Towards Forced Eddy Simulation of Airframe Induced Noise Radiation from Coherent Hydrodynamic Structures of Jet Flow

Abstract

The application of Forced Eddy Simulation (FES) is studied in the context of Direct Noise Computation of jet installation noise from nozzle-wing configurations with small relative distance between jet axis and wing trailing edge of the order of the nozzle diameter. Direct noise computations are performed solving the Navier-Stokes equations in perturbation form over a given background RANS flow to realize a zonal RANS/LES simulation approach in the Non-Linear Disturbance Equation (NLDE) framework. The direct noise computation is tackled with a modified version of the full compressible Navier-Stokes equations suitable for moderately compressible flow problems as often present in Computational Aeroacoustics. The formulation enables a formulation of the viscous stress and subfilter contributions in terms of a vector force model that supports an efficient computational treatment. The presented FES method carries on with the development of a stochastic backscatter model for technical applications. The subfilter forcing model provides a combination of dissipation and forcing that yields an additional driving mechanism of the turbulent energy cascade–otherwise not present in purely dissipative models – which enables a rapid onset of fluctuations in the simulation without gray areas. First, simulations of two isolated single stream jets in static condition with nozzle exit Mach number 0.6 and 0.9 are performed to verify the simulation method for the simpler test case of an isolated jet. A second configuration concerns an installed Ultra High Bypass Ratio (UHBR) nozzle below a wing with deployed flap in forward flight at approach condition with a flap deflection of 25°. The simulation considers the entire wind tunnel setup of a related experiment conducted in the Acoustic Windtunnel Braunschweig (AWB).