Turbomachinery_Turbines

Turbines

It is defined as, "component which extract energy off the flowing fluid".

• Torque is exerted by the fluid on the rotor in its direction of rotation.
• The shaft power generated is available to drive generator or other devices.

There are two types of Hydraulic Turbines:

1. Impulse Turbines 
2. Reaction Turbines

1. Impulse Turbines

It is defined as, "The jet hits the Pelton wheel buckets, gets deflected, thus resulting in the change of the momentum".

• Water is supplied from a high head.
• Large gravitational potential head which is converted into high velocity head.
• Penstock   →   Water moves down through the conduit.

Working:

• High speed stream  →  further accelerated  →  through nozzle  →  produce greater velocity jet (convert static pressure into dynamic pressure).

Analysis of Impulse Turbine

2. Reaction Turbines

The fluid fills the space (blade, guide, rotor) completely through which it flows. Pressure, velocity and angular momentum of fluid decreases (i.e. rotor's energy increases).

• Francis Turbine   →   Radial and Mixed Flow Turbines.
• Kaplan Turbine    →   Axial flow or the Propeller Turbines.

A. Francis Turbine

It is defined as, "Radial inflow and axial outflow from the rotor".

• Has Volute/Spiral Casing, guide vanes, runner (rotor) and a draft tube at the exit.
• Penstock   →   opens the stream to the spiral.
• Spiral Casing   →   helps maneuver the flow uniformly into the guide vanes(decreasing area, act as Nozzle, velocity increases).
• Guide Vanes   →   accelerate and direct the stream onto the runner blades at an optimal direction.
• Francis Turbine (Rotor)  →  if run opposite (in reverse direction) → act as pump.

B. Kaplan Turbine

It is defined as, "a propeller-type water turbine which has adjustable blades".

• Flow is axial to the rotor.
• Adjustable guide vanes  →  accelerate and direct the stream onto the runner blades at an optimal direction.
• Rotor has the exhaust fan blades shape.

Draft Tube 

It is defined as, "Mechanical component installed at the exit of reaction type hydraulic turbine".

• Area gradually increases  →  convert velocity head into static head to avoid backflow.
• Due to Converging or Nozzle type geometry of vanes and rotor blades  →  Static pressure converted into Dynamic pressure.
• Backflow  →  when static pressure at exit < Patm  →  large diffuser is used to counter this effect.

Dimensionless Parameters

It is useful in planning and the execution equipment (to find out the dependency of parameters).

• In case of Centrifugal pump  →  dependent parameter hO, Shaft power and Efficiency.
• Variables  →  geometric, material and flow nature of the setup.
• Dependent Variables  →  Function (Diameter, Li, Relative Roughness, Flowrate, Angular Velocity, Viscosity, Density).

References:

• Material from Class Lectures + Book named Fundamentals of Fluid Mechanics by Munson, Young & Okiishi's (8th Edition) + my knowledge. 
• Pics and GIF from Google Images.  
• Videos from YouTube (Engineering Sights).