Unsteady Aerodynamics Turning Off

Hello,

I’m getting warning messages saying unsteady aerodynamics have been turned off. Does this new condition without unsteady aerodynamics persist for the entirety of the simulation?

Could this explain why my power, thrust curves appear to be insensitive to turbulence intensity?

Best wishes,
Sam

Dear Sam,

In AeroDyn v15, warnings regarding “turning off unsteady aerodynamics due to high angle-of-attack” are triggered if the local angle of attack at a given airfoil exceeds the value of input parameter UACutout, as specified in the airfoil data input file (if set to DEFAULT, UACutout = 45 degrees). You can eliminate this warning by setting UACutout higher or by ensuring the angles of attack don’t get so high (e.g. by setting proper initial conditions).

For each aerodynamic analysis node that triggers this warning, the UA model will be disabled for the entirety of the simulation.

I doubt that the disabling of UA is resulting in the insensitivity to turbulence intensity that you reported earlier.

Best regards,

Dear Sir,
Why would this warning pop-up even when the UACutOut is default.
Thanks in advance

Dear Akheel,

The DEFAULT value for UACutOut is 45 degrees; you’ll receive this warning if the local angle of attach exceeds 45 degrees. I would not expect this warning to appear frequently. Receiving this warning frequently would suggest a problem with your model setup, e.g. poorly set model initial conditions.

Best regards,

Dear Jason,

I am trying to run simulations for IEC-61400 Part 3, DLCs 1.1, 1.3 & 1.4. I found in some of the blade node sections the angle of attack is greater than 45 deg (1 or 2 blade nodes are having angle of attack of 60 deg at the start of the simulation) even after giving proper initial conditions. In the case of DLC 1.4 with large skewed condition, I also found many blade nodes are having angle of attack greater than 45 deg during the rotor skew angle increase.
I understand from the above post (http://forums.nrel.gov/t/unsteady-aerodynamics-turning-off/2258/4)
that the UACutout (default 45 deg) can be set to a higher angle. I would like to know if there is any upper limit cut off angle for the Beddoes-Leishman unsteady aerodynamic model?

Regards
Ramya

Dear Ramya,

I’m not sure I can answer your question generally. UACutOut is really there to ensure users do not apply the unsteady airfoil aerodynamics model beyond what the model is valid for.

Do you have a sense of what the unsteady airfoil aerodynamic hysteresis loop (e.g., Cl versus AoA) should look like for the airfoils you are simulating, particularly at large AoA (e.g., based on airfoil data from wind tunnel tests or CFD)? If so, you could plot this hysteresis loop and verify that the solution make sense, particularly for large AoA. The hysteresis loop is most easily generated through the standalone unsteady airfoil aerodynamics driver.

Best regards,