Supersonic Flight Flashcards
What is the equation of continuity?
rhoAV = constant
What is Bernoulli’s equation?
P + 0.5rhoV^2 = Constant
If density is constant (as assumed with subsonic flow), what is the velocity of the fluid proportional to?
The cross sectional area of the duct
For subsonic flow in a convergent duct, what occurs when cross sectional area decreases, what happens to the flow velocity and the static pressure?
Velocity increases and static pressure will decrease
For subsonic flow in a divergent duct, what occurs when cross sectional area increases?
Flow velocity decreases and static pressure increases.
For supersonic flow in a divergent duct, what is the assumption about the flow at the throat?
It is at least Mach 1.0
What occurs to supersonic flow as it moves into the expanding area of a divergent duct?
1) The flow will momentarily maintain a constant True Air Speed (TAS) due to inertia
2) Due to constant TAS and area increasing, density and temperature will decrease as air must expand to fill the space.
3) Pressure is reduced as flow density decreases, resulting in an acceleration of the flow.
4) Temperature reduction results in a reduction in the speed of sound resulting in an increase in Mach number.
What occurs to supersonic flow in a convergent duct?
1) Due to inertia, velocity of flow remains constant initially
2) If TAS remains constant while area decreases, the density must increase as the air is compressed to fill the space
3) As density increases so does the temperature and pressure
4) Adverse pressure gradient results in a reduction in TAS
5) Increase temperature results in a higher speed of sound and Mach number will decrease.
What occurs for pressure, density and velocity for subsonic flow for divergent and convergent ducts?
Divergent: Pressure, density increases, velocity decreases
Convergent: Pressure, density decreases, velocity increases
What occurs for pressure, density , temperature and velocity for supersonic flow for divergent and convergent ducts?
Divergent: Pressure, density decreases, temperature deceases, velocity increases
Convergent: Pressure, density increases, temperature increases, velocity decreases.
What occurs to supersonic flow around expansive corners?
Supersonic flow around an expansive corner will accelerate and decrease pressure.
What is a Mach line?
Flow near the surface senses the change in the surface whilst the flow further away senses the change fractionally later, this discontinuity forms a Mach line.
What is an expansion fan?
An infinite number of Mach lines which form a fan type effect.
Is a mach line/expansion fan a shock wave?
No, as it doesn’t undergo compression
Is the Mach number downstream of a expansion corner greater than original Mach number?
Yes
What occurs to supersonic flow on a compressive corner?
The flow will slow and increase pressure as it passes through the shockwave associated with the compressive corner.
Are shockwaves formed around compressive corners?
Yes they are
Does the normal bow shockwave of a compressive corner become more oblique as speed increases?
Yes
What occurs to velocity, mach number, pressure, density and temperature through a shockwave?
- Velocity and Mach number decrease
- Pressure, density and temperature increase.
What are the two types of shockwaves?
- Normal
- Oblique
How is a normal shockwave oriented to the surface?
Always oriented perpendicular to the direction of flow and remains detached from the source.
Does the direction of the flow change through a normal shockwave?
No it doesn’t
Are there large energy losses through normal shockwaves? What does this manifest itself as on the aircraft?
Yes, causes larges amount of drag on the aircraft.
What is an oblique shockwave?
Oriented at an angle other than 90 degrees to the direction of flow
What factors influence the angle of the oblique shockwave?
1) The speed of the flow
2) The shape/angle of the obstruction
Is the flow ahead of an oblique shockwave always supersonic? Can flow decrease to either supersonic of subsonic?
Yes it is, can decrease to either supersonic or subsonic.
Are the effects on the air through an oblique shockwave lesser than those of a normal shockwave?
Yes
What occurs to the X and Y components of airflow through an oblique shockwave?
X component decreases
Y component remains the same.
What is a bow wave?
A normal shockwave that occurs ahead of the object.
Is there significant heat buildup between the bow wave and the leading edge of the wing?
Yes, very significant, mucho heato.
