A Method to Simulate Non-Stationary Vehicle Interior Wind Noise

As speeds and directions of the vehicle and wind change, the unsteady flow creates variations in wind noise, which can be referred to as non-stationary wind noise. To investigate people's perceptions of non-stationary wind noise, a method to simulate the non-stationary wind noise is needed. Previously, a method was developed that used stationary recordings taken at several wind speeds and directions to form functions that relate the 1/3 octave sound pressure level with wind speed and direction. These functions are used to create time-varying filters based on provided time histories of wind speed and direction. A reference wind noise measurement is then filtered to produce the sounds. To reduce the time cost of taking many stationary measurements, an improved method was investigated. At each yaw angle, one speed sweep wind tunnel measurement was used to estimate the relationship between sound pressure level and wind speed. Two partially correlated white noise signals were then filtered to simulate binaural sounds that had a similar coherence structure between the left and right ear sounds to that observed in binaural measurements in the vehicle. The accuracy of the simulations was validated by comparing wind noise simulations with wind tunnel and on-road vehicle interior noise measurements. For the on-road measurements, a noise decomposition method based on noise source measurements was used to estimate the road/tire noise, which was then added to the simulated wind noise to make it comparable with the measured on-road noise. The time-varying loudness, and power spectral densities of the simulated and measured sounds were found to be well consistent. Besides, a method to simulate the turbulent wind speed time histories, which can be used as inputs to the wind noise simulation method, was developed. The von Karman model predicts the spectra of wind turbulence by assuming it to be a stationary random process. White noise signals can then be filtered to simulate the stable variations of wind speeds. The discrete gusts, which are the transient events in wind speed time histories, were also simulated by using an 8-parameter piecewise function. Eventually, the non-stationary wind noise and the turbulent wind speed simulation method can be a powerful tool when investigating sound perceptions of vehicle interior wind noise.