'Overset-LES of Passive Methods for Trailing Edge Noise Reduction

Title: Overset-LES of Passive Methods for Trailing Edge Noise Reduction Abstract: With an ever-increasing air traffic, aircraft noise has become a pressing issue in the recent times. During the landing phase of an aircraft, airframe noise is comparable to the propulsion noise. Hence, reducing the airframe noise is imperative to reducing the overall aircraft noise. In this regard, the current study focused on noise reduction concepts in a classical trailing-edge as well as in an extended flap configuration. In the latter case, the flow was kept attached to the flap by the application of a Coanda jet. The nature inspired passive noise mitigating methods explored in the current study included porous materials and stream-wise arranged finlets. Scale resolving simulations were carried out following a multi-fidelity zonal Overset-Large Eddy Simulation approach (Overset-LES). In this approach, perturbed compressible Navier-Stokes equations were solved on a steady background flow. The effect of porous material was modelled with a volume averaged approach, resulting in a linear Darcy term and a non-linear Forchheimer term. The inflow forcing required for the zonal method was provided by the Fast Random Particle Mesh method. To obtain far-field sound pressure levels, the fluctuating Lamb vector term was averaged and used as the sound source in the Acoustic Perturbation Equations. Application of porous material to the DLRF16 trailing edge resulted in an overall 5 dB noise reduction in the far-field. The computed turbulent statistics showed good agreement with the experimental data. Breakdown of the span-wise coherence in combination with a reduction in the convection velocity of the pressure carrying eddies were found to be the noise reduction mechanisms. The sound pressure level spectrum revealed a noise reduction in the low-mid frequency range and a penalty noise in the form of a `broadband hump' in the mid-high frequency range. This effect was assumed to be related to the friction between the flow and the porous material. Furthermore, scale resolving simulation of the Coanda jet equipped flap was performed. The Overset-LES qualitatively and quantitatively corrected the background flow. The aero-acoustic source ranking revealed that the curvature noise, arising from the flow acceleration over the curvature, to be greater than the flap trailing-edge noise in all directions except for ?? ?? [180°, 280°]. Finally, Overset-LES of a NACA0012 profile treated with stream-wise finlets was carried out. Application of finlets resulted in pushing the most energetic eddies away from the wall, resulting in a weaker edge scattering phenomenon. The finlets reduced the intensity of surface pressure fluctuations in the mid-high frequency range. The observed phenomena were confirmed by numerical and experimental studies found in the literature.