Craig Law

Influence of Cathode Shape on Vacuum Arc Thruster Performance and Operation

Vacuum arc thrusters (VATs) are a potentially useful technology for use as microthrusters, given their simplicity, low mass, and low-power requirements. However, further development is still needed to improve and mature their performance and operation. In an effort to improve thruster characteristics, we investigate the use of conically shaped convergent cathode surface profiles in a low-power coaxial VAT design. Experimental measurements of ion current density distribution, thrust, and erosion rate were taken for a range of cathode profiles and materials. Results show that modifying the profile of the cathode face can affect the plasma jets plume distribution and even improve thrust production in certain cases. One likely cause of the thrust improvement is speculated to be increased charge exchange collisions resulting in a lower average ion charge state of the ejecting plasma.

Real-Time Control of the Heating of an Airfoil

Dynamic Data-Driven Application Systems constitute nowadays one of the most challenging applications of simulation-based Engineering Science [1]. DDDAS imply a set of techniques that allow the linkage of simulation tools with measurement devices for real-time control of systems and processes [2]. DDDAS entails the ability to dynamically incorporate additional data into an executing application, and in reverse, the ability of an application to dynamically steer the measurement process. These systems need accurate and fast simulation tools, hence the off-line computations to limit as much as possible the on-line computations. In order to obtain the most efficient solver, all the sources of variability are introduced as extra-coordinates as to solve only once the model off-line to obtain its most general solution to be then considered in on-line purpose. However, such models result defined in highly multidimensional spaces. A technique recently proposed, called Proper Generalized Decomposition [3], allows circumventing this redoubtable curse of dimensionality.Copyright

Shear Layer Evolution in Shock Wave Diffraction

All previous studies on shock wave diffraction in shock tubes have spatial and temporal limitations due to the size of the test sections. These limitations result from either the reflection of the expansion wave, generated at the corner, from the top wall and/or of the reflection of the incident diffracted shock from the bottom wall of the test section passing back through the region of interest. This has limited the study of the evolution of the shear layer and its associated vortex which forms a relatively small region of the flow behind the shock and yet is a region of significant interest. A special shock tube is used in the current tests which allows evolution of the flow to be examined at a scale about an order of magnitude larger than in previously published results, with shear layer lengths of up to 250 mm being achieved. Tests were conducted at Mach numbers from 1.4 to 1.6 with wall angles of 10, 20, 30 and 90°

Two-dimensional numerical study of planar shock-wave/moving-body interactions

Abstract.The interaction of a planar shock wave with a body moving at supersonic speed has been considered with particular focus on shock-on-shock interactions. Three interaction types were previously identified by Smyrl (1964). This work adds a fourth type to these interactions and restates the interaction type classification and the transitions between the various interaction types. A pseudo-steady analysis of key interaction points and flow features is used to predict the various transitions. The criteria presented here are compared to results from a numerical Euler model of the interactions. A comparison of results from the numerical model with experimental results shows good agreement and thus the existence of the various interaction types and transition criteria have been confirmed using the numerical model.