Uploaded December 2017 | Updated September 2026, 2 weeks ago

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In my converging-diverging (CD) nozzle video (link below), we saw that there were seven different flow conditions in a nozzle. If know what exit-to-reservoir pressure ratio our engine is operating at (see notes below), then we can define what condition our nozzle is operating at based on three pre-computed pressure ratios:

1) Choked Isentropic Subsonic
2) Normal Shock at Nozzle Exit
3) Choked Isentropic Supersonic

In this video, we will compute the pressure ratios needed to obtain the three states listed above for a given nozzle area ratio (Ae/At).

===== NOTES =====
→ In this video, we can say that At = A* for each case because the flow is choked, and we do have sonic flow at the throat.

→ We generally know the exit-to-reservoir pressure ratio that our engine is operating at. For instance, if we are analyzing the Space Shuttle Main Engine (RS-25) on the launchpad, then we know the exit pressure is approximately 101.325 kPa. We also know from the engine's specifications that the reservoir (or chamber) pressure is approximately 20.64 MPa. Dividing the two appropriately gives the pressure ratio we are looking for.

===== RELEVANT LINKS=====
→ Blog Post - Converging-Diverging Nozzle Pressure Delineations
joshtheengineer.com/2017/12/17/converging-diverging-nozzle-pressure-delineations

→ Solving the Area-Mach Number Relation
joshtheengineer.com/2016/11/16/solving-the-area-mach-number-relation

→ CD Nozzle MATLAB Code - GitHub
github.com/jte0419/Converging_Diverging_Nozzle

→ Compressible Flow Relations Code - GitHub
github.com/jte0419/Compressible_Flow_Relations

===== RELEVANT VIDEOS =====
→ Explained: Converging Diverging Nozzle
goo.gl/7MBSck

→ Area-Mach Number Relation [CPG]
goo.gl/t8QE9T

→ Normal Shock Relations
goo.gl/Bvv2jj

→ Stagnation Relations
goo.gl/yrT9D4

===== REFERENCES =====
► Modern Compressible Flow, Anderson
► Gas Dynamics, Volume 1, Zucrow and Hoffman
► Elements of Gasdynamics, Liepmann and Roshko