Acoustic Simulation of Hot Coaxial Jets Using Cold Helium-air Mixture Jets

This work examines the ability of small-scale, helium-air-mixture, coaxial jets to capture the acoustics of large-scale hot jets representing the exhaust of separate-flow turbofan engines. Experiments at University of California, Irvine (UCI) employed a one-eighth-scale model of a separate-flow nozzle being used at the Nozzle Acoustic Test Rig (NATR) of NASA Glenn Research Center. Comparisons were conducted for two set points using the following methods: matching velocity and density, and matching velocity and Mach number. For both methods, the UCI data compare very well with the NATR data in all measures of noise: spectral shapes, spectral levels, and overall sound pressure levels. The method of matching velocity and Mach number gives slightly better agreement in the spectral shapes at angles close to the jet axis, and in the overall sound pressure levels. The overall agreement between the UCI and NATR data is within one decibel.