Schlieren Based Seedless PIV for High Frequency Cavity Flow Control Applications in Large Scale Wind Tunnel Facilities

Flow control using high-frequency actuation to reduce acoustic and vibrational loading from weapons bays and sensor apertures requires a diagnostic approach that can capture instantaneous flowfield data at rates of several kHz. Moreover, large wind tunnel facilities suffer the difficulty of particle seeding for techniques such as Particle Imaging Velocimetry (PIV). The opportunity addressed by this proposal is that of extending a focused schlieren-PIV technique for high-speed imaging of density gradients and seedless velocimetry for studies of high-frequency flow control. During phase I, a bench-top focusing schlieren-PIV system capable of millimeter-range depth-of-field has been designed and fabricated and successful measurements were made in the center-plane of a supersonic turbulent boundary layer. During phase II, we propose to develop cost-effective schlieren-PIV system which can be used to make measurements in large and small scale wind tunnel facilities and also in combustion environments. We will address the challenging issues such as conditions for successful velocity measurements in a 3-D cavity flowfield, sensitivity of the system, alternate light sources, and image processing. The integrated cost-effective system will be delivered to AFRL at the end of the program and significant commercial efforts will be made in order to enhance fluid dynamics research at government, academia, and industrial laboratories.