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Oscillating Aerofoil Analysis Advice

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Old   February 7, 2016, 14:51
Default Oscillating Aerofoil Analysis Advice
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Hi,

I'm new to CFD, and CFX but have completed a number of tutorials to try and improve my learning and understanding. I'm currently working on a project with an oscillating aerofoil, which pitches with a sinusoidal motion about a mean angle of attack. I'm looking to mount it wall to wall in a wind tunnel, and was hoping to use the test results to validate a 2D CFD model initially. I've only ever used a stationary mesh in the past, an am not sure of the best way to analyse this problem. Having read the CFX manual in part, I did see mention of a UDF, but am not sure if this is the best way to solve the problem or whether there is a simple alternative. Any advice would be much appreciated.

The aerofoil has a chord of 50 mm, a span of 250 mm, and the maximum free stream velocity of the tunnel is 20 m/s
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Old   February 7, 2016, 16:54
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How quickly is the foil pitching?

If the pitching is slow relative to the flow motion then this can be assumed to be a series of steady state conditions and you do not need moving mesh at all - much simpler. But if the pitching of the foil is of a similar time scale to the flow motion they are likely to be coupled together and a full transient moving mesh simulation is required.
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Old   December 27, 2020, 00:59
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Quote:
Originally Posted by ghorrocks View Post
How quickly is the foil pitching?

If the pitching is slow relative to the flow motion then this can be assumed to be a series of steady state conditions and you do not need moving mesh at all - much simpler. But if the pitching of the foil is of a similar time scale to the flow motion they are likely to be coupled together and a full transient moving mesh simulation is required.

Hi dear ghorrocks
I try to analyze the movements of اHeave and the Pitch of an airfoil by CFX. But I could not create these two moves at the same time in CFX. Can you help me please?
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Old   December 27, 2020, 04:28
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If the flow is pseudo steady state then you can do this by changing the angle of your foil in you mesher, or by changing the inlet flow direction. This gives you the drag/lift forces versus the heave and pitch angles.

If the flow is not psuedo steady state then you have to do it with moving mesh. Then you need to defines moving mesh equation which describes your motion.
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Old   December 27, 2020, 05:18
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If the flow is pseudo steady state then you can do this by changing the angle of your foil in you mesher, or by changing the inlet flow direction. This gives you the drag/lift forces versus the heave and pitch angles.

If the flow is not psuedo steady state then you have to do it with moving mesh. Then you need to defines moving mesh equation which describes your motion.
thanks for your reply.
It's not psuedo steady state becuease i need to gain thrust forces of moving airfoil.
Is it possible to oscillate the input flow?
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Old   December 27, 2020, 05:42
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No, that is not what I meant by psuedo steady state. Let me explain it better.

What I meant by psuedo steady state is that as the airfoil sweeps from one AOA to another (or pitch, heave, yaw, whatever) it does so with the lift and drag at any AOA equal to the steady state lift and drag at that AOA. What this means the system can be modelled as on ODE with a lift and drag versus AOA curve - no coupled CFD is required.

If it is not psuedo steady state then this does not apply as some form of inertial or other effect causes the lift and drag to differ from the steady state one at the same condition. If your model is in this regime then the only to model it is with a coupled solver, either rigid body or FSI depending on how it is constrained.

Moving the input flow angle only works for the psuedo steady state cases. Hopefully you can work out why, now that I have explained what I meant by it.
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