Measurement of turbulent velocity gradient on the wall is important for further understanding wall turbulence and mechanism of heat and mass transfer near the wall. This paper describes the principle of such a measurement
and a semicircular electrode pair is suggested for the measuring of the two dimensional fluctuations of velocity gradient on the wall. In a fully developed turbulent pipe flow
with pipe diameter of 0.194m and electrode pair diameter of 5 × 10-4m
using iodine-potassium iodide solution as fluid medium
the measured axial and transverse turbulent intensities of velocity gradients are 0.3-0.33 and 0.11-0.12 respectively.