Chapter 9 Flashcards
In general, a shock wave will make an ____ angle with respect to the upstream flow.
Oblique
Supersonic flows are also characterized by oblique expansion waves where the pressure _______ across the wave.
pressure decreases continuously
Whenever a shockwave is “turned into itself” as shown in Fig 9.2a in the textbook, an _____ will occur.
Oblique Shock Wave
How do pressure, temperature, density, and Mach number change across an oblique shockwave.
Mach number decreases
All other properties increase
Whenever a supersonic flow is “turned away from itself” as shown in Figure 9.2b in the textbook ______ will occur.
An expansion wave will occur.
Describe how Mach number, temperature, pressure, and density change as a particle travels through an expansion wave.
Mach Number increases
Pressure, temp, and density decrease
Describe the physical mechanisms that create shockwaves.
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.
Is total temperature still constant across an oblique shockwave?
Yes.
Pg. 622
Changes across an oblique shockwave are governed only by the component of velocity _____.
Normal to the wave.
Pg 623
Changes across an OSW are dependant on what two parameters?
The upstream Mach number and the shock angle (beta).
Pg. 624
If theta is greater than theta max for a particular match number, does a solution exist for a straight OSW?
No
Pg. 624
If theta is greater than theta max what two physical phenomena will take place?
The shockwave will be detached and curved.
Pg. 624
Between the weak and strong shock solutions, which contains the higher M_n1 and the larger pressure ratio (p2/p1) ?
The strong shock.
Pg. 628
In nature, which shock solution is usually found?
The weak solution.
Pg. 628
For the strong shock solution, the downstream Mach number is always _____.
Subsonic.
Pg. 628
For the weak shock wave (except for cases where theta is close to the maximum value) the downstream Mach number is _____.
Supersonic.
Pg. 628
Normal shockwaves belong to the family of ____ shock solutions.
Strong.
Pg. 628
As the upstream Mach number increases the shock angle beta ____.
Decreases.
Pg. 628
The p2/p1 ratio will be higher or smaller for a larger upstream Mach number?
Higher
Pg. 629
In general, for attached shocks with a fixed upstream Mach number, as the deflection angle increases, the wave angle beta ____ and the shock becomes _____.
Increases
Stronger
Pg. 630
Can the theory developed in section 9.2 for general OSW’s be used to evaluate supersonic flow over wedges without any simplifying assumptions?
Yes.
Pg. 634
Supersonic flow over a wedge is characterized by ____.
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
True or False
Wedge flow is two-dimensional.
True
Pg. 635
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.
True
Pg. 635
True or False
A conical body has a small wave angle than a wedge body.
True
Pg. 635
Streamlines behind an OSW on a conical body are ____.
Curved
Pg. 625
The surface pressure on a cone is ____ than the surface pressure on a wedge.
Less than
Pg. 635
The cone surface Mach number is ____ than that of a wedge.
Greater
Pg. 636
State the main three differences between supersonic flow over a cone and wedge.
- Shock wave on the cone is weaker
- The cone surface pressure is lower
- The streamlines above the cone surface are curved rather than straight.
Pg. 636
True or False
The strength of a reflected shock wave is stronger than the incident shock.
False
The reflected shock is weaker than the incident.
Pg. 640
Describe what properties are the same across a slip line.
- Pressure is constant.
- Direction (but not necessarily the magnitude) of the velocity is the same.
All other properties (most notably entropy) are different.
Pg. 641
On a bow shock, away from the center point of the wave, the shock wave gradually becomes ___ and ____.
Curved and weaker.
Pg. 645
True or False
The oblique shock can produce no momentum change parallel to the plane in which it lies.
True, this is how the oblique shock relations can be deduced from the normal shock relations.
Ref: Carscallen Book Pg. 135
For a bow shock, directly in front of the nose of the body in motion, the shockwave can be considered ____.
A normal shock wave.
Ref: Pg 645
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.
curved and weaker
mach wave
Ref: Pg 645
How is an expansion wave formed?
When supersonic flow is turned away from itself.
Ref: Pg 648
An expansion wave can be thought of as composing of an _____.
An infinite number of Mach waves.
Ref: Pg 649
Why can an expansion wave be considered isentropic?
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
What happens to Mach number across an expansion wave?
It increases
Ref: Lecture Slides
How do pressure temperature and density change across an expansion wave?
They all decrease
Ref: Lecture Slides
How does the Mach number vary across an Oblique Shock wave?
It decreases
Ref: Lecture Slides
How do pressure, temperature, and density change across an oblique shock wave?
They all go up.
Ref: Lecture Slides
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 single normal shock wave is formed on the reflecting wall. This is commonly referred to as a Mach reflection.
Ref: Lecture Slides
For a compression curve, the deflection angle theta is positive or negative?
Negative
Ref: Lecture Slides
