The Validity Of Clauser’s Method For Determining Shear Velocity, U*, In A Curved Channel

Abstract

In a straight open channel flow, the Clauser‘s method, which is based on the measured velocity profile and the logarithmic velocity law, can be used to determine the wall shear velocity, u*, accurately. For a curved open channel flow, however, with its complexities, it can be questionable whether the Clauser‘s method can still be used or not. In this paper, the validity of the Clauser‘s method in a curved channel was evaluated, based on the inner region data of velocity profiles, plotted in the form of logarithmic coordinate; if the plotted data show linear correlation, it means that the Clauser‘s method can still be used to determine the wall shear velocity. Thirty-five of laboratory velocity profiles data obtained from seven different cross-sections of 180-curved open channel flow, were evaluated to determine the wall shear velocity. The analyses of the measured data showed that in the beginning of the curved channel, i.e., from the angle of 0 to 30, all of the measured velocity profiles data were observed still following the logarithmic velocity distribution, either for the measured data in the middle or in the edge part of the channel. However, starting from the angle of 60 to 180, some of the data, especially those close to the inner and outer banks of the curved channel, begin to deviate from the logarithmic law. The deviations become more significant for the larger angle of the curved channel. Nevertheless, in the middle part of all of the cross sections of the curved channel, there are at least one or two profiles which still follow the logarithmic velocity distribution, and the friction velocities, thus, can still be calculated by using the Clauser‘s method with some restrictions.