Simulation of subcritical flow at open-channel junction

The spectrum of this survey turns on the evaluation of various existing theoretical combining models, when invoked within the internal boundary condition management at a junction. Based on the assumption that: when the Froude number is low (i.e. the flow is subcritical), the energy equation at the junction can be approximated by the stages heads equality. Actual literature and many commercial packages rather use this concept for the treatment of the junction’s internal boundary handling because it is easy to implement and it avoids the solving of nonlinear equations. In the last decade, many nonlinear combining models, based on the momentum conservation through the junction, have been reported. However, using them to operate within the internal boundary condition treatment of an open-channel confluence has not yet been investigated. Hence, this research focuses on studying the practical aspect of several combining models, once applied within the junction’s internal boundary management. Therefore, the recent nonlinear models of Gurram, Hsu and Shabayek have been briefly detailed together with the traditional concept of assuming water stages equality at the junction. Subsequently, an experimental examination was performed according to available experiments as mean to pre-evaluate (separately at the junction) the four junction models in the steady state. Moreover, according to the latter inspection the attention was constrained to study the effect of high/low subcritical Froude number at the junction. Finally, two hypothetical hydraulic problems were defined and computed in order to exhibit the performance of these junction models when used to contend the junction’s internal boundary handling. The problems involved: (a) steady and transient flows; (b) high and low (subcritical) Froude number at the junction. Supported by the experimental and numerical investigations, it can be concluded that even while the Froude number spectrum is subcritical, precautions have to be taken when dealing with the concept of energy heads equality, notably for a Froude higher than 0.35 at the junction.