Bernd Crouse

Fundamental Aeroacoustic Capabilities of the Lattice-Boltzmann Method

The Lattice Boltzmann Method (LBM) was used to model four canonical problems in acoustics. The goal was to show that the LBM, which recovers the transient, compressible, and viscous Navier-Stokes equations, allows the accurate capture of time-dependent acoustic phenomena. The first case was that of a planar propagating sound wave. The dispersion of an initial Gaussian pulse in a two-dimensional domain was then investigated. Grid resolution requirement for minimizing numerical dispersion were determined for these two cases. The influence of noise and that of the numerical bulk viscosity was investigated and is discussed. The case of a driven standing-wave tube was then used to investigate the possibility of implementing sound-absorbing boundaries. Finally the case of a Helmholtz resonator was investigated. Results that are consistent with basic acoustic theory were obtained for all cases. The results illustrate the capability of the LBM to model acoustic problems accurately. Since these numerical schemes are already utilized for the modeling of external fluid flows, they are useful for the modeling of strongly coupled fluid-acoustic interactions.

Simulation of Wall Pressure Fluctuations on Simplified Automobile Shapes Using a Lattice Based Method

A comparison of experimental data and CFD simulation results of wall pressure fluctuations on simplified geometries that generate flow structures similar to an automobile are presented. The numerical results have been obtained using the commercial software PowerFLOW 3.4p4a. The simulation kernel of this software is based on the numerical scheme known as the Lattice Boltzmann Method (LBM), combined with an RNG turbulence model. This scheme accurately captures time-dependent aerodynamic behavior of high Reynolds number flows over complex geometries, together with the acoustics. The geometries considered for this study represent the green house and the side mirror of a car. Spectral analysis is performed on the simulation data and the results are compared to the experimental data. This comparison provides good correlation between the simulation and experiment, and demonstrates the capability of this numerical scheme in predicting turbulent fluctuations due to complex flow phenomena.Copyright

Numerical Simulation of Leakage Effects on Sunroof Buffeting of an Idealized Generic Vehicle

Sunroof buffeting is a flow-acoustic resonance phenomenon that causes high interior noise leading to discomfort for the passengers. In order to make a priori predictions about the tendency of a given vehicle to experience buffeting with a high degree of reliability, it is important to understand the sensitivity of this phenomenon to various noise parameters. The current investigation studies the mechanism and the effect of leakage on an SAE Type 4 body. For this, the CAA tool PowerFLOW was used and good agreement of the peak SPL over a wide range of velocities between experiment and simulation was observed for the baseline configurations and the leakage configurations. This allows the analysis and identification of the mechanism for how the artificial leakage affects the buffeting behavior. I. Introduction UNROOF and side-window buffeting in passenger vehicles results in high sound-pressure levels in the interior and can cause considerable discomfort for the passengers. It is well understood that this phenomenon is a result of an unsteady shear layer in the sunroof or window opening which induces an acoustic resonance in the passenger compartment. Pragmatic design solutions for suppressing sunroof buffeting at various wind speeds and geometric configurations are well-known. However, a complete solution to this problem without resorting to expensive design measures has not been achieved in the industry. Recent numerical investigations 9,10 on real cars exhibiting real world effects have successfully predicted the effect of a deflector on buffeting suppression in an SUV. In a validation study 9 , the efficiency of a deflector system was studied on a sedan and an SUV. It was shown conclusively that a sunroof system which works well to mitigate buffeting on one vehicle cannot be assumed to be universally effective. Ref. 16 provided a detailed review of previous experimental and numerical investigations of this problem and concluded that many open questions remained in previous experimental and numerical studies and attempted a systematic investigation of the phenomenon of buffeting in automotive applications. Experiments were carried out on an SAE Type 4 body, a geometrically simple and structurally rigid vehicle model. This removed experimental uncertainties associated with geometric details and structural and acoustic properties of real vehicles. Two different wind tunnels were used to measure the acoustic response of the body at various wind speeds, in order to address wind tunnel affects. Ref. 15 which covered only the experimental portion of the study also investigated the effect of leakage on the overall buffeting behavior at various wind speeds. The leakage was represented by a round hole of 200 mm in diameter in the rear wall of the SAE Body. This study validates the buffeting behavior of the leakage configuration using numerical predictions over the relevant range of velocities.

Experimental and Numerical Investigation of Automotive Wind Throb Phenomenon

Sunroof wind throb can generate annoyingly high sound-pressure levels (SPL) inside the vehicle cabin. In this study, several deflector configurations were installed to investigate this flow-acoustic coupled resonance phenomenon in passenger cars. In each condition, comparisons between the experimental results and numerical simulations were performed over a range of wind speeds to validate the capability of the PowerFLOW numerical simulation for wind throb prediction. Experiments were performed at the Suzuki full scale wind tunnel. One microphone in the cabin was set to record the pressure history and SPL. Flow around the sunroof was also measured by PIV. In both experiments and simulations, the following phenomena were observed. In case of strong wind throb, flow separates from the deflector and strong periodic vortices in the shear layer were observed. These vortices break down due to the impingement at the back-end of the sunroof and generate a strong peak noise in the cabin. In case of no wind throb, the periodic vortices were not observed resulting in a very weak peak with low SPL in the cabin. The deflector study shows that wind throb is a highly sensitive phenomenon where even a small geometry variation at the critical region can affect the phenomenon significantly. In this study, the same trend was obtained in the experimental results and simulations. It shows that the numerical simulation can be used for a priori predictions in the early stages of the vehicle design process.© 2011 ASME

Computational Prediction of Noise Generation and Radiation from Antennas using a Lattice Boltzmann Scheme

Noise generated from isolated automobile antennas is computationally predicted and compared to experimental data. Two different antenna configurations were considered for this study. The numerical results have been obtained using the commercial software PowerFLOW 4.0a. The simulation kernel of this software is based on the numerical scheme known as the Lattice Boltzmann Method (LBM), combined with an RNG turbulence model. This scheme accurately captures time-dependent aerodynamic behavior of high Reynolds number flows over complex geometries, together with the acoustics. A hybrid approach which couples the transient aerodynamic predictions from the LBM to the Ffowcs Williams and Hawkings analogy to predict the far-field radiated sound is applied for this study. Detailed analysis was done on the simulation results to understand the influence of the antenna shapes on the characteristics of the tones generated by them. Flow visualizations were done to demonstrate the noise generation mechanism and the sound radiation pattern. Spectral analysis is performed on the simulation data captured by a microphone which is 3 inches away from the antenna and the results are compared to the experimental data. This comparison provides good correlation between the simulation and experiment, and demonstrates the capability of this numerical scheme in predicting the aerodynamic and acoustic pressure fluctuations that result in far-field noise from extruded bluff bodies.