Functions
Optional[float]	contraction_ratio_of (cg)
float	nozzle_stagnation_loss (Optional[float] contraction_ratio, float gamma)
float	expansion_ratio_for_exit_pressure (CEACache cea_cache, float MR, float Pc, float Pe, Optional[float] contraction_ratio=None)
dict	calculate_thrust (float Pc, float MR, float mdot_total, CEACache cea_cache, Any config, float Pa=101325.0, Optional[Dict] reaction_progress=None, bool debug=False)

Detailed Description

Nozzle model: RPA delivered thrust + isentropic exit state.

This is the AUTHORITATIVE nozzle: every runner.evaluate() call uses it (flight sim,
time series, pintle, and Layer-1 finalization). Delivered thrust is the RPA basis

    F(Pa) = zeta_n * Cf_vac * P0 * At - Pa * Ae

where Cf_vac is CEA's shifting-equilibrium vacuum thrust coefficient from the cache
tables, zeta_n = nozzle_efficiency, and combustion efficiency zeta_c (eta_c*) rides
in through the efficiency-reduced Pc from the chamber solve — so delivered
Isp = zeta_c * zeta_n * Isp_ideal. See docs/thrust_efficiency_bug_analysis.md for
why the former momentum-method reconstruction (ideal-Tc exhaust velocity) was
retired: it never applied combustion efficiency and over-predicted thrust by
~(1 - zeta_c*zeta_n). The exit state reported here (P_exit, T_exit, M_exit) is CEA's
shifting-equilibrium expansion at the same (P0, O/F, eps); thrust does not depend on it.
Pc is the injector-end pressure; the nozzle expands from P0 = Pc/kappa, the Rayleigh
stagnation loss of a finite-area combustor.

The numba accelerator (engine/accel/kernels.py) computes the SAME delivered
formula from the same tables for the Layer-1 inner loop; parity is enforced live by
tests/test_native_ab_parity.py.

Function Documentation

◆ calculate_thrust()

dict engine.core.nozzle.calculate_thrust	(	float	Pc,
		float	MR,
		float	mdot_total,
		CEACache	cea_cache,
		Any	config,
		float	Pa = 101325.0,
		Optional[Dict]	reaction_progress = None,
		bool	debug = False )

Calculate delivered engine thrust (RPA methodology).

    F(Pa) = zeta_n * Cf_vac * P0 * At - Pa * Ae,   P0 = Pc / kappa

Cf_vac is CEA's shifting-equilibrium vacuum thrust coefficient (cache lookup);
zeta_n is config.chamber_geometry.nozzle_efficiency; combustion efficiency
zeta_c (eta_c*) is already carried by the efficiency-reduced Pc from the
chamber solve, so delivered Isp = zeta_c * zeta_n * Isp_ideal. The exit state
also returned here (P_exit, T_exit, M_exit: CEA shifting equilibrium) is
reporting-only; thrust does not depend on it. See the module docstring and
docs/thrust_efficiency_bug_analysis.md.

Parameters:
-----------
Pc : float
    Chamber pressure [Pa]
MR : float
    Mixture ratio (O/F)
mdot_total : float
    Total mass flow rate [kg/s]
cea_cache : CEACache
    CEA cache for thermochemical properties
config : PintleEngineConfig
    Complete engine configuration
Pa : float
    Ambient pressure [Pa] (default: sea level)
reaction_progress : dict, optional
    Chamber reaction progress; accepted for the call signature, not used

Returns:
--------
results : dict
    Dictionary containing:
    - F: Delivered thrust [N]
    - F_momentum: vacuum term zeta_n*Cf_vac*P0*At [N]
    - F_pressure: ambient back-pressure term -Pa*Ae [N]
    - Cf / Cf_actual: delivered thrust coefficient F/(P0*At)
    - Cf_ideal: CEA ambient thrust coefficient at this Pa
    - P_exit, T_exit, M_exit: CEA shifting-equilibrium exit state; v_exit the ideal
      exhaust velocity on the same basis (reporting-only)
    - Pc_ns, stagnation_loss_kappa: nozzle stagnation pressure and Pc/Pc_ns
    - Isp: Delivered specific impulse [s]

Definition at line 67 of file nozzle.py.

References contraction_ratio_of(), info, and nozzle_stagnation_loss().

◆ contraction_ratio_of()

Optional[float] engine.core.nozzle.contraction_ratio_of ( cg )

A_chamber/A_throat of a ChamberGeometryConfig, or None when the bore is not declared.

Definition at line 31 of file nozzle.py.

Referenced by calculate_thrust().

◆ expansion_ratio_for_exit_pressure()

float engine.core.nozzle.expansion_ratio_for_exit_pressure	(	CEACache	cea_cache,
		float	MR,
		float	Pc,
		float	Pe,
		Optional[float]	contraction_ratio = None )

Area ratio whose CEA shifting-equilibrium exit pressure is Pe (optimum expansion is
Pe = Pa, Sutton & Biblarz ch. 3). ``Pc`` is the injector-end pressure; with a declared
contraction ratio the nozzle expands from Pc/kappa.

Definition at line 57 of file nozzle.py.

References nozzle_stagnation_loss().

◆ nozzle_stagnation_loss()

float engine.core.nozzle.nozzle_stagnation_loss	(	Optional[float]	contraction_ratio,
		float	gamma )

kappa = P_injector_end / P0_nozzle of a finite-area combustor (constant-area heat
addition, Rayleigh line; Huzel & Huang sec. 2, Sutton & Biblarz Table 3-2):

    kappa = (1 + gamma M^2) / (1 + (gamma-1)/2 M^2)^(gamma/(gamma-1)),

M the chamber-end Mach number, A/A* = contraction ratio on the subsonic branch.
Reproduces CEA's finite-area "Pinj/Pinf" to 3e-5. 1.0 when the bore is unknown.

Definition at line 40 of file nozzle.py.

Referenced by calculate_thrust(), and expansion_ratio_for_exit_pressure().