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Aerodynamics

3. A truck has a drag coefficient based on frontal area of Cp = 0.86. The truck has a mass of 12,750 kg anda frontal area of 10.5 m2. If the truck is traveling at constant speed on a level road, the forces retarding itsforward progress are the drag and the rolling friction. The force due to rolling friction can be written as

where V is the truck speed in m/s, Vo = 30 m/s and fr (the coefficient of rolling resistance) is approximately0.008 for a truck on concrete or asphalt. Plot the total power the engine must supply as a function of trucks peed, V. Comment on the relative importance of drag and rolling friction in the fuel consumption of the truck.

F_{\mathrm{rf}}=W f_{r}\left(1+\frac{V}{V_{0}}\right)

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Aerodynamics

2. A sign is exposed to a 15 m/s wind on a standard day. Estimate the drag on the sign if

(a) the sign is aligned lengthwise to the wind.

(b) the sign is crosswise to the wind.

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Aerodynamics

1. Suppose you purchase a 4x8 piece of plywood from Home Depot. You don't have a pickup truck (nor does your friend), but you do have a roof rack with cross bars on your car. So you will have to secure the plywood to the roof rack in order to get it home. Your friend (the one who does not have a pickup truck) suggests-that you tie the plywood on sideways (so that the short edge is front to back) and drive at about 13 mph.Use standard sea-level conditions p= 0.002369 slugs/ft3 and µ = 3.7372 x 10-7 slugs/ft-s.

(a) Estimate the drag on the plywood for the case suggested by your friend.

(b) Estimate the drag on the plywood if you turn the sheet so that the long edge is front to back.

(c) Explain why your friend suggested the sideways configuration.

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Aerodynamics

a) Develop a relation between local static pressure P and freestream static pressure P.. Assume the stagnation pressure remains unchanged (i.e.,isentropic flow).

b) Write the local pressure coefficient C, in terms of free stream Mach number M, and the ratio P/P .

c) Combining your results from a) and b), write an expression for the local pressure coefficient C, in terms of local and free stream Mach numbers.

d) If the peak C, in incompressible flow is -0.43, estimate the critical Mach number. Hint: place all terms on one side of the equation and use a trial and error approach.

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Aerodynamics

A small wind turbine has three rotor blades, each comprised of a NACA 0009airfoil section with a constant chord of 0.5 m and zero twist. The blades are 4mlong, rotate at 20 RPM, and are pitched 8 above the disk plane. Freestream conditions are p, =1.2kg/m² , P. = 100kPa , and U, =1.0m/sec.

a) Using the blade element method and 2 elements, estimate the power coefficient of the turbine. For the section coefficients, let C, = 2ra ,C, =0.005+0.004C’.

b) Is your result consistent with the Betz limit? Why or why not?

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Aerodynamics

The NP-2000 propeller is an 8 blade design used on the C-130 and E-2 aircraft,which has a radius of 2 m. Assume sea level conditions (p=1.2kg/m ) and a stationary aircraft such that velocity far upstream is zero. Assume actuator disk theory.

a) Consider the blades rotating at 2000 RPM. If the velocity far downstream ofthe propeller is measured to be 40m/sec, find the resulting thrust coefficient.

b) For the same RPM, the collective is now changed so that C, = 0.006 . What is the percent change in the velocity far downstream?

c) What is the distribution of thrust on the disk? Explain your answer.

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Aerodynamics

Describe how finite difference and finite volume methods for solving transport equations are formulated. What are the relative advantages and disadvantages of these approaches versus influence coefficient methods?

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Aerodynamics

Discuss the factors that contribute to drag divergence as Mach 1 is approached from subsonic speeds. Describe the two discoveries that helped alleviate this problem in transonic aircraft design.

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Aerodynamics

s)Explain, in terms of the geometric changes that occur, why a flap deflection alters the lift produced by an airfoil, positive or negative. Expand on this discussion fora multi-element airfoil with a deployed flap and slat, in terms of how the geometric changes augment the lift produced for a 3D wing.

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