Development of a Prelimenary Aerothermal Design Tool for Airbreathing Propulsion Systems: Turbojet, Turbofan, Ramjet and Scramjet Engines

Abstract

Airbreathing propulsion systems are engines that generate thrust for aeronautical vehicles and missiles. There are different types of airbreathing propulsion systems such as turbojet, turbofan, turboprop, turboshaft, ramjet, and scramjet engines. In the present study a computational tool that can be used for the preliminary design of turbojet, turbofan, ramjet, and scramjet engines is developed. Preliminary design process of a propulsion system is an important stage in the way of decreasing computational and test costs. For these reasons there some major commercial softwares such as GasTurb, NPSS and GSP that deal with the preliminary design of the airbreathing propulsion systems used by the engineers. The first step in preliminary design is performance calculations of design and off-design propulsion calculations. The first requirement for performance calculations is performing design point calculations and related parametric studies. Most important design parameters are decided to fulfil the mission design requirements such as thrust, thrust specific fuel consumption (TSFC) and specific thrust. After setting the design point parameters, working behaviour of the engine is also analysed at different offdesign points. In this study, software for design point performance calculations was developed for turbojet, mixed/unmixed turbofan, ramjet, and scramjet engines. Firstly, a numerical performance model was implemented into the code. After this point, design point calculations for each engine were validated based on some well-studied engines in the literature. The developed program reads Rayleigh Flow tables which were integrated into the code for calculated specific heat ratios for ramjet, scramjet combustors and afterburners. In addition, basic efficiency estimation tools for compressor, combustion chamber and turbine were implemented into the software. The comparison of results obtained with present methodology and the GasTurb results show very good agreement. The developed software has also an improvement against GasTurb for the design of supersonic intake components. GasTurb uses some ad hoc military standard correlations to calculate the total pressure recovery factor (TPRF) for supersonic intakes. The present methodology uses oblique shock relations based on the number of inlet ramps and ramp angles addition to the mentioned military correlations used by GasTurb. It should be clear that the results obtained using the oblique shock equations are more realistic compared to the military standards