Time-Resolved Flow Properties in a Turbine Driven by Pulsed Detonations

Abstract

Theoretically, pressure-gain combustion like that of a pulsed-detonation combustor allows heat addition with reduced entropy loss compared to a typical steady deflagration combustor. The pulsed-detonation combustor is inherently unsteady, and time-resolved measurements are required to identify unsteady flow processes at the turbine inlet and exit. In this study, the radial turbine of a Garrett automotive turbocharger was coupled directly to and driven, full admission, by a pulsed-detonation combustor fueled by hydrogen or ethylene. Full-cycle time-resolved turbine inlet and exit pressures were obtained from pressure transducers mounted to wall static pressure ports. Tunable diode laser absorption spectroscopy was used to obtain full-cycle time-resolved turbine inlet and exit temperatures and velocities. Optical access permitted the use of high-speed video for particle streak velocimetry to obtain time-resolved turbine inlet velocities during blowdown with a 20 Hz ethylene-fueled pulsed-detonation combustor with 0.9 fueled fraction and 0.5 purge fraction. A comparison of laser-based and video-based measurements was made for the blowdown portion of the pulsed-detonation combustor cycle. First-ever full-cycle time histories of turbine inlet and exit velocities, total temperature, total pressure, mass flow, and total enthalpy rate revealed reflected pressure waves and showed momentary reverse flow, and thus unsteady accumulation and expulsion of mass and enthalpy.