Investigation of Wall Shear Stress Distribution in Open Channel Uniform Flow using an Accurate Instrument and Numerical Simulation

With the aim of investigating the distribution of wall shear stress in an open channel with a rectangular
cross section and a smooth bed, an accurate needle type probe has been developed and after
verification, it has been used for shear stress measurement in various cases of open channel uniform
flows. In this instrument, capacitive type pressure transducers with 0.1 Pascal accuracy and 100Hz
sampling rate were used to measure pressure fluctuations. Measured bed shear stresses are compared
with the result of available analytical models and CFD simulations using FLUENT code for
instrument verification. Variations of the measured local bed shear stresses at channel centerline with
respect to channel aspect ratios, mean bed shear stresses and the lateral distribution of local bed shear
stresses compare favorably with the previous experimental and analytical results and with the results
of the present numerical simulations. Experimental measurements and numerical simulations show
that the secondary currents affect the distribution of side wall shear stress more than the bed shear
stress. Because of the presence of the alternate low-high velocity zones at the near bed region, the
lateral distribution of the bed shear stress exhibits an oscillatory pattern.