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International Journal of Fluid Mechanics Research
ESCI SJR: 0.206 SNIP: 0.446 CiteScore™: 0.5

ISSN Imprimir: 2152-5102
ISSN En Línea: 2152-5110

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International Journal of Fluid Mechanics Research

DOI: 10.1615/InterJFluidMechRes.v37.i5.60
pages 459-469

Effect of Particle Separation and Sand Erosion in a Hydraulic Turbine

Bhola Thapa
Department of Mechanical Engineering, Kathmandu University, Kathmandu, Nepal

SINOPSIS

Sand erosion is one of the major operational problems of hydropower plants in the Himalayan Rivers. Size is the main factor responsible for particle transport and erosion. For the particles flowing in the curved path or swirl flow, centrifugal force is caused by tangential component of absolute velocity while drag force is caused by absolute velocity. The equilibrium of these two forces gives critical diameter of the particle which will be rotating in the orbit. Such critical diameter is a function of the drag coefficient, specific gravity of the particle, radius at which the particle is moving and ratio of particle velocity in peripheral direction to the absolute velocity of water. Particles larger than the critical diameter move away from the center of the flow path and thus hit the wall whereas but smaller particles flow along with the water. The swirl flow test rig was designed and developed at Norwegian University of Science and Technology to study the effect of particle separation. This test rig simulates the flow in between guide vane outlet and runner inlet of Francis turbine. The flow of particle in the swirl flow was observed by naked eye and high speed video camera. The value of coefficient of drag from this experiment was found to be in between 0.1 -0.2 and compared well with literature data against particle Reynolds number. In the full opening position, the guide vanes can be fixed from 10 to 40° which creates strong swirl. For the turbine of radius 1m at inlet, sand particles of diameter larger than 2 mm will stay rotating in swirl flow damaging guide vanes positioned around 10°. At higher Reynolds number and drag coefficient 0.1, even small particles of 1 mm size will stay rotating and hitting the guide vane wall. The experimental setup helps to develop operational guidelines for Francis turbine operating with large sand particles. If the particle size in the water is larger than the critical particle size, the turbine should not be operated at low guide vane opening. The experimental observation reveals that smaller turbines are more prone to sand erosion.

REFERENCIAS

  1. Thapa, B., Sand Erosion in Hydraulic Machinery.

  2. Chevallier, P. and Vannes, A. B., Effect on a Sheet Surface of an Erosive Particle Jet upon Impact.

  3. Tabakoff, W., Hamed, A., and Metwally, M., Effect of Particle Size Distribution on Particle Dynamics and Blade Erosion in Axial Flow Turbines.

  4. Thapa, B. and Brekke, H., Effect of Sand Particle Size and Surface Curvature in Erosion of Hydraulic Turbine.

  5. Brekke, H., Design and Operation of Medium and High Head Turbines.

  6. Thapa, B. and Skare, P. E., Inspection Report: Fortune Power Plant.

  7. Spurk, J. H., Fluid Mechanics.


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