Experimental Investigation of non-suppressed sill effect with different geometry on flow pattern and discharge coefficient of sluice

Introduction: The ease of installing sluice gates and simplicity of their equations resulted in sluice gates as one of the most widely used hydraulic structures in regulating and controlling the water level. Several factors are discussed on the discharge coefficient of the sluice gate, including the effect of sill under the gate. The most important application of sill under sluice gate is to increase its discharge coefficient. Geometry and widths of sill is one of the important factors on discharge coefficient. also use of non-suppressed sills changes the flow pattern and the general equation of discharge coefficient. discharge coefficient of sluice gate with sill was studied by Jalil et al. (2016). In this study, the effect of sill under sluice gate was experimentally investigated on flow discharge coefficient. Results showed that the coefficient of discharge decreases with an increase of relative sill height to the head upstream. Rezavand (2018) investigated the effects of the hydraulic parameters on the flow discharge coefficient by Fluent software. Results showed that the sill under the gate has a positive effect on the flow discharge coefficient. The goal of this study is to investigate the geometry of sill with changes in its width on flow pattern and discharge coefficient in free-flow conditions. According to previous studies effect of sill width parameter with different geometric shapes on discharge coefficient and flow pattern has not been studied.
Methodology: The experiments were performed in a hydraulic laboratory with flume dimensions of 5 m in length, 0.30 m in width, and 0.45 m in height. The walls are made from Plexiglass in order to provide good visibility. The inlet flow were measured by two rotameters with± 2% accuracy. Rotameters were installed at the outlet of the pump and measured with a point gage with an accuracy of 1 mm. a sluice gate with a 1 cm thickness is installed with the distance of 1.5 m away from the inlet of flow. The gate opening was fixed at 4 cm in all experiments. Sills including cylindrical, semicylindrical, pyramidal, and rectangular cubic were prepared in order to investigate the shape effect. All four sill shapes were prepared with widths of 5, 7.5, 10, 15, and 20 cm in order to study the effect of sill width under the gate. The height of all sills in this study was considered to be a fixed value of 3 cm. A total of 20 physical models were tested. In this study, flow discharge in the range of 475 to 700 liters per minute was applied to all models. A total of 200 experiments were performed in order to investigate the effect of sill shape and width on flow pattern and discharge coefficient in free conditions.
Results and Discussion: Results of sluice gate patterns with sill and without sill situations were investigated. The results of these experiments, similar to previous studies, show that a sluice gate with sill increases the discharge coefficient. The results showed that sills with different geometries affect flow under the gate. Also, using non-suppressed sills under the gate breaks the flow lines. As the downstream progress, v-shaped sections are formed. Investigation of flow patterns in cylindrical and semi-cylindrical and pyramidal sills showed pyramidal sill causes a significant uniformity flow lines compared to other geometric shapes due to its sloping side at downstream. while sill with rectangular cube geometry improves rotational flows at downstream of sill. The results of placing sill in different geometric shapes under sluice gate indicate that using semicy-lindrical sill compared to other shapes increases in discharge coefficient and the highest values of discharge coefficient after this sill are allocated to cylindrical, pyramidal and rectangular cubic sills, respectively. semicylindrical average discharge coefficient increased 19.1 percent compared with the gate without sill. According to the laboratory findings, it was observed that increased sill width with decreased gate opening increases the discharge coefficient. Placing a sill with a width of 20 cm in all geometric shapes increases the discharge coefficient by an average of 10% compared to a sill with a width of 5 cm.
Conclusion: The study of discharge coefficient in 20 physical models showed that the highest values of discharge coefficient after semicircular sill are allocated to circular, triangular, and square sills, respectively. This increase is expressed because the semicircular, circular, triangular, and square sills at the smallest width (b = 5 cm) increased discharge coefficient by 6.5, 5.6, 3.5, and 1.6% compared to non- sill state, respectively. Changing sill width from 5 to 20 cm showed that discharge coefficient of semi-cylindrical, cylindrical, pyramidal and rectangular cubic increased by an average of 19.1, 17.2, 14.7, and 12.1% compared to non- sill state.