation.  To do this I’m using a sliding mesh interfaces and a Define_Zone_Motion UDF for each. The rotor geometry is very similar to fluent tutorial as shown in the image below. The mesh motion is working correctly and the blade motion is correct.

I’m plotting the CD and CL monitors on the blades for each time step and the CD values for each of the blades are correct and identical but 90 degrees out of phase as expected. When looking at the CL values the blades at 12 and 6 o’clock are correct and the same, but the blades and 3 and 9 o’clock are the same but incorrect mainly in the area shown below. The setup for each of the blades is identical in terns of mesh and geometry and UDF. I’m slightly confused by it as the issue is not replicated in the CD values. I have rechecked my setup and can’t see anything that would cause the issue between the blades. I’m running the model for 40 rotations and sometimes the error starts to emerge around half way through the solution but not always. I am solving the problem with the k-ω SST model with low Reynold’s Correction. I’m using a coupled based solver with second order implicit transient formulation.

I was just wondering if this problem has arisen before and what options I could try/what the probable cause could be?

Comments

  • RobRob UKForum Coordinator

    It'll take a few cycles to establish the flow field due to the blade-wake interaction(s). Given that the coefficients are based on the reference values monitor the forces too.

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