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Compressible Flow > Chapter 9 > Flashcards

Chapter 9 Flashcards

1
Q

In general, a shock wave will make an ____ angle with respect to the upstream flow.

A

Oblique

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2
Q

Supersonic flows are also characterized by oblique expansion waves where the pressure _______ across the wave.

A

pressure decreases continuously

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3
Q

Whenever a shockwave is “turned into itself” as shown in Fig 9.2a in the textbook, an _____ will occur.

A

Oblique Shock Wave

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4
Q

How do pressure, temperature, density, and Mach number change across an oblique shockwave.

A

Mach number decreases

All other properties increase

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5
Q

Whenever a supersonic flow is “turned away from itself” as shown in Figure 9.2b in the textbook ______ will occur.

A

An expansion wave will occur.

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6
Q

Describe how Mach number, temperature, pressure, and density change as a particle travels through an expansion wave.

A

Mach Number increases

Pressure, temp, and density decrease

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7
Q

Describe the physical mechanisms that create shockwaves.

A

If the upstream flow is supersonic, the disturbances caused by the body in motion cannot work their way upstream; rather, at some finite distance from the body, the disturbance waves pile up and coalesce. This forms a standing wave in front of the body.

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8
Q

Is total temperature still constant across an oblique shockwave?

A

Yes.

Pg. 622

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9
Q

Changes across an oblique shockwave are governed only by the component of velocity _____.

A

Normal to the wave.

Pg 623

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10
Q

Changes across an OSW are dependant on what two parameters?

A

The upstream Mach number and the shock angle (beta).

Pg. 624

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11
Q

If theta is greater than theta max for a particular match number, does a solution exist for a straight OSW?

A

No

Pg. 624

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12
Q

If theta is greater than theta max what two physical phenomena will take place?

A

The shockwave will be detached and curved.

Pg. 624

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13
Q

Between the weak and strong shock solutions, which contains the higher M_n1 and the larger pressure ratio (p2/p1) ?

A

The strong shock.

Pg. 628

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14
Q

In nature, which shock solution is usually found?

A

The weak solution.

Pg. 628

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15
Q

For the strong shock solution, the downstream Mach number is always _____.

A

Subsonic.

Pg. 628

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16
Q

For the weak shock wave (except for cases where theta is close to the maximum value) the downstream Mach number is _____.

A

Supersonic.

Pg. 628

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17
Q

Normal shockwaves belong to the family of ____ shock solutions.

A

Strong.

Pg. 628

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18
Q

As the upstream Mach number increases the shock angle beta ____.

A

Decreases.

Pg. 628

19
Q

The p2/p1 ratio will be higher or smaller for a larger upstream Mach number?

A

Higher

Pg. 629

20
Q

In general, for attached shocks with a fixed upstream Mach number, as the deflection angle increases, the wave angle beta ____ and the shock becomes _____.

A

Increases
Stronger

Pg. 630

21
Q

Can the theory developed in section 9.2 for general OSW’s be used to evaluate supersonic flow over wedges without any simplifying assumptions?

A

Yes.

Pg. 634

22
Q

Supersonic flow over a wedge is characterized by ____.

A

An attached, straight, oblique shock wave from the noise, a uniform flow downstream of the shock with streamlines parallel to the wedge surface, and a surface pressure equal to the static pressure behind the oblique shock p2.

Pg. 634 and 635

23
Q

True or False

Wedge flow is two-dimensional.

A

True

Pg. 635

24
Q

True or False
On a conical body moving through a supersonic flow, a consequence of the three-dimensional relieving effect is that the shock wave on the cone is weaker than on the wedge.

A

True

Pg. 635

25
Q

True or False

A conical body has a small wave angle than a wedge body.

A

True

Pg. 635

26
Q

Streamlines behind an OSW on a conical body are ____.

A

Curved

Pg. 625

27
Q

The surface pressure on a cone is ____ than the surface pressure on a wedge.

A

Less than

Pg. 635

28
Q

The cone surface Mach number is ____ than that of a wedge.

A

Greater

Pg. 636

29
Q

State the main three differences between supersonic flow over a cone and wedge.

A
  1. Shock wave on the cone is weaker
  2. The cone surface pressure is lower
  3. The streamlines above the cone surface are curved rather than straight.

Pg. 636

30
Q

True or False

The strength of a reflected shock wave is stronger than the incident shock.

A

False
The reflected shock is weaker than the incident.

Pg. 640

31
Q

Describe what properties are the same across a slip line.

A
  1. Pressure is constant.
  2. Direction (but not necessarily the magnitude) of the velocity is the same.

All other properties (most notably entropy) are different.

Pg. 641

32
Q

On a bow shock, away from the center point of the wave, the shock wave gradually becomes ___ and ____.

A

Curved and weaker.

Pg. 645

33
Q

True or False

The oblique shock can produce no momentum change parallel to the plane in which it lies.

A

True, this is how the oblique shock relations can be deduced from the normal shock relations.

Ref: Carscallen Book Pg. 135

34
Q

For a bow shock, directly in front of the nose of the body in motion, the shockwave can be considered ____.

A

A normal shock wave.

Ref: Pg 645

35
Q

For a bow shock, away from the leading point, the shock waves gradually become ____ and ____. Eventually devolving into a ___ at large distances from the body.

A

curved and weaker
mach wave

Ref: Pg 645

36
Q

How is an expansion wave formed?

A

When supersonic flow is turned away from itself.

Ref: Pg 648

37
Q

An expansion wave can be thought of as composing of an _____.

A

An infinite number of Mach waves.

Ref: Pg 649

38
Q

Why can an expansion wave be considered isentropic?

A

Because they are composed of an infinite number of Mach waves and by definition, the change in entropy across a single Mach wave is zero.

Ref: Pg 649

39
Q

What happens to Mach number across an expansion wave?

A

It increases

Ref: Lecture Slides

40
Q

How do pressure temperature and density change across an expansion wave?

A

They all decrease

Ref: Lecture Slides

41
Q

How does the Mach number vary across an Oblique Shock wave?

A

It decreases

Ref: Lecture Slides

42
Q

How do pressure, temperature, and density change across an oblique shock wave?

A

They all go up.

Ref: Lecture Slides

43
Q

With regard to a reflected shockwave, if the Mach number and deflection angle behind the incident shock are in such a condition that no oblique shock solution exists what occurs?

A

A single normal shock wave is formed on the reflecting wall. This is commonly referred to as a Mach reflection.

Ref: Lecture Slides

44
Q

For a compression curve, the deflection angle theta is positive or negative?

A

Negative

Ref: Lecture Slides

Compressible Flow (7 decks)

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