Comparison of the newly developed method of designing plug clustered nozzle with other designing methods


Аuthors

Ezugbaya G. D.1, Kochetkov Y. M.2*

1. NPO Energomash named after academician V.P. Glushko, 1, Burdenko str., Khimki, 141400, Russia
2. Keldysh Research Centre, 8, Onezhskaya str., Moscow, 125438, Russia

*e-mail: swgeorgy@gmail.com

Abstract

The work contains the results of numerical simulation of the flow of an ideal gas in the plug clustered nozzles of a liquid propellant rocket engine (LPRE), conducted in the ANSYS CFX software package. Nozzle contours were designed by three methods: a newly developed method based on the analysis of streamlines, the parabolic method and the classical method of characteristics. Each approach has its own theoretical foundations and practical limitations, which has determined the need for their comparative analysis in terms of effectiveness.
The parabolic method is based on the construction of second-order curves with geometric parameters (flow inlet and outlet angles, radii of curvature of the critical section) and is widely used in engineering practice due to its simplicity. However, its disadvantage is insufficient adaptation to difficult gas dynamic conditions, especially in the supersonic zone. The characteristics method, in turn, takes into account the physics of supersonic flow, where disturbances propagate strictly along the characteristics at a Mach angle. This method provides high accuracy, but requires significant computational resources and detailed boundary conditions, which limits its use in the early stages of design.
The new developed method arose as a result of the analysis of experiments with nozzles of solid-fuel rocket engines (SFRE). Studies have shown that under intense heat exposure, the erosion pattern of the inner surface of the SFRE nozzle repeats the natural flow lines of the supersonic flow. This observation suggested that such profiles have increased aerodynamic efficiency. Were adapted this principle for li-quid propellant engines, despite the differences in operating conditions: the lack of ablation of materials in liquid engines makes the task non-trivial. The theoretical basis was the assumption that the optimal nozzle profile should minimize friction losses and wave resistance, which is achieved by following the geometry of the current lines.
Numerical simulation was performed in ANSYS CFX using the Navier-Stokes equations for an ideal gas and the SST turbulence model. The grid independence of the results was tested on three sequentially shredded grids, which provided a calculation error of less than 1 %. The boundary conditions included setting the mass flow rate and temperature at the nozzle inlet, as well as the atmospheric pressure at the outlet.
The vacuum specific impulse and thrust of the engine are selected as the efficiency criteria. These parameters directly determine the energy characteristics of the liquid propellant in vacuum. The specific impulse was calculated taking into account the incompleteness of gas expansion and friction losses, and the thrust was calculated by integrating the pressure along the nozzle surface and the impulse flow at the slice. A comparison of the methods showed that the new approach provides an increase in specific impulse and thrust.

Keywords:

lug nozzle, aerospike nozzle, nozzle contour, numerical simulation, vacuum specific impulse, thrust

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