Large-scale three-dimensional particle image velocimetry study of wing tip vortex

Particle Image Velocimetry (PIV) is a technique used to make instantaneous measurements of fluid velocities. PIV uses small tracer particles to accurately track the fluid flow. The tracer particle positions are illuminated and frozen using short pulse duration, high-powered laser light illumination in the form of a laser sheet. The positions of the tracer particles are captured using a standard photographic lens in conjunction with a digital camera. The displacement of the tracer particles over a short duration of time greater than 300 ns is used to calculate fluid velocities from two sequential digital images.; The traditional two-dimensional PIV technique makes two component velocity measurements in the plane of the laser sheet. The new three-dimensional PIV system permits three-dimensional fluid velocity measurements at a plane. The three-dimensional PIV system is an off-axis PIV system that uses two cameras in a stereoscopic arrangement. Each camera system determines a different perspective velocity measurement of the same flow field. A unique camera system calibration is used to determine the optical parameters that are necessary for a reconstruction of the three-dimensional velocities within the laser sheet.; The three-dimensional PIV system was applied to a study of a wing tip vortex. The wing tip vortex study resulted in a large amount of data and served to characterize numerous facets of the flow field. The PIV data was used to determine the position of the vortex, the vortex strength as characterized by the circulation, and the vortex core size. Due to the nature of the instantaneous three-dimensional PIV data, the vortex wander was also captured. Furthermore, the global PIV data provided information on the vortex structure at several planes of measurement. The three-dimensional PIV data were compared to Laser Velocimetry data previously taken in another investigation using the same model. The wing tip vortex study served to illustrate the capabilities and benefits of the PIV system with respect to other experimental measurement techniques, and to provide further insight into a complicated flow field.