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Department of Technical Education, Branch – Mechanical Engineering, e – Lecture On, Hydraulics and Pneumatics, Unit 6: Francis Turbine, By , Meenu Dwivedi , Lecturer, Department of Mechanical Engineering, Government Polytechnic, Lucknow

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Introduction, Francis turbine is a most popular reaction type hydraulic turbine which was first developed by an American engineer James B. Francis ., It was a typically inward radial flow turbine i.e. inlet to the turbine should be at a higher radial location to the axis of rotation . , The modern Francis turbine is a mixed flow turbine in which the water enters the runner radially at its outer periphery and leaves axially at its centre.

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Main components of Francis Turbine, A Francis turbine comprises mainly the four components:, Spiral Casing, Guide or Stay Vanes, Runner Blades, Draft-Tube

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It is a closed passage whose cross-sectional area gradually decreases along the flow direction. The water from penstocks enters a scroll casing which completely surrounds the runner. , The purpose of casing is to provide an even distribution of water around the circumference of the turbine runner, maintaining an approximately constant velocity for the water so distributed., Spiral Casing

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Guide Vanes, The basic purpose of the guide vanes or stay vanes is to convert a part of pressure energy of the fluid at its entrance to the kinetic energy and then to direct the fluid on to the runner blades at the angle appropriate to the design. , The guide vanes are pivoted and can be turned by a suitable governing mechanism to regulate the flow while the load changes.

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Runner, The runner consists of a series of a curved vanes evenly spaced around the circumference. , The change in direction of flow of water, as it passes through the runner produces a circumferential force on the runner which makes the runner to rotate .

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Draft Tube, A draft tube is a pipe or passage of gradually increasing cross-sectional area which connects the runner exit to the tail race. , The primary function of the draft tube is to reduce the velocity of the discharged water to minimize the loss of kinetic energy at the outlet. , It permits a negative or suction head to be established at the runner exit .

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Net Head, The effective head across any turbine is the difference between the head at inlet to the machine and the head at outlet from it. , The total head H1  at the entrance to the turbine can be found out by applying the Bernoulli's equation between the free surface of the reservoir and the inlet to the turbine

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