Abstract
Abstract Investigations on the combined effect of unsteady wakes and purge flows in high-speed low-pressure turbines at engine-relevant conditions are scarce. This study aims at filling the gap of knowledge concerning unsteady interactions in high-speed low-pressure turbine geometries tested at engine-relevant Mach and Reynolds numbers, unsteady wake velocity triangles and purge massflow ratio. The time-resolved aerodynamics of a high-speed low-pressure turbine were investigated in a linear cascade. The tests were performed at an outlet Mach and Reynolds numbers of 0.90 and 70k, respectively. The unsteady wakes were characterized by a reduced frequency of 0.95. A secondary air system was used to inject purge flow at two purge rates. The wake deficit from midspan to the endwall between the wake generator and purge flow slot was characterized. The inlet boundary layer displacement thickness was found to be modulated within +-10% of its mean value. The unsteadiness induced by the purge flow was investigated at the blade leading edge plane. The modulation of the purge flow was found to be insensitive to massflow ratio. The unsteadiness of the secondary flow structures was characterized at the outlet. In the time-averaged frame, the loss cores were found to be characterized by high turbulence intensity. The modulation of the secondary flows increased by replacing the flat endwall with the cavity slot, and with increasing purge flow rate. In particular, the passage vortex was found to be nearly suppressed between adjacent wake passings.
Published Version
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