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The role of acoustic cavity modes in vehicle NVH (noise, vibration and harshness) development is well established in the automotive industry today. Prior knowledge of these modes can help prevent potential issues later in the development cycle, as well as aid in root cause analysis of vibro-acoustic issues. OEMs utilize them as part of their overall modal alignment strategy and cascade them to major system and sub-system suppliers for robust NVH designs. Today, acoustic cavity modes can be obtained rather easily using CAE (computer aided engineering) methods early in the development cycle. However, unlike acoustic modal testing, the CAE normal mode solution cannot scale the relative amplitudes of the modes. The sheer number of acoustic modal frequencies to be avoided can be a serious deterrent during the early design phase. This paper proposes an alternate approach for acoustic modal analyses using CAE to scale the relative amplitudes of cavity modes.

A high performance rigid airfoil profile sunroof wind deflector has been developed for high speed freeway driving with the sunroof open. This deflector is clearly superior to the conventional bar type deflector and less expensive compared to tall flexible fabric mesh deflectors applied on high end vehicles today. It provides superior speech intelligibility under high speed driving with sunroof open. The criterion for designing this deflector was to get the highest airspeed possible to span the sunroof opening under all conditions. The customized shape also utilizes flow unsteadiness, including those at the onset of buffeting, in order to condition the shear layer. The airfoil profiled deflector yielded superior mid and high frequency acoustic performance with acceptable low frequency performance. A shorter airfoil deflector was sufficient to keep the external airflow from entering the forward tilted sunroof opening on a mid-size SUV under test.