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Drag and Lift Monitors for Oscillating Hydrofoil in a Dynamic Mesh

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Old   May 15, 2019, 03:57
Default Drag and Lift Monitors for Oscillating Hydrofoil in a Dynamic Mesh
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Erwin Phillippe T. Beronio
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I am simulating an oscillating hydrofoil initially rotated 30 degrees clockwise, with its initial oscillation motion going upwards. I need to monitor the lift and drag coefficients throughout the whole cycle, but since the default options only enable a single value for the force vectors (X and Y) in each monitor I am only correctly monitoring lift and drag for one angle. How would I properly monitor the lift and drag coefficients with the angle of attack changing per timestep?

Upon researching, I have read that the monitors in the GUI cannot keep up with the changing angle of attack during the transient simulation. Is there a way to resolve this limitation?
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Old   May 16, 2019, 03:29
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By the look of your mesh, you are inclining your aerofoil to a given AoA and keeping your velocity vector constant (along the x axis)? From this position you are oscillating in pitch?

If this is the case, remember that the lift acts perpendicular to the velocity and drag acts parallel. This means that during your oscillations if you have a lift monitor measuring wall forces in the y direction and drag monitor in the x direction then they will always be measuring lift and drag (velocity vector not changing). If you want to have the normal and axial forces, this requires some simple post processing using the relations found on this page:

http://www.aerospaceweb.org/question...cs/q0194.shtml

Have fluent write the timestep data to a file so you can easily post process. You can figure out your AoA from your pitch rate and the time history.
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Old   May 16, 2019, 12:28
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Quote:
Originally Posted by tbwake View Post
By the look of your mesh, you are inclining your aerofoil to a given AoA and keeping your velocity vector constant (along the x axis)? From this position you are oscillating in pitch?

If this is the case, remember that the lift acts perpendicular to the velocity and drag acts parallel. This means that during your oscillations if you have a lift monitor measuring wall forces in the y direction and drag monitor in the x direction then they will always be measuring lift and drag (velocity vector not changing). If you want to have the normal and axial forces, this requires some simple post processing using the relations found on this page:

http://www.aerospaceweb.org/question...cs/q0194.shtml

Have fluent write the timestep data to a file so you can easily post process. You can figure out your AoA from your pitch rate and the time history.
Thank you for the reply, tbwake. Yes, the airfoil is given an initial AoA of 30deg and with a constant velocity vector of 2m/s along the x-axis. It oscillates in pitch (rotates from 30deg to 0deg at the top, then 0deg to -30deg in the middle, then -30deg to 0deg at the bottom, then finally 0deg to 30deg back to the original position) and in heave (translates 1m upward, 2m downward, and then 1m upward to its original position). I have the animation for one cycle but it failed to attach due to the file size limit.

When I did the steady-state runs in order to generate the lift and drag curves for an airfoil steady at 0deg AoA, I remember that it was the velocity vectors and the monitors that I changed for each AoA since the monitors gave incorrect values when its vectors were unchanged. I'll take a look at how the lift and drag curves would be generated given the theory you stated.

What are the steps involved in the post processing? My adviser told me it involved generating an iso-surface and obtaining values from there.
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