I just want know why AOA (angle of attack) has no role on acoustic features of an airfoil/ flat plate. If we go for aerodynamics AOA plays a vital role but this is absent in acoustics case why is it so?
The sound produced by an airfoil does strongly depend on the angle of attack. In particular heavy stall produces strong periodic vortex shedding and associated low frequency sound. Also high frequencies for angle of attack below stall depend on the angle of attack. The boundary layer structure changes drastically with the angle of attack. Sound is produced due to interaction of the turbulence in the boundary layers and the trailing edge of the airfoil. If you do not see any effect, it is possible that you are considering a laminar flow (Reynolds based on the cord below 1E5 ).
I guess u misunderstood. Acoustic also depends on AOA. When the property of flow changes such as T,P,D due to aoa then there will be flow field noise
Acoustic is nothing but the study of the pressure field. Therefore, the answer is that an airfoil that changes its AOA changes also the pressure field and the propagation of acoustic waves
Acoustic signature will be strong function of AOA, specially at post-stall conditions. Question is how are you characterizing your acoustic field? That method may be deficient and should be replaced.
Tapan K Sengupta Sir If we do the experiment for same Reynolds number and for different AOA no change will be observed in tha SPL v/s frequency plot. Same thing will be observed in post stall condition also. So how we can say that AOA is affecting Acoustic features??? And paper are there which support my point... thats why i am bit confuse y AOA is not affecting ??
Filippo Maria Denaro Sir AOA have no effect on Acoustic features..... I just want to know why it is so?
Shailesh KUMAR Jha : As I hinted that all is not well with your method of predicting acoustic field. It is a case of blaming your tools, and not about the physical process. You have not mentioned as to how you calculate SPL. As Filippo also mentioned that with AOA shed vortices will be different. That is bound to change sound generated aerodynamically. I hope that you are not a victim of commercial software!
Tapan K. Sengupta sir I have not used any software in this. Sir I am sending paper's name :
"Effect of Angle of Attack and Airfoil Shape on Turbulence-Interaction Noise"
" On the leading edge noise and aerodynamics of thin aerofoil subjected to the straight and curved serrations "
In this also they have clearly mention that AOA plays no significant role in Acoustics features. There are many more literature are available which is confirming that AOA not affect acoustic features of airfoil.And my experiments also says the same thing. That's y i have this confusion sir.
Shailesh KUMAR Jha
The paper Conference Paper Effect of Angle of Attack and Airfoil Shape on Turbulence-In...
stated:
"The radiated noise is investigated only in the mid-span plane of the airfoil, at some far-field distance (2 m), so that the effect of the side-plates is minimized."
That does not mean at all that the pressure field is not affected by the AOA but only that the far-field measurement (in a specific section) did not highligt difference.
The sound produced by an airfoil does strongly depend on the angle of attack. In particular heavy stall produces strong periodic vortex shedding and associated low frequency sound. Also high frequencies for angle of attack below stall depend on the angle of attack. The boundary layer structure changes drastically with the angle of attack. Sound is produced due to interaction of the turbulence in the boundary layers and the trailing edge of the airfoil. If you do not see any effect, it is possible that you are considering a laminar flow (Reynolds based on the cord below 1E5 ).
Shailesh KUMAR Jha, if you are right, then you will hardly notice any sound variation from a hovering helicopter. Secondly, SPL reports only second order statistics. One would even notice changes related to mean (first order statistics) flow quantities. That would mean changes in vorticity, pressure and all other flow variables. This is irrespective of whether the flow is laminar or turbulent. This should be noted in the conference paper, if measurements are done carefully, for both the near and the far field.
Is it possible to do two-phase simulation for 3D pipe leakage using FW-H Acoustics model?
This seems very ambitious. Two-phase simulations are quite complex.
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