The Effect of Anti-Vortex Plates on Vortex Dissipation, Discharge Coefficient and Inlet Loss Coefficient in Hydropower Intakes

Document Type : Research Article

Authors

1 No. 9, Shahid Moosavi Alley, Karoun Street

2 Associated Professor, Razi University

Abstract

Introduction
The formation of vortices at the intake and the air entertainment into the intake duct is an important hydraulic phenomenon that usually occurs in the dam intakes and causes such problems as energy loss and reduction of intake discharge coefficient. Among different types of intakes exposed to the vortex phenomenon are hydropower intakes used to supply water to turbines and generate electricity. These intakes are mainly horizontal. To prevent the formation of strong surface vortices, their strength must be physically controlled. A practical solution for this is to use anti-vortex structures. These structures mainly eliminate the vortex by reducing the flow velocity near the intake, lengthening the flow path between the free water surface and the mouth of the intake, as well as energy dissipation. Some studies on the structural methods of vortex dissipation have been done by Amiri et all (2011), Tahershamsi et all (2012), Monshizadeh et all (2018), Taghvaei et all (2012). In this study, the effect of horizontal perforated plates on the dissipation of the strong vortices, the intake discharge coefficient and inlet loss coefficient of the intake is studied, so far no special studies have been done in this area.
Methodology
In the present study, a physical model was used to investigate the performance of horizontal perforated plates. This model was designed to produce the strongest type of vortex with air core and different strengths. The main components of the experimental setup are: reservoir, intake duct, pump and electromotor speed controller device. The dimensions of reservoir is 1.3 m in wide, 3.5 m long and 2 m high. The mouth of intake extends 20 cm into the reservoir and is positioned so that the side walls and the bottom of the reservoir do not affect the flow conditions. The length of the intake pipe is 4.5 m and its diameter is 16 cm. At a distance of 2 m upstream of the intake in the reservoir, some blades are installed vertically that by changing their angle relative to the intake axis, the angle of inflow to the intake can be changed. This makes it possible to strengthen the upstream vorticity to reach stronger vortices. For modeling the perforated anti-vortex plates, some plastic mesh with different openings and different thicknesses were used. For each plate, the corresponding mesh was placed in a metal coil and this coil is screwed to the reservoir wall so that the perforated plate be placed on the mouth of the intake. By creating 36 types of strong vortices, the performance of 10 types of perforated plates with different dimensions, thicknesses and openings was tested.
Results and Discussion
Calibration tests showed that in the range of 1.5D to 2D (D is the diameter of the intake pipe) for submergence depth, flow discharges of 15 to 30 lit/s and blade angles of 0 to 20 degrees, the stable strong vortices are formed. A total of 36 strong vortices (three relative submergence depths, four flow discharges and three blade angles) were formed with different strengths in the model. In order to consider the appropriate confidence limit in this study, the performance of each of the anti-vortex plates in the model was considered so that it is able to dissipate vortex type-six or decrease to type-two vortices. Therefore, the conditions in which the strength of a type-six vortex was reduced by the relevant anti-vortex plate to a type-three (or higher) vortex are known as critical conditions. It should be noted that the type of vortex is determined based on its appearance. Finally with 360 tests it was concluded that the effect of opening of the plates to eliminate the vortex strength is more than the dimensions and the thickness of the plates. In addition, the effect of using perforated horizontal plates on discharge coefficient and inlet loss coefficient of the intake was investigated. It was concluded that the use of perforated anti-vortex plate with openings of 70%, 58% and 50% reduces the intake discharge coefficient by 5.9%, 10.5%, and 13.4%, respectively. It is also caused 12.9%, 24.7% and 33.5% for inlet loss coefficient of the intake, respectively.
Conclusion
The effect of submergence depth on the vortex strength is greater than the flow discharge and it is also greater than the geometric asymmetry. Dimensions of the plate have little effect on the vortex dissipation. The thickness of the plates has little effect on the vortex strength. The opening rate of the plates has a great effect on the vortex and a plate with 50% opening, was able to dissipate all strong vortices. The vortex strength has a direct relationship with the inflow angle and the flow discharge and is inversely proportional to the submergence depth. As the flow discharge increases, the discharge coefficient decreases and the inlet loss coefficient increases.

Keywords


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Volume 17, Issue 3 - Serial Number 173
September 2022
Pages 15-29
  • Receive Date: 01 September 2021
  • Revise Date: 18 January 2022
  • Accept Date: 22 March 2022
  • First Publish Date: 08 June 2022