Aerofoil broadband and tonal noise modelling using Fast-Random-Particle-Mesh method and Large Eddy Simulation

Abstract

The aim of this work is to critically examine state-of-the art numerical methods used in computational aero-acoustics with the goal to further develop methods of choice that satisfy the industry requirements for aero-acoustic design, that is being fast, physical and potentially applicable to a variety of airframe noise problems. At the core of this thesis, two different modelling techniques are applied to benchmark aerofoil noise problems. One is based on a modern Fast Random Particle Mesh (FRPM) method with the mean flow and turbulence statistics supplied from the Reynolds-Averaged Navier-Stokes (RANS) simulation. The second technique is a Large Eddy Simulation (LES) method utilising the new in-house fast-turn-around GPU CABARET code. The novelty of the work presented herein consists in the development of new modifications to the stochastic FRPM method featuring both tonal and broadband noise sources. The technique relies on the combination of incorporated vortex-shedding resolved flow available from Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulation with the fine-scale turbulence FRPM solution generated via stochastic velocity fluctuations in the context of vortex sound theory. In contrast to the existing literature, proposed methodology encompasses a unified treatment for broadband and tonal acoustic noise sources at the source level, thus, accounting for linear source interference as well as possible non-linear source interaction effects. Results of the method’s application for two aerofoil benchmark cases, with sharp and blunt trailing edges are presented. In each case, the importance of individual linear and non-linear noise sources was investigated. Several new key features related to the unsteady implementation of the method were tested and brought into the equation. The source terms responsible for noise generation in accordance with the vortex sound theory are computed to assess the validity range of a digital filter calibration parameter used in the FRPM method for synthetic turbulence generation as compared to the same source reconstructed from the first principle LES solution. Such comparison at the source level has been achieved for the first time in the modelling literature, which allows for the physical interpretation of results obtained by the FRPM method. Finally, solutions of the FRPM method with the calibration parameter tailored in accordance with the LES are used for far-field noise predictions which are compared with experimental measurements