Compressible Flow Questions & Answers  
Question by Student 201383227
Sir , I have a doubt in understanding the slip line . Is slip line is like shear layer flow ? . And is it formed to make the flow to balance the pressure between the two shock wave's.
11.24.13
A shear layer is a viscous flow phenomenon. Here we are solving inviscid flow. In inviscid flow, the slip line is the boundary between two flow regions. The two flow regions have the same pressure and their velocity vectors point in the same direction. However, the temperature, density, and the magnitude of the velocity may differ.
Question by Student 201793107
Hello Sir,
​ In Assignment 1, Question No.3, I am getting all the values correctly except the maximum attainable velocity by the gas. I am getting, \begin{equation} V_{2,max}=672.185\, m/s \end{equation} instead of $647\,m/s$ as given by you.
​ I assumed \begin{equation} M_{2}=1 \end{equation}and hence \begin{equation} V_{2,max}=\sqrt{\gamma R T} \end{equation} Sorry if I am wrong for your precious time.
09.19.17
But if $M_2=1$, then $T_2$ will have a different value than the one you computed..
09.20.17
Question by Student 201793101
Good morning professor,

I'd like to confirm if I understood a point on supersonic nozzles.
If the exit pressure decreases (or back pressure increases) after the shockless case and oblique shock waves start to appear.

Further decreasing exit pressure, weak shock waves start to collapse into strong oblique shock waves, which in turn become a normal shock wave centered on the flow middle line. The limit is therefore defined by the minimum value to achieve a strong solution.

Is the reasoning correct?

Thank you.
12.09.17
I guess you refer here to the last problem of the last assignment. If so, then yes your reasoning is correct. The only thing missing in your reasoning is that you need to first assess whether the first oblique shock is weak or strong by looking at the wave pattern.. If there is a reflected shock, then for sure the first oblique shock is weak because a strong oblique shock would lead to a subsonic flow, hence preventing a shock reflection.
Question by Student 201783220
in mid term exam question 3, how can i assume for isentropic between 1 to 3? I think flow can be produced at least single shock wave in converging section.
12.17.17
In 1D (as schematized in the midterm exam Q3), it's definitely possible to have an inlet with no shock. In 2D, you could design the inlet so that the flow slows down isentropically to Mach 1 through a Prandtl Meyer compression fan. In practice this is hard to achieve because such a design would only work for one specific Mach number and lead to major losses in performance at slightly different Mach numbers. Thus, inlets generally have several shocks to allow for some variation in geometry. But this is not mentioned (or schematized) in the question statement, so you can assume the flow isentropic through the inlet here.
Question by Prasanna
Professor, I think the answer for Problem #1 of Assignment #1 should be 0.746 bar, 277.609 K, 83.06 kg/s, 586.67 km/hr when using the temperature and pressure values at 12000 feet from 1976 U.S. Standard Atmosphere table and for $m_{\infty}$=0.5 and $A_i=0.6\ m^2$.
09.26.18
I corrected the answers. Check again.
Question by Student 201893243
Good afternoon, professor. I'm curious about the lack of explanations in the assignments 1 I submitted. I guess that the short comment on the shape of the nozzle after obtaining the Mach number and pressures of the entry and exit in Question 2 was not enough explain. If you tell me what approach was lack in the process of problem solving, I will supplement what I misunderstand. Sincerely thank you Sir.
09.27.18
It's best if you come visit me in my office for this. We'll look through your quiz together.
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