Douglas R. Smith

A digitally controlled voltage generation and measurement unit optimised for high-precision electrical metrology is described. It is optically isolated from the controlling computer and contains specially constructed isolated power supplies allowing continuous operation without the need to recharge batteries. The source has a simple microcontroller that is pre-programmed with firmware to control operation and to carry out simple repetitive measurement tasks, such as generation and quantisation of signals using uniform sampling. The merits of the developed unit are demonstrated by three example applications: (i) the application of the unit to control a Josephson voltage standard, (ii) the implementation of a transfer standard for the calibration of the electronic instrumentation of fatigue testing machines traceable to the primary electrical standards and (iii) the force measurement of an ion thruster traceable to the primary electrical standards at the industrial user level.

A new technology for the control of next-generation airplanes using virtual wing shaping with synthetic jet actuators is presented. In this approach, an array of actuators is used to modify the aerodynamic performance of a wing and mimic control surface deflections. In the model, the control effect is represented with a nonlinear, parameterized model, derived from experimental data. An adaptive compensation scheme for the implementation of such actuator arrays on a nonlinear tailless aircraft model at low angles of attack has been developed. Adaptive inverse arrays (set of adaptive inverse models of the actuators) are employed for cancelling the effect of the jet nonlinearities. A nonlinear state feedback control law is designed, wherein a set of intermediate states are used as controls for other aircraft states. Parameter projection-based adaptive laws are used to ensure desired closed-loop stability.

An investigation into the interaction of a synthetic jet actuator array with a thick, turbulent boundary layer was conducted and the results are presented here. This paper documents an experimental effort that was directed towards improving the understanding of synthetic jet actuator arrays and the mechanism by which these actuators control flows at scales much larger than themselves. Of specific interest in the interaction of a synthetic jet flow and the boundary layer flow on a flat or curved wall where the axis of the synthetic jet is perpendicular to the direction of the oncoming flow. The investigation addressed, in broad terms, a typical control application involving internal flows. A synthesis of the results will provide guidance and direction in future actuator designs and implementation strategies, and feed design input to test plans for an extensive study of actuator control effects in a duct with variable pressure gradient and variable streamline curvature.

Experiments were conducted to investigate the response of a high-Reynolds-number turbulent boundary layer in a supersonic flow to the perturbation presented by a forward-facing ramp. Two ramps were used: one with sharp corners, the other with rounded corners having radii of curvature equal to 15 initial boundary layer thicknesses. The flow was turned through 20° in each of the compressions and expansions. Hence, there was no net change in the flow direction over the ramps and only a small change in free-stream conditions due to the entropy increase across relatively weak shocks. The two experiments gave similar results. In the middle of the relaxing boundary layer, the streamwise Reynolds stress undershot the undisturbed levels and exhibited a response similar to that observed in subsonic boundary layer flows recovering from an impulse of streamline curvature (Smits, Young & Bradshaw 1979b). The turbulent shear stress vanished throughout most of the boundary layer, and an overall destruction of the turbulence production mechanisms was apparent as the boundary layer exhibited a slow recovery.