Nozzle Flow Model

Nozzle Flow Model Screen

The program can either calculate the combustion parameters in the combustion chamber, or perform the complete engine performance analysis, calculating the flow through the nozzle.

Clear the checkbox "Calculate nozzle flow", in order to choose the first possibility, or mark it to start the nozzle flow analysis:

Nozzle conditions

If you are solving the nozzle flow problem, you have to define at least nozzle exit conditions, specifying one of three parameters: nozzle exit pressure, nozzle expansion area ratio, or nozzle expansion pressure ratio.

Nozzle conditions (Lite Edition)

Nozzle conditions (Standard Edition)

The program can calculate the performance for a combustion chambers with finite or infinite cross section area. The default model assumes the infinite cross section area of the chamber. To switch to the finite-area model, mark the checkbox "Nozzle inlet conditions", and then specify the chamber contraction area ratio Ac/At or mass flux in the combustion chamber.

If specified, the nozzle inlet and exit conditions are used for chamber and nozzle sizing, together with additional parameters on the screen Chamber Geometry (press the button Chamber spec to jump directly to the that screen). (only available in RPA Standard Edition)

The program can calculate the performance with respect to the shifting and frozen chemical equilibrium in the nozzle. The default model assumes the shifting chemical equilibrium in the whole nozzle. To switch to the frozen chemical equilibrium model, mark the checkbox "Frozen equilibrium flow", and then specify the nozzle section, where application of this model should be started.

Nozzle Shape and Efficiencies

The program calculates both theoretical and delivered engine performance. You can define correction factors on the screen Nozzle Shape and Efficiencies, otherwise the program estimates it on the basis of defined engine parameters, such as chamber pressure, propellant components and nozzle conditions.

Nozzle Shape and Efficiencies (Lite Edition)

Nozzle Shape and Efficiencies (Standard Edition)

In RPA Standard Edition, you can also control the considered by the program nozzle flow effects:

Switch off the flag Consider multiphase flow and phase transition in order to suppress the calculation of multiphase flow effects. Note that for the most of solid propellant problems this flag should be switched on.

Switch off the flag Consider species ionization effects in order to to suppress the calculation of species ionization effects.

Switch off the flag Estimate performance loss due to flow separation in order to disable the additional calculation of flow separation effects.

Ambient condition

By default the program calculates performance of the rocket engine at the sea level conditions (pa=1 atm, or 14.7 psi), optimum nozzle expansion (pe=pa), and vacuum conditions (pa=0).

To calculate the performance at desired ambient conditions, you can also explicitly specify either the specific ambient pressure or the range of ambient pressures given as high and low range values.

Ambient condition

The pressure is an absolute pressure and can be entered using one of the following units: MPa, atm, kg/sm2, bar, psi, Pa.

Throttle settings

By default the program calculates performance of the rocket engine assuming the propellant flow rate that correspond to nominal thrust.

To calculate the performance at desired throttle settings, you can also explicitly specify either the specific throttle value, or the range of throttle values given as high and low range values.

Throttle settings

The throttle value is a ratio of propellant flow rate at desired throttle setting to flow rate that correspond to nominal thrust (100% flow rate).

Last modified: February 22, 2011