The drag on a 2-m-diameter satellite dish due to an 81-km/hr wind is to be determined through a wind tunnel test using a geometrically similar 0.4-m-diameter model dish. Assume standard air for both model and prototype. (a) At what air speed should the model test be run

The correct answer is - 405 km/hr

Explanation:

given:

2-m - = diameter satellite dish

81-km/hr = Y

0.4-m - = diameter model dish.

Reynolds number is essential for this, thus,

Vm Dm/vm = VD/v

(D is the diameter of the dish)

Vm = (vm/v) (D/Dm) Y

and if vm/v = 1, then

Vm = (2/0.4) (81)

= 405 km/hr

Thus, the correct answer is - 405 km/hr