On Various Aspects of the Unsteady Aerodynamic Effects on Cars Under Crosswind Conditions 2007-01-1548
Currently, the aerodynamic development of a car concentrates on steady state aerodynamic forces. Development is mainly performed in wind tunnels with very low turbulence. On the road we find other boundary conditions. Natural wind, other cars and trucks influence the yawing moment and the side force. During acceleration and deceleration the vehicle speed is not constant, the effect of unsteady aerodynamic forces is especially important and can not be neglected.
The approach to measure unsteady effects is to use a wind tunnel that has the capability to produce unsteady flow and in addition to instrument a car to drive under natural windy conditions.
The wind tunnel, with its reproducible conditions, allows measurements to be made with well defined frequencies of the approaching flow. This is important since the aerodynamic forces are not sensitive to all frequencies in the same way. One way to increase driving comfort is to reduce these forces at specific frequencies.
In addition a car is instrumented to acquire information about the resultant velocity, yaw angle, yawing moment and side force for different natural wind conditions. The topology of typical natural gusts can be analyzed and correlation between the aerodynamic forces and the yaw angle can be found.