On-Road Investigation of a Vehicle's Longitudinal Response to Wind Gusts

The objective of this work is an attempt to investigate the longitudinal aerodynamic response of a vehicle to ambient wind. The natural wind environment is usually unsteady and causes therefore slight oscillations of the vehicle's velocity around its cruising speed. The additional force superposed to the steady drag caused by the smooth oncoming air flow is generated by ambient turbulence. For the on-road investigation of the vehicle's longitudinal response to the ambient turbulent flow field both vehicle velocity and relative airspeed in driving direction are recorded by independent data acquisition systems during a set of coastdowns. The deceleration data and the vehicle's response to the airspeed fluctuations are derived by numerical filtering techniques and differentiation of the motorcar's velocity-time history. The study results in a frequency-dependent response function.