Florida Center for Advanced Aero Propulsion

Three-dimensional flowfield measurements within a separated swept shock wave/boundary-layer interaction are acquired using a four-camera tomographic particle image velocimetry system in the present study. The turbulent, Mach 2 incoming flow has a unit Reynolds number of , and the shock interaction is produced by a sharp, unswept fin with a deflection angle of 15 deg from the freestream flow. Three volumes are examined to focus on different regions of the flow: 1) conically developed flow away from the wall spanning almost the entire interaction, 2) near the fin surface, a region that remains relatively unexplored, and 3) parallel to the floor in the near-wall region of the interaction. The flowfield is investigated in depth by visualizing velocity isosurfaces, with special emphasis on the growth of the interaction as one moves away from the interaction origin, which is a unique feature of swept interactions with strong crossflow. Initial results of the flowfield response to microjet actuation at four separate locations within the interaction are also discussed. The effect of introducing disturbances using upstream actuators is found to be the most prominent in the region near flow separation, where the streamlines are modified and overall separation size is reduced.

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The effect of flexoelectricity on the formation and evolution of domain structures in ferroelectric materials is developed by integrating strain gradient theory into a finite element phase field model. Length scales associated with elastic strain gradients and the corresponding polarization gradient across a domain wall are integrated into the time-dependent Ginzburg–Landau theory and numerical simulated. Theoretical relations of a shear strain gradient along an electrode/dielectric interface are first solved and verified numerically using the finite element model. A singularity in the strain gradient–induced polarization is shown to occur as the elastic strain gradient length scale approaches a flexoelectric length scale. The theory and finite element modeling is then extended to quantify strain gradient electromechanics near 180° and 90° tetragonal phase domain structures. It is shown that the strain gradient length scale [Formula: see text] strongly influences changes in strain across the domain walls but has a negligible effect on the polarization. Strain gradient effects become negligible when [Formula: see text], where [Formula: see text] is the polarization domain wall length scale.

A fluidically driven microactuator that generates supersonic, pulsed microjets has been implemented with smart materials to actively and precisely control the frequency of the microjets in a closed-loop manner. Since this actuator relies on a number of microscale flow and acoustic phenomena to produce the pulsed microjets, its resonant frequency is determined by its geometry and other flow parameters. The design discussed in this paper integrates piezoelectric stacks by connecting them to movable sidewalls within the actuator such that the microactuatorʼs internal geometry can be controlled by varying the voltage across the piezo-stacks. An open-loop control scheme demonstrates the frequency modulation capabilities that are enabled with this design: very large frequency deviations (up to ) around the actuator design frequency are attained at very high rates (up to 1 kHz). Closed-loop control of the microactuatorʼs frequency was also demonstrated, and the results indicate that (combined with appropriate sensors) this actuator could be used effectively for active, feedback control in high-speed, resonance-dominated flowfields. This proof of concept study clearly illustrates the ability of this robust and compact actuator to produce perturbations that can be modulated and controlled based on the desired control objective.

We report a chip-scale electrodynamic synthetic jet actuator that integrates both a coil and a wax-bonded NdFeB permanent magnet using standard silicon micromachining processes. A copper micro-coil and a poly-dimethyl-siloxane (PDMS) diaphragm with the magnet are fabricated onto two different dies. An orifice, through which the jet is synthesized, is laser cut on the coil die. The dies are then assembled together to create a device with the dimensions 7.5 mm × 7.5 mm × 1 mm. Operating at 180 Hz and 20 mW input power, the device generates a fluidic jet with a peak velocity of 2.1 m/s.

Vortex dynamics of wakes generated by rectangular aspect-ratio 2 and 4 and twodimensional pitching flat plates in free stream are examined with direct numerical simulation and water tunnel experiments. Evolution of wake vortices comprised of tip, leading-edge and trailing-edge vortices is compared with force history for a range of pitch rates. The plate pivots about its leading edge with reduced frequency from /8 to /48, which corresponds to pitching over 1 to 6 chord lengths of travel. Computations have reasonable agreement with experiments, despite large differences in Reynolds number. Computations show that the tip effects are confined initially near the wing tips, but begin to strongly affect the leading-edge vortex as the motion of the plate proceeds, with concomitant effects on lift and drag history. Scaling relations based on reduced frequency are shown to collapse aerodynamic force history for the various pitch rates.