ES330 Section 2
Exam#2
Name:
You will have 1.5 hours to complete the exam. Please show all work and list any
assumptions you are making. You must draw a control volume, free body diagram, and
coordinate system if required by the problem to receive credit for your work.
Problem #1 (25 points)
Drafting in car racing occurs when two cars are in
close proximity to each other. The affect of this is to
reduce the drag on both cars so that allowing them
to go faster as a pair than they can individually.
In this problem the drag force F
d
on a car is a
function of the speed, V, length of the car, L,
density of the air,
ρ
, viscosity of the air,
μ
, and
distance between the cars, d
(i.e. F
d
=
f
(V, L, d,
ρ, μ).
a)
(15 points) Using the Buckingham Pi Theorem derive the nondimensional
parameters that characterize the problem. Use V, L,
ρ
as your repeating variables.
b)
(10 points) If V=200 mph and L=15 ft for the race cars in question, what speed
should a 1/10
th
scale model be tested at in air? (You must show your work and
justify your answer).
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Exam#2
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 Spring '08
 Bohl
 Fluid Dynamics, Fluid Mechanics, VE, nozzle contraction ratio

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