Single-Cycle Impulse from Detonation Tubes with Nozzles

Experiments measuring the single-cycle impulse from detonation tubes with nozzles were conducted by hanging the tubes in a ballistic pendulum arrangement within a large tank. The detonation-tube nozzle and surrounding tank were initially filled with air between 1.4 and 100 kPa in pressure simulating high-altitude conditions. A stoichiometric ethylene–oxygen mixture at an initial pressure of 80 kPa filled the constant-diameter portion of the tube. Four diverging nozzles and six converging–diverging nozzles were tested. Two regimes of nozzle operation were identified, depending on the environmental pressure. Near sea-level conditions, unsteady gas-dynamic effects associated with the mass of air contained in the nozzle increase the impulse as much as 72% for the largest nozzle tested over the baseline case of a plain tube. Near vacuum conditions, the nozzles quasi-steadily expand the flow, increasing the impulse as much as 43% for the largest nozzle tested over the baseline case of a plain tube. Competition between the unsteady and quasi-steady-flow processes in the nozzle determine the measured impulse as the environmental pressure varies

Effect of Porous Thrust Surfaces on Detonation Transition and Detonation Tube Impulse

As pulse detonation engine development matures, it becomes increasingly important to consider how practical details such as the implementation of valves and nozzles will affect performance. Inlet valve timing and valveless inlet designs may result in flow of products back upstream and, consequently, reduction in impulse over the ideal case. Although proper inlet design or operation under flowing conditions may minimize these losses, our study addresses the worst-case effect that a porous thrust surface may have on the measured impulse. A series of single-cycle tests have been carried out to measure the impulse in stoichiometric ethylene–oxygen mixtures, initially between 20 and 100 kPa, in a detonation tube with a porous thrust surface. The tested thrust surfaces had blockage ratios ranging from completely solid (100% blockage ratio) to completely open (0% blockage ratio). A 76% loss in impulse was observed with a thrust surface blockage ratio of 52% at an initial pressure of 100 kPa. The time to detonation transition was found to be more dependent on the mixture’s initial pressure than on the thrust surface blockage ratio. A model of the impulse in detonation tubes with porous thrust surfaces was developed

Detonation Tube Impulse in Subatmospheric Environments

Thrust from a multicycle pulse detonation engine operating at practical flight altitudes will vary with surrounding environment pressure.We have carried out the first experimental study using a detonation tube hung in a ballistic pendulum arrangement within a large pressure vessel to determine the effect that the environment has on the single-cycle impulse. Air pressure decreased below 100 kPa, whereas initial pressure of the stoichiometric ethylene–oxygen mixture inside the tube varied between 100 and 30 kPa. The original impulse model (Wintenberger et al., Journal of Propulsion and Power, Vol. 19, No. 1, 2002, pp. 22–38) was modified to predict the observed increase in impulse and blowdown time as the environmental pressure decreased below 1 atm. Comparisons between the impulse from detonation tubes and ideal steady-flow rockets indicate incomplete expansion of the detonation tube exhaust, resulting in a 37% difference in impulse at a pressure ratio (ratio of pressure behind the Taylor wave to environmental pressure) of 100

Impulse Correlation for Partially Filled Detonation Tubes

The effect of nozzles on the impulse obtained from a detonation tube of circular cross section has been the focus of many experimental and numerical studies. In these cases, the simplified detonation tube is closed at one end (forming the thrust surface) and open at the other end, enabling the attachment of an extension. A flowfield analysis of a detonation tube with an extension requires considering unsteady wave interactions making analytical and accurate numerical predictions difficult (especially in complicated extension geometries). To predict the impulse obtained from a detonation tube with an extension (considered a partially filled detonation tube), we utilize data from other researchers to generate a partial-fill correlation

Supporting Computer-supported collaborative work (CSCW) in conceptual design

In order to gain a better understanding of online conceptual collaborative design processes this paper investigates how student designers make use of a shared virtual synchronous environment when engaged in conceptual design. The software enables users to talk to each other and share sketches when they are remotely located. The paper describes a novel methodology for observing and analysing collaborative design processes by adapting the concepts of grounded theory. Rather than concentrating on narrow aspects of the final artefacts, emerging “themes” are generated that provide a broader picture of collaborative design process and context descriptions. Findings on the themes of “grounding – mutual understanding” and “support creativity” complement findings from other research, while important themes associated with “near-synchrony” have not been emphasised in other research. From the study, a series of design recommendations are made for the development of tools to support online computer-supported collaborative work in design using a shared virtual environment