Problem 4 [Marks 2.0]

The aerodynamic drag of a new sports car is to be

predicted at a speed of 100 km/h at an air temperature of

25°C. Automotive engineers build a 1:2 scale model of the

car to test in a wind tunnel. The temperature of the wind

tunnel air is also 25°C. The drag force is measured with a

drag balance, and the moving belt is used to simulate the

moving ground (from the car's frame of reference). The

aerodynamic drag on the model in the wind tunnel is

measured to be 200 N. Determine:

Wind tunnel test section

Moving belt

Drag balance

FD.m

1) How fast (in km/h) the engineers should run the wind tunnel to achieve similarity

between the model and the prototype.

2) The aerodynamic drag force (in N) on the prototype car if the drag force on the model

is measured to be 200 N when the wind tunnel is operated at the speed that ensures

similarity with the prototype car.