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 (d₅₀ = 0.45 mm and d₅₀ = 0.88 mm) with solids concentrations of up to C_max = 1.6% by volume, and for flow Reynolds numbers of 10⁵ < R_D < 6 × 10⁵. 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_S, and the wall shear stress, τ_o, given by τ_o^l/³ = AP_S + 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.