Compressible Flow Questions & Answers  
Question by Prasanna
Professor, I have a doubt regarding the problem 5(c) and 5(d) of assignment 4. I could solve a similar problem[l] where the stagnation pressure and temperature behind the reflected shock is calculated given the speed of the incident shock($v_s$). However, in problem 5, having calculated the required stagnation pressure and temperature to drive the gun tunnel, I am unable to calculate the incident shock speed. It seems I require either the speed of the air behind the incident shock or the speed of the reflected shock to solve the problem. Can this problem be solved without knowing these speeds in prior?
Yes it can. You need to determine the incident shock speed that will give the right stagnation temperature. The reflected shock speed can be found from the incident shock speed. The speed of the air behind the incident shock is function of the incident shock speed and shouldn't be specified or the problem would be overspecified.
Question by Prasanna
Professor, I'm sorry for repeating the question I asked in class. For the problems in Assignment #6, if I use the weak oblique shock tables, I am able to use only the solution corresponding to the flow deflection angle($\delta$) which are multiples of 2($\delta$=2.0°,4.0°,6.0°...) as given in the table. Using the 'Family of Hodograph Shock Polars' chart, I am unable to use the solution corresponding to precise values of $\delta$, for example, $\delta$=9.1°, if I use a protractor. I could use a root finder program to calculate the wave angle corresponding to an incoming Mach number and a flow deflection angle, but I cannot use that in the quiz. How should I proceed with calculating the solution behind a weak oblique shock for different values of flow deflection angle $\delta$?
Well, use what you feel is best suited. You can't measure 9.1 degrees precisely on the shock polar, but you can do it approximately and this will be good enough to get all your points. One problem of the shock polar is when the deflection angle is 2 degrees or so. Then, better to use the oblique shock tables.
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