Experimental and numerical investigations of trailing edge injection in a transonic turbine cascade.

Trailing edge mixing flows associated with coolant injection are complex, in particular at transonic flows, and result in significant aerodynamics losses. A series of tests and calculations on a high-pressure turbine vane cascade with trailing edge injection were conducted to investigate the influence of trailing edge injection on the loss characteristics of the transonic profile. Wake traverses with a five-hole probe and measurements of the pressure distribution on the profile were taken for injection mass flow ratios of 0 and 4.1% under a test Mach number of 0.7. In the meantime, two-dimensional numerical predictions were carried out for exit isentropic Mach numbers of 0.7, 0.85 and 1.1 and injection mass flow ratios of 0, 4.1%, 4.7% and 5.2%. Numerical predictions show a reasonable agreement with the experimental data, and wake total pressure losses and flow angles as well as pressure distributions on the profile were compared to calculations without trailing edge injection, showing a significant effect of trailing edge injection on the wake development and its blockage effect on the flow in the vane cascade passage. The outlet total pressure loss and flow angle are increased with increasing exit Mach number. The trailing edge injection of 4.1% increases the static pressure in the rear part of vane suction side, and then reduces the vane loading, thus causing decreased wake losses at different exit Mach numbers. At transonic flows, the injection also reduces the strength of the shock wave at the trailing edge pressure side. In addition, the injection decreases the outlet pressure circumferential-unevenness at an exit isentropic Mach number of 0.7, while it increases the pressure circumferential-unevenness at higher exit Mach numbers. [ABSTRACT FROM AUTHOR]