Predict Wing’s Flutter Using Aerodynamic Damping

[gstzortz]

Hey Ansys Forum,

I am trying to predict wing's flutter with a less expensive computational method than 2WAY-FSI. I have seen a method about calculting aerodynamic damping (if AD>0 then system damped if AD<0 then flutter occured). In this ANSYS link says that i can use Transient Blade Mode (CFX) that has built-in the parameter of AD.

https://innovationspace.ansys.com/knowledge/forums/topic/how-to-use-the-aerodynamic-damping-capability-of-tbr-for-non-turbo-applications/

I followed the instructions, and as I increased the speed, the variable increased positively, which seems strange to me. For this reason, I would like to share the process I followed so you can help me identify if I made any mistake somewhere.

the instructions i followed are from this video:

https://www.youtube.com/watch?v=CuaMKl0IllM

I did everything it says (according to my problem) except the normalization step, since at first i want to find if it's negative or positive.

What's wrong? Isn't this methodology suitable for my wing's flutter problem? If anyone could help it will be apriciated.

Just to clarify in CFX I use only the flyid domain, so the Boundary, in which i Calculate the AD are the Fluid Faces Interaction (i dont know if that the problem an i have to input the structural geometry in CFX also)  

 

 

 

[rfblumen]

The workflow you outlined appears to be correct and is applicable to modelling blade flutter in a wing.  As pointed out in the video and in the CFX flutter tutorial, it's not necessary to model the solid region in CFX but only the fluid region.

What you're indicating is that as the flow velocity is increased, the aerodynamic damping becomes more positive in value.  This indicates less of a tendency to flutter.  Assuming that everything was set up and run properly (i.e. using the lowest frequency mode from the modal analysis, applying a reasonable displacement amplitude in CFX, using appropriate boundary conditions, running the solver for a sufficient number of periods), another factor in the analysis may be angle of attack.  Performing the blade flutter analysis over a range of angle of attack at different flow velocities may reveal different results.

[gstzortz]

Dear rfblumen,

Thank you very much for your reply.

I am planning to perform the wing flutter analysis over a range of angles of attack to investigate potential variations in results. Regarding the setup for properly running the analysis, are there any papers or ANSYS documentation on how to appropriately select these parameters? For example, I chose a frequency (the fifth mode) with a mode shape that combines both torsion and bending, and for the amplitude, I applied the maximum modal displacement of this mode shape. Any further recommendations or references you could provide would be greatly appreciated.

[RS]

hi , When the speed is increased, aerodynamic damping can exhibit different behaviors depending on the specific conditions. For instance, in some cases, as the speed increases, aerodynamic damping may initially increase, contributing to system stability. However, as the speed approaches certain critical points, such as the vortex-locked critical point, aerodynamic damping can transition from positive to negative, indicating potential instability. This behavior is observed in various studies, including those on tall buildings and bridges, where aerodynamic damping shows a nonlinear increase with reduced wind speed until a critical point is reached. 

In open web can find more details on the above mentioned, by searching with key words " Flutter Controlling Effect and Mechanism" or " Xiujuan Jiang" etc

I am not saying that your simulation too would behave in a similar manner. Try running it further and check if the positive changes to negative. 

Hope you have gone through some examples already. If not, shared below links from Ansys Learning Hub workshop. Try checking AD variation with speed. After gaining confidence, can attempt your project. 

Gas Turbine Labyrinth Seal Flutter (ABP) - Gas Turbine Labyrinth Seal Flutter

Gas Turbine Labyrinth Seal Flutter (ABP) - Input Files: Gas Turbine Labyrinth Seal Flutter

 

[gstzortz]

Dear Ravi,

Thank you very much for your reply.

Your suggestions are very useful and will greatly support my project.

Unfortunately, an error occurred when I tried to sign in to enroll in this project. I have contacted ANSYS Training Support, and I hope a solution comes up soon.