Effects of heaving and pitching motions on underside aerodynamics of a sedan vehicle

Unsteady pressure distributions around a simplified sedan automobile model were investigated by conducting dynamic wind-tunnel testing using the newly developed forced oscillating apparatus, HEXA-X3, which can produce 6-degrees-of-freedom motion. The effects of heaving and pitching oscillation were investigated as the model simulated a vehicle running on a flat road at approximately 40 m/s and 1 Hz oscillation. The effects of the ground plate on unsteady pressure distributions over the model surfaces were measured while simulating heaving and pitching motion at Strouhal-number conditions similar to those for actual vehicles. The influence of the tubing on the frequency response of the pressure sensor was evaluated to be negligible by conducting a calibration experiment first. In the static case, the overall pressure distribution was consistent with that for a typical sedan, and the influence of the local relative flow velocity changes due to the contraction effect was observed in the underside of the model. In the forced oscillation tests, the effect of heaving and pitching motions on the flow around the underside was investigated. Effects of oscillation parameters, specifically amplitude and frequency, were investigated using the gain and phase-lag normalized by data from the steady model. Results of the test indicate that there is a characteristic distribution in pressure fluctuation, and the phenomena that become dominant in the flow around the underside vary according to location. The dynamic heaving motion was shown to change the pressure distribution, possibly due to changes in the effective angle of attack in addition to the static effect. The pitching test showed that a dynamic camber effect works in addition to those effects.