The yaw angle is the difference in direction between the direction of movement and the direction in which the car is pointing. A few similar topics that may go hand in hand with this study are the roll and pitch angles of the vehicle. The yaw angle is about the rotation in the z-axis (vertical axis), the roll angle is about the rotation in the x-axis (through front of the car and out the tailgate), and the pitch angle is along the y-axis (from the right car doors to the left car doors). All axis pass through the centre of mass of the vehicle.
Yaw specifically comes into play when cornering or when cross-winds are introduced. The greater the yaw angle is the sharper the car turns.
One purpose of this study is to figure out the optimal yaw angle that will generate the most speed while our vehicle is cornering. The second purpose is to research and decide on an optimal aero-body of the car to achieve our goal of increasing speed.
An experiment conducted on a vehicle aerobody was done in a wind tunnel testing out different pitch angles. The yaw and pitch angles being defined as the direction of the wind relative to the direction that the front of the car was pointing. The way that they tested it was by keeping a consistent yaw angle of 60 degrees when testing out pitch. The took a pressure reading for each aerobody model (10, 20, 30 degree pitch respectively) and were able to come up with a Reynolds number for each model. A Reynold’s number being defined as:
They then plotted the Reynolds number against the coefficient of drag for each model. Shown here:
This shows that a 30 degree pitch angle produces the least amount of coefficient of drag. Therefore a 30 degree angle would be optimal.
A similar experiment was done to get an optimal yaw angle. This time the pitch was kept consistent and the yaw angles of 50, 60 and 70 degree models were experimented on. Using the same definition of Reynold’s number a similar graph was produced:
This shows that a 50 degree yaw angle may be optimal when attempting to reduce drag.
Sources:
Basic overview - https://www.youtube.com/watch?v=1GEQwWGUEBI