Short Answer:

Runner blades are the main curved vanes or blades fixed on the runner of a turbine. Their primary purpose is to convert the energy of water (either kinetic or pressure energy) into mechanical energy by rotating the runner. The design, shape, and angle of runner blades depend on the type of turbine and the head under which it operates. In reaction turbines like the Francis turbine, runner blades are enclosed and water flows through them continuously to transfer energy effectively.

Runner blades play a crucial role in maintaining the efficiency of the turbine. They help in changing the direction of water flow and transferring momentum to the runner shaft. The smooth and streamlined shape of the blades ensures minimal energy loss and proper utilization of water power. The number and curvature of the blades are carefully designed to achieve maximum energy conversion and mechanical stability during operation.

Detailed Explanation :

Runner blades

Runner blades are one of the most important components of a hydraulic turbine. They are mounted on the runner, which is the rotating part of the turbine connected to the shaft. The main function of the runner blades is to receive the high-energy water flow and convert its hydraulic energy into mechanical rotational energy. This mechanical energy is then used to drive an electric generator or perform mechanical work. The efficiency and performance of any turbine largely depend on the design, material, and orientation of its runner blades.

In the case of impulse turbines (like the Pelton wheel), the runner blades or buckets are designed to change the direction of the water jet striking them. Water hits the blades tangentially at high speed, and the change in momentum causes the runner to rotate. Each bucket or blade splits the water jet into two equal parts to balance the forces acting on the wheel. Thus, the impulse blades operate under atmospheric pressure and convert only the kinetic energy of water into mechanical energy.

In reaction turbines (such as the Francis and Kaplan turbines), the runner blades are enclosed and work under pressure. Here, water flows through the blades, and both pressure and kinetic energy are utilized for energy conversion. The shape of these blades is more complex and curved to allow a smooth and continuous flow of water. In a Francis turbine, the flow of water is partly radial and partly axial, while in a Kaplan turbine, it is completely axial. The design ensures that the velocity and direction of flow change gradually, avoiding sudden shocks and energy losses.

The shape and angle of runner blades are determined based on the head, discharge, and speed of the turbine. For high-head and low-flow turbines, fewer and smaller blades are used, whereas for low-head and high-flow turbines, larger and more curved blades are preferred. The blade curvature helps to direct the flow efficiently and ensure even distribution of water pressure. Computational Fluid Dynamics (CFD) methods are often used in modern turbine design to analyze the flow pattern and optimize the blade geometry for better performance and reduced wear.

The material of the runner blades must be strong enough to resist erosion, corrosion, and cavitation caused by high-speed water flow. Common materials include stainless steel, bronze alloys, or high-grade cast steel. The surface of the blades is polished to reduce friction and improve water flow efficiency. In some cases, protective coatings are also applied to increase durability and prevent damage from impurities or sand particles in the water.

Proper maintenance of runner blades is essential to ensure long-term efficiency. Over time, continuous exposure to water pressure and flow causes erosion and minor deformation of the blade edges. This can reduce the performance and output of the turbine. Therefore, regular inspection, cleaning, and repair of damaged blades are carried out to maintain optimum efficiency and balance of the turbine runner.

Runner blades also influence the speed regulation and load variation of the turbine. Adjustable or movable blades, as seen in Kaplan turbines, allow control of the water flow angle to suit different load conditions. This adaptability helps maintain high efficiency even when the water discharge or head changes. Fixed blades, on the other hand, are simpler but less flexible under variable flow conditions.

Overall, runner blades serve as the heart of the turbine mechanism. Their design directly affects the conversion efficiency, stability, and lifespan of the turbine. A well-designed runner with properly shaped blades ensures smooth energy transfer, minimal losses, and high performance even under varying operating conditions.

Conclusion:

Runner blades are the key energy-converting parts of a turbine. They transform the hydraulic energy of flowing water into useful mechanical rotation. The shape, material, and arrangement of the blades are designed for maximum efficiency, durability, and smooth operation. Properly designed runner blades not only enhance turbine performance but also ensure reliable and long-term operation of hydroelectric power systems.