Energy Analysis of Pulsating Coolant Ejection

High-pressure turbines are subjected to high expansion ratios which may result in supersonic vane or rotor outlet. In the supersonic regime, shock waves are formed at the vane trailing edges that periodically impact on the downstream rotor blades and the neighboring vane. Pulsating cooling was proposed to modulate the trailing edge shocks to diminish the detrimental efficiency abatement and structural problems. A large test section equipped with three airfoils, replicated the actual loading of a transonic vane. Tests were performed in a short duration compression tube facility at four Mach numbers (0.8, 0.95, 1.1 and 1.2) and two different Reynolds numbers (4 and 6 million). Coolant was fed to the trailing edge of the central airfoil through a siren valve, that allowed to study four different coolant blowing cases: no-blowing, continuous blowing at three pressure levels and a pulsating coolant blowing condition. Unsteady numerical simulations of the flow over the airfoil model were performed using ANSYS 14 (Fluent) flow solver. In order to understand the impact of the different steady and unsteady cooling schemes on the efficiency of high pressure turbine bladings, the individual contribution of trailing edge and profile losses were calculated. The coolant ejection generated a significant reduction of the trailing edge loss. The overall losses also diminished by the introduction of cooling as compared to no blowing case. Improvements in loss levels owing to pulsating cooling observed to be more pronounced for the engine representative cooling rates (∼3%). The trends in loss variation with respect to cooling scheme show that pulsating cooling may become superior for high blowing cases.