Abstract
At the exit of a Couette flow cell, the spatial distribution and the temporal change of velocity were measured under sharkskin-like instability. A particle tracking method and laser Doppler velocimetry were applied through microscopic optical system. Under the flow instability, high velocity was detected when adhesion failure inside the cell induced a valley on the free surface, and low velocity was detected when inside adhesion recovery induced a ridge. The high velocity corresponds to complete slip at the cell exit, and it is suggested that weak slip occurs before adhesion failure. Inside the cell, adhesion failure causes the cavity penetration from the cell exit, which induces flow stagnation upstream of adhesion failure. This stagnation relaxes high shear upstream of the region of adhesion failure, and then suppresses the increase in the penetration length of cavity.
