On the discrepancies of vortexShed result

[windseacn]

Hello, I just tested vortexShed case, and found that the results are not consistent with different analogy methods, take the N1 observer as example, first the results from OF Curle Analogy and libAcoustics Curle Analogy are not the same, as in the figure below， I think they should match exactly as the same method is used. The version is v2112.

Next, the results from OF Curle Analogy is of opposite sign of that from FWH Analogy, as shown in the figure below, I want to know whether this is right or not?

[eacfd]

Hello!

1. The Curle analogy is implemented differently in the OpenFOAM and our library. The total resultant force from libForces is used in the libAcoustics. This is the equivalent of a point source. In the OF Curle acoustic pressure is calculated using the sum of forces from a unit area (dS) of the solid body. Therefore, the distance to observer changed for each single point, because the cylinder has a non-zero radius. This fact significantly changes the result of the acoustic pressure at small distances to the observer (see N.Curle 1955 https://doi.org/10.1098/rspa.1955.0191 ), but if the distance increases, the results should be the same. Please check results for different observers, e.g N3.
2. In the OF Curle analogy the retarted time is not taken into account.

Regards, AE

[windseacn]

Thanks for your explanation.

[windseacn]

Hello, I reopen this issue for the second question.

My question is that the results from OF Curle Analogy is of opposite sign of that from FWH Analogy, if this is due to the neglect of retarted time in OF Curle, there should be a time shift between these two results. From the above figure it is clear that this is not the case.

Furthermore, the results for observer1 with OF Curle is always positive, while the results from FWH is negative. It seems that these two implementations are not consistent.

[windseacn]

As a short summary, the results from OF Curle Analogy and libAcoustics Curle Analogy are similar, while the results from libAcoustics FWH are of opposite sign of those from Curle Analogy.

I check the libAcoustics implementation of Curle Analogy, and find that the forces from OpenFOAM are used, which I think is the forces by the fluid on the solid body. From Curle (1955), it seems that the force used by Curle Analogy should be that exerted upon the fluid by the solid, which is opposite of forceEff(). I guess this is the reason for the inconsistent results discussed above. If this is the case, the Curle Analogy implementations from OF and libAcoustics should be modified.

[unicfdlab]

Actually, I think that there is no need in modification of Curle analogy implementation.

1. When we analyze acoustics we work with spectrum of pressure, not with time histories. Therefore, sign and temporal shift are of less interest than amplitude and frequency.
2. Current implementation of Curle analogy pursues educational purposes and it is correct under these assumptions.
3. FWH analogy applied to solid impermeable body reduces to Curle.