Aerospace Engineering
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Browsing Aerospace Engineering by Subject "active flow control"
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Item Experimental Analysis and Analytical Modeling of Synthetic Jet-Cross Flow Interactions(2007-05-02) Ugrina, Sandra; Flatau, Alison; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Synthetic jet actuators are light, compact fluidic devices that have demonstrated efficient energy transfer capabilities important in preventing or delaying flow separation. The unique operational mechanism of these actuators suggests they could be used to induce significant load distribution changes at lower angles of attack, where the flow is fully attached. This research was motivated by an interest to study the design challenges and performance aspects of these control systems needed to maneuver unmanned/micro aerial vehicles without the need of utilizing conventional control surfaces. Axisymmetric, 32-mm diameter synthetic jet actuators, based on piezoelectric composite technology were manufactured and characterized. Velocity and turbulence intensity of synthetic jets issuing at a frequency of 2200 Hz changed as a function of geometry parameter ratios, Strouhal and Reynolds numbers. Maximum mean synthetic jet velocity of approximately 30 m/s was achieved. The influence of these synthetic jets on fully attached flows was tested at free stream velocities ranging from 3 to 20 m/s. It was found that a jet-to-free stream velocity ratio (R) of at least one was needed for the synthetic jet to penetrate the boundary layer and affect the potential flow above it. Second part of this research was directed towards developing a basis for an analytical model that would offer flexibility for investigating the sensitivity of the actuator placements, frequency, size, issuing velocity and injection angles on aerodynamic loads and moments. Integral methods were used to predict the jet trajectory, velocity and diameter changes as a result of various synthetic jet-cross flow conditions. Fair agreement with experimental data was reached for jet-to-free stream velocity ratios above one. Solutions of this model in conjunction with a modified lifting surface theory was then used to determine the change in the lift coefficient on a 0.07 m chord rectangular flat plate with a 0.3 m span as a function of synthetic jet actuator location, diameter and velocity. An approximate 4% lift augmentation was estimated using these techniques due to a single actuator operation implying more benefits when future perturbations produced by an array of synthetic jet actuators are implemented.Item Flow Control Using Plasma and Synthetic Jet Actuators on Bluff Bodies(2007-09-17) Haack, Sarah Jo; Flatau, Alison B; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis shows the time-averaged effect of plasma and synthetic jet actuators on flow over bluff body shapes for delaying flow separation and, therefore, reducing pressure drag. The percentage of pressure drag reduction is used to evaluate the effectiveness of these two unique actuators for varied applied voltage, actuator position and flow velocity on a circular cylinder and 2D extrusion of a rotorcraft tail boom cross section. Two non-dimensional parameters were used to evaluate the effect of the actuators: coefficient of momentum (Cμ) and non-dimensional surface distance between the location of the actuator and the flow separation point (SD). Both actuation techniques beneficially affect the pressure distribution by decreasing the pressure near the location of the actuators and increasing the pressure in the separated flow region. Contour plots displaying the variation of the percentage of drag reduction as Cμ and SD vary illustrate optimal operating conditions based on these parameters.