Detonation Driven Ejector Exhaust Flow Characterization Using Planar DPIV

Planar Digital Particle Image Velocimetry (DPIV), being a well-established technique for the measurement of the two-components of velocity within a fluid plane, was used to characterize the transient flow fields downstream of an axisymmetric ejector coupled to a pulse detonation engine (PDE). The PDE, comprised of a single constant area detonation tube 25.4-mm in diameter and 915.0-mm in length, was operated through the stoichiometric combustion of hydrogen and air at atmospheric conditions. The 76.2-mm diameter, 428.6-mm long ejector, positioned 38.1-mm downstream of the tube exit plane, was driven at a combustion frequency of 20 Hz. Conditional sampling of the high temperature, high velocity exhaust flows was performed using a dynamic pressure transducer located within the detonation tube as a trigger source. The PDE-driven ejector exhaust flow was sampled over a range of ninety (90) phase steps to fully map the complete 50.0-ms operating cycle of the engine. The fifty (50) instantaneous velocity vector maps evaluated at each time step were used to determine both mean and fluctuating flow properties. Data acquisition was performed at a single hydrogen/air flow rate corresponding to a detonation tube fill fraction of 1.05. Additional measurements of the PDE exhaust flows without the coupled injector in place were performed, under identical engine operating conditions, in order to characterize the ejector’s ability to lower the strength of the starting vortex ring (through conversion) and hence reduce the unsteadiness of the engine exhaust flow field. The data are believed to be the first quantitative DPIV measurements obtained of the unsteady flow field downstream of an operating pulse detonation engine and are anticipated to provide a validation benchmark database suitable for computational solutions of PDE, and PDE-driven ejector, exhaust flows.