Transitional and turbulent flow in a circular microtube

The water flow in a glass microtube with a diameter of 230 μm was investigated using micro particle image velocimetry (micro-PIV). The streamwise mean velocity profiles and turbulence intensities were measured at Reynolds number ranging from 1540 to 2960. Experimental results indicate that the flow transition from laminar to turbulent occurs at Re = 1700–1900 and the turbulence becomes fully developed at Re > 2500. The details of flow structure such as streamwise streaks and transverse vortices were observed in the transitional flow fields for 1800 < Re < 2100. The instantaneous velocity fields by micro-PIV reveal large scale coherent structures, such as streamwise streaks, ejections, sweepings and packet of the transverse vortices in the turbulent flow in the microtube. These observations are consistent with the experimental and simulation data of turbulent flow at the macroscale.