Measurement of Wall Shear Stresses of Open-Channel Flow by PTV

Abstract

Wall shear stress distributions of open-channel flows were measured making use of the binary image cross-correlation method (BICC), one of the PTV techniques. Flow fields close to the wall were visualized by a laser light sheet with small tracer particles and the particle images were recorded on a DV format tape using a digital video camera. The images were transferred to a personal computer as a movie file(an AVI file), divided into a series of bit map files(BMP files), and finally transformed to gray-scale binary data before the PTV analysis. Thousands of consecutive images were successfully captured by using this procedure. The shear stresses were estimated from the distributions of turbulence properties very close to the wall. Several estimation methods were compared and their accuracy was discussed in detail.