Abstract
A design for the fail-safe mechanism of a guide vane in a Francis-type hydro turbine is proposed and analyzed. The mechanism that is based on a shear pin as a sacrificial component was designed to remain simple. Unlike the requirements of conventional designs, a shear pin must be able to withstand static and dynamic loads but must fail under a certain overload that could damage a guide vane. An accurate load determination and selection of the shear pin material were demonstrated. The static load for various opening angles of the guide vane were calculated using the computational fluid dynamics Fluent and finite element method Ansys programs. Furthermore, simulations for overload and dynamic load due to the waterhammer phenomenon were also conducted. The results of load calculations were used to select an appropriate shear pin material. Quasi-static shear tests were performed for two shear pins of aluminum alloy Al2024 subjected to different aging treatments (i.e. artificial and natural aging). The test results indicated that the Al2024 treated by natural aging is an appropriate material for a shear pin designed to function as a fail-safe mechanism for the guide vanes of a Francis-type hydro turbine.
Highlights
Fail-safe mechanisms have been designed for various mechanical systems to reduce losses in terms of cost, time, and human life and to reduce environmental damage.[1,2,3] A fail-safe mechanism should be implemented in a system and be assured to function properly
We focus on the load determination for both the guide vane and the shear pin
Validation experiments indicated that Al2024 subjected to a natural aging treatment is a suitable shear pin material, with an average tu of 186 MPa
Summary
Fail-safe mechanisms have been designed for various mechanical systems to reduce losses in terms of cost, time, and human life and to reduce environmental damage.[1,2,3] A fail-safe mechanism should be implemented in a system and be assured to function properly. Shear pins are widely used for the fail-safe mechanism. Shear pins are installed on gear trains, aircraft mounting engines,[4] valves,[5] couplings,[6] and flocculators.[7] The most challenging problem in analyzing shear pins is the requirement to simultaneously fulfill two constraints in their design. A shear pin must be able to withstand certain operational loads but fail when an overload condition occurs
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