Design Analysis of Parts of Francis Turbine

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Design Analysis of Parts of Francis Turbine

• P M V Subbarao
• Professor
• Mechanical Engineering Department

Provision of Features to Blend some Reaction into
Impulse
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Spiral Casing

• Spiral Casing The fluid enters from the
  penstock to a spiral casing which completely
  surrounds the runner.
• This casing is known as scroll casing or volute.
• The cross-sectional area of this casing decreases
  uniformly along the circumference to keep the
  fluid velocity constant in magnitude along its
  path towards the stay vane/guide vane.

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Design of Spiral Casing
How to select Q ?
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Spiral Casing for 35 MW Vertical Francis Turbine
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Design of Spiral Casing
Select a suitable value of discharge per unit Q
But maximum allowable value is 10 m/s Maximum
allowable head loss in Penstock 2 to 4 of
available head
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At any angle q, the radius of casing is
A full spiral is generally recommended for high
head 300m, semi-spiral is recommended for low
head lt 50m.
In general k 1.0, however corrected using CFD.
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Flow Distribution Analysis of Casing
Stay vanes or Guide vanes
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Static Pressure Distribution in Casing.
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Mega Civil Works for Mechanical Power Generation
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Parts of A Francis Turbine
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Geometrical Description of A Francis Turbine
Parts
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Stay Vanes Guide Vanes

• The basic Purpose of the stay vanes guide 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.
• Moreover, the guide vanes are pivoted and can be
  turned by a suitable governing mechanism to
  regulate the flow while the load changes.
• The guide vanes are also known as wicket gates.
• The guide vanes impart a tangential velocity and
  hence an angular momentum to the water before its
  entry to the runner.
• The guide vanes are constructed using an optimal
  aerofoil shape, in order to optimize off-design
  performance.

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Design of Guide Wheel (Stator) Low Specific Speed
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Design of Guide Wheel (Stator) High Specific
Speed
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Design of the Guide VanesDiameter of guide vane
shaft
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Design of the Details of Stay Guide Vane Wheels
Theory of Relatively free Whirling flow

• The inlet angle can be calculated by assuming a
  free vortex from the flow coming from the spiral
  casing

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Pressure drop versus discharge
Pressure drop versus Flow Rate
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Global Symmetric Flow Domain through Statinary
Vanes
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Operational Configurations of Guide Vanes
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The correlation between the turbinedischarge and
the guide vane opening angle.
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Pressure drop versus guide vane angle
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Design of the Guide Vanes
How to choose the guide vane maximum angle a0 at
full load ?
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Design of the Guide VanesLevel of Overlapping of
the guide vanes
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Design of Guide Vanes
.
L length of vane
L15 to 30 of Dgo
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Runner inlet (F 0.870m)
Guide vane outlet for designa) (F 0.913m)
Closed Position
Max. Opening Position
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Design of the Guide Vane Outlet Angle

• The outlet angle can be calculated by assuming a
  free vortex from the flow in the gap between the
  runner and the guide vanes

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Design of the Guide VanesHow to choose the
number of vanes

• The number of guide vanes has to be different
  from the number of runner vanes.

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Water particle
Water from spiral casing
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Number of guide vanes
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Number of Guide Vanes
Ns Dge,mm Z8 10 12 14 16 18 20 24
lt200 lt250 250 - 400 400 - 600 600 - 800 800 - 1000 1000 1250 1250 1700 gt1700
gt200 lt300 300 - 450 450 - 750 750 - 1050 1050 1350 1350 1700 1700 2100 gt2100
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The Runner
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Mean Velocity triangles Across Runner
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Velocity triangles
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The transposition of the profiles for all the 11
streamlines
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