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Technical Paper

Surface Pressure Fluctuations in Separated-Reattached Flows Behind Notched Spoilers

Notched spoilers may be used to suppress flow-induced cavity resonance in vehicles with open sunroofs or side windows. The notches are believed to generate streamwise vortices that break down the structure of the leading edge cross-stream vortices predominantly responsible for the cavity excitation. The objectives of the present study were to gain a better understanding of the buffeting suppression mechanisms associated with notched spoilers, and to gather data for computational model verification. To this end, experiments were performed to characterize the surface pressure field downstream of straight and notched spoilers mounted on a rigid wall to observe the effects of the notches on the static and dynamic wall pressure. Detailed flow velocity measurements were made using hot-wire anemometry. The results indicated that the presence of notches on the spoiler reduces drag, and thus tends to move the flow reattachment location closer to the spoiler.
Technical Paper

Sunroof Buffeting of a Simplified Car Model: Simulations of the Acoustic and Flow-induced Responses

Sunroof buffeting of a simplified car model was investigated experimentally and numerically in order to assess the potential of numerical methods to design sunroofs that are quiet and functional. The numerical results have been obtained using the commercially available software PowerFLOW. 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 acoustic response of resonant systems. In this work, a simplified car model with a sunroof was used for validation. A simulation methodology to determine the acoustic response of the passenger cabin was investigated and verified experimentally. The sunroof buffeting phenomenon was simulated over a range of flow conditions, and the results were found to be in good agreement with experimental data.
Technical Paper

Friction-Induced Vibrations of Window Sealing Systems

The problem of squealing from vehicle windows opened or closed in partly wet conditions has been investigated. Experiments were conducted using a glass-run seal sample and a tangentially moving glass piece installed on a test bench. The instantaneous velocity of the glass was measured along with the total dynamic frictional force for varying normal static loads and sprayed-water distributions. The characteristics of squeal vibrations and the influence of normal load and water distribution are discussed. The relation between friction force and speed was also investigated. An idealized model consisting of a one-dimensional continuous rod excited by a moving frictional point force was then investigated. The method of averaging was applied to solve the nonlinear equations of motion. The response became unstable when the magnitude of the negative slope and the normal force were large regardless of boundary conditions.
Journal Article

Effects of Notches on Surface Pressure Fluctuations Downstream of a Leading Edge Spoiler

Notched spoilers have been observed to be more effective than uniform spoilers to suppress the flow-induced cavity resonance of vehicles with open sunroofs. In this study, a few mechanisms possibly involved in buffeting suppression from notched spoilers were investigated experimentally and numerically. One objective was to investigate the spatial coherence and phase of the wall pressure fluctuations downstream of notched spoilers in comparison with the same quantities for uniform spoilers. Another objective was to gather detailed measured data to allow the verification of computer simulations of the flow over the notched spoiler. Experiments were performed to measure the velocity and wall pressure fields downstream of spoilers mounted on the rigid floor of a closed test section wind tunnel for different spoiler heights. Efforts were made to reproduce the spoiler and wind tunnel geometry and boundary conditions of the experimental set-up in the numerical simulations.
Technical Paper

Simulation of Friction-Induced Vibrations of Window Sealing Systems

In this study, friction-induced vibrations of the window sealing system of a vehicle were investigated using a detailed numerical model. A lumped element, single-degree-of-freedom model was first developed for verification of the numerical procedures. An approximate expression for the frequency of the stick-slip oscillations was obtained. The model indicated that the frequency decreased as the normal force and the difference between the static and kinetic friction coefficients were increased. Stick-slip oscillations were then simulated using a finite element model of a glass run seal using an explicit time marching method. The motion of the seal during the slipping phase was in the direction of the friction force. The peak frequency was found to vary according to the glass position on the seal surface. The results indicated that both the periods of the stick and slip phases of the seal motion affect the frequency of the stick-slip oscillations.
Technical Paper

Effects of Window Seal Mechanical Properties on Vehicle Interior Noise

One dominant “wind noise” generating mechanism in road vehicles is the interaction between turbulent flows and flexible structures which include side glass windows. In this study, the effects of seal mechanical properties on the sound generated from flow-induced vibration of side glass windows were investigated. The primary goal was to assess the influence of seal support properties on the noise generated from a plate. Two different models to calculate the optimal support stiffness of the seal that minimizes the velocity response are presented. The results show that both the velocity response and the sound radiation are strongly influenced by dissipation of vibration energy at the edges. It is demonstrate that support tuning can yield significant noise and vibration reduction.