Effect of Periodic Pressure Pulses on Axial Turbine Performance

Abstract

Pulse detonation engines show potential to increase the efficiency of conventional gas turbine engines if used in place of the steady combustor. However, since the interaction of pressure pulses with the turbine is not yet well understood, we built a rig to compare steady flow with pulsing flow. Compressed air is used in place of combustion gases and pressure pulses are created by rotating a ball valve with a motor. This work accomplishes two main objectives that are different from previous research in this area. First, we compare steady flow through an axial turbine closely coupled with full annular pulsed flow. Second, the error in turbine efficiency is approximately half the error of previous research comparing steady and pulsed flow through an axial turbine. Our data shows that a turbine driven by full annular pressure pulses has operation curves that are similar in shape to steady state operation curves, but with a decrease in turbine performance that is dependent on pulsing frequency. We demonstrate that the turbine pressure ratio increases with pulsed flow through the turbine and that this increase is less for higher pulsing frequencies. For 40 Hz operation the turbine pressure ratio increases by 0.06, for 20 Hz it increases by 0.12, and for 10 Hz it increases by 0.14. We demonstrate that the peak turbine efficiency is lower for pulsed flow when compared with steady flow. The difference between steady and pulsed flow peak efficiency is less severe at higher pulsing frequencies. For 40 Hz operation the turbine efficiency decreases by 5 efficiency points, for 20 Hz it decreases by 9 points, and for 10 Hz it decreases by 11 points. We demonstrate that the specific power at a given pressure ratio for pulsed flow is lower than that of steady flow and that the decrease in specific power is lower for higher pulsing frequencies. On average, the difference in specific power between steady and pulsed flow is 0.43 kJ/kg for 40 Hz, 1.40 kJ/kg for 20 Hz, and 1.91 kJ/kg for 10 Hz.