As we explained in earlier chapters, the air resistance to the motion of a vehicle is something important that engineers investigate. The drag force acting on a car is determined experimentally by placing the car in a wind tunnel. The air speed inside the tunnel is changed, and the drag force acting on the car is measured. For a given car, the experimental data generally is represented by a single coefficient that is called drag coefficient. It is defined by the following relationship: F, where air resistance for a car that has a listed C, = drag coefficient (unitless) measured drag force (N) drag coefficient of 0.4 and width of 190 cm and height of 145 cm. Vary the air speed in the range of 15 m/s

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Chapter8: Natural Convection
Section: Chapter Questions
Problem 8.36P
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As we explained in earlier chapters, the
air resistance to the motion of a vehicle
is something important that engineers
investigate. The drag force acting on a
car is determined experimentally by
placing the car in a wind tunnel. The air
speed inside the tunnel is changed, and
the drag force acting on the car is
measured. For a given car, the experimental
data generally is represented by a
single coefficient that is called drag
coefficient. It is defined by the following
relationship:
F,
where
air resistance for a car that has a listed
C, = drag coefficient (unitless)
measured drag force (N)
drag coefficient of 0.4 and width of 190 cm
and height of 145 cm. Vary the air speed
in the range of 15 m/s <V < 35 m/s,
and change the air density range of
1.11 kg/m³ <p <1.29 kg/m?. The given
air density range corresponds to 0° C to
45° C. You may use the ideal gas law to
the density of the air to its temperature.
Present your findings in both kilowatts and
horsepower. Discuss your findings in terms
of power consumption as a function of speed
and air temperature.
F.
p - air density (kg/m³)
V = air speed inside the wind tunnel
(m/s)
A – frontal area of the car (m2)
The frontal area A represents the frontal
projection of the car's area and could be
approximated simply by multiplying 0.85
times the width and the height of a rectangle
that outlines the front of the car. This is the
area that you see when you view the car
from a direction normal to the front grill.
The 0.85 factor is used to adjust for rounded
corners, open space below the bumper, and
so on. To give you some idea, typical drag
coefficient values for sports cars are between
0.27 to 0.38 and for sedans are between
0.34 to 0.5.
The power requirement to overcome air
resistance is computed by
P = FV
where
P = power (W)
The purpose of this problem is to see how
the power requirement changes with the car
speed and the air temperature. Determine
the power requirement to overcome the
Transcribed Image Text:As we explained in earlier chapters, the air resistance to the motion of a vehicle is something important that engineers investigate. The drag force acting on a car is determined experimentally by placing the car in a wind tunnel. The air speed inside the tunnel is changed, and the drag force acting on the car is measured. For a given car, the experimental data generally is represented by a single coefficient that is called drag coefficient. It is defined by the following relationship: F, where air resistance for a car that has a listed C, = drag coefficient (unitless) measured drag force (N) drag coefficient of 0.4 and width of 190 cm and height of 145 cm. Vary the air speed in the range of 15 m/s <V < 35 m/s, and change the air density range of 1.11 kg/m³ <p <1.29 kg/m?. The given air density range corresponds to 0° C to 45° C. You may use the ideal gas law to the density of the air to its temperature. Present your findings in both kilowatts and horsepower. Discuss your findings in terms of power consumption as a function of speed and air temperature. F. p - air density (kg/m³) V = air speed inside the wind tunnel (m/s) A – frontal area of the car (m2) The frontal area A represents the frontal projection of the car's area and could be approximated simply by multiplying 0.85 times the width and the height of a rectangle that outlines the front of the car. This is the area that you see when you view the car from a direction normal to the front grill. The 0.85 factor is used to adjust for rounded corners, open space below the bumper, and so on. To give you some idea, typical drag coefficient values for sports cars are between 0.27 to 0.38 and for sedans are between 0.34 to 0.5. The power requirement to overcome air resistance is computed by P = FV where P = power (W) The purpose of this problem is to see how the power requirement changes with the car speed and the air temperature. Determine the power requirement to overcome the
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