Mid-span losses in turbine blades at subsonic and supersonic speeds

The effects of compressibility are intrinsic to many axial flow turbomachines, is. Both subsonic and supersonic speed ranges are considered in this investigation. Subsonic surface base pressures, and wake energy separation, are a direct result of periodic von Kármán vortex shedding. This is the principal cause of both wake energy separation and the related subsonic base static pressure deficit. At high subsonic speeds a 17oC temperature difference across the wake was observed. This time-averaged temperature separation was a manifestation of the energy separation (Eckert-Weise) effect. At supersonic speeds the trailing edge base pressure, and the wake energy separation, exhibit different characteristics from the subsonic behavior. Shock waves from the trailing edge may impinge on the adjacent suction surface adversely affecting the downstream boundary layer. Supersonic flows usually cause shock and expansion waves and this may occur in steady flows. Other wake modes may also involve von Kármán vortex shedding from the confluence region of the wake. This is not the only form of shedding and anomalous, or exotic, shedding may also play an important role.