C. Birzer

Quasi-One-Dimensional Model of Hydrogen-Fueled Scramjet Combustors

A computationally efficient, quasi-one-dimensional, supersonic combustion ramjet (scramjet) propulsion model has been produced for use in hypersonic system design studies. The model solves a series of ordinary differential equations using a fourth-order Runge–Kutta method to describe the gas dynamics within the scramjet duct. Additional models for skin friction and wall heat transfer are also included. The equations are derived assuming an open thermodynamic system with equilibrium or simplified-chemistry combustion models. The combustion is also assumed to be mixing-limited rather than kinetically limited. This assumption allows simplification of the modeling and is justified when the model is compared against experimental results. Three test cases are used to validate the performance of the scramjet propulsion model: 1) a reflected-shock-tunnel hydrogen-fueled scramjet experiment, 2) a continuous-flow hydrogen-fueled scramjet ground test, and 3) a segment of the HyShot II flight test. The results show that the model simulates scramjet propulsion with a reasonable degree of accuracy.

Reliability investigations of leadless QFN packages until end-of-life with application-specific board-level stress tests

We report board level stress tests of leadless QFN packages (pitch 0.5 mm) with focus on different application fields. We did temperature cycling tests, drop test, bend test, and power cycling tests, with special focus on the influences of board design and soldering technology. We performed the stress tests until end-of-life and determined the dominating failure modes. In our temperature cycling study on 2.35 mm thick boards solder joints of SnAgCu performed slightly worse than SnPbAg. We were able to optimize the thermal pad design on the PCB to improve the temperature cycling reliability. For drop test we achieved an excellent reliability by comparing different board designs. This was achieved by avoiding copper trace cracking within the board. This failure mode we verified also with cyclic bend tests. Additionally we performed power cycling investigations using different power consumptions and solder pastes for board assembly (SnAgCu and SnPbAg). A strong lifetime dependence on power and a superior behavior of SnAgCu solder was found. The results were successfully correlated with finite element simulations. In our stress tests we observed clear evidence for influence of soldering technology and board design/technology on board level reliability performance. For different application fields satisfactory reliability can be achieved in case specific measures on board assembly and printed circuit board design are taken

Quasi-one-dimensional modeling of hydrogen fuelled scramjet combustors

A computationally efficient, quasi-one-dimensional supersonic combustion ramjet propulsion model has been produced for use in hypersonic system design studies. The model uses a series of ordinary differential equations, solved using a 4th order Runge-Kutta method, to describe the gas dynamics within the scramjet duct. Additional models for skin friction and wall heat transfer are also included. The equations were derived assuming an open thermodynamic system with equilibrium or simplified chemistry combustion models. The combustion was also assumed to be mixing rather than kinetically limited. This assumption allows simplification of the modeling and was found to be justified when the model was compared against experimental results. Three test cases are used to validate the performance of the scramjet propulsion model: (1) modeling a reflected shock tunnel hydrogen fuelled scramjet experiment, (2) a continuous flow hydrogen fuelled scramjet ground test and (3) a segment of the HyShot II flight test.

The role of primary and secondary air on wood combustion in cookstoves

ABSTRACT A two-stage solid fuel research furnace was used to examine the claim that through forced draught greater mixing and more complete combustion could be achieved. By varying the primary air (PA) and secondary air (SA) flow the influence on the combustion process was investigated. In the first part of the combustion, when the release of volatile compounds predominates, the variation of neither PA nor SA had a significant influence. In the second part when mainly char is oxidised an increase in both PA and SA lead to a rising nominal combustion efficiency ()), with a greater impact observed with SA. Furthermore higher air flows caused the heat transfer, to a pot above the furnace, to decline. Therefore forced draught does lead to greater mixing and mitigation of emissions, but in the presented configuration a trade-off between a higher NCE and a lower heat transfer needs consideration.

Atmospheric plasma thruster: Theory and concept

Dielectric barrier discharge plasma actuators generate a net response force that exhibits potential for thrust applications such as propulsive systems. In this work, an angled actuator in which the exposed and encased electrodes are not parallel has been investigated using direct force measurements and particle image velocimetry. It was shown that the induced force was nonlinearly increased by increasing the angle between the electrodes. In addition, the direction of the upstream component of the ionic wind was changed by varying the electrode angle. Modifying the angle between the electrodes changes the electric field strength in the vicinity of the plasma actuator, thereby changing the response force produced. Analytical calculations were used to compare expected results with results obtained experimentally. Then, using the results obtained experimentally, a plasma thruster was designed as proof of concept for dielectric barrier discharge plasma actuators as propulsive devices.

Laser Attenuation Correction for Planar Nephelometry Concentration Measurements

Planar imaging of optically dense media using laser diagnostics is subject to measurement errors due to the occurrence of laser attenuation. Laser attenuation effects are particularly significant in Planar Nephelometry, a technique which infers particle concentration from the intensity of light scattered from particles. The current study presents an iterative correction method for Planar Nephelometry concentration measurements to account for errors due to laser attenuation. This method minimizes the influence of laser attenuation by applying the corrections directly on instantaneous planar images of the medium investigated. As instantaneous images are used, the method is suitable for measurements of highly turbulent flows that require instantaneous planar information. The proposed correctionmethod is validated experimentally using Planar Nephelometry concentration measurements. Experiments conducted used neutrally buoyant spherical particles suspended in water at various known concentrations. Results indicate that corrections can be used to improve the accuracy of concentration measurements from 65% to approximately 90%.

Dynamic- and post-stall characteristics of pitching airfoils at extreme conditions:

Post-stall flow structure and surface pressures are evaluated to determine the effects of large angles of attack, perching like manoeuvres on the flow about a NACA 0021 airfoil exposed to dynamic stall. Phase-averaged particle image velocimetry was performed to assess the load development during the constant angular velocity pitch-up motion and in post-stall conditions. Evaluation of the resultant aerodynamic loads indicates that initial airfoil rotation generates significant delays in force response. Furthermore, the reduced frequency is shown to influence the angle of attack at which deep stall is initiated, to the extent that fully separated flows are delayed to an angle of attack of 60°. Vortex structures are linked to lower surface pressures with increased angle of attack and also for post-stall flow conditions. Likewise, the presence of the vortex structures shifts the centre of pressure significantly along the airfoil chordline immediately after cessation of the airfoil rotation. At the maximum angle of attack, the centre of pressure is shown to move aft for fully separated flow conditions. The variation in location of the centre of pressure, not only changes the moment generation and aero-elastic characteristics of the airfoil, but also increases structural torsional loading and fluctuations that result in increased fatigue of helicopter rotor shafts and horizontal-axis wind turbines.

Investigation into the effect of electrode angle on force production of a dielectric barrier discharge plasma actuator

Dielectric Barrier Discharge (DBD) plasma actuators impart a momentum transfer to the surrounding medium that in turn produces a net response force. The amount of force generated is directly proportional to the electric field strength. The electric field strength of a DBD plasma actuator can be modified by changing the angle between the electrodes. A larger electrode angle produces a higher magnitude electric field and therefore higher magnitude response force. Direct force measurements were made to measure the change in response force produced with changing electrode angle, with higher response forces generated experimentally with larger electrode angles. By analyzing the electrode configuration of a DBD plasma actuator as a capacitor, a theoretical relationship between electrode angle and thrust produced was developed and matched to the experimentally determined results. Results indicate changing the angle between the electrodes increases the electric field strength and therefore response force.

Humanitarian technology research group: Developments at the University of Adelaide

The recently established Humanitarian Technology Research Group at the University of Adelaide, Australia, utilizes world-class research facilities and researchers in the fields of combustion, fluid mechanics and laser diagnostics in order to develop affordable technology for resource-constrained communities. The motivation of the research group is to save lives and improve quality of life for all. Recent and on-going developments include bio-char producing, dung-burning cookstoves that produce 90% less carbon monoxide emissions compared with traditional three-stone fires; and continuous-feed solar disinfection (SoDis) water treatment devices designed to eradicate water-borne pathogens. New projects include development of design guidelines to build wind turbines based on a range of manufacturing capabilities; bio-digesting toilets; and guidelines for the establishment of cookstove manufacturing plants. This paper highlights some recent results and developments from these projects.