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 that particle seeding is problematic 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. Sharp-focusing optics will be employed to demonstrate the feasibility of achieving near-planar imaging of density gradients and velocity. Another important challenge that will be addressed in the current work is the extension of Schlieren “PIV” to non-turbulent freestream flows away from wall boundary layers and shear layers. This may be accomplished by combining Schlieren “PIV” with techniques such as jet injection or laser-energy deposition. Alternatively, plasma actuation for flow control would naturally lead to local density gradients that could be tracked using the proposed approach. Proof-of-concept shakedown tests will be performed in an axisymmetric helium jet and on the center-plane of a supersonic wind tunnel facility in preparation for studies of high-frequency actuation in Phase II.