Application of a 3-D PTV to the Measurement of Turbulent Air Flows

Abstract

A three-dimensional particle tracking velocimeter (3-D PTV) is applied to the measurement of an air turbulent boundary layer on a flat plate with a free-stream velocity of 4 m/s. To capture particles’ images that are relevant for PTV measurement, a unique illumination technique is developed by using three strobe lamps and a multi-channel signal retarder. Tracer particles used are plastic micro-balloons, whose average diameter and weight density are 50 μm and 36 kg/m³, respectively. Examination of particles’ traceability confirms that they can follow periodic velocity yariation of the surrounding fluid up to 100 Hz, and that the traceability is good enough to resolve streamwise velocity fluctuations under the present flow conditions. Measured turbulence statistics, including the mean velocities, the turbulence intensities and the Reynolds stress, compare reasonably well with hot-wire measurement, previous LDV measurement and DNS data, hence verifying applicability of the present 3-D PTV to the measurement of turbulent air flows. It is, however, found that near wall measurement needs further refinement to deal with adhesion of the particles to the wall.