midterm exam 1 fall 2017 v4 - weeklyjoys | me practice … · 2017-12-22 · midterm exam 1...
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AAE 333, Fall 2017
Midterm Exam 1 INSTRUCTIONS:
DO NOT OPEN THIS TEST UNTIL TOLD TO DO SO. THIS TEST IS CLOSED BOOK AND CLOSED NOTES. You may use a one‐sheet double‐sided handwritten original formula sheet.
Not a photocopy, computer‐generated, or computer‐printed formula sheet.
You must show your work to receive credit (except for problem 3(e)). Non‐graphing, non‐internet calculator permitted.
In 1976, U.S. Air Force SR‐71 Blackbird flew from New York to London in less than two hours, reaching speeds exceeding Mach 3 and setting world records that have held up for nearly four decades. But those world records may not stay unbroken for long. That’s because today, at the birthplace of the Blackbird –
Lockheed Martin’s Skunk Works – engineers are developing a hypersonic aircraft that will go twice the speed of the SR‐71. It’s called the SR‐72. The SR‐71 was developed using 20th century technology. It was envisioned with slide rules and paper. It wasn’t managed by millions of lines of software code. And it wasn’t powered by computer chips. All that changes with the SR‐72. Envisioned as an unmanned aircraft, the SR‐72 would fly at speeds up to Mach 6, or six times the speed of sound. At this speed, the aircraft would be so fast, an adversary would have no time to react or hide.
http://www.lockheedmartin.com/us/news/features/2015/sr-72.html
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1. [30 points] In a high‐speed wind tunnel, air in the test section has the following conditions: M∞=4,
p=667.5 Pa, ρ=0.0339 kg/m3, T=68.6 K, a =166 m/s, and =0.4625×10‐5 kg/(ms). Assume that the
largest model that will fit in the test section is 15 cm long. You want to simulate in the wind tunnel an
object flying at Mach 4 at an altitude of 30 km where the air properties are: p=1171.8 Pa, ρ=0.01801
kg/m3, T=226.65 K, a =301.8 m/s, and =1.48835×10‐5 kg/(ms).
a) [10 points] How long can the full scale object be if you maintain dynamic similarity?
b) [10 points] If the drag measured on the model is D=10 N, what will the drag be on the full scale object
(assuming it is the maximum size you computed in part (a))?
c) [10 points] If the full scale object is 3 m long, how much longer would the wind tunnel test section
need to be (assuming the same flow conditions) to have dynamic similarity?
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2. [30 points]
At the city's wastewater treatment plant, water is put into large outdoor tanks in order to allow
particulates to settle out. The water in the tanks then forms two layers ‐‐‐ clear water on top and sludge
on the bottom. Treat the sludge layer as if it were a liquid with a density s = 3000 kg/m3. The density
of the clear water is w = 1000 kg/m3. The tank is open to the air, where the atmospheric pressure is
pa = 1.01x105 N/m2. The clear water has a depth of hw = 1 m, and that of the sludge is hs = 0.5 m.
a) [10 points] Find the pressure as a function of position in each of the two liquid layers.
b) [20 points] The tank has long straight vertical walls as shown below. Treat the problem as if it were
two‐dimensional and find the net force on the wall due to the pressure and the net moment about its
base. (These are the force and moment per unit span since this is a 2‐d problem.)
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3. [8 questions, (a) – (h), each question is worth 5 points]
a) If the pressure coefficient at a point on airfoil surface is equal to ‐0.5, and the freestream is at a pressure ∞ 100kPa, density 1 kg/m3 and velocity of 100 m/s, what is the static pressure at this point? b) The volumetric flow rate per unit area across a surface defined by the unit normal vector
√ ̂ √ ̂ 0 , caused by a velocity of √2m/s ̂ 0 ̂ 0 is:
A. ‐1 m/s
B. √2 m/s
C. 0 ̂ 0 ̂ 1 m/s D. Zero E. None of the above. c) In a pool of water, what is the rate of change of pressure, dp/dz, with respect to vertical direction, z? Note that z is chosen such that z increases in the upward direction.(The water density is 1000 kg/m3 and the acceleration due to gravity is 9.8 m/s2.)
A. ‐9.8 kgm‐2s‐2 B. ‐9.8 kgm‐3s‐2
C. ‐9.8x103 kgm‐2s‐2
D. ‐9.8x103 kgm‐3s‐2 E. None of the above
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d) Consider the vector field ̂ 2 ̂ . What can u1 be equal to if this field is divergenceless: A. 2xy+x+const B. 2x+const C. –y+2x+const D. Zero E. Answers B and C. e) Which of the following statements about Reynolds number is true (note: no justification is required): A. Reynolds number is the ratio of viscous to inertial forces B. Reynolds number is the ratio of inertial to viscous forces C. Matching the Reynolds numbers is one of the conditions for dynamic similarity between wind tunnel tests and full‐scale flight D. Both A and C E. Both B and C
f‐g) Liquid hydrogen at the temperature of 20 K ( ‐253 oC) and the density of 68 kg/m3 is supplied from
the external tank to the Space Shuttle main engine at a rate of 200 kg/s through a 17‐inch diameter
circular pipe. (Note: 1 inch = 2.54 cm.)
f) What is the volumetric flow rate of liquid hydrogen?
g) What is the average velocity of liquid hydrogen in the pipe?
(continued on next page)
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h) Find the magnitude of the gradient of the pressure field at the location (x,y) = (3,1) when the pressure
field is given by: 2( , ) 2 4 3p x y x xy
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