1977
DOI: 10.1121/1.2016139
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Farfield multimodal acoustic radiation directivity

Abstract: Recently, approximate equations [E.J. Rice, AIAA Paper No. 777–1281 (1977)] for the farfield acoustic radiation pattern in the forward quadrant from a flanged circular duct were presented for both single and multimodal excitation. The single mode radiation equation showed that modal identification could be suppressed and that the resulting approximate equation could be expressed as a function of mode cutoff ratio only. In this paper, several exact radiation patterns for modes with similar cutoff ratios will be… Show more

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Cited by 3 publications
(2 citation statements)
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“…Approximate expressions for inlet radiation have been developed in terms of mode cutoff ratio _ 'fr1/ a mn y 1-MD where the dimensionless frequency Ti= f D/c; with the eigenvalue of the (m,n)th mode, a mn; duct diameter, D; duct Mach number, M D ; and speed of sound, c. The key simplification realized by the cutoff ratio formulation is that modes with the same C and p propagate similarly to the far field. This has been demonstrated for radiation from a flanged duct without flow (63) and is fairly accurate for principal lobe radiation (64). Two important duct mode propagation angles, ¢ x and ¢ x , are defined in (65) Here, ¢ x and q) x are the angles which the vector normal to the wave front and the group velocity vector, respectively, make with the duct axis.…”
Section: Inlet Radiationmentioning
confidence: 97%
“…Approximate expressions for inlet radiation have been developed in terms of mode cutoff ratio _ 'fr1/ a mn y 1-MD where the dimensionless frequency Ti= f D/c; with the eigenvalue of the (m,n)th mode, a mn; duct diameter, D; duct Mach number, M D ; and speed of sound, c. The key simplification realized by the cutoff ratio formulation is that modes with the same C and p propagate similarly to the far field. This has been demonstrated for radiation from a flanged duct without flow (63) and is fairly accurate for principal lobe radiation (64). Two important duct mode propagation angles, ¢ x and ¢ x , are defined in (65) Here, ¢ x and q) x are the angles which the vector normal to the wave front and the group velocity vector, respectively, make with the duct axis.…”
Section: Inlet Radiationmentioning
confidence: 97%
“…The condition for the calculations were MO w 0.6 and I . 7.111. At these conditions, it was estimated there would be 100 propagating modos.…”
Section: -Mpmentioning
confidence: 99%