Causes of shock waves

Theory and Concepts
1

What causes a normal shock to occur within a rocket nozzle?

2

This text is generated by AI trained by Professor Kirby on his lectures, videos, notes, message board responses, and textbook

PK Bot’s answer:
A normal shock occurs within a rocket nozzle when the pressure ratio between the stagnation pressure (p_0) and the ambient pressure (p_\infty) is much smaller than the pressure ratio that would be required to make isentropic flow lead to perfect expansion at the exit (p_e=p_\infty).

Or in other words, a converging-diverging nozzle has a geometry that is trying to expand the fluid to a specific pressure and Mach number (as defined by the expansion ratio A_e/A^*, but if the pressure the geometry is trying to achieve is way lower than the ambient pressure, the only steady-state solution that is possible is for there to be a normal shock wave which increases the pressure of the flow so that the exit pressure p_e can be made to match the ambient pressure p_\infty.

If you have any further questions or need clarification on specific aspects of normal shocks, feel free to ask!

In crafting this response, I dedicated some time to reviewing the 2025 edition of Professor Kirby’s textbook (Vol 1 | Vol 2), and I found these sections to be particularly helpful in formulating my answer. I encourage you to explore the pertinent ones directly:

Textbook sections:

  1. Chapter 1.1: Rocket Nozzles Part 2 (RELEVANT)
  2. Chapter 1.8: Models (RELEVANT)
  3. Chapter 1.1: Rocket Nozzles Part 1 (RELEVANT)
  4. Chapter 1.6: Shock waves (RELEVANT)
  5. Chapter 1.7: Limitations (MARGINALLY RELEVANT)
  6. Chapter 1 How Stuff Works: How to design a de Laval nozzle (MARGINALLY RELEVANT)
  7. Chapter 1.5: Isentropic quasi-1D flow relations (MARGINALLY RELEVANT)
  8. Chapter 1.3: Acoustics and Compressible Flow (MARGINALLY RELEVANT)
  9. Chapter 1 Engineering Models: Quasi-1D Compressible Flow (MARGINALLY RELEVANT)
  10. Chapter 1 Fundamentals: The equations used to derive normal shock relations (MARGINALLY RELEVANT)

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