INVESTIGATION OF WALL TURBULENCE USING A DIFFUSION-CONTROLLED ELECTRODE.
Scientific rept. no. 1, 1962-1965,
ILLINOIS UNIV URBANA ENGINEERING EXPERIMENT STATION
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This study was performed to demonstrate that a diffusioncontrolled electrode technique can be used to measure the average and fluctuating shear stresses at a pipe wall and to obtain a better understanding of the structure of turbulence near the wall. The technique was established after compensations for two effects, also common to the hot wire anemometer, were determined. The problem of nonuniform flow across the electrode was solved by determining experimentally a correction factor, whereas the problem of the time response of the electrode to fluctuations in the shear stress was handled by numerically solving the governing equations. The data for fully developed turbulence showed that the limiting velocity intensity at the wall was 0.32, based on the local average velocity, and that it was independent of Reynolds number. The circumferential scale was found to be very small near the wall but the longitudinal scale did not decrease from the values reported for the center of a pipe. Some velocity disturbances near the wall appeared to be as large as the local average velocity. A simplified model for a low frequency disturbance near the wall was investigated and found to be promising although several of the assumptions were not well substantiated. Author