Comparison of near‐field military jet aircraft noise with similarity spectra.

Abstract

The jet mixing noise from high‐performance military aircraft is broadband and, like other jets, appears to have two origins: the fine‐scale turbulent structures (FSSs) close to the nozzle and the large‐scale turbulent structures (LSSs) farther down the plume. The intense LSS noise dominates the radiation at inlet angles greater than 125 deg, and the more omnidirectional FSS noise is the dominant source of noise to the side and aft of the aircraft. An extensive set of measurements was taken of F‐22 Raptor noise at different engine conditions in 2009. The F‐22 noise is compared to the self‐similarity spectra generally applied to describe the contributions of the LSS and FSS in jet noise [Tam and Zaman, AIAA J. 38, 592–599 (2000)]. For large inlet angles, the shapes of the noise spectra fit the LSS self‐similarity spectra at low frequencies, but the self‐similarity spectra roll off more steeply for frequencies above 1 kHz with the engine at military power and afterburner. Closer to the sideline, the FSS self‐similarity spectra do not match the shape of the data spectra very well at high engine power. Possible reasons for these discrepancies are investigated. [Work sponsored by the Air Force Research Laboratory.]