Effects of mechanical properties of sealing systems on aerodynamic noise generation inside vehicles

Junhong Park, Purdue University

Abstract

One dominant “wind noise” generating mechanism in road vehicles is the interaction between turbulent flows and flexible structures: specifically door seals and side glass windows. In this study, the effects of seal mechanical properties on interior aerodynamic noise were investigated. The sound transmission characteristics of seals were first investigated. The vibration response together with the radiated sound power was computed using FE-analysis. Experimental data obtained for several seal specimens using reverberation room test methods was used in the validation of numerical models. The developed tools were used to compare sound transmission characteristics of seals made of EPDM and TPE. The validated numerical model was then utilized to investigate the influence of various design parameters on the sound transmission characteristics of seals. It was found that any unconstrained structural coupling between seal walls should be avoided to minimize sound transmission. The sound radiated by a seal-supported, rectangular plate excited by turbulent flows was then investigated. The primary goal was to assess the influence of support properties on the noise generated from the plate. The flow-induced vibration of the plate was calculated using the Corcos model for the surface pressure loading and an assumed-modes method. The results showed that support tuning can yield significant reduction in vibration amplitudes for a fixed excitation amplitude. Two different methods to calculate the optimal support stiffness were developed. The first model, based on a one-dimensional transverse wave assumption, yielded a good first cut approximation of the optimal properties. The second model, based on the assumed-modes method, yielded more accurate estimations. The optimal support stiffnesses calculated from the two different methods were in close agreement. Finally, experimental techniques to measure viscoelastic properties of foamed elastomers at high frequencies were developed and applied to measure mechanical properties of seal materials. The measurements were performed for foams with various void fractions, from which the relationship between the void fraction and the dynamic moduli was measured. The measurement results were compared to the predictions from several different micromechanics models. The results can be used to determine optimal seal mechanical properties that minimize the aerodynamic noise.

Degree

Ph.D.

Advisors

Siegmund, Purdue University.

Subject Area

Mechanical engineering|Automotive materials

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