A Comparison of Fluidic and Physical Obstacles for Deflagration-to-Detonation Transition

摘要

A fluidic obstacle has been proposed as an alternative to conventional deflagration-to-detonation transition (DDT) enhancement devices for use in a Pulsed Detonation Engine (PDE). Experimental results have been obtained utilizing unsteady reacting and steady non-reacting flow to gain insight on the relative performance of a fluidic obstacle. Using stoichiometric premixed hydrogen-air, transition to detonation has been achieved using solely a fluidic obstacle with comparable DDT distances to that of a physical orifice plate. Flame acceleration is achieved due to the intense turbulent mixing characteristics inherent of a high-velocity jet and the blockage created by the virtual obstacle. Turbulence intensity (T.I.) measurements, taken downstream of both obstacles with hot-film anemometry during non-reacting steady flow, show a conservative trend that a fluidic obstacle produces approximately a 240% increase in turbulence intensity compared to that of a physical obstacle. Ignition times were reduced approximately 45%, attributable to the increase in upstream T.I. levels relative to the fluidic obstacle during the fill portion of the PDE's cycle. Transition to detonation was obtained for injection compositions of both premixed stoichiometric hydrogen-air and pure air.