Study of counteracting the secondary flow in open channel bends

Abstract

In terms of the importance of reducing the influences of curvature induced circulation secondary flow, several counteracting techniques/measures have been studied. Although the previous techniques have obtained good results yet, they involve fixed and permanent construction works in the channel. Most of the techniques have a negative impact on navigation, and may be damaged under extreme flow conditions. Therefore, the use of new technique has become very significant and must be studied. The aim of this paper to study a new technique as an indirect tool to counteract the impact of the secondary flow on the banks and bed at channel bends by re-distribution of the main flow velocity in the curved section through water jets. In a previous experiment, air bubbles are induced as a bubble screen (air media) with an appropriate velocity, through a porous tube placed near the outer bank in the sharply open channel bend 193°. In this paper, one of the previous experiments is modeled with the same shape and conditions, however, the induced air bubbles from the porous tube in the experiment are replaced by a water screen to act as a source of momentum. A numerical model FLUENT was implemented and a realizable K-ε turbulent model was used to scrutinize and predict the velocity pattern in the channel bend. The impact of the change in lateral water jets flow from the porous tube was also investigated and results presented and compared. The results revealed that the water screen technique contributes in reducing the downward movement of the secondary circulation, dragging the flow upward, leading to the distribution of the secondary circulation, and shifting the core of maximum downstream velocities away from the outer bank towards the inner bank at the junction of generated circulation. The results also showed that the water screen is able to counteract the effect of the main flow circulation cells provided that this secondary flow is not less than 20% of the main flow and the corresponding velocity is also not less than 40% of the main flow velocity.