PIV investigation of the leakage flow through clearance gaps in cambered hydrofoils

[+] Author and Article Information
Sailesh Chitrakar

Department of Energy and Process Engineering, Norwegian University of Science and Technology, Norway

Hari P. Neopane

Department of Mechanical Engineering, Kathmandu University, Nepal

Ole G. Dahlhaug

Department of Energy and Process Engineering, Norwegian University of Science and Technology, Norway

1Corresponding author.

ASME doi:10.1115/1.4036269 History: Received December 06, 2016; Revised March 06, 2017


In Francis turbines, which are normally designed at a reaction ratio of 0.5, the available pressure energy in the fluid is converted into 50% kinetic energy before entering the runner. This causes high acceleration of the flow in guide vanes, which adds to the unsteadiness and losses in the turbine. In sediment affected power plants, the hard sand particles erode and gradually increase the clearance gap between the guide vane and facing plates, which causes more disturbances in downstream turbine components. This study focuses on investigating the flow through the clearance gap of the guide vane with cambered hydrofoil shapes by using Particle Image Velocimetry (PIV) technique. The measurements are carried out in one guide vane cascade rig, which produces similar velocity fields around a guide vane, as compared to the real turbine. The investigation is done in two cases of cambered guide vane NACA profiles and the comparison of the velocity and pressure distribution around the hydrofoil is done with the results in symmetric profile studied earlier. It is seen that the pressure distribution around the hydrofoil affects the velocity field, leakage flow and characteristics of the vortex filament developed inside the cascade. NACA4412, which has flatter suction side than NACA2412 and NACA0012, is seen to have smaller pressure difference between the two adjacent sides of the vane. The flow inside the clearance gap of NACA2412 enforces change in the flow angle, which forms a vortex filament with a rotational component. This vortex along with improper stagnation angle could have greater consequences in the erosion of the runner inlet and more losses of the turbine.

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