Experimental Analysis and Analytical Modeling of Synthetic Jet-Cross Flow Interactions

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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.