Solving for shock wave angle using Mach and deflection angle

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Discussion Overview

The discussion centers on determining how the shock wave angle (Beta) varies with changes in the Mach number while keeping the deflection angle (theta) constant. Participants explore the theta-beta-Mach relation and methods for solving the implicit equation involved.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant presents the equation relating shock wave angle and deflection angle, expressing difficulty in solving for Beta.
  • Another participant recalls an approximate relationship between Beta and theta for large Mach numbers, referencing a specific text, but notes it may not be applicable for the current problem.
  • A third participant indicates that the graphical solutions available in their resources do not provide sufficient detail for higher Mach numbers.
  • Some participants suggest using numerical methods, such as fsolve or Newton's method in Matlab, to tackle the implicit nature of the equation.

Areas of Agreement / Disagreement

Participants generally agree that the equation is implicit and that numerical methods may be necessary to solve it. However, there is no consensus on the best approach or the applicability of the referenced relationships for the specific scenario being discussed.

Contextual Notes

The discussion highlights the limitations of existing resources in providing detailed solutions for high Mach numbers and the challenges posed by the implicit nature of the equation.

Who May Find This Useful

This discussion may be useful for students and professionals in gas dynamics, particularly those interested in shock wave behavior and numerical methods for solving related equations.

twmggc
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I am trying to show how the shock wave angle varies as I hold the deflection angle constant and increase the Mach number. I am trying to solve for Beta (shock wave angle) using the theta-beta-mach relation:

tan(θ)= 2cot(β) * (M2sin2(β)-1) / (M2(1.4+cos(2β))+2)

This seems like it should be a simple problem, but I can't seem to figure it out.
Note, I am using constant specific heats hence the 1.4 in the equation.

Any hints?
 
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If I remember my gas dynamics correctly that equation is implicit with respect to beta.
However, "Elements of Gas Dynamics", by Liepmann and Rosko give an approximate relationship between β and θ when the mach number is large:

\beta ≈ (\gamma +1)/2 * \theta

L&R provide a graphical solution to the weak and strong shocks on page 87. This is probably the best method to show the relationship between deflection angle and shock angle. Also, they note that for a specific mach number there is a maximum possible deflection angle, θ.
 
Thank you for the response, but since I am attempting to model the change in Beta with constant deflection angle the Liepmann and Rosko equation won't help me too much. As far as the graphical solutions go, I have an anderson book with theta-beta-mach relations plotted but they don't go to into detail for higher mach numbers.
 
It's just an implicit equation. Plug it into fsolve or something similar in Matlab. You can't solve it explicitly exactly.
 
Yep, gogo Newton's method. Gotta love Matlab.
 
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