An experimental investigation was completed to determine the acoustic benefits of three Internal Exhaust Gas Mixers (IEGMs). The IEGMs had 12-lobes, 20-lobes and 24-lobes. Data presented is for ideally expanded jet velocities of approximately 1330 ft/sec (jet Mach number = 1.0) and for flight Mach numbers from 0.20 to 0.27. Acoustic data, LDV (Laser Doppler Velocimetry) data and Schlieren images indicate the existence of a core and fan mixing region located within approximately 1.5 nozzle diameters downstream of the nozzle exit. This 'residual mixing' region exists because of incomplete mixing within the nozzle. The Effective Perceived Noise Level (EPNL), and indicator of the perceived noisiness of an aircraft, is sensitive to the residual mixing frequencies. The residual mixing noise levels at these frequencies are several decibels above the simple jet noise and the IEGM's internal noise levels. Consequently, improvements to the IEGMs are needed to increase EPNL reductions. The improvements should be directed toward eliminating the residual mixing by completely mixing the core and fan streams within the nozzle. Once the residual mixing is eliminated, the next noise floor may be the internal noise that acoustically lined exhaust nozzle may help reduce.
Core and fan streams' mixing noise outside the nozzle for subsonic jet engines with internal mixers
Kern- und Gebläseströmungs-Mischgeräusch außerhalb der Schubdüse für Unterschallstrahltriebwerke mit internen Abgasmischern
1996
14 Seiten, 7 Bilder, 1 Tabelle, 14 Quellen
Aufsatz (Konferenz)
Englisch