Different Types of Propeller Turbines

A propeller turbine is a type of inward flow reaction turbine that features a propeller-shaped runner, usually being found in ships, submarines, and hydraulic sites with high flow rates. Generally, it is equipped with fixed or adjustable blades, and water flow is regulated by adjustable guide vanes that move the water into a runner to transfer its energy to the blades. To better understand how propeller turbines work, this blog will cover their varying types and the advantages they have over other variations.

Most reaction turbines are of the propeller variety, those of which are designed with three to six blades that receive strikes of water at a constant rate. Apart from the blades being fixed or adjustable, propeller turbines are also designed with a runner, a scroll case, guide vanes (wicket gates), and a draft tube. The main part of the runner is the propeller including the rotating hub and blades which carry the fluid potential and kinetic energy to the shaft attached to the turbine.

Propellers can be classified based on different methods, but the most popular way is to categorize them by number of blades or blade pitch. Meanwhile, the flow direction is axial for a majority of propellers, which is parallel to the axis of rotation. These propellers are often categorized as mid-flow turbines. Early versions of propeller turbine units were manufactured with vertical shafts.

Today, propeller turbines take advantage of a horizontal shaft, and the blades of the propeller turbine are typically attached to the hub, those being known as fured-blade runners. The runner blades may also be adjustable, ensuring that the turbine can work more efficiently in an array of flow conditions. Propeller turbines with adjustable blades and gates are called Kaplan turbines in honor of their inventor, Viktor Kaplan, and those with adjustable blades and fixed gates are frequently called semi-Kaplans.

Propeller turbines are manufactured for heads that range from 1.5 to 60 meters, but are usually used for heads less than 30 meters. In a fixed propeller turbine, the range of flow operation is optimal between 75% and 100% of best efficiency point (BEP) flow. Kaplan turbines, on the other hand, may operate between 25% and 125% of the best efficiency discharge rate, and the head range that helps achieve adequate performance from these turbines is from 20% to 140% of the design head.

Propeller Turbine Types

While the most popular type of propeller turbine is the Kaplan variation, there are numerous others, three of which we will cover in the next section.

Bulb Turbine

In bulb turbines, the turbine and generator are sealed and installed directly in the water flow. Moreover, they are better suited for low heads which measure less than 25 meters. Because of the straight design of the water flow, there are lower costs associated with this type of turbine. More than that, they take up little space because the turbine and generator are sealed, but this often makes it difficult to access turbine components for maintenance or repairs.

Straflo Turbine

Also known as rim-generator turbines, Straflo turbines have gained this particular name as an abbreviation for “straight flow.” In this turbine, the turbine and generator are combined, leading to less required space for installation. It also includes a group of axial turbines, where the generator is arranged concentrically outside the flow channel. More specifically, the generator is affixed to the propeller runner periphery, and the stator is installed within the civil works surrounding the water channel. It is worth noting that the rotor has a larger diameter that creates greater unit inertia than that of bulb generators, providing additional operating stability.

Tube Turbine

Tube turbines have penstock curves before and after the runner, creating a straight-line link to the generator. This direct drive configuration consists of the turbine and generator being mounted on the same shaft using common bearing and seals. More than that, the output power generated by tube turbines ranges from 20 to 700 kW. The main features of tube turbines include a compact arrangement, stainless steel construction, installation flexibility, and large service intervals.

Conclusion

Aircraft Aftermarket Parts is a leading distributor of high-quality propeller turbines and their related components. As our network of distribution centers stretch across the globe, our database features products by a wide range of well-known manufacturers that we trust. Get started with the submission of an RFQ form or contact us directly; we are available around the clock!