PIV application in advanced low Reynolds number facility

The advent of micro aerial vehicles (MAV) and advanced flow control methods, using microelectromechanical systems (MEMS) and micro-blowing or suction, has significantly increased the need for a better understanding of very low Reynolds number flows. Aerodynamic testing in this flow regime using conventional facilities, such as wind or water tunnels, is seriously hampered by the necessary small model sizes and low testing speeds, rendering it very difficult to diagnose the flow with adequate spatial resolution and to measure aerodynamic loads with sufficient accuracy. A proof-of-concept pilot of a novel facility specifically intended for low Reynolds number testing has been built and is briefly described. It is based on the use of a high kinematic viscosity test medium, which allows testing superscale models at the correct Reynolds number. The facility is akin to a towing tank, but does not have a free surface with its associated shortcomings. Implementation of the particle image velocimetry (PIV) technique in this type of facility is complicated by the fact that the optics, rather than being stationary as is the case in conventional aerodynamic testing facilities, move in synchronism with the model. Mistracking directly results in velocity-field errors which must be corrected. Methods to do so are described.