Aerodynamics - II Mid - I, September - 2014

1.Density of air has significant effects on the airplane’s capability. Which of the following statements is not true?
  • As air becomes less dense, it increases thrust because of less resistance
  • As air becomes less dense, it reduces power because the engine takes in less air
  • As air becomes less dense, it reduces lift because the thin air exerts less force on the airfoils
  • All of the above
Answer: A
2.Consider one dimensional isentropic flow at a mach number of 0.5. If area of cross section of a stream tube increases by 3% somewhere along the flow, the corresponding change in density is
  • 3
  • 2
  • 1
  • 4
Answer: C
3.Consider a flow at Mach 0.8. Find out the ratio of the kinetic and internal energies per unit mass of a fluid element moving along a stream line. Assume the fluid is a calorically perfect gas with heat capacity ratio of 1.5.
  • 0.14
  • 0.24
  • 0.64
  • 0.48
Answer: B
4.Which one of the following statements is not true for a supersonic flow?
  • Over a gradual expansion, entropy remains constant
  • Over a sharp expansion corner, entropy can increase
  • Over a gradual compression, entropy can remain constant
  • Over a sharp compression corner, entropy increases
Answer: B
5.The aerodynamic centre of a supersonic airfoil, with chord C, is located at
  • The leading edge
  • 0.25C
  • 0.5C
  • 0.75C
Answer: C
6.Consider flow over a thin aerofoil at Mach number, M∞ = 0.5 at an angle of attack α. Using the Prandtl – Glauert rule foe compressibility correction, the formula for lift coefficient CL, can be written as
  • 5.44α
  • 6.28α
  • 7.26α
  • 14.5α
Answer: C
7.The geometrical features of a super critical airfoil are
  • Round leading edge, flat upper surface and high camber at the rear
  • Sharp leading edge, curved upper surface and high camber at the rear
  • Round leading edge, curved upper surface and no camber at the rear
  • Sharp leading edge, flat upper surface and no camber at the rear
Answer: A
8.A uniform supersonic stream with M1 = 3.0 encounters a compression corner that deflects by an angle of 200 . Given that the shock wave angle occurs at 37.50 and that the normal component of the flow (w.r.t the shock) experiences a normal shock reducing the normal component of the Mach number by.989 times, find the downstream Mach number of the flow.
  • 2.56
  • 2.22
  • 2.11
  • 2.03
Answer: D
9.In a convergent – divergent (CD) nozzle of a rocket motor, the wall heat flux is maximum at
  • The exit of the divergent portion of the CD nozzle
  • The entry to the convergent portion of the CD nozzle
  • The throat of the CD nozzle
  • The mid-length of the divergent portion of the CD nozzle
Answer: B
10.If 1 and 2 (subscripts) denote the conditions before and after a stationary normal shock, which of the following statements is true w.r.t a normal shock?
  • ρ1u2 = ρ2u1
  • M1* M2* = 1
  • ρ1u22 = ρ2u12
  • M1* = M2*
Answer: B
11.Compressible flow is considered for Mach number less than _________________.
Answer: 0.3
12.Across a normal shock _____________ remains constant but ________________ decreases
Answer: Total temperature, total pressure
13.For a flow across an oblique shock, Component of velocity normal to shock _____________ while tangential component is ______________________.
Answer: Decreases, unchanged
14.An Irrotational and inviscid flow can become rotational on passing through a _______________
Answer: Curved shock wave
15.For a flow through a Prandtl-Meyer expansion wave ___________________ stays constant
Answer: Entropy
16.The Mach number at the inlet of a nozzle is 1.1. The shape of the nozzle should be __________
Answer: Diverging
17.The critical Mach number of an airfoil is attained when the Mach number somewhere on the airfoil is________________________________
Answer: Unity
18.The critical Mach number for a flat plate of zero thickness at zero angle of attack, is ___________
Answer: 1
19.One of the criteria for high speed airplanes is that critical Mach number should be as high as possible. Therefore, high speed subsonic airplanes are usually designed with __________ airfoils
Answer: Thin
20.For a perfect crystal __________________ is zero at perfect
Answer: Entropy