Sub-idle compressor map generation with enhanced physical background

Abstract

Consulta en la Biblioteca ETSI Industriales (Riunet)

[EN] Sub-idle is an essential operating region since it comprises engine windmilling performance, relight and pull-away, which are essentially matters of safety in aviation. Moreover, to accurately predict the engine’s behaviour, it is imperative to provide performance solvers with precise component maps. However, the data obtained from rig tests is usually insufficient at the low speeds and other methodologies have to be applied to generate the sub-idle region of compressor maps. Reliable sub-idle and relight performance solvers are essential during the first stages of the design for engine manufacturers to accomplish the contractual and certification obligations regarding engine relight. The current work deals with the sub-idle compressor map generation of two different compressors. The objective of this project is to generate the sub-idle region of these two compressors, enhancing as much as possible the physical background. However, since the amount of data available differs from one to another compressor, different methodologies were applied. The data available for Compressor A was limited to the original compressor map, therefore, an extrapolation from above-idle map to the sub-idle region was accomplished. Traditionally, the linearized parameters have been utilised to perform the extrapolation method. Nevertheless, as this group of parameters cannot be defined at locked rotor conditions, the extrapolation of the quasi nondimensional mass flow, pressure ratio and specific torque has been proposed and developed in the current work. As a result, more consistent results have been obtained since, contrary to the linearized parameters, the negative pressure ratios and negative torques characteristic at very low speeds, can be defined with this set of parameters. Apart from the original compressor map, detailed geometry as well as some experimental data were available for Compressor B. This allowed the computation of the zero speed line by means of analytical methods. Subsequently, the sub-idle characteristic was interpolated between the zero-speed line and the above-idle given speed lines. The experimental data available was used to calibrate the interpolation equations. In addition, to enhance the physical background of the generated map, the steady state windmilling line was computed, based on analytical methods, and a methodology is proposed and carried out to verify the generated map with the use of this line. Finally, the interpolated map is compared to several speed lines generated through CFD simulations performed in a parallel research project. The final outcome is the sub-idle region of the compressor map of Compressor B, physically enhanced by the physics of the zero speed line, the experimental data and the study of the steady state windmilling line.