GD Midterm 1 Review - Section 2 Flashcards
What are the assumptions used in deriving the generalized 1D flow equations?
- Steady uniform flow.
- Neglect body and gravitational forces
- Calorically perfect gas
True or False
For isentropic flow with area change, the stagnation pressure, stagnation temperature, and entropy remain constant.
True.
Section 2, Page 14
Summarize the choking condition for a flow in a variable area duct. The flow is adiabatic and frictionless.
Once flow in a variable area duct has reached Mach 1, the area must be at a minimum, or further area changes will result in shock waves (if supersonic) or an adjustment in inlet conditions (if subsonic) - usually through adjustments in
mass flow rate.
Section 2, Page 14
For subsonic flow through a heated duct, which of the following will increase/decrease:
» Mach number and velocity
» Pressure, density, and stagnation pressure
» Entropy
» Temperature
Increase:
Mach number and velocity
Entropy
Temp if 0 < M < 1/sqrt{\gamma}
Decrease
Pressure, density, and stag pressure
Temp if 1/sqrt{\gamma} < M< 1
For subsonic flow through a cooled duct, which of the following will increase/decrease:
» Mach number and velocity
» Pressure, density, and stagnation pressure
» Entropy
» Temperature
Increase:
Temp if 1/\sqrt{\gamma} < M < 1
Decrease
All others.
For supersonic flow through a heated duct, which of the following will increase/decrease:
» Mach number and velocity
» Pressure, density, and stagnation pressure
» Entropy
» Temperature
Increase:
Pressure, density, and temperature, stagnation pressure
Entropy
Decrease:
Mach number and velocity
For supersonic flow through a cooled duct, which of the following will increase/decrease:
» Mach number and velocity
» Pressure, density, and stagnation pressure
» Entropy
» Temperature
Increase:
Mach number and velocity
Decrease:
Pressure, density, temperature, stagnation pressure
Entropy
Describe the * condition for Rayleigh flow.
The ∗ condition for Rayleigh flow is defined as the sonic condition achieved by heating or cooling the flow until it reaches Mach 1.
On the T-s curve, which branches corespond to subsonic and supersonic flow?
Lower branch = supersonic
Upper branch = subsonic
On the T-s curve, the point of maximum entropy corresponds to the __________.
Sonic point.
Describe the sonic condition for Rayleigh flow.
If the flow reaches Mach 1 and the duct continues to be heated, if the flow is subsonic upstream, the mass flow rate will decrease such that the upstream Mach number is lower, and the flow does not reach Mach 1 until the end of the duct. If the flow is supersonic upstream, shocks will form and the flow will become subsonic.
For fanno flow, which of the following will increase, remain constant, or decrease when the flow is subsonic (M<1):
> > Mach number, velocity, entropy
Pressure, density, temperature, and stagnation pressure
Stagnation temperature
Increase:
Mach number, velocity, and entropy
Decrease:
Pressure, density, temperature, and stagnation pressure
Constant:
Stagnation temperature
For fanno flow, which of the following will increase, remain constant, or decrease when the flow is supersonic (M>1):
> > Mach number, velocity, entropy
Pressure, density, temperature, and stagnation pressure
Stagnation temperature
Increase:
Pressure, density, temp, entropy.
Decrease:
Mach number, velocity, stag pressure.
Constant:
Stagnation temperature
Describe the * condition for fanno flow.
The ∗ condition for Fanno flow is defined as the sonic condition
achieved by accelerating or decelerating the flow to Mach 1 through only friction.
Describe the choking condition for fanno flow.
If the duct is too long and the flow will reach Mach 1 before the end of the duct for the given inlet conditions, then the flow will choke.
If the flow is subsonic at the inlet, the inlet conditions will adjust such that the flow does not choke until the end of the duct. This occurs through a drop in mass flow rate which lowers the inlet Mach number.
If the flow is supersonic, the adjustment will occur through the formation of a normal shock which forces the flow to become subsonic.
