Experimental Investigation into Modulated Aeroacoustic Cabin Noise arising from Unsteady Flow Conditions

The unsteady wind conditions experienced by a vehicle whilst driving on the road are different to those typically experienced in the steady-flow wind tunnel development environment, due to turbulence in the natural wind, moving through the unsteady wakes of other road vehicles and travelling through the stationary wakes generated by roadside obstacles. This paper presents an experimental approach using a large SUV-shaped vehicle to assess the effect of unsteady wind on the modulated noise performance, commonly used to evaluate unsteady wind noise characteristics. The contribution from different geometric modifications were also assessed. The approach is extended to assess the pressure distribution on the front side glass of the vehicle, caused by the aerodynamic interactions of the turbulent inflow in straight and yawed positions, to provide insight into the noise generation mechanisms and differences in behaviour between the two environments. The vehicle response to unsteady wind conditions was assessed using two approaches: a dynamic upstream unsteady flow the using active side wind generator of the FKFS wind tunnel and through quasi-steady measurement at a series of fixed yaw angles. The study examines the characteristics of modulated wind noise with respect to its frequency and amplitude modulation across different vehicle configurations. Pressure distribution analyses revealed a correlation between increased unsteadiness in the upstream flow, and the distribution of modulated, blustery noise perceived in cabin which varied with geometric modifications. The insights obtained can be used to understand modulation noise characteristics better and make design decisions during the vehicle development process.