Noise Predictions for High Subsonic Single and Dual-Stream Jets in Flight

Abstract

This paper presents numerical jet noise predictions for single and dual-stream jets in ight. The goal of the present work is to study ight e ects in high subsonic Mach number jets. To perform the turbulent ow simulation, a parallel unsteady Reynolds-averaged Navier-Stokes (URANS)-Large Eddy Simulation (LES) solver is used. A modi ed Detached Eddy Simulation (DES) model is used to generate the turbulent ow downstream of the nozzle. A structured multi-block grid approach is used to attain a reasonable grid resolution with high order spatial discretization. Solutions of the Ffowcs Williams and Hawkings (FWH) equation are used to predict the jet noise spectra at fareld observer locations. The ow parameters and the noise prediction results are compared with PIV and microphone measurements. The computational domains have grid points ranging from 5 million to 9 million and include 14 to 26 blocks. A baseline single stream convergent nozzle and a dual-stream coaxial convergent nozzle are used for the ow and noise analysis. Calculations for the convergent nozzle are performed at a high subsonic jet Mach number of Mj = 0.9. The parallel ow constitutes the ight e ect which is simulated with a coow Mach number, Mcf varying from 0 to 0.28. The statistical properties of the turbulence and heated jet e ects (TTR = 2.7) are studied and related to the noise characteristics of the jet. Both ow and noise predictions show good agreement with the PIV and microphone measurements. The ight velocity exponent, m is calculated from the noise reduction in overall sound pressure levels and relative velocity (10Log10[Vj=(Vj Vcf )]) at all observer angles. There is a distinct variation of the ight velocity exponent with angle: it increases gradually from 3.0 at lower polar angles (relative to the inlet) 50 to 105 to about 6.0 at 110 to 150. A scaling method using the exponent is shown to provide good collapse of the spectra obtained in forward ight. The coaxial nozzle is a Boeing designed convergent nozzle with an area ratio of As=Ap = 3.0, where the primary nozzle extends beyond the secondary nozzle. This con guration is representative of the large turbofan engines in commercial service. The jet ow conditions are: Mpj = 0.9 and Msj = 0.95 with heated core ow, TTRp = 2.26 and unheated fan ow. Only one coow case with Mcf = 0.2 is used. The subscripts p and s represent the primary (core) nozzle and the secondary (fan) nozzle, respectively. The preliminary ight e ect ndings for the dual-stream jet suggest a di erent trend of ight velocity exponent as compared to single stream jet, though only limited predictions are available.