Nicholas Caldwell

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.

Experimental Analysis of a Hybrid Pulse Detonation Combustor / Gas Turbine Engine

Two major studies are conducted to better understand the flow field inside a hybrid pulse detonation combustor / gas turbine engine. In the first investigation, an innovative measurement method is used to capture high-speed fluctuations in the speed of a turbine rotor being driven by a pulse detonation combustor. Using a low-power laser and a photodiode, blade passing frequencies are converted into rotor velocity measurements which result in speed measurements at sampling rates on the order of 250 Hz. At this sampling rate, individual detonation pulses are discernible in the time history of the turbine rotor speed, and the changes in speed can be used to determine the energy transmitted to the rotor during each pulse. The second study investigates the interaction between two combustor tubes in the form of detonation wave speed measurements and a shadowgraph flow visualization. It is found that when two tubes are fired simultaneously, their decaying leading shocks coalesce into a larger shock front resembling a single shock emanating from the midpoint of the two detonation tubes. When a small time delay is introduced, the blowdown jet of one tube appears to degrade the leading shock of the adjacent tube.

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.

Performance Analysis of a Hybrid Pulse Detonation Combustor / Gas Turbine System

To gain a more comprehensive understanding into the ∞ow dynamics present inside a hybrid pulse detonation combustor / gas turbine engine, two major experimental studies are conducted to indirectly ascertain the ∞ow fleld. The flrst is an examination of the length and time scales over which shock re∞ection and blowdown jet interaction become signiflcant. Based on this work is the suggestion that these phenomena could be useful in minimizing overall noise signatures and internal structural damage due to high magnitude pressure ∞uctuations by attenuating leading shock waves after all reactive mixtures have been combusted. Design considerations are presented which could best take advantage of these phenomena. The second investigation is an in-depth analysis of the high-speed ∞uctuations in the speed of a turbine rotor being driven by a pulse detonation combustor. Using a low-power laser and a photodiode, blade passing frequencies are converted into rotor velocity measurements which result in speed measurements at sampling rates on the order of 250 Hz. At this sampling rate, individual detonation pulses are discernible in the time history of the turbine rotor speed, and the changes in speed can be used to determine the energy transmitted to the rotor during each pulse.

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.

Heat Transfer Model for Blade Twist Actuator System

DOI: 10.2514/1.23120 A lumped mass heat transfer model is developed for a blade twist actuator system that uses thermally activated shape memory alloys to alter the shape of a wing. These alloys are coupled with thermoelectric modules that supply the heat necessary to activate the shape alteration characteristics of the material. The model predicts the unsteady temperatures in different portions of the actuator system, and comparisons between experimental data and the heat transfer model are made. Furthermore, parametric studies are made of system variables to optimize the numerical model, and the effect of each variable on the comparison is examined. Differences between the numerical and experimental models are discussed, and efforts are made to minimize this difference through variations in the numerical variables. The potential for using this technology to increase range and payload of aircraft is discussed. Nomenclature cp = specific heat, J=kg K h = convective heat transfer coefficient, W=K I = electrical current, A N = number of thermoelectric modules in row n = number of time steps q = heat flow, W R = electrical resistance, � T = temperature of thermal zone or atmosphere, C t = time, s � = Peltier coefficient, V=K � t = time step, s � = thermal conductivity, W=K

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.