CD-Nozzle-Lib

1D converging-diverging nozzle flow simulator – educational & preliminary design tool.
Built for the Advanced Gas Dynamics course, this library computes flow properties (Mach, pressure, temperature, density) along a CD nozzle given geometry, gas properties, and boundary conditions.

Features

• 5 modular classes:
  • Constants – stores input parameters
  • NozzleGeometry – computes radius & area along nozzle axis
  • ThermoRelations – thermodynamic relations for 1D isentropic / Fanno / Rayleigh flow (as needed)
  • FlowSolver – solves flow regimes with three flexible input options
  • PlotFunc – visualization of results & animated back‑pressure effect
• Solver outputs:
  • Array with [x, M, P/P0, T/T0, rho/rho0, P0/Pref]
  • Flow type classification:
    • Fully subsonic
    • Choked subsonic
    • Normal shock inside nozzle
    • Fully supersonic (under‑/ideal/over‑expanded)

Inputs

Category	Parameters
Nozzle geometry	Converging length Lc, diverging length Ld, inlet radius Ri, throat radius Rth, exhaust radius Re
Gas properties	Specific heat ratio GAMMA (γ), gas constant R
Inlet conditions	Stagnation pressure P0
Ambient (back) pressure	Static back pressure Pe

Dependencies

• Python 3.7+
• numpy
• matplotlib
• scipy

Install them with:

pip install numpy matplotlib scipy

Usage

See the example script Demo_CD_Nozzle.py in the examples/ directory. It demonstrates how to import classes, define inputs, call the solver, and plot results.

The FlowSolver.solver_flow function accepts three modes:

solve_flow(Pe=<user defined value>) – provide ambient static pressure value

solve_flow(shock_position=<user defined value>) – provide normal shock location along nozzle axis

solve_flow(M_throat=<user defined value>) – provide throat Mach number (typically 1 for choked flow)

Results can be visualized using PlotFunc.plot_nozzle_results. An animation of back‑pressure effects can be generated with PlotFunc.create_flow_animation using an array Pe_range.

Outputs

Column	Quantity	Description
x	Distance (m)	Along nozzle axis
M	Mach number	Local Mach number
P/P0	Pressure ratio	Static pressure / stagnation pressure
T/T0	Temperature ratio	Static temperature / stagnation temperature
rho/rho0	Density ratio	Static density / stagnation density
P0/Pref	Total pressure ratio	Local total pressure / inlet total pressure (indicates shock losses)

flow_type string indicates the regime (e.g., Fully Supersonic (Under Expanded)).

Use Cases

Education – understand 1D gas dynamics, normal shocks, over/under‑expansion, and back‑pressure effects.

Preliminary design – evaluate nozzle performance for given geometry and operating conditions.