Large-eddy simulation and passive control of flows for a low pressure turbine cascade

A rectangular bar which just likes a forward-backward facing step was designed to passive control of the Low-Pressure Turbine (LPT) PakB cascade suction surface separation. Large-eddy simulation (LES) was adopted to analyze the separated-transition flows for the PakB cascade with and without the rectangular bar at Re (Reynolds number based on inlet condition and axial chord) of 86,000 and the freestream turbulence intensity of 1%. Computed results of uncontrolled condition agree well with the experimental data of Lake et al.[6, 7]. And the LES results shown that the rectangular bar control device was successful to control the LPT cascade suction surface separation and provides about 10% kinetic loss coefficient reduction from the uncontrolled one. Unsteady flow structures were also investigated in detail. Static pressure fluctuation frequency at six locations, ranging from 0.56C_x to 0.95C_x axial chord location and with a constant wall normal distance y/h=1.0, was the same to the separation bubble vortex shedding frequency. Unsteady fluctuation velocity was examined too, which confirmed that the separation bubble vortex frequency was the same to the suction surface static pressure fluctuation frequency.