Application of Two-Color digital PIV for turbomachinery flows

The potential application of a Two-Color Digital-Particle-Image-Velocimetry (DPIV) system to turbomachinery-type flows was evaluated. This system records double-exposed color images onto a single CCD sensor (3060 x 2036 pixel) and eliminates the photographic-film processing time and subsequent digitization time as well as the complexities associated with conventional image-shifting techniques. The system was calibrated using simulated known displacements and gradients and was applied to the flowfield in a 20-in.-dia. axial fan. DPIV implementation issues such as optical access, seeding strategies, and blade-passage synchronization related to turbomachinery flows were explored. Instantaneous velocity measurements were made at different spanwise locations. These measurements provided instantaneous information on the blade wake region, the flow separation off the blades, and the interaction between successive blades and also allowed a greater understanding of the impact of these phenomena on turbomachinery performance.