Numerical loss analysis on slot-type casing treatment in a transonic compressor stage

To understand the loss mechanism of slot-type casing treatment, a numerical loss analysis
has been carried out in a 1.5 axial transonic compressor stage with various slots. Spanwise
and streamwise distribution curves of pitch-averaged entropy have been presented to survey
the development of loss generation. Further, detailed entropy distributions at eight axial
cuts, which have been taken through the blade row and slots, have been further analyzed
to interpret the loss mechanism. The most dramatic loss growth occurred above 95% span,
which directly resulted from slots injection flow upstream the leading edge. Loss generations
with smooth casing have been primarily ascribed to low-momentum tip leakage flow/vortex
and suction surface separation at the leading edge. CU0 slot, the arc-curved slots with
50% rotor tip exposure, has been capable of suppressing the suction surface separation loss.
Meanwhile, accelerated tip leakage flow brought about additional loss near the casing and
pressure surface. Upstream high entropy flow would be absorbed into the rear portion of
slots repeatedly, which resulted in further loss.