Self-Excited Fluidic Oscillators for Gas Turbines Cooling Enhancement: Experimental and Computational Study

Pulsed flow has been shown to enhance heat transfer coefficients of impinging jets. This paper considers the use of pulsed impinging jets, derived from a self-excited fluidic oscillator, for gas turbine cooling. Self-excited oscillatory behavior was demonstrated in simulations over a wide range of inlet to outlet pressure ratios from poi /p2 = 1.0025 to Poi /P2 = 2.18 for a device with a nozzle throat to splitter length of 10.4 mm. Heat transfer simulations at two test points (460 and 769 Hz) resulted in Nusselt number enhancement of 13 and 15% over corresponding cases with nonperiodic flow at the same time-mean mass flow rate. Increased oscillation frequency was found to increase Nusselt number enhancement. In the range 10 < f < 20 kHz (0.04 < f L lv < 0.08), the Nusselt number approximately doubled. A computational geometry optimization study was performed to increase oscillation frequency, resulting in a 30% increase. Validation experiments were performed using thin-film gauge (high-frequency) and calorimeter (low-frequency) measurement techniques. Experimental results were broadly in line with numerical results; a Nusselt number enhancement of approximately 20% (186 < f < 322 Hz) was achieved. Despite the enhancement in heat transfer, the fluidic oscillator is far from an ideal solution due to extreme pressure losses inside the device.