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Thermodynamics 2 > Compressible Flow > Flashcards

Compressible Flow Flashcards

1
Q

What is Stagnation Enthalpy?

A

A term that combines enthalpy and Kinetic Energy

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2
Q

What is the defining formula of stagnation enthalpy?

A

h_0 = h + V^2/2

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3
Q

What are stagnation properties?

A

The properties of the fluid at stagnation state

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4
Q

What is the formula for stagnation temperature of an ideal gas?

A

T_0 = T + (V^2)/(2c_p)

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5
Q

What is stagnation temperature?

A

The temperature an ideal gas would obtain if brought to rest adiabatically

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6
Q

What is the formula relating the static pressure and stagnation pressure of fluid to static/stagnation temperature?

A

P_0 / P = (T_0/T)^{k/(k-1)}

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7
Q

What is the formula relating the static density and stagnation density of fluid to static/stagnation temperature?

A

\rho_0 / \rho = (T_0/T)^{1/(k-1)}

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8
Q

What is the speed of sound defined as?

A

The speed at which an infinitesimally small pressure wave travels through a medium.

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9
Q

What is the formula for speed of Sound for an ideal gas? (Both differential and normal form)

A

c = \sqrt{(dP/d\rho)} = \sqrt{kRT}

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10
Q

What is the Mach Number?

A

The ratio of the actual velocity of the fluid to the speed of sound at the same state.

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11
Q

What is the throat velocity of a converging diverging nozzle if exit velocity is supersonic?

A

Sonic Velocity

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12
Q

For an ideal gas with constant specific heat, what is the formula for ratio of stagnation/static Temperature?

A

T_0/T = 1 + ((k-1)/2)Ma^2

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13
Q

For an ideal gas with constant specific heat, what is the formula for ratio of stagnation/static Pressure?

A

P_0/P = [1 + ((k-1)/2)Ma^2]^{k/(k-1)}

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14
Q

For an ideal gas with constant specific heat, what is the formula for ratio of stagnation/static Density?

A

\rho_0 / \rho = [1 + (k-1/2)Ma^2]^{1/(k-1)}

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15
Q

What are critical ratios?

A

The static-to-stagnation property ration when Mach number is 1

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16
Q

What is back pressure?

A

The pressure outside the exit plane of a nozzle

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17
Q

What is choked flow?

A

Flow when back pressure is lower than the critical pressure

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18
Q

What is a shock?

A

A region that causes sudden change in properties of flow

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19
Q

Is flow through shock reversible or irreversible?

A

Highly irreversible

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20
Q

What is Rayleigh Flow?

A

Steady one-dimensional flow of an ideal gas with constant specific heats through a constant-area duct with heat transfer and negligible friction

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21
Q

Why are most relations from this chapter not applicable to steam?

A

Water vapor at moderate or high pressure deviates significantly from ideal gas behavior.

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22
Q

What is supersaturation?

A

The delay of condensation of steam

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23
Q

What is the Wilson Line?

A

The Locus point where condensation takes place regardless of the initial temperature and pressure of the nozzle entrance

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24
Q

What does the critical pressure ratio for steam depend on?

A

On the nozzle inlet state and on whether the steam is superheated or saturated at the nozzle

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25
Q

What is the mass equation for Rayleigh flow?

A

\rho_1 V_1 = \rho_2 V_2

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26
Q

What is x-momentum equation for Rayleigh flow?

A

P_1 + \rho_1 V_1^2 = P_2 + \rho_2 V_2^2

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27
Q

What is the effect of heat transfer on stagnation enthalpy and temperature in Rayleigh flow?

A

Increase when heat is transferred to flow, decrease when it is removed from flow

28
Q

What is the only source of entropy change in Rayleigh Flow?

A

Heat transfer

29
Q

What is the Rayleigh line?

A

The plot of Rayleigh flow on a T-s diagram

30
Q

What is Mach Number at maximum entropy in Rayleigh Line?

A

Ma = 1

31
Q

What is Mach number at maximum temperature at Rayleigh line?

A

Ma = 1 / sqrt{k}

32
Q

Where can subsonic states be found on a Rayleigh line?

A

Above point of maximum entropy

33
Q

What is the effect of heating on Mach number in sub and supersonic flow in Rayleigh Flow?

A

Heating increases Mach number for subsonic flow and decreases it for supersonic flow.

34
Q

What is the effect of heating on stagnation temperature for sub/supersonic flow in Rayleigh flow?

A

Increase in both cases

35
Q

What is the effect of adding heat to Rayleigh flow after point of maximum Temperature on Temperature?

A

Temperature decreases

36
Q

What is the effect of heat gain on static pressure in sub/supersonic Rayleigh flow?

A

Decreases with heat gain in subsonic flow, increases in supersonic flow

37
Q

What is the effect of heat gain on density in sub/supersonic Rayleigh flow?

A

Density decreases with heat transfer in subsonic flow but increases with heat transfer in supersonic flow

38
Q

What are Oblique Shocks?

A

A complicated Shock pattern consisting of oblique shocks

39
Q

When is a straight oblique shock wave produced?

A

When a supersonic flow hits a wedge and is turned by an angle

40
Q

What is deflection angle equal to in a straight oblique shock?

A

Wedge half-angle

41
Q

What is the effect of oblique shock on Mach number?

A

Decreases, however does not necessarily become subsonic

42
Q

Which component of fluid velocity does not change across an oblique shock?

A

Tangential component (aligned with shock)

43
Q

What is the effect of an oblique shock on stagnation enthalpy?

A

No effect

44
Q

Why does stagnation enthalpy not change across oblique shock?

A

No work done by control volume and no heat transfer

45
Q

What happens if the wedge angle is more than the maximum wedge angle?

A

The shock becomes curved and detaches from the nose of the wedge

46
Q

What is the Mach wave?

A

Weakest possible oblique shock at a given Mach Number

47
Q

When are Prandtl-Meyer waves formed?

A

When angle of attack is greater than half angle of wedge

48
Q

What is Prandtl-Meyer flow an example of?

A

Expanding Flow

49
Q

Describe Prandtl-Mayer flow?

A
  • No shock
  • Expansion Fans
50
Q

Why is Prandtl-Mayer flow isentropic?

A

Because individual expansion waves are nearly isentropic

51
Q

Which set of equations can help us understand properties of fluid after shock?

A

Conservation of mass/energy/momentum

52
Q

What is the Fanno Line?

A

Line combining conservation of mass and energy

53
Q

What is the Rayleigh Line?

A

Line combining conservation of mass and momentum

54
Q

What is the point of maximum entropy on Fanno and Rayleigh lines

A

Points where Mach number is 1

55
Q

What points do the Rayleigh and Fanno Line converge on and what do they represent?

A

Two points representing points where all the involved equations are satisfied, one before and one after the shock

56
Q

What happens to P, P_0, V, Ma, T, T_0, \rho, and s after normal shock?

A

P increases
P_0 decreases
V decreases
Ma decreases
T increases
T_0 constant
\rho increases
s increases

57
Q

What is the highest velocity to which flow can be accelerated in a converging nozzle?

A

Sonic velocity

58
Q

What is the lowest pressure that can be obtained at the throat?

A

The sonic pressure

59
Q

What is the critical Mach number?

A

The ratio of local velocity to speed of sound at throat

60
Q

What is the only property that the speed of sound in an ideal gas depends on?

A

Temperature

61
Q

What causes increase in velocity past throat?

A

Rapid decrease in density

62
Q

What are the property variations across a subsonic nozzle?

A

P decreases
V increases
Ma increases
T decreases
\rho decreases

63
Q

What are the property variations across a subsonic diffuser?

A

P increases
V decreases
Ma decreases
T increases
\rho increases

64
Q

What are the property variations across a supersonic nozzle?

A
65
Q
A

Thermodynamics 2 (4 decks)

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