Numerical study of the effects height of the rectangular side orifice crest on the flow characteristics around a side orifice

Structures such as side orifices, side weirs, and side sluice gates are known as flow diversion structures. Side orifices are flow diversion structures which have wide application in hydraulic and environmental Engineering. This flow diversion structure has been extensively used in irrigation and drainage networks, wastewater treatment plants, sedimentation tanks, etc. Therefore, Study of the characteristics and flow pattern such as flow velocity components and free surface adjacent to the side orifice is important. In this paper, the flow over a sharp-crested rectangular side orifice in an open channel was simulated by FLOW-3D software. RNG turbulence model was used to apply the Navier-Stokes equations and the VOF method was used to model the free surface profile changes. In the present study, at first, the results related to the side orifice discharge and flow patterns obtained from numerical simulation were compared with experimental data. In this study, some experimental data of Hussian et al (2011) were used for model verification. In this study, the discharges through the orifice resulted from the present numerical simulation and the experimental research, along with the relative errors are reported. All relative error quantities were about 8-9%, thus there was relatively good agreement between numerical and experimental results. Therefore, the numerical model can be employed as a powerful tool for studying flow through side orifices in open channels. Then the effects of height of the side orifice crest on the flow velocity components and free surface adjacent to the side orifice was investigated. The results indicated that the discharge ratio, ratio of the discharge through the side orifice to the inlet discharge of the main channel increases with decreasing heights of the side orifice crest. Maximum and minimum longitudinal velocity for all heights of the side orifice crest was occurred at the beginning and end of the side orifice, respectively. By decreasing the height of the side orifice crest, maximum and minimum longitudinal velocity increases and decreases, respectively. By decreasing the height of the side orifice crest, the longitudinal velocity in the vicinity of the side orifice is negative because of the reverse flow formed in this area. Examining the lateral velocity component variation showed that this component increased with decreasing height of the orifice crest. That is why the discharge through the side orifice increased with decreasing height of the orifice crest. At height 2.2 cm of the orifice crest, the flow direction is upward then in all cases vertical velocities in the orifice length are positive. In the other hand, at height 6.7 cm of the orifice crest, the flow direction is downward then in all cases vertical velocities in the orifice length are negative. Also, the absolute value of the vertical velocity increases with by decreasing the height of the side orifice crest because more flow is diverted to the side orifice with decreasing the height of the side orifice crest. Also, increasing height of the orifice crest caused significant changes in the free surface profiles especially in the vicinity of the side orifice.