Experiments on Exhaust Noise of Tightly Integrated Propulsion Systems

Abstract

A wide-ranging series of tests have been completed that seek to map the effects of installation, including jet by jet interaction effects, on exhaust noise from various nozzles in forward flight. The primary data was far-field acoustic spectral directivity. The goals of the test series were (i) to generate enough data for empirical models of the different effects, and (ii) to provide data for advanced computational noise predictions methods applied to simplified yet realistic configurations. Data is presented that demonstrate several checks on data quality and that provide an overview of trends observed to date. Among the findings presented here: (i) Data was repeatable between jet rigs for single nozzles with and without surfaces to within ±0.5dB. (ii) The presence of a second jet caused a strong reduction of the summed noise in the plane of the two plumes and an increase over the expected source doubling in most other azimuthal planes. (iii) The impact of the second jet was reduced when the jets were unheated. (iv) The impact of adding a second isolated rectangular jet was relatively independent of the nozzle aspect ratio up to aspect ratio 8:1. (v) Forward flight had similar impact on a high aspect ratio (8:1) jet as on an axisymmetric jet, except at the peak noise angle where the impact was less. (vi) The effect of adding a second round jet to a tightly integrated nozzle where the nozzle lip was less than a diameter from the surface was very dependent upon the length of the surface downstream of the nozzle. (vii) When the nozzles were rectangular and tightly integrated with the airframe surface the impact of a second jet was very dependent upon how close together the two jets were. This paper serves as an overview of the test; other papers presented in the same conference will give more detailed analysis of the results.

Subsonic Round and Rectangular Twin Jet Flow Effects

“…For round and 2:1 and 8:1 rectangular twin jets at their closest spacings, turbulence levels between the two jets decreased about 10% due to enhanced jet mixing at near static conditions. This decrease in TKE corresponds with a decrease in SPL shown in acoustic measurements 1,2,3,4 . When M f is increased to 0.25, the flow around the twin jet model creates a velocity deficit between the two nozzles.…”

“…In addition to far-field acoustic measurements, phased array and mean flow field measurements were obtained 2 . Recently, another series of experiments were performed at NASA Glenn Research Center to include more nearby surface variation as well as the effect of twin rectangular nozzles 3 . This set of experiments included far-field acoustic measurements 4 and Particle Image Velocimetry (PIV) measurements.…”

Effect of de-correlating turbulence on the low frequency decay of jet-surface interaction noise in sub-sonic unheated air jets using a CFD-based approach

“…In this section we show results from three--dimensional SolidWorks® Flow Simulations [36]& [37] of jet flows with acoustic Mach numbers, Ma = (0.5,0.7,0.9) through rectangular jet nozzles of aspect ratios, AR = (2,4,8) in the vincity of a flat plate trailing edge. The SolidWorks® Flow Simulation automatic gridding program provides a way to mesh and solve the flow field around complex geometries and is, therefore, rather convenient for the jet surface interaction problem and was used by Bridges & Wernet [70], amoung others.…”

“…( y 2 ;ω ,k 3 ) = A(( y 2 − y d )2 ;ω ,k3 ) + ( y 2 − y d )B(( y 2 − y d ) 2 ;ω ,k 3 ) (A.22)where the spanwise--temporal Fourier transform isΩ ( y 2 ;ω ,k 3 ) ≡ 1 (2π ) 2 lim T →∞ e iω ( z− y 3 k 3 ω ) −T T ∫ ! ω c (z, y T ) dz −∞ ∞ ∫dy3 , (A.23) and where B = O( y d −1 ) in order that (A.22) remain dimensionless.…”

An experimental investigation of resonant interaction of a rectangular jet with a flat plate

“…Thus, while detailed experiments on jet-surface interaction simulating realistic flight situations were conducted in the AAPL (Bridges, Brown & Bozak 2014;Brown & Wernet 2014), the resonance phenomenon was pursued further in the smaller facility. The latter study involved the simple geometry of a rectangular flat plate of large width placed on one side of the jet.…”