Discussion of 'Evaluation of Flow Resistance in Smooth Rectangular Open Channels with Modified Prandtl Friction Law'

摘要

Although the experimental work of the authors must be acknowledged, their theoretical reasoning leads to conclusions that are questionable. In particular, (1) we show subsequently that the main result of the work, namely, the use of a modification coefficient, m_R,, depending on the aspect ratio and affecting the Reynolds number in the Prandtl friction law, is not supported by observation; (2) the statement that their Eqs. (20) and (23) also apply for narrow channels cannot be generally acceptable without providing empirical evidence (for all experimental observations, the channel width, B, is greater than the flow depth, h); and (3) the approximation in Eq. (23) is not justified because usually the flow depth is not given, and therefore iteration is not avoided. Furthermore, we will introduce some arguments showing that the friction coefficient for open-channel turbulent flow does not depend on the details of the velocity distribution.