PROBING TURBULENCE WITH 3-DIMENSIONAL PARTICLE-TRACKING VELOCIMETRY

Recent developments in three-dimensional particle-tracking velocimetry (3-D PTV) are reviewed. The instrumentation, data processing algorithm, and applicability range of the 3-D PTV developed at the University of Tokyo are introduced, and then its application to turbulence measurements is presented with some of the authors' perspectives on future 3-D PTV research directions. The 3-D PTV has become a powerful tool for measuring an instantaneous distribution of all three velocity components in turbulent flows. With a highly automated digital image processing technique, motions of neutrally buoyant tracer particles suspended in a flow are tracked, and the three-dimensional displacement of each particle is efficiently calculated from a set of consecutive TV frames; velocity vectors are readily determined by dividing the displacement by the time interval. The results obtained in several turbulent shear flows demonstrate that the measurement uncertainty intervals can be made sufficiently small by the employment of three TV cameras and a precise camera calibration procedure. This technique is most unique in providing not only conventional one-point turbulence statistics but also information on the spatial structure of a flow field, for example, multiple-point correlation tensors. These characteristics are particularly advantageous for studying the quasi-coherent turbulence structures in various complex flows.