Dynamic pressure loads associated with twin supersonic plume resonance

Abstract

The phenomenon of twin supersonic plume resonance is defined and studied as it pertains to high-level dynamic loads in the internozzle region of aircraft like the F-15 and B-1B. Using a l/40th-scale-model twin jet nacelle with powered choked nozzles, it is found that intense internozzle dynamic pressures are associated with the phased coupling of each plume's large-scale structure. This condition is most prevalent when each plume's large-scale structure has constituent elements composed of the B-type helical instabilities. The coupling of each plume's large-scale structure forces each plume to flap spatially in a preferred direction. Suppression of these dynamic loads was accomplished by simple geometric modifications to only one plume's nozzle. These modifications disrupt the natural selection of the B-type mode and thereby decouple the plumes. NomenclatureD = jet exit diameter Dj = fully expanded jet plume diameter, Eq. (4) f s = plume resonance frequency L = average plume shock cell spacing, Eq. (5) M c = convection Mach number large scale structure M d = nozzle design Mach number MJ = fully expanded plume Mach number St = Strouhal number, Eq. (3) V c = convection velocity of large-scale structure Vj = fully expanded jet plume velocity 7= ratio of specific heats X = acoustic wavelength

Twin-jet screech suppression

“…References 6-11 represent most of the work that has been directed toward the twin-jet screech problem. It was shown by Seiner et al 6 that the twin-jet coupling process can increase the screech tone amplitude by 6 dB (a factor of 4). Full-scale ground run-up data 7 from an F-15 aircraft also show a narrowband tone near the predicted screech frequency.…”

Acoustic Noise-Source Identification in Aircraft-Based Atmospheric Temperature Measurements

“…This type of coupling has been reported in the literature 19 for aircraft such as the F-15 and B-1B where the centerline spacing between engines is two nozzle diameters or less. The centerline spacing on the GII is larger at seven nozzle diameters.…”

Acoustic characteristics of equal and unequal twin circular slot jets

“…The phase locking of screech instabilities with the twin jet also leads to higher amplitude screech tones even at lower NPRs. There is a possibility of fatigue damage to the structural parts due to these amplified screech tones and enhanced dynamic pressure in the internozzle region [5][6][7][8][9]. Some earlier work on twin jets is summarized below.…”

“…Seiner et al [5] revealed the generation of higher dynamic pressures in the inter nozzle region due to the phase coupling of flapping mode. Wlezien [6] concluded that coupling occurs at lower spacings at lower Mach numbers and at higher spacings at higher Mach numbers in twin jets from convergent nozzles.…”