Quiz 2

• An oblique shock is a straight compression shock wave inclined at an angle to the upstream flow direction. Basically, "Turned into itself"
• Two types of supersonic flow over a corner.

  1. Oblique shock
  2. Expansion fan
• When supersonic flow is "turned away from itself" it's an expansion wave.
• These changes in flow streams for supersonic flow over a corner happen across the wave.
• Flow across a shock wave is adiabatic but not isentropic because it is irreversible.
• What does flow look like when no straight oblique shock solution exists?

  Detached shock or bow shock is formed ahead of the body.
• The smaller the shock angle, the weaker the shock solution
• Expansion fans are isentropic.
• Total pressure decreases for an oblique shock. However, local pressure, temperature, and density increases. The total pressure remains constant for expansion waves. While, the local pressure, temperature, and density decreases.
• Non-isentropic is when the change of entropy is greater than zero.
• In oblique shock wave, the normal component is the only thing change and not the tangential component. The tangential components of velocity in front of and behind the wave are equal. However the tangential components of the Mach number are not the same.
• Another way to write the mach angle equation is

  $Tan μ =$$1/(√M^2-1)$
• The thermodynamic properties across the oblique shock are dictated by the normal component of the upstream Mach number.
• Boundary layer separation in subsonic flow is caused by adverse pressure gradients that the speed of the boundary layer relative to the surface has stopped and reversed direction. The flow becomes detached from the surface and instead takes the forms of eddies and vortices.
• The reason for loss of total pressure is because of

  an increase of entropy
• Drag is directly proportional to entropy.
• A concave corner will generate an

  Oblique shock wave or compression wave.
• A convex corner will generate an

  Expansion fan
• Reflection wave interaction has two types of characteristics.

  1. Specular (Angle of reflections are equal to each other)
  2. Non-specular (Angles are not equal to each other)
• In Mach waves what type of waves form?

  1. Compression Waves = Coming together
  2. Expansion Waves = Going away
• Pressure coefficient equation

  $Cp =$$(P_2 - P_1)/(0.5ρ_1V_1^2)$
• Dynamic Pressure in high speed

  $q_1 =$$(γ/2)P_1M_1^2$
• Strong shocks are caused by large shock angles and weak shocks are caused by small angles.
• Incoming waves impinging on a solid wall, the reflected waves are the same family.
• Incoming waves impinging on a free boundary (e.g. constant pressure surface), the reflected waves are of opposite family.
• Governing assumptions of Quasi-one-dimensional flow

  1. Compressible flow
  2. Steady flow
  3. Calorically Perfect Gas
  4. Adiabatic flow
  5. Isentropic flow except for any shock wave
• In supersonic flow, (MACH is greater than 1)

  Area increases as velocity increases but pressure decreases. Vice versa.
• Area velocity equation

  $dA/A =$$(M^2-1)dV/V$
• M is equal (in supersonic) what

  1 in a throat for a nozzle and diffuser.
• How does total enthalpy vary across a P-M wave?

  Constant
• Does static pressure increase across an oblique shock?

  Yes
• How does total pressure vary across a bow shock?

  It goes down
• Oblique shock relations are basically the same as those for a

  normal shock except M1 is replaced by Mn1.
• What is the quickest way to determine po2/po1 across an oblique shock.

  Go to table T.A.2 of Anderson
• Turning a supersonic flow "into" itself will produce an

  oblique shock wave
• Turning a supersonic flow "away from" itself will produce an

  P-M Expansion fan
• Can we analytically determine T2/T1 across an oblique shock?

  Yes
• How does static pressure vary across a P-M expansion wave?

  It goes down
• How does entropy vary across an oblique shock wave?

  It goes up
• How does static temperature vary across a P-M expansion wave?

  It goes down