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Tutorial 03

Size a nozzle and understand expansion state.

Connect the design point to throat size, exit size, contour family, expansion state, and downstream export decisions.

What you will learn

How to set expansion ratio, use auto expansion, choose Bell/Conical/TIC geometry, and read expansion and separation screening notes.

Prerequisites

Set propellants, chamber targets, and a sizing basis. A non-stale solve is required before trusting Review geometry or DXF export.

Steps

  1. Open Define > Engine. Enter Expansion ratio in Operating conditions.
  2. For a finite ambient matched design, click Auto Ae/At for selected ambient. The Matched-Expansion epsilon dialog reports epsilon, exit Mach, exit pressure, gamma used, and the basis.
  3. If Ambient pressure is 0, the app opens Vacuum Auto-Expansion. Choose a finite strategy: Maximum expansion ratio, Maximum exit diameter, Maximum nozzle length, Minimum practical exit pressure, or User-specified design epsilon, then click Set ε.
  4. Open Define > Hardware > Chamber and Nozzle. Select Bell (Rao), Conical, or TIC.
  5. Set Characteristic length, Contraction ratio, Min chamber L/D, Converging angle theta (deg), Conical / start half-angle alpha (deg), and the Bell-only Bell exit half-angle alpha_e (deg) and Bell length fraction when applicable.
  6. Click Solve, then open Review > Geometry and Review > Thermochemistry. Check throat diameter, exit diameter, nozzle length, exit pressure, and warnings.
Nozzle expansion controls and solved Review Geometry outputs
Expansion controls and solved nozzle geometry.

Expected result

The solved case reports a nozzle contour, throat diameter, exit diameter, chamber dimensions, exit pressure, and expansion-regime notes. Separation language is a screening flag for design review, not a certified prediction.

Common notes

  • After applying a new epsilon, re-solve before using Review values, Flowfield Studio, PDF reports, or DXF export.
  • TIC derives entry/exit behavior analytically; Bell exit angle and length fraction apply to the Rao bell option.
  • Overexpansion and separation-risk notes are design insight for validation planning and should be reviewed with the rest of the case assumptions.