Numerical analysis of an impinging jet in a turbulent flow field

Computational Fluid Dynamics (CFD) deals with the numerical analysis of flow phenomena. The Navier-Stokes equations, which govern the motion of a Newtonian viscous fluid, are the base of almost all CFD problems. The method of dealing with any fluid dynamics problem is to solve these equations for the appropriate boundary conditions. There are some software packages available that solve fluid flow problems, as for instance FLUENT that is used in this thesis. The goal of this project is the investigation of flow fields and degrees of turbulence with regard to microphones which are used in cars for the purpose of hands free speaking systems. The fact that these microphones are usually positioned near the air condition outlet flow fields leads to decrease in the quality of voice recording. Hence there is a need for a better understanding of flow fields inside of vehicle interiors for the microphone producer. For the analysis of these fluid flows different setups of turbulence generators are positioned in the test wind tunnel in order to produce turbulence, so microphones can be tested under defined turbulence flow conditions which match the flow conditions in the vehicle interior. This thesis deals with the numerical analysis of the different degrees and spectra of turbulence that are produced by different setups of turbulence generators located in the test wind tunnel. First, several steady CFD simulations are performed for each turbulence generator to investigate the characteristic of the fluid flow, and the numerically generated results for the velocity components and the turbulent kinetic energy are compared to experimental results. Unsteady CFD simulations for the quantitative analysis of the turbulent flow fields are then performed. The correlations between local velocity fluctuations and pressure fluctuations near the microphones are investigated and compared to experimental results. Among steady CFD simulations the RNG k-ε model compared best to experimental data, however steady solutions cannot always be delivered, transient DES have been performed to provide frequency spectra which show that prominent features of the spatial frequency behavior are well captured. The position of the shear layers, the separation and the combination of the turbulent regions can be observed easily. The comparison of the experimentally and numerically generated frequency spectra offer the possibility to find out where CFD simulations are effective and it shows that the simulation gives results approximately equivalent to the experimental results. For the geometry and mesh generation the software tool GAMBIT is used. All CFD simulations have been performed on a Linux cluster at the Austrian Institute of Technology. This thesis was undertaken within the 'TUNICA-Project', which is a collaboration of the Austrian Institute of Technology, an industrial partner and the Vienna University of Technology. This work was supported by the Austrian Research Promotion Agency (FFG). The experimental and numerical results of the TUNICA project have been presented at national as well as international conferences.