The effect of the intake head wall slope and the installation of a trash rack on the type and strength of vortices are studied experimentally. The strength within each vortex was determined by measuring its tangential velocity utilizing an Acoustic Doppler Velocimeter (ADV). Experiments were carried out with a projected intake and an intake with various head wall slopes, discharges and submerged depths. The results from the projected intake tests indicated that Type 6 vortex was present. However, the vortex strength and type reduced as the intake head wall slope increased up to the vertical position. In addition, increasing the intake head wall slope increased the vortex instability. All tests were repeated with a trash rack. A relationship was developed for vortex strength and the intake critical submerged depth based on the intake Froude number and the head wall slope. Moreover, a relationship has been found between vortex strength and type.
In the present study, flow patterns around a single spur dike (also termed a groyne) with free-surface flow was simulated using a numerical model known as Fluent. The model solved the fully three-dimensional, Reynolds-averaged Navier-Stokes equation to predict flow near the structure where threedimensional flow is dominant. To treat the complex free-surface flow, the volume of fluid method with geometric reconstruction scheme was applied and turbulence was simulated using standard k − v equations. In this research work, both a structured and an unstructured mesh were used and the density of the mesh spacing was selected the highest near the walls and also free surface to obtain more accurate results. Comparison of free surface and velocities of 3D model showed good agreement with three experimental flume data obtained by other researchers. The reattachment length for various conditions was computed using the numerical results and flow pattern was presented for repelling, attracting and vertical spur dikes together. Also, bed-shear stress distribution was presented and the effects of flow discharge and the length and angle of the spur dike upon the bed shear-stress distribution were evaluated.
Fluent software has been used to simulate flow over a circular spillway and results were compared with experimental data. As the flow over a circular spillway is turbulent and has a free surface, its characteristics are complex and often difficult to be predicted. This study assesses the performance of some turbulence models to predict the hydraulic condition of flow over circular spillways. The Volume of Fluid (VOF) method is applied to obtain the free surface in each case. Such cases include highly swirling flows, stress-driven secondary flows and flows over circular spillways. Finally it is concluded that the results of RSM, RNG k-, Realizable k-, SST k-ω turbulence models agree well with experimental data.
ABSTRACT:In the present work, a numerical study was performed to analyze the flow behavior in a reservoir in the presence of strong vortices. A challenging subject in this study was the flow field in the reservoir and the mechanism of vortex formation. The numerical model was verified with the available theories and experimental data. Experiments were conducted in a reservoir in which strong vortices were formed over an intake. Measurements of the flow field were carried out with an Acoustic Doppler Velocimeter (ADV) for a constant intake submerged depth and two different intake Froude numbers. The agreement between numerical and experimental results for 3D velocity field was good. Finally, using the validated numerical results, the flow behavior in the reservoir was analyzed. A funnel shape flow pattern was recognized in the reservoir toward the intake and its boundaries were identified. Another flow pattern observed was a spiral vortex motion from the water surface towards the intake. The present paper intends to make a deep understanding of flow field in a reservoir due to water withdrawal.
The efficiency of horizontal perforated and solid plates, installed on top of an intake for prevention of surface vortex formation, was experimentally investigated. The experiments were conducted on a horizontal intake of a reservoir. By changing the angle of the approach flow, submergence of the intake and the discharge, 36 air-core surface vortices with different strengths were generated. The strengths of these vortices were evaluated by measuring tangential velocities using an acoustic Doppler velocimeter. A relationship between the strength of the surface vortex and the necessary percentage of uniform opening of the perforated plate is presented. It was found that a perforated plate of width 1D and 1·5D length normal to the intake (D is the tunnel diameter) with 50% uniform opening and a solid plate of 1·5D width and 2D length eliminated all surface vortices at the intake. Pressure was also measured in a section immediately downstream of the intake by means of four transducers. By using the measured pressure values, the effect of anti-vortex plates on local loss at the intake was determined.
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