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Journal Article

Unsteady Aerodynamic Response of a Vehicle by Natural Wind Generator of a Full-Scale Wind Tunnel

In recent years, the automotive manufacturers have been working to reduce fuel consumption in order to cut down on CO2 emissions, promoting weight reduction as one of the fuel saving countermeasures. On the other hand, this trend of weight reduction is well known to reduce vehicle stability in response to disturbances. Thus, automotive aerodynamic development is required not only to reduce aerodynamic drag, which contributes directly to lower fuel consumption, but also to develop technology for controlling unstable vehicle behavior caused by natural wind. In order to control the unstable vehicle motion changed by external contour modification, it is necessary to understand unsteady aerodynamic forces that fluctuating natural wind in real-world environments exerts on vehicles. In the past, some studies have reported the characteristics of unsteady aerodynamic forces induced by natural winds, comparing to steady aerodynamic forces obtained from conventional wind tunnel tests.
Journal Article

Identification of Vortical Structure that Drastically Worsens Aerodynamic Drag on a 2-Box Vehicle using Large-scale Simulations

It is important to reduce aerodynamic drag for reducing fuel consumption. Conventionally reduction of aerodynamic drag has been carried out by shape optimization of each part of a vehicle based on the investigations of the time-averaged flows around the vehicle. However, the general tendency of drag reduction has been saturated recently and it is required to develop a new flow-control technique to achieve further reduction in aerodynamic drag. We therefore focus on the unsteadiness of the flow around a vehicle to achieve it because the aerodynamic drag of a vehicle fluctuates over time due to repetitions of generation, growth, merging and disappearance of various sizes of vortices around it. These vortices are formed by flow separations, for which the longitudinal coherent vortices inside turbulent boundary layers on vehicle surfaces are presumably playing an important role.
Journal Article

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

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.