Abstract
A comparison of experimental wind tunnel and CFD simulation results for
wall pressure fluctuations on the side-glass (driver´s window) of a full scale production
automobile for different geometry configurations at 140 km/hr free stream air speed is
presented. The numerical results have been obtained using the commercial software
PowerFLOW 3.5c. The simulation kernel of this software is based on the numerical
scheme known as the Lattice Boltzmann Method (LBM), combined with a two-equation
RNG turbulence model. This scheme accurately captures time-dependent aerodynamic
behavior of turbulent flows over complex detailed geometries, including the pressure
fluctuations causing wind noise. Spectral analysis is performed on the simulation data for
several microphones on the side-glass and the results are compared to the experimental
data. This comparison shows good agreement between the simulation and experiment for
all microphone locations, and demonstrates the capability of this numerical scheme in
predicting turbulent fluctuations due to complex flow phenomena. Avisualization
technique is presented which allows the entire surface region of interest to be colored
with sound pressure levels (SPL) in preferred frequency bands. Using this technique, area
weighted SPL in 1/3 octave bands for the entire side-glass region on the driver side for
different geometry configurations are calculated and compared to each other. In addition
the detailed 3D transient flow structures arevisualized in several different ways. This
type of analysis and visualization helps to identify the noise producing flow structures as
a function of frequency, and to compare across different designs. Also the frequency
range for which each separated flow structure dominates can be determined.
Keywords - Wind Noise, Wall Pressure Fluctuations, Automotive Aeroacoustics,
Lattice Boltzmann Method, Computational Aeroacoustics