Lecture 2 Flashcards
Under which conditions is total enthalpy constant?
- Adiabatic Flow
- No external work
- Stationary Flow
- No viscous effects
Does the total conditions relation for Temperature require s=const?
No
But the rest of them (rho and pressure) yes
At which position in a nozzle can M=1 be reached?
If it is reached at some point, it would be in the smallest cross section area. This is because the Area of the nozzle is directly proportional to the inverse of the mass flow denstiy, and as we can see in the plot in page 20 and as we plotted ourselves in MATLAB, its maximum is reacher when M=1.
Can flows featuring shocks be isentropic?
No, the thermodynamic conversion of the properties of a flow before and afer a shock wave cannot be considered isentropic.
A shock wave is an irreversible process. An isentropic flow is reversible and adiabatic.
Shocks have an increase in entropy.
Give the definition of the critical Mach number
What’s the other name it receives?
Lowest free-stream Mach number at which the local flow somewhere on the body (nozzle in our case) first reaches Mach 1.
Equation: M* = M/c; where, for c we use T*
Other name: Laval number
What does “critical temperature” mean in a fluid mechanics sense?
Temperature of a fluid when its Mach number is exactly 1 (basically we are at critical conditions).
How is the relative mass flow density defined?
Basically is the mass flow (phou) divided by its critical quantities (pho c*).
Sketch relative mass flow density against Mach number.
It is the plot at page 20, and what we have plotted in MATLAB. Important to remember that it grows until M=1, reaching its maximum and then starts decreasing until being 0 for large Much numbers. That’s the reason for achieving (if possible), M=1 at the smallest cross section; because the mass flow density is directly proportional to the inverse of A.
Give the equation that relates total Temperature and Pressure with the static variables
Slides 10 and 14
