An enhanced compressor map extension method suited for spool speeds down to 1%

Physically sound compressor maps are the key to accurate simulations of aircraft engine performance. The simulation of ground starting and windmilling requires maps which include speeds down to 1% as well as pressure ratios less than unity. The author has described a physics-based compressor map extension method in his ISABE Paper 2019-24299. The map tables use auxiliary coordinates – so-called β-lines – to make reading values from them unambiguous. A single set of parabolas as auxiliary coordinates is well-suited for usual performance simulation tasks. During practical application of the method, it became obvious that extending the map to spool speeds less than 10% is difficult because the use of correlations between work and flow coefficient becomes extremely sensitive. The problem is resolved by introducing a second set of β-lines, in which all parabolas begin at the map origin (flow = 0; pressure ratio = 1) and end on a grid-dividing speed line. The shape of the primary β-line grid, for speeds greater than the grid dividing speed, can be freely selected. The author has already described starting and windmilling simulations using maps generated with the enhanced methodology in an article published in the GPPS Journal 2023.