Aaron Glaser

Performance of an Axial Flow Turbine Driven by Multiple Pulse Detonation Combustors

Experimental studies were carried out to investigate the performance of a hybrid propulsion system integrating an axial flow turbine with multiple pulse detonation combustors. The integrated system consisted of a circular array of six pulse detonation combustor (PDC) tubes exhausting through an axial flow turbine. Turbine component performance was quantified by measuring the amount of power generated by the turbine section. Direct comparisons of specific power output and turbine efficiency between a PDC driven turbine and a turbine driven by a traditional steady flow combustor were made. It was found that the PDC driven turbine had comparable performance to that of a steady burner driven turbine across the operating map of the turbine.

Study on the Operation of Pulse-Detonation Engine-Driven Ejectors

Experimental studies were performed to improve the understanding of the operation of ejector augmenters driven by a pulse-detonation engine. The research employs an H 2 -air pulse-detonation engine at an operating frequency of 30 Hz.Static pressure was measured along the interior surface of the ejector, including the inlet and exhaust sections. Thrust augmentation provided by the ejector was calculated by integration of the static pressure measured along the ejector geometry. The computed thrust augmentation was in good agreement with that obtained from direct thrust measurements. Both straight and diverging ejectors were investigated. The diverging ejector pressure distribution shows that the diverging section acts as a subsonic diffuser and has a tremendous impact on the behavior of the inlet entrainment flow. Static-pressure data were also collected for various ejector axial positions. These data supported the thrust augmentation trends found through direct thrust measurements. Specifically, the optimum axial placement was found to be downstream of the pulse-detonation engine near x/D PDE = +2, whereas upstream placements tend to result in decreasing thrust augmentation. To provide a better explanation of the observed performance trends, shadowgraph images of the detonation wave and trailing vortex interacting with the ejector inlet were obtained.

Acoustic Measurements of an Integrated Pulse Detonation Engine with Gas Turbine System

A rig has been designed to integrate an annular array of six pulse detonation engines (PDEs) with a common gas turbine engine. The purpose of this rig is to allow for the examination of the acoustic and performance effects of such integration. The overall effect of this combination is a more compact, simplified engine concept whereby the core (the high pressure compressor, combustor, and high pressure turbine) of a typical gas turbine engine is replaced by the PDE tubes, and combustion occurs in an unsteady manner instead of that which comes from typical steady flow combustors. Success in such integration would result in a more efficient form of combustion that would use less fuel while reducing the weight and cost of the engine dramatically. This paper describes the design of the integration rig, and presents some preliminary pressure history results based on the flow inside the PDE tube, inside the rig itself, and the flow downstream of the turbine to provide an understanding of the behavior of the PDE flow passing through the blades of the turbine.

ACOUSTIC MEASUREMENTS OF A PULSE DETONATION ENGINE

An experimental investigation on the directivity of acoustic emissions from a pulse detonation engine (PDE) was performed in an anechoic facility using a circular array of eight microphones (62 to 167 deg). The acoustic pressure-time traces for the baseline configuration were observed to be composed of an impulsive shock followed by a fast transient decay to ambient conditions. The spectra were characterized by a fundamental broadband distribution in the low frequency range of less than 1 kHz and a 20dB/decade decay rate at frequencies greater than 10 kHz. The higher frequency content is a result of the impulse source of the PDE blast-wave, while the fundamental mode was attributed to the approximate 1 to 2 ms transient following the blast-wave. The PDE operating conditions were systematically varied during the tests to quantify their effects on the acoustic emissions. The results showed an increase in OASPL with fill-fraction and a logarithmic increase with PDE cycle frequency. Fill-fraction was found to be an appropriate parameter for normalizing PDE acoustic data from different detonation tube lengths. In addition, three modes of operation of the PDE were also identified based on the value of fill-fraction. The sensitivity of the PDE acoustic levels to exhaust nozzle geometry was also studied. A converging nozzle showed global reduction in OASPL at all fill-fractions, while diverging nozzles experienced OASPL reductions in only the downstream angles. The results suggest that the acoustic levels were sensitive to both the nozzle length and area ratio, and it was observed that this sensitivity changed with fillfraction.

Acoustic Interactions of a Pulse Detonation Engine Array with a Gas Turbine

*† ‡ Peak pressure attenuation data is presented for pulse detonation combustor (PDC) firing into a single stage axial flow turbine. Cases are presented for both single PDC tubes and for an annular array of six PDC tubes. Pressure attenuation is characterized for a wide array of PDC operating parameters, including fill fraction, equivalence ratio, nitrogen dilution percentage, and firing frequency. Effects of additional cold air flow mixed into the PDC exhaust prior to the turbine inlet are also quantified. It is shown that certain PDC operating conditions lead to a maximum peak pressure attenuation, which should correspond to the greatest energy extraction by the turbine from the PDC exhaust flow.

Experimental Study of Ejectors Driven by a Pulse Detonation Engine

Experimental studies were performed in order to better understand the operation of ejector augmenters driven by a pulse detonation engine (PDE). This research employed a H2air PDE at 30 Hz operating frequency. Static pressure was measured along the interior surface of the ejector including the inlet and exhaust sections. Thrust augmentation provided by the ejector was calculated by integration of the static pressure measured along the ejector geometry. The calculated thrust augmentation was in good agreement with the augmentation found from direct thrust measurements. Both straight and diverging ejectors were investigated. It can be seen from the diverging ejector pressure distribution that the role of the diverging section is to act as a subsonic diffuser. Ejector axial position was also studied. The ejector pressure data follows the same trend as that of the direct thrust measurements. The optimum axial placement was found to be downstream of the PDE near x/DPDE=+2, while upstream placements tended towards a decreasing thrust augmentation. In order to better explain the observed performance trends, shadowgraph images of the detonation wave and trailing vortex interacting with the ejector inlet were obtained.

Effects of Tube and Ejector Geometry on the Performance of Pulse Detonation Engine Driven Ejectors

Experimental studies are carried out to investigate the performance of various pulse detonation engine (PDE) driven ejector configurations. In particular the effects of detonation tube length and ejector-to-PDE diameter ratio (DR) are studied. This research employs a H2-air PDE at 25 Hz operating frequency. Performance was quantified by thrust measurements. It was found that decreasing the detonation tube length increases the ejector thrust augmentation. An optimum ejector-to-PDE diameter ratio was found to exist in the range DR=3 to DR=3.67. The specific impulse of the PDE increases from the baseline no ejector value of 3400 s to approximately 6080 s with an ejector installed.

Acoustic Characterization of a Pulse Detonation Engine

*† ‡ A far-field acoustic analysis of a pulse detonation engine is performed, showing the effect of the major operating parameters on the acoustic signature of the engine. Several simple exit nozzle configurations are installed on the exhaust of the engine in an attempt to reduce or redirect the acoustic energy output from the system, and the effects of these geometries is presented. Shadowgraph imaging is performed to qualitatively account for the impact of these geometries on the shock wave and supersonic jet that characterize the engine exhaust flow. Proprietary noise attenuation mufflers are also installed on the engine to quantify their acoustic benefits.

Performance Measurements of a Pulse Detonation Engine Array with a Turbine

Measurements taken on a hybrid pulse detonation combustor/gas turbine engine show the effect of operating parameters and configuration settings on the specific power output of the system. Utilizing three detonation combustor tubes firing into a power turbine, the effect of various firing patterns and effective firing frequencies is quantified, as well as the effect of adding bypass air into the engine. A further investigation quantifies the benefit of using a stator blade row in this hybrid engine with an unsteady flow field entering into the turbine section.

Acoustic Measurements of Multiple Pulse Detonation Engines Firing Out of Phase

The far-field acoustics of a system comprised of two pulse detonation engines are investigated to determine the effects of geometric and timing parameters. Initially a comparison is made between a single detonation tube and the dual-tube system to isolate the effects of adding the second tube. Then a study is conducted in which the firing time delay between the detonation tubes is varied to determine if any leading shock interactions affect the far-field noise. It is found that tubes fired perfectly out of phase result in the greatest overall sound pressure levels. Further investigation is made into the cross-talk between the detonation tubes, and it is found that although each detonation tube experiences a weakened form of the leading shock from the adjacent tube, there is no significant effect on the detonation cycles due to tube interactions. A final study quantifies the effects of the separation distances of the detonation tubes.