Comparison between wave rotor and regenerative cycles in propulsion

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To compare the behaviour of regeneration and wave rotor techniques in jet propulsion a numerical code has been developed and some interesting results has been obtained. The code simulates the thermodynamic behaviour of different jet engines (simple turbojet, turbofan and turboprop), for different operative conditions and engine parameters. The numerical analysis has been carried on considering several efficiencies of regeneration and wave rotor pressure ratio. The simulations have put in evidence the effect of regeneration particularly on the specific fuel consumption and the effect of wave rotor mainly on the specific power. INTRODUCTION. The need of increasing the total efficiency of air breathing engines, led, in last decades to the development of turbo fan engines. These, infact, improve the propulsive efficiency and the global one. Another way to increase the performances of such engines is to improve the thermodynamic cycle and it's efficiency, now a days the possible ways to reach *Graduate Student. t Associate Prof, of Aircraft Propulsion AIAA Senior Member. {Assistant Prof, of Aircraft Propulsion AIAA Member. Copyright © 2001 The American Institute of Aeronautics and Astronautics Inc. All rights reserved. this result are represented by regeneration and wave rotor cycles. The regeneration consists in recovering part of the heath of hot gases (usually before entering the exhaust nozzle), to pre-heath the air coming from the compressor, before introducing it in the combustion chamber. In this way it is possible to improve the thermal efficiency, the specific fuel consumption and the propulsive efficiency. The wave rotor unit is a promising pressure-gain device used in high pressure, high temperature topping cycles for turbine engines.In the wave rotor, unsteady gasdynamic waves are used to tranfer energy to and from the working fluid. This device can be used to increase the maximum pressure and temperature of the cycle improving the performances of aircraft engines. To compare the performances of these two solution, a numerical code, simulating the engine thermodynamic behaviour, has been developed. The code allows to determine the working cycle and the performances of different aicraft engines, such as simple turbojet, turbofan and turboprop, varying both operative conditions and engine parameters, as altitude , flight Mach number, turbine inlet temperature , pressure 1 American Institute of Aeronautics and Astronautics (c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization. ratio, effectiveness of regeneration and wave rotor pressure ratio. The introduction of regeneration and wave rotor changes the shape of a traditional Brayton cycle (see fig. 1 and 2) and the scheme of the engine (fig. 3 and 4). healh exchange air side Healh exchange 6R gas side Fig.l Thermodynamic cycle of a turbojet with regeneration cycle with ware rotor Fig. 2 The cycle of a turbojet with wave rotor. Fig. 4 Scheme of a turbojet engine with wave rotor In figure 2 clearly appears that wave rotor leads to a gain in inlet turbine pressure, this gain depends on Pr and on the temperature ratio across the wave rotor T5w/T3 as shown in detail in fig 5. Many configurations can be adopted to install a regenerator or a wave rotor in an aircraft engine. In this work the regenerator has been placed, for all the engines exhamined, after the last turbine stage. Concerning the wave rotor, only the four-port pressure