TY - GEN

T1 - The robustness of acoustic analogies

AU - Freund, Jonathan B.

AU - Samanta, Arnab

AU - Wei, Mingjun

AU - Lele, Sanjiva K.

PY - 2005

Y1 - 2005

N2 - Acoustic analogies for the prediction of flow noise are exact rearrangements of the flow equations N(q→) = 0 into a nominal sound source S(q→) and sound propagation operator ℒ such that ℒq→ = S(q→). In practice, the sound source is typically modeled and the propagation operator inverted to make predictions. Since the rearrangement is exact, any sufficiently accurate model of the source and inversion of ℒ will yield the correct sound, so other factors must determine the merits of any particular fonnulation. Using data from a two-dimensional mixing layer direct numerical simulation (DNS), we evaluate the robustness of four analogy formulations to different errors intentionally introduced into the source. The motivation is that since S can not be perfectly modeled, analogies that are less sensitive to errors in S are preferable. Our assessment is made within the framework of Goldstein's generalized acoustic analogy, in which different choices of base flow used in constructing ℒ give different consistent sources S and thus different analogies. We evaluate a uniform base flow (Lighthill-like) formulation, a globally parallel base-flow (Lilley-like) formulation, a spreading mean-flow base-flow formulation, and a locally parallel approximation of this spreading mean-flow formulation, which is not a formally exact consequence of the flow equations. The Lighthill-like formulation is found to be considerably less robust to source errors than the others, which all perform about equally well.

AB - Acoustic analogies for the prediction of flow noise are exact rearrangements of the flow equations N(q→) = 0 into a nominal sound source S(q→) and sound propagation operator ℒ such that ℒq→ = S(q→). In practice, the sound source is typically modeled and the propagation operator inverted to make predictions. Since the rearrangement is exact, any sufficiently accurate model of the source and inversion of ℒ will yield the correct sound, so other factors must determine the merits of any particular fonnulation. Using data from a two-dimensional mixing layer direct numerical simulation (DNS), we evaluate the robustness of four analogy formulations to different errors intentionally introduced into the source. The motivation is that since S can not be perfectly modeled, analogies that are less sensitive to errors in S are preferable. Our assessment is made within the framework of Goldstein's generalized acoustic analogy, in which different choices of base flow used in constructing ℒ give different consistent sources S and thus different analogies. We evaluate a uniform base flow (Lighthill-like) formulation, a globally parallel base-flow (Lilley-like) formulation, a spreading mean-flow base-flow formulation, and a locally parallel approximation of this spreading mean-flow formulation, which is not a formally exact consequence of the flow equations. The Lighthill-like formulation is found to be considerably less robust to source errors than the others, which all perform about equally well.

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U2 - 10.2514/6.2005-2940

DO - 10.2514/6.2005-2940

M3 - Conference contribution

AN - SCOPUS:29244470537

SN - 1563477300

SN - 9781563477300

T3 - Collection of Technical Papers - 11th AIAA/CEAS Aeroacoustics Conference

SP - 1775

EP - 1782

BT - Collection of Technical Papers - 11th AIAA/CEAS Aeroacoustics Conference

PB - American Institute of Aeronautics and Astronautics Inc.

T2 - Collection of Technical Papers - 11th AIAA/CEAS Aeroacoustics Conference

Y2 - 23 March 2005 through 25 March 2005

ER -