High resolution PTV system and its application in the measurement in viscous sub layer in smooth open channel flow

Viscous sublayer has an important role in open channel flow,and shear stress and vorticity areboth derived from this area. Due to its physical dimensions is in the order of 0.1 mm in fully developed tur-bulence flow,common measurement methods are difficult to observe viscous sub layer. This paper illus-trates a High-Resolution PTV coupled PIV system built for measuring the inner and outer layer of openchannel flow. The threshold iteration increasing method,gray truncation method,elliptical indicator and fill-ing indicator are used for High-Resolution PTV image processing. Probability matching method is used formatching the particles and calculating the velocities. The mean velocity,turbulence intensity,skewness andkurtosis distribution in viscous sublayer are got in open channel flows. The friction velocities were got by fit-ting the mean velocity distribution in viscous sublayer,and the results are consistent with the Newtonianfluid constitutive equation. The mean velocity,turbulence intensity and Reynolds stress of inner and outerlayer can all be converted into reasonable dimensionless by the friction velocity from fitting the mean veloci-ty distribution in viscous sublayer,and data in the share region between HR-PTV and PIV can connectsmoothly. Various distribution of open channel flows were compared with the data from direct numerical sim-ulations in channel flow to verify the results.