Time-Resolved Stereoscopic PIV Measurement of Unsteady Wingtip Flowfield

Abstract

Time-Resolved Particle Image Velocimetry (TR-PIV) which can measure velocity fields at sampling rate of 10 kHz or higher sapling rate is now widely applied to practical flow problems. The TR-PIV provides the two dimensional distributions of the spectrum of the velocity fluctuation because it can measure the two dimensional velocity distributions at high sampling rate. But flow fields in industrial wind tunnel applications are three dimensional. Three-dimensional velocity measurement is strongly needed. The objective of this research is to develop time-resolved stereoscopic PIV system for industrial wind tunnels and to apply the system to unsteady wingtip flowfield on a single rectangular wing. The objective flow fields are unsteady, not uniform, and strongly influenced by a probe. Generally, it is difficult to measure such unsteady velocity fields. For example, hot wire anemometer which is widely used for unsteady velocity measurement is not suitable for the objective flowfield due to the intrusiveness. The time-resolved stereoscopic PIV can measure such flow fields precisely because it is not intrusive. Thus, the time-resolved stereoscopic PIV is suitable to investigate the objective flow fields. Time-resolved stereoscopic PIV system was developed for industrial wind tunnel testing. Unsteady wingtip velocity field was measured by the time-resolved stereoscopic PIV system in JAXA 2m x 2m low-speed wind tunnel. The wingtip vortices behavior of NACA0012 rectangle wing model was investigated. Finally, the power spectrum density distributions of the velocity fluctuation were shown to clarify the vortex behavior and to demonstrate the effectiveness of the time-resolved stereoscopic PIV data to specify the unsteady flow phenomena.