Understanding Kaplan Turbine Classification

Hydraulic turbines are classified based on various factors, including the direction of water flow through the runner. The flow direction significantly impacts the design and operation of the turbine.

Turbine Classification by Flow Direction

Based on the direction of water flow relative to the axis of rotation of the runner, hydraulic turbines can be broadly classified into the following types:

• Axial flow turbines: In these turbines, the water flows parallel to the axis of rotation of the runner.
• Radial flow turbines: In these turbines, the water flows in a radial direction (either inward or outward) relative to the axis of rotation.
• Mixed flow turbines: These turbines involve both radial and axial flow components. Water might enter radially and leave axially, or vice versa.
• Tangential flow turbines: In these turbines, the water strikes the runner blades tangentially to the path of rotation.

Kaplan Turbine: An Axial Flow Turbine

A Kaplan turbine is a type of propeller turbine with adjustable blades. It is widely used in situations with low head and high flow rates. The key characteristic of a Kaplan turbine, in terms of flow direction, is how the water passes through its runner.

In a Kaplan turbine, the water flows through the runner in a direction parallel to the axis of the runner's rotation. This specific flow pattern is the defining feature of axial flow turbines.

Therefore, based on the direction of water flow through its runner, a Kaplan turbine is classified as an axial flow turbine.

Comparing it to other types:

• A Francis turbine is typically a mixed-flow turbine.
• A Pelton turbine is a tangential-flow turbine.
• Early reaction turbines like the Fourneyron turbine were radial flow.

The unique adjustable blades of the Kaplan turbine help maintain high efficiency over a range of flow conditions while maintaining the fundamental axial flow characteristic.