The effect of forward flight on the noise and flow field of inverted profile jets

• Published in: Journal of sound and vibration Vol. 93; no. 1; pp. 39 - 55
• Main Authors: Petersen, R.A., Sarohia, V.
• Format: Journal Article
• Language: English
• Published: Legacy CDMS Elsevier Ltd 08.03.1984; Elsevier
• Subjects: Aircraft Propulsion And Power; Exact sciences and technology; Fluid dynamics; Fundamental areas of phenomenology (including applications); Nonhomogeneous flows; Physics; Geometrical shape; Noise; Flow(fluid); Acoustic spectrum; Supersonic flight; Far field; Annular jet; Flow field; Velocity; Acoustic power
• ISSN: 0022-460X; 1095-8568
• DOI: 10.1016/0022-460X(84)90350-X

Noise and flow field measurements are reported for an inverted profile coannular jet (where the annular jet speed exceeds the center jet speed) under simulated flight conditions. The annular and center jets were cold and both were operated subsonically. Forward flight was simulated by placing the coannular jet inside a larger open jet. Acoustic measurements show the effects of inverted profile shape and simulated flight on far field directivity, total radiated power, and spectral content. Measurements of total acoustic power demonstrate that the acoustic efficiency of inverted profile jets is about 3 dB less than the efficiency of “top hat” profile jets, and that the noise decreases as the seventh power of the relative jet velocity in the limit of small flight velocity, U f . Flow measurements demonstrate that the jet spreading parameter λ = ( U j − U f )/( U j + U f ) scales the thickness of the outer shear layer and the passage frequencies of the large turbulence scales. Comparisons between the turbulence time scales and the noise spectra suggest that coherent noise sources may become more important in forward flight.