Abstract
Keywords
Aerodynamic noise, Computational Aeroacoustics, Wind tunnel testing, Stochastic reconstruction of turbulence, Flush mounted microphones.
Abstract
The availability of accurate, affordable noise prediction tools is becoming crucial for car makers to meet customers increasing demand for quieter vehicles. A new approach to flow noise prediction based on stochastic reconstruction of turbulence coupled with an acoustic solver has been investigated.
A production car, namely a FIAT Punto, was chosen for the first application, as acoustic measurements representative of real car environment could be performed. Measurements of internal and external noise (with microphones in passenger compartment and microphones mounted flush to side window) were performed in FIAT acoustically treated wind tunnel. A masking technique was used in order to highlight the contribution to the external noise of the upper shape of the car.
As LES is still prohibitive in an industrial environment for acoustic simulation of a complete car at high Reynolds numbers, an alternative approach has been tested.
The software package CFD++ was used for the simulation, to be performed in two steps: first the turbulent Reynolds stresses were calculated on a fine mesh with the use of an anisotropic cubic k-eps turbulence model, then an unsteady acoustic simulation through Lighthill integral equation or Euler equations. was performed on a much coarser and more uniform grid, using the reconstructed turbulent time histories.
Base configuration with and without external mirror were tested and simulated. The main sources were recognized to be the wake from the external mirror and the separated flow from the A-pillar. The results of acoustic simulations consisted in five seconds long pressure time histories at external microphones locations, whose autospectra were compared with experiments.
The experimental validation has shown that this tool can discriminate between different car shapes from the point of view of noise generation, and could be applied at design stage in order to improve the aeroacoustic properties of new vehicles under development.