Effect of Engine Installation on Jet Noise using a Hybrid LES/RANS Approach

Installation effects arising from propulsion airframe interaction are known to produce substantial variations in the in-situ jet noise. A hybrid LES/RANS computational framework is proposed for prediction of noise from the engine and airframe, and interactions between airframe and propulsion systems. The basis of LES (large eddy simulation) is that the energy-bearing turbulent eddies in the dominant noise-generating region are directly captured in the simulation. Since LES must resolve the turbulent eddies it requires a grid which captures these motions; the number of grid points needed for LES is much larger than those for RANS and thus a brute-force LES of the entire noise producing region in a propulsion-airframe interaction problem is not feasible. However, the noise generation physics of these flows allows a logical assembly of a hybrid simulation tool where low-fidelity models (RANS) in one region of the flow are combined with turbulence-resolving models (LES) in other regions of the flow. Acoustic effects are another segment of propulsion-airframe interaction problem. Sound generated by various components of engine is altered by the presence of wing, fuselage, deployed flap etc. In the present proposal, alteration of sound due to the presence of airframe is added through application of Boundary Element Method (BEM) and an acoustic projection technique (FW-H surface method). To demonstrate the feasibility of using this framework, we focus on simulating flow configuration corresponding to a separate-flow nozzle of by pass ratio 5 with round fan and nozzle operating at the takeoff cycle point of with freestream Mach number of 0.28. Simulation results will be validated against experiments carried out in the Low Speed Aeroacoustics Wind Tunnel (LSAWT) at NASA Langley's Jet Noise Laboratory (JNL). The high-fidelity model developed and validated in Phase I will be extended to explore more complex engine/airframe configurations in Phase II.