Development of a high-frame-rate high-resolution particle image velocimetry system and applications to the characterization of synthetic jet actuators

Abstract

This thesis presents the hardware development for two high-frame-rate particle image velocimetry systems. One of them is based on the use of a high-speed film camera, with a frame-rate of up to 10,000 frames per second and an image resolution of 1,400 by 1,000 equivalent pixels. A computerized digitizing station for automated conversion of images from entire film rolls into digital format was developed for this system. The second PIV system is based on the use of a CCD camera with frame-rates of up to 3,000 frames per second and a maximum image resolution of 512 by 512 pixels. The performance of these systems was demonstrated by utilizing them to experimentally characterize the flowfield generated by a synthetic jet actuator, operating at a frequency of up to 100 Hz. The synthetic jet actuator was capable of generating two completely different flowfields. At low amplitudes of oscillation, the actuator produces a suction flow, while at high amplitudes it produces a flowfield resembling a jet. The lack of instantaneous flow axisymmetry, which is typical of the flowfield generated by these devices due to the presence of natural instability and unsteadiness in the shear layer, would have been missed if conventional point-measurement techniques were used such as hot-wires or LDV. These asymmetries/instabilities are not periodic but rather quasiperiodic and even ensemble-averaging techniques would have missed them. The utilization of the developed PIV systems enabled the measurement of the instantaneous velocities at many points within a 2-D plane of the flowfield, the documentation of the temporal evolution of the flowfield, and the temporal characterization of quasi-periodic phenomena occurring within the flowfield.