Simultaneous Cinematographic PIV and PLIF measurements at kilohertz frame rate for turbulent cavity flows

A temporally-resolved flow visualization method has been developed for simultaneous measurement of velocity and concentration quantities in time-varying flows through the combination of cinematographic Particle Imaging Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF). PIV images are acquired using two high-speed CMOS cameras that were optically combined and registered by using a non-polarizing beam splitter and a calibration target with known dimensions. The alignment uncertainty contributes up to 5{\%} to the overall velocity measurement uncertainty. A third camera was added to simultaneously record PLIF images. The illumination of both particles and fluorescent dye is provided by two high repetition rate frequency-doubled Nd:YAG lasers. A long-pass color filter in front of PLIF camera eliminates the laser light reflected by PIV particles. A sequence length of 1083 image pairs with 1600 x 800 pixels was obtained at 1500 frames per second while simultaneous PLIF images with a full resolution of 800 x 600 pixels are taken through synchronizing signal generator. Both mean and instantaneous velocity and concentration fields are presented along with dynamic pressure data to illustrate the effect of the large-scale structures on the self-sustained oscillation inside the cavity. Correlations between the fluctuating velocities and concentration in the impinging shear layer reveal the dynamics of the transient mixing process.