Performance characterization of swept ramp obstacle fields in pulse detonation applications

Abstract

Pulse Detonation technology offers the potential for substantial increases in thrust and fuel efficiency in subsonic and supersonic flight Mach ranges through the use of a detonative vs. deflagrative combustion process. One of the approaches to reliably obtain a fuel-air detonation is to accelerate a deflagration combustion wave to detonation through the use of turbulence devices, known as detonation-to-deflagration transition. Current geometries for deflagration-to-detonation transition sacrifice much of the gains through losses from high velocity flows over obstacle fields required for detonation initiation. In this study, experimental swept ramp obstacle fields were characterized in an effort to realize decreased pressure losses while still creating the gas dynamic and turbulence necessary for detonation initiation. Characterization included measurement of pressure loss across the combustor during "cold flow" operation with no ignition or fuel present, and detonability testing that employed ion probe measurement of combustion wave velocity. Minimizing pressure losses existing in current designs will result in dramatic improvement of system performance. In addition to swept ramp fields, other configurations were analyzed using computational fluid dynamics (CFD) and subjected to performance testing. Of particular interest were obstacles of similar blockage area, but without the swept sides associated with streamwise vorticity in the flow field. Testing of unswept configurations allowed insight into the mechanisms for DDT and narrowed the field of practical obstacle geometries.