Wall Shear Measurment in Sand-Water Mixture Flows

The wall shear stress was measured in clear-water and sand-water mixture flows with the use of a flush-mounting hot-film shear-sensor. Data were obtained with two shear-sensors and two different sands (d\d5\d0 = 0.45 mm and d\d5\d0 = 0.88 mm) with solids concentrations of up to C\dm\da\dx = 1.6% by volume, and for flow Reynolds numbers of 10\u5 < R\dD < 6 x 10\u5. The “measured” sensor wall shear stresses were compared with the “true” wall shear stresses obtained with the energy head loss measurements conducted in a pipeline system. The results of the tests in the clear-water flows confirmed the relationship between the sensor power output, P\dS, and the wall shear stress, τ\N\do, given by τ\N\do\ul\u/³\N = AP\dS + B, in which A and B are calibration coefficients. The tests with the low-concentration sand-water mixtures in a vertical pipe indicated that for the present range of experiments, sensor power outputs with the mixtures exceeded those for clear-water by an average of 5%. It is shown that the shear-sensors are delicate but accurate instruments that can be used for the measurement of the wall shear stress.