Short Answer:

A propeller turbine is a type of reaction turbine in which water flows in an axial direction parallel to the turbine shaft. It is mainly used for low heads and high water flow conditions. The turbine has fixed blades shaped like a ship’s propeller, which rotate when water passes through them, converting the water’s energy into mechanical energy.

This turbine is suitable for heads ranging from 2 to 40 meters and operates efficiently at high discharge rates. It is similar to the Kaplan turbine but with fixed blades. The propeller turbine is widely used in low-head hydroelectric power stations and irrigation systems.

Detailed Explanation :

Propeller Turbine

A propeller turbine is an axial flow reaction turbine that converts the energy of flowing water into mechanical energy. It gets its name because its runner resembles a ship’s propeller, having 3 to 6 fixed blades attached to a hub. The water flows parallel to the axis of rotation, and the pressure of water decreases as it passes through the runner blades. The mechanical energy produced by the rotation of the runner is then used to drive an electrical generator for producing electricity.

Propeller turbines are designed for low head (2–40 meters) and high discharge conditions. They are highly efficient in such environments and are commonly used in low-head hydroelectric plants, tidal power plants, and run-of-river projects.

1. Construction of Propeller Turbine

The main components of a propeller turbine are simple yet effective in converting hydraulic energy into mechanical power.

• Scroll Casing:
  The scroll casing is a spiral-shaped housing that distributes water uniformly around the runner through guide vanes. It ensures steady pressure and uniform velocity at the turbine entrance.
• Guide Vanes:
  These are adjustable vanes that control the flow and direction of water entering the runner. They regulate the discharge and maintain turbine efficiency.
• Runner and Blades:
  The runner is the main rotating part of the turbine. It consists of 3 to 6 fixed blades shaped like a propeller. The water strikes these blades, causing the runner to rotate. The shape of the blades is designed to ensure smooth flow and high energy transfer.
• Draft Tube:
  The draft tube is fitted at the exit of the runner. It is a gradually expanding pipe that helps recover the kinetic energy of water leaving the runner and converts it into pressure energy before discharging it into the tailrace.
• Shaft and Bearings:
  The runner is connected to a shaft which transmits mechanical energy to the generator. Bearings support the shaft and ensure smooth rotation.

2. Working Principle of Propeller Turbine

The working of a propeller turbine is based on the reaction principle, where both pressure energy and kinetic energy of water are utilized to rotate the turbine runner. When water flows from the scroll casing through the guide vanes, it gains proper direction and velocity before striking the runner blades. The pressure of water decreases as it passes through the runner, and this energy difference causes the runner to rotate.

The flow of water is axial, meaning it moves parallel to the turbine shaft. The runner blades, shaped like a ship’s propeller, convert the water’s hydraulic energy into rotational motion. The rotation of the runner is transmitted through the shaft to the generator, which converts mechanical energy into electrical energy. Since the blades are fixed, the efficiency of the turbine remains nearly constant for a specific flow condition.

3. Operating Conditions

The propeller turbine operates best under low head and high discharge conditions. It can efficiently generate power in locations where water is available in large quantities but with a small vertical height. The speed of rotation is generally high compared to reaction turbines like the Francis turbine. The efficiency of a propeller turbine is typically around 85% to 90% under ideal operating conditions.

4. Types of Propeller Turbine

There are mainly two types of propeller turbines:

• Fixed Blade Propeller Turbine:
  In this type, the blades are fixed to the hub. The turbine is designed for a specific head and discharge and gives high efficiency only under those conditions.
• Kaplan Turbine (Adjustable Blade Type):
  A Kaplan turbine is a modified form of the propeller turbine in which the runner blades can be adjusted according to the water flow and load conditions. This adjustment maintains high efficiency over a wide range of operations.

5. Advantages of Propeller Turbine

• Suitable for low head and high discharge operations.
• Compact design and simple construction.
• High rotational speed allows smaller generator sizes.
• Smooth and vibration-free operation.
• Low maintenance requirements.

6. Limitations of Propeller Turbine

• Efficiency decreases if the water flow or head changes significantly.
• Suitable only for fixed operating conditions.
• Cavitation may occur if not properly designed for water flow conditions.

7. Applications

• Low-head hydroelectric power plants.
• Irrigation systems.
• Tidal power plants.
• Run-of-river hydro projects.
• Small-scale rural power generation systems.

These turbines are often used in locations where a continuous supply of water is available but the elevation difference is small.

Conclusion:

A propeller turbine is a reaction-type axial flow turbine used to generate electricity from low-head and high-flow water sources. Its fixed-blade runner operates like a ship’s propeller, converting the kinetic and pressure energy of water into mechanical energy. Although it performs best at constant flow conditions, its simple design, compact size, and high efficiency make it an ideal choice for low-head hydroelectric power generation. The propeller turbine represents an important step in the development of modern water turbines, combining reliability and simplicity for effective energy conversion.