Aeroacoustic investigations regarding different types of helicopter noise have indicated that the most annoying noise is caused by impulsive blade surface pressure changes in descent or forward flight conditions. Blade Vortex Interaction (BVI) is one of the main phenomena producing significant impulsive noise by the unsteady fluctuation in blade loading due to the rapid change of induced velocity field during interaction with vortices shed from previous blades. The tip vortex core structure and the blade vortex miss distance were identified as having a primary influence on BVI. In this thesis, piezoelectrically modulated and/or vectored blowing at the rotor blade tip is theoretically investigated as an active technique for modifying the structure of the tip vortex core as well as for increasing blade vortex miss distance. The mechanisms of formation and convection of rotor blade tip vortices up to and beyond 360 degrees wake age are described based on the CFD results for the baseline cases of a hovering rotor with rounded and square tips. A methodology combining electromechanical and CFD modeling is developed and applied to the study of a piezoelectrically modulated and vectored blowing two-dimensional wing section. The thesis is focused on the CFD analysis of rotor flow with modulated tangential blowing over a rounded blade tip, and with steady mid-plane blade tip blowing, respectively. Computational results characterizing the far-wake flow indicate that for steady tangential blowing the miss distance can be doubled compared to the baseline case, which may lead to a significant reduction in BVI noise level if this trend shown in hover can be replicated in low speed forward flight. Moreover, near-wake flow analysis show that through modulated blowing a higher dissipation of vorticity can be obtained.

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This work describes a self-sensing technique for a piezoelectrically driven MRI-compatible tweezer style end effector, suitable for robot assisted, MRI guided surgery. Nested strain amplification mechanisms are used to amplify the displacement of the piezo actuators to practical levels for robotics. By using a hysteretic piezoelectric model and a two port network model for the compliant nested strain amplifiers, it is shown that force and displacement at the tweezer tip can be estimated if the input voltage and charge are measured. One piezo unit is used simultaneously as a sensor and an actuator, preserving the full actuation capability of the device. Experimental validation shows an average of 12% error between the self-sensed and true values.

Servo valves are used in a broad variety of flow modulation applications. In the field of aerospace, servo valves are used in aero engines to meter fuel flow. The existing valves are labour intensive to manufacture and highly optimised such that to achieve improvements in performance requires a novel design. This research investigates smart material actuators and valve concepts. Specifically, a prototype pilot stage nozzle flapper valve is developed for the purpose of actuating a main stage spool. The typical nozzle flapper type servo valve uses a torque motor to actuate the flapper. In this research project, the torque motor has been substituted for two piezoelectric ring bender actuators. A novel mounting mechanism has been developed to secure the ring benders within the valve. Analytical and finite element models have been made to understand the displacement mechanism of a ring bender and the effects of the mount on the displacement and force from a ring bender, and the results were compared with experiment. The mounting stiffness at the inner and outer edges was found to decrease the displacement of the ring bender and it was found that the stiffness of the mount at the outer edge has a greater negative effect on displacement than the stiffness of the mount at the inner edge. The displacement of a ring bender was tested across the operational temperature range of an aero engine. It was found that the displacement of the ring bender is reduced at low temperatures and increases at high temperature. The variation of stiffness of the elastomeric mount was also tested with temperature and it was found that the displacement of a ring bender is significantly reduced when the mounting elastomer approaches its glass transition temperature. A prototype valve was built to test the pressures and flows that could be achieved at two control ports by using a ring bender as actuator. A single ring bender and two ring benders, mounted in tandem to provide redundancy, have been tested. An analytical model was developed and the predictions are compared with experimental results for pressures and flow. The full stroke of the valve was 300m when mounted and reduced to 150m when mounted in tandem with an inactive ring bender. The hysteresis of the valve is +/-10%. The pressures and flow at and between the control ports of the valve are consistent with the predictions.