There are many methods that are often used to determine the wall shear velocity, u*, in open channel flow. Among the methods available in literature, the two most commonly used methods are the Clauser's method, which is based on the inner region of measured velocity profile data, and the Reynolds shear-stress method, which is based on the Reynolds shear stress profile data. In straight open channel flow, either in uniform or non-uniform flow, both methods have been verified to be valid for predicting accurately the wall shear velocity, u*. In this study, the validity of the Clauser's method for determining the wall shear velocity, u~*_c, in 180°-curved open channel flow was evaluated, and the obtained values of the wall shear velocity were then compared with those evaluated from the Reynolds shear-stress method, u~*_r, both,in fixed and eroded beds channel. Ninety profiles of velocities and Reynolds shear-stresses data, measured by using Acoutic Doppler Velocimeter (ADV) and obtained from nine different cross-sections of 180°-curved open channel flow of fixed and eroded beds, were evaluated and analyzed in this study. The analysis of the measured data showed that in curved channel, the Clauser's and the Reynolds shear-stress methods can still be used to determine the wall shear-velocity,u~*, satisfactory. For fixed bed channel, the average difference between the two methods is 9.51%, with the maximum difference is 24.8%, while for eroded bed channel, the average difference is 19.03%,with the maximum difference is 130%. It can be also noted that there are at least one or two velocity profiles in curved channel sections that still follow the logarithmic velocity distribution, which can be interpreted that the wall shear velocity, u~*, can still be determined by using the Clauser's method with some restrictions.
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