Shock Losses in Transonic Compressor

StBoXIC compressors were, for many years, limited to relative flow velocities equal to a Mach number of 0.75 or below. This limitation was a result of increasing losses, which occurred above this relative Mach number and, for the low energy additions utilized, caused a sizable loss in compressor efficiency. However, by the use of blade shapes less susceptible to shock losses, good compressor performance was obtained with a transonic compressor (ref. [1])1 in which the tip relative flow velocity was slightly supersonic. The data from this early transonic compressor seemed to be a simple extension of that obtained from subsonic compressors. The loss data obtained from this transonic compressor rotor could he correlated with subsonic compressor losses by use of the loading parameter D factor. The D factor is described in reference [2] and defined in the symbol list in the Appendix. Because of this correlation, it was felt that the shock losses in this transonic compressor rotor were negligible. However, as more data became available over a wider range of loadings, Mach numbers, and solidit y it was obvious that the D factor was not sufficient to establish design conditions of transonic compressors. A study was made of the blade element loss taken from 14 transonic compressor rotors in reference [3]. Fig. 1 is reproduced from reference [31 in which the tip element loss has been plotted against the D factor for minimum loss operation. Superimposed on this plot is the usual loss band as shown in the D factor report (ref. [ 2 ]) . It is apparent that the bulk of the transonic data falls well above the