Aaron Jerome Glaser

Investigations of Thrust Generated by a Valved, Multitube PDE with Exit Nozzles

A thrust stand capable of measuring the time averaged thrust produced by a PDE was designed and tested. The study quantified the effect of exit nozzles on a valved multi-tube PDE system with three tubes arranged in a close-packed configuration. Three nozzle geometries were considered; straight, converging, and converging-diverging. Numerical simulations were also performed of a single detonation chamber with the same nozzle exit geometries. The test measurements are used to validate the predictions of time-resolved pressure, and the thrust predictions from the limit cycle model of PDE. Comparisons of trends in test measurements and model predictions of pressure-time traces and thrust show good agreement, for all the nozzles considered in the present study.

Experimental and Numerical Investigation of a Valved Multi-Tube PDE

A valved multi-tube PDE system with three tubes arranged in a close-packed configuration has been tested using three different exit nozzle geometries (straight, converging and converging-diverging). The PDE was operated using ethylene-air mixtures with each tube firing at 20 Hz in a sequential pattern. High frequency pressure transducers were installed throughout the flow path to investigate the time-resolved chamber pressure. Numerical simulations were also performed of a single detonation chamber with the same nozzle exit geometries. Analysis of the experimental data revealed that the converging and converging-diverging nozzles had similar behavior and increased the average pressure rise by 40% when compared to the straight nozzle. Although the numerical simulations matched the experimental trends, they over-predicted the static pressure-rise. The numerical results represent an upper bound, in guiding the design of an optimized PDE system.

Measurement of Pressure -Rise in a Pulse Detonation Engine

*† ‡ § Experimental measurements of static pressure -rise and thrust are made in a pulse deton ation engine (PDE). The research employs a valved ethylene -air 3 -tube PDE at an operating frequency of 20 Hz per tube. New terminology and definitions for pressure -rise in a PDE are introduced. The mean PDE fired static pressure was quantified with both low and high frequency pressure sensors. Pressure measurements were obtained at the combustor head -end and tail -end for configurations with straight and converging exit nozzles. It was determined that the high frequency pressure measurements provided a more accurate measure of the mean PDE fired pressure. The test measurements are used to validate computational predictions obtained using a quasi -1D limit cycle code. The overall PDE pressure -rise was found to be sensitive to system flow losses and the e xit nozzle geometry. It was observed that in an un -optimized configuration, with straight exit nozzle, the PDE operated with an overall pressure loss instead of a pressure gain. However, an overall pressure gain was observed when the PDE included a conve rging exit nozzle. The PDE thrust was quantified using a thrust stand to measure thrust directly, and by using tube pressure measurements to calculate thrust. The thrust calculated by pressure measurements was found to over -predict both the thrust stand measured thrust and computational thrust predictions.