ABSTRACT
Fluid is the common name given to gas and liquid. Flow cannot be at rest when there is shearing stress. In addition, most fl ows occurring in nature and engineering applications are turbulent, in which fl ow velocity varies rapidly with randomness and irregularity in space and time, diffi cult to predict accurately. To understand the turbulent fl ow motion in detail, we need to measure the quantitative velocity profi le or distribution of the fl ow.
