Publication

Prediction of Francis Turbines Efficiency Alteration by travelling Bubble Cavitation

François Avellan, Philippe Dupont
1998
Conference Papers

Abstract

The setting level of a hydraulic machine, specially for low head machines, is decided with respect to the possible alteration of the efficiency due to the cavity development. This alteration can easily be noticed by plotting the evolution of the efficiency 'eta' as a function of the Thoma number 'sigma' leading to the so-called 'eta'-'sigma' cavitation curves. ln order to protect the efficiency at the best operating point against the travelling bubbles effects, the IEC norms suggest some measures relating to turbines standards cavitation tests. A prediction method of the efficiency drop due to the outlet travelling bubble cavitation is then so needed to guide the runner geometry design in the first state of the project. The main objective of this paper is the presentation of a cavitating pressure field prediction method in the runner in order to calculate the corresponding efficiency alteration.

Official source

https://infoscience.epfl.ch/entities/publication/32dc31f9-1add-4d2c-aa23-0ea37ecd5ca5

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François Avellan, Philippe Dupont
1998
Conference Papers

Abstract

Official source

https://infoscience.epfl.ch/entities/publication/32dc31f9-1add-4d2c-aa23-0ea37ecd5ca5

About this result

Related concepts (32)

Energy conversion efficiency

Energy conversion efficiency (η) is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The input, as well as the useful output may be chemical, electric power, mechanical work, light (radiation), or heat. The resulting value, η (eta), ranges between 0 and 1. Energy conversion efficiency depends on the usefulness of the output. All or part of the heat produced from burning a fuel may become rejected waste heat if, for example, work is the desired output from a thermodynamic cycle.

Thermal efficiency

In thermodynamics, the thermal efficiency () is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, steam turbine, steam engine, boiler, furnace, refrigerator, ACs etc. For a heat engine, thermal efficiency is the ratio of the net work output to the heat input; in the case of a heat pump, thermal efficiency (known as the coefficient of performance) is the ratio of net heat output (for heating), or the net heat removed (for cooling) to the energy input (external work).

Cavitation

Cavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, called "bubbles" or "voids", collapse and can generate shock waves that may damage machinery. These shock waves are strong when they are very close to the imploded bubble, but rapidly weaken as they propagate away from the implosion. Cavitation is a significant cause of wear in some engineering contexts.

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Prediction of Francis Turbines Efficiency Alteration by travelling Bubble Cavitation

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