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Keywords: CFD, Elbow draft tube, Numerical analysis, Ansys CFX
Abstract
Numerical simulations of the flow in the elbow draft tube of a Kaplan turbine were carried out in order to elucidate the effects of tail water level on draft tube performance and flow stability. The influence of the tail water level is explored considering the correct boundary condition at the inlet of the draft tube. It is found that the increasing tail water level affects the inlet boundary condition of the draft tube, the flow rate through the turbine, and draft tube. Thus, head recovery, efficiency and the possibility of cavitation phenomena decreases. However, the head loss increases, and the flow rate through the turbine and draft tube decreases.
Povzetek
Izvedene so bile numerične simulacije toka v kolenasti sesalni cevi kaplanove turbine z namenom preučitve vpliva spodnjega nivoja gladine vode na brezdimenzionalne karakteristike in na stabilnost toka v sesalni cevi. Vpliv nivoja spodnje vode je raziskan z upoštevanjem pravilnih robnih pogojev na vstopu. Ugotovljeno je bilo, da naraščanje spodnjega nivo vode vpliva na pretok skozi turbino in posledično na vstopni robni pogoj sesalne cevi. Posledično se izkoristek in verjetnost nastanka kavitacije zmanjša. Na drugi strani se hidravlične izgube povečajo, pretok skozi turbino in sesalno cev pa se zmanjša.
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1INTRODUCTION
Hydropower plays an important role in the energy sector and helps to meet increasing demand for energy. The hydraulic turbines convert hydro energy into electric energy and, therefore, the increase in efficiency of the turbine is an important task. Each component of turbine has some specific function, and hence the design of every component of the turbine is equally important. However, out of all components, draft tube converts kinetic energy coming out of runner into useful pressure energy that would otherwise be wasted. Therefore, the design of the draft tube is important and contributes to improving the efficiency and overall performance of the turbine.
The main aim of this research was to examine flow conditions within the draft tube of a hydropower plant at different tail water levels using 3D CFD simulation to inspect for possible irregularities within the flow.
Numerical flow simulation has been carried out for steady viscous turbulent flow in a Kaplan turbine assembly consisting of a...