Abstract
A 3-D PTV (three-dimensional particle tracking velocimeter) is constructed for the measurement of an air turbulent boundary layer with zero-pressure gradient at free stream velocity of 4 m/s. A unique illumination technique is developed by using three strobe lamps and a multi-channel signal retarder to obtain relevant particles images in air flows of relatively high velocities. Tracer particles used are plastic micro-balloons (Expancel, Japan Fillite co., Ltd.), whose average diameter is 501μtm and density is 36 kg/m3. Examination of particles' traceability verifies that they can follow periodic variation of fluid motions up to 100 Hz, and therefore that their traceability is good enough to resolve streamwise velocity fluctuations in the turbulent boundary layer measured presently. Turbulence statistics including mean velocities, turbulence intensities and the Reynolds stress are presented and compared with hot-wire measurement, previous LDV measurement and DNS data. The present results are in general agreement with those data, thus demonstrating validity and usefulness of the present technique for the measurement of air turbulent flows. However, near wall measurement encounters difficulty caused by adhesion of the particles to the wall.
