Vibration Control of Body-Mounted Plastic Mirror Design

The goal of this study was to predict the unsteady forces acting on the plastic side-view mirror of a prototype vehicle traveling at a certain speed using computational fluid dynamics (CFD) techniques. These unsteady forces are flow induced because of the vortex shedding behind the mirror. It was observed during field testing that the mirror was vibrating excessively at certain speeds because of the unsteady forces. The frequency of vortex shedding depends on the geometry of the mirror and the angle of impingement of the incoming air. The initial step was to compute the steady state flow solution around the mirror. The pressure distribution on the mirror was used to compute the steady state flow forces on the mirror. In this CFD model most of geometric detail around the mirror were included which made the model very large. Unsteady solution could not be obtained because the model was very large for the available computational resources. It is important to realize that due to the unsteadiness of the flow, a steady state flow solution does not provide information on the frequency of the forces acting on the mirror. In the second phase of this study, the model was simplified so that the unsteady flow solution could be computed, therefore the instability was observed using this model. The CFD results qualitatively show the vortex shedding and the frequency of forces on the mirror. The authors are currently evaluating techniques to determine the frequency of vortex shedding on a detailed model and correlated with the available experimental data.