Brief Introduction of Axial Flow Turbine and Cross Flow Turbine

Today, Hydraulic Turbine Generator Supplier will give you a brief introduction to the related knowledge of axial flow turbines and tubular turbines.

Kaplan Turbine

1. Axial turbine

The main difference between the axial turbine and Francis Turbine is that the runner type is different. Axial flow runner is composed of three parts: blade, hub and drain cone. The shape is relatively simple and the number of blades is relatively small. Generally, there are four leaves, and there are two, three or six leaves. When the water flows between the blades, it pushes the runner to rotate. This type of hydraulic turbine is called axial flow type because the water flow into and out of the runner is axial.

There are three different types of runner structures for axial turbines: paddle, semi-rotor, and fixed paddle. The paddle-type blade can rotate around the blade axis in structure. When the water head and the output force change during operation, the blade can be rotated at any time according to the change of the water flow, so that the blade always maintains a most suitable condition for the water flow Inclined position to reduce water flow energy loss and improve turbine efficiency. However, the structure of this runner is relatively complicated, and small hydropower stations are not used.

The semi-rotary paddle type is also known as the adjustable paddle type. After the machine is stopped, the blades can be removed and installed at an angle. The performance of the semi-rotor type runner is better than that of the fixed paddle type, and the structure is not very complicated. The fixed-blade type blade is fixed on the hub and cannot be changed in structure. It is similar to a general propeller, so it is also called a propeller type. This type of runner structure is the simplest and is most commonly used in small hydropower stations, but because the blades are fixed, it cannot adapt to changes in water flow caused by changes in water head and output, so the average efficiency during operation is low. In order to make up for this shortcoming, general propeller-type turbines are often designed as runners with different installation angles, which allows users to use them optimally according to the hydraulic conditions of the power station.

The above-mentioned blade mounting angle or turning angle refers to a relative angle. Different angle values have different performances such as turbine efficiency. We set the blade installation angle to zero when the turbine efficiency is highest (water flow energy loss is lowest) under a certain head of water, and use the installation position as a reference to determine the installation angles "+" and "-". When it increases to “+”, the opening between the blades increases, and the flow and output increase. When it increases to “-”, the opening decreases, and the flow and output decrease. The unit of design and manufacture of each type of hydraulic turbine should indicate the specific value of the installation angle and its corresponding performance on the drawings for users to choose.

2. Tubular turbine

Tubular turbine is a kind of turbine with higher efficiency and better performance. Its basic components include radial guide vanes, runners, supports, and draft pipes. The runner of a cross flow turbine is the same as the axial flow, so in fact it is also an axial flow turbine. The water flow from the guide vane to the runner is relatively straight, so it is called cross flow. The flow path of this turbine is smooth, the water passing capacity is large, and the hydraulic loss is small. Unlike in the axial flow type, the water flow from the turbine room to the guide vane and then from the guide vane to the runner requires changing the flow direction, which will cause a large Hydraulic loss, so the efficiency of cross-flow turbine is higher.

At the same time, it does not have a complex volute, the structure is relatively simple, and the unit spacing is relatively small. Tubular turbines are divided into two categories, one is a full-through flow type and the other is a semi-through flow type. The full-flow type is a method in which the rotor of a generator is installed on the periphery of a turbine runner, and the water flow passes through the runner. It is rarely used because the hermetic insulation of the generator part is very difficult. Semi-through flow type, its water turbine and generator are still divided into two independent parts, and different transmission forms can be used between the units. Now, the practical use of small-scale hydropower stations belongs to this type. With the vigorous development of hydropower construction, especially the vigorous development of low-head hydraulic resources, this type of semi-turbine turbine has greatly developed, a variety of structural forms have appeared, and the scope of use has been expanded.

The above is the knowledge of axial turbines and cross-flow turbines introduced by Kaplan Turbine supplier.