Christoph Reichl

Application of Numerical and Experimental Techniques for the Aero-Acoustic Characterisation of a Car Rear-View Mirror

Numerical as well as experimental approaches are used to capture aero-acoustic characteristics of a car rear-view mirror. The numerical study splits up into several parts. Using an actual production mirror, particular emphasis must be put on the geometry preparation and mesh generation. Initially, a CFD simulation of the entire car aerodynamics is performed to extract the proper flow boundary conditions for the aero-acoustic simulation of a smaller section surrounding the mirror. Pressure fluctuations on the surfaces extracted during an LES generate the data base required for the aeroacoustic post-processing. The acoustic pressure at several monitoring points is then calculated using Lighthills Acoustic Analogy. To include refraction effects of the nearby surfaces a direct BEM approach is also employed. Utilizing the PIV method, local areas of increased turbulence are identified experimentally. Microphone measurements with and without the exterior mirror are performed.

On the correlation of the acoustic signal of microphones mounted on a flat plate to the turbulence of an impinging jet

An axial symmetric fan driven by a brushless actuator with variable frequency is used to generate a turbulent circular jet leading to typical core‐velocities of around 10 m/s (Re = 99000). The jet impinges on a flat plate. Turbulence is generated using different sets of turbulence generators in the pipe consisting of meshes, rods, cubes and spikes. The turbulent flow field downstream of the pipe outlet is measured using two‐axis hot wire anemometry with a temporal resolution of a minimum of 48 kHz. The CTA probe is positioned using an automated three‐axis traversing system. 12 Microphones are mounted on a flat plate and are used to capture the wall pressure fluctuations. CFD calculations are performed for the different turbulence generators and are compared to the acoustic and CTA signals. An important aspect of the work is the simultaneous recording of both the CTA‐ and the acoustic signals in the experimental and numerical approach. This allows for the calculation of correlation patterns between turbule...