What is the major difference in the flow fields when a car i

What is the major difference in the flow fields when a car is road tested and when it is placed in an unmodified wind tunnel? (assume that the relative velocity btw the car and the flow is the same for both cases)

Solution

The wind tunnel to road comparison is reasonable at low yaw angles, but the wind tunnel becomes progressively more optimistic with yaw.
The on road turbulence is the main reason behind the lack of correlation.
The wind tunnel only consistently over predicts the drag savings at higher yaw angles.
Higher yaw angles can only be generated when there is a significant ambient wind.

The wind tunnel has been designed mainly for vehicle aerodynamics.

The road and tunnel flow field measurements enabled new insights into the low-level flow field which is considered to be an important “driver” for the spray generated by cars on wet roads.