Aeroacoustic study of Internal Mixing Nozzles with Forced Lobed Mixers using a High-Mach Subsonic Lattice Boltzmann Scheme

Abstract

Numerical simulation of the transient compressible flow through lobed mixers inside turbofan engine nozzles was performed. A novel entropic Lattice Boltzmann (LB) scheme was used for the computational studies. The very large eddy simulation scheme (LBM-VLES) was used to capture sub-grid scale flow structures. The sound generation process was investigated using the porous Ffwocs William-Hawkings (FW-H) surface integral method. A contoured dual-stream nozzle with a standard 12-lobed mixer (12CL) was selected as a test case to validate the LBM simulation. A detailed model of the mixer and the nozzle was concurrently created to simulate both the internal flow through the mixer and the external jet plume. All operating boundary conditions were imposed based on available measured data for the same mixer geometry. The transient and mean flow characteristics of the flow field were obtained both inside the nozzle and within the jet plume. The transient behavior of the streamwise vortices at the nozzle exit was visualized and quantified. The Reynolds number based on nozzle exit diameter was 2.02×10 6 and the acoustic Mach number reached 0.94. Both near field and far field results and trends were in good agreement with experimental data. Specifically the predicted averaged velocity field was within the range of measure values. The overall radiated sound pressure was within 2-3dB of measured sound at all directional angles.Nomenclature c i = particle velocity f = particle distribution function f i eq = equilibrium distribution function D J = jet diameter M = Mach number (M=U /a) P = pressure P a = ambient pressure Re D = jet Reynolds number (Re D = U j D j / υ j ) T = temperature T a = ambient temperature t = time * Corresponding Author, Research assistant -AIAA member, Email: kaveh.habibi@mail.mcgill.ca. † Professor, Senior AIAA member ‡ Technical director, AIAA member § Senior physics validation Engineer, AIAA member Downloaded by ROKETSAN MISSLES INC. on February 8, 2015 | http://arc.aiaa.org |

Hermite regularization of the lattice Boltzmann method for open source computational aeroacoustics

“…Interesting result have been obtained also for subsonic jet noise computations. 17,18,19 Lew et al 18,19 successfully simulate the noise generated for low and high subsonic jet including the nozzle geometry in the computational domain. The LBM turns out to be computationally more efficient with respect to the traditional NS-LES for low Mach number flow.…”