Numerical loss analysis in a compressor cascade with leading edge tubercles

A numerical analysis of loss has been carried out to explore the loss mechanism of leading
edge tubercles in a high speed compressor cascade. Taking the lead from flippers of the
humpback whale, tubercles are passive structures of a blade for flow control. Evaluation
of the overall performance in terms of entropy increase shows that the loss reduction is
achieved both at high negative and high positive incidence angles, while a rise in the loss is
obtained near the design point. And a smaller wave number as well as a smaller amplitude
results in lower additional losses at the design point. Spanwise and streamwise distributions
of pitchwise-averaged entropy increase combined with flow details have been presented to
survey the loss development and, subsequently, to interpret the loss mechanism. The tubercle
geometry results in the deflection flow and the consequent spanwise pressure gradient. This
pressure gradient induces formation of counter-rotating streamwise vortices, transports away
the low-momentum fluid near wall from crests towards troughs and leads to local high loss
regions behind troughs as well as loss reduction behind the crests in comparison to the
baseline. The interaction between these vortices and flow separation by momentum transfer
leads to separation delay and the consequent loss reduction at the outlet.