Transonic Relief in Fans and Compressors

Abstract Every supersonic fan or compressor blade row has a streamtube, the “sonic streamtube,” which operates with relative inlet Mach number of one. A key parameter in design streamtube” is area ratio between throat and upstream passage area, Athroat/Ainlet. In this article, it shown that one unique value exists for ratio. If differs, even slightly, from value, then either chokes its suction surface boundary layer separated due to strong shock. Therefore, surprising practice designers have relatively little problem designing sections an close unity. This article shows occurs physical mechanism known as “transonic relief.” designer makes mistake designs wrong ratio, relief” will self-adjust spanwise streamtube height automatically moving toward optimal correcting designer’s error. Furthermore, incidence changes, self-adjusts, effectively controlling blade’s range. Without relief,” transonic would be impossible. develops simple model allows decoupled other mechanisms systematically studied. The on based thus determined universal relationship core preliminary presented. Finally, implications relaxing manufacturing tolerances future distortion tolerant blades are discussed.