Experimental Investigation of Aeroacoustic Cabin Noise in Unsteady Flow by Means of a New Turbulence Generating Device 2017-01-1545

With advancement of aeroacoustic wind tunnels and CAE technology, aeroacoustic cabin noise in steady flow has been improved. On the other hand, passenger comfort is also impacted by aeroacoustic noise in unsteady flow. There have been comparatively few studies into this area, and the mechanism remains unclear. Considering the future proliferation of autonomous driving, drivers will pay more attention to cabin noise than previously, and aeroacoustic noise is expected to become more prominent. Thus, the reduction of fluctuating aeroacoustic noise is important. Most of the previous research relied on road tests, which don’t provide reproducible conditions due to changing atmospheric and traffic conditions. To solve these problems, research using devices that generate turbulence are being conducted. However, the fluctuations of flow generated in previous studies were small, failing to simulate on-road conditions sufficiently. In this report, the development of a new turbulence generating device for 1/1 scale wind tunnel is described. This device consists of dampers and airfoils at the nozzle, producing turbulence intensity up to 13%. Then the analysis of the fluctuating aeroacoustic noise generated using this device is presented. When the fluctuation frequency of the incoming flow is as high as 5Hz, aeroacoustic noise shows time delay and peak value declines in comparison to simulated cabin noise predicted by quasi-steady technique using the cabin noise and flow velocity measured in steady flow. It is also shown that the change of modulation of aeroacoustic noise due to the modification of vehicle shape could be evaluated quantitatively using this device.