A computational method for the steady 2-D flow in axially symmetrical rocket nozzles with a given profile is developed, in order to determine the Maximum thrust contour of rocket engine nozzles with large expansion ratio. The optimized nozzles proved a more than 10% increase in the integral specific impulse recorded during the variable altitude atmospheric flight of rocket vehicles. The method is well suited for application in the design of the optimum contour for axially-symmetric nozzles for atmospheric rocket ascent, specifically for aerospike type nozzles, as for other similar industrial applications in gas and steam turbine technology.

In this paper we address the subject of mathematical modelling, more precisely the optimization of algorithms for numerically solving partial differential equations. The problem proposed to be tackled in this paper is the implementation of an algorithm for solving partial differential equations in a significantly faster way than that obtained through applying finite difference schemes. The proper orthogonal decomposition (POD) method is a modern and efficient method of reducing the number of variables that occur as a result of applying centred difference schemes to partial differential equations, thus reducing the running time of the algorithm and the accumulation of truncation errors. Therefore, the POD method has been implemented to obtain a reduced order scheme applied to different partial differential equations, with some practical applications and comparisons with the analytical solutions.

Nitrous oxide has recently entered violently the arena of space propulsion and gained interest, due to its high energy and gasification potential and despite its low oxygen content as an oxidizing chemical and its instability over some 600 C. However, its physical and chemical instability soon proved to be a potential hazard and led to a renewed interest in the study of its behavior as a fluid. In the present contribution computer simulation of the liquid phase flow of the nitrous oxide under high pressure is used to predict and avoid the cavitation into the feeding line tract of rocket engines, specifically of the compound rocket engines feeding line. The method involves a substantially simplified 1-D description of the fluid motion with sufficiently accurate determination of cavitation risk where the feeding duct suffers blunt variations of the cross area or steep turns and corners involving sensible static pressure variations of the fluid. A means of avoiding dangerous behaviors of the nitrous oxide is thus developed that could increase safety margins during the handling of this quite unpredictable oxidizer for the compound, combined or hybrid rocket engines.

Unsteady, non-isentropic, discontinuous flows with energy exchange, during solar heating transients of air turbine towers are approached through a proprietary computational front method, initially developed for the study of ignition in solid propellant rocket motors. Its application in the discontinuous flows with energy exchange also proves highly efficient. Computational efficiency is demonstrated by CFD simulation of transients in the air accelerator of the SEATTLER solar mirror, turbine tower. This is a typically unsteady flow simulation for slender channels. A 1-D computational scheme was developed to simulate the interference between zones with different flow conditions. Given values for the thermochemical properties of the working gas are considered and two zones of different flow characteristics are identified. The first zone is the heat exchanger, where a nonisentropic flow develops. At the aft end of this heating zone a second zone of the channel is encountered after a blunt passage, where an isentropic expansion of the gas begins and extends along the tower up to the upper exit. Into the 1-D, unsteady flow scheme of computation, the discontinuity of equations of motion at the interface between the two zones induces very specific precautions and this methodology is detailed into the paper. Consequently, the computational front scheme covers the dual behavior of the fully non-isentropic flow with mass addition and mixing in the heater and of the fully isentropic flow at the exhaust of the gravity draught tall tower, typical for the solar-gravity draught power plants. Small perturbations of the flow, in the form of developing weak shocks, and blunt discontinuities are simultaneously covered. Code robustness is demonstrated and revealed through diagrams. The 1-D numerical scheme is based on the enhanced method of the computational front with resolution of the expansion wave development.

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