Types turbines

WHAT IS A TURBINE?

Last week we looked at the history of turbine blades in our ALL ABOUT BLADES column. This week we will focus on what a turbine is, how it works and what makes it different.

A turbine is a machine for continuous power generation in which a wheel or rotor, usually with blades, is made to rotate by a fast-flowing stream of water, steam, gas, wind, or other fluid. Examples include Hoover Dam or the mighty Niagara Falls, where water flows through turbines spinning under the pressure of falling water to generate nearly 4.9 million kilowatts that power 3.8 million homes. Did you know that there are 7,254 hydroelectric power plants in Germany as of 2020? Or think of the famous old windmills in Holland, the forerunners of today's wind turbines, which are an effective and inexpensive source of renewable energy for generating electricity.

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DIFFERENT TYPES OF TURBINES

In mechanical engineering, turbomachines are machines that transfer energy between a rotor and a fluid or steam. This includes both turbines and compressors, which are frequently used in the automotive industry (turbochargers), aerospace (aircraft turbines), the energy sector (gas and steam turbines) and industry (compressors).

Turbines can be divided according to the direction of flow. The three main areas are radial, diagonal and axial, and the flow medium determines which type of turbine it is. The four main types are steam, gas, water and wind. All turbines are important and play a major role in the industry, but we will focus only on steam and gas, which leads us to look at axial and radial flow direction.

What is the difference between axial and radial turbines? In a radial turbine, the flow is uniformly oriented perpendicular to the axis of rotation and drives the turbine in the same way that water drives a water mill. The result is less mechanical stress (and less thermal stress in the case of hot working fluids), which allows a radial turbine to be simpler, more robust, and more efficient (in a similar power range) compared to axial turbines. In the axial turbine, the working fluid flows parallel to the shaft axial compressor and converts the flow of the fluid into mechanical rotational energy.

All turbines are important, but it is the complex profile of the jet turbine that we measure most often.

MORE ABOUT AXIAL TURBINES AND COMPRESSORS

#allaboutblades is essentially about turbine blades, and so we want to focus on axial turbomachinery. Axial turbines and compressors consist of several stages. Stages are the combination of a pair of rotating and stationary blades (vanes). The blades are connected to the rotor, and the vanes are connected to the casting. The main function of the blades is to provide energy transfer between the gas and the rotor. The vanes, on the other hand, prepare the gas for entry into the next set of rotating vanes and redirect the flow of passing gas from the previous set of vanes to the next set of vanes. This results in a directed flow of compressed air, high-energy steam, or exhaust gas through the turbine/compressor to transfer the maximum amount of energy possible.

Axial turbines and compressors are different types of turbomachinery with the same basic principles, only in reverse. Turbines are fed with high-energy gas that flows through the turbine. Stage by stage, it transfers its energy to the blades. The gas flowing through relaxes, expands, and as a result the blades and vanes increase in size along the axial flow path of the gas. In the end, all the energy is transferred to the blades and thus to the rotor to eventually drive another machine. In power generation in power plants, the turbine is connected to a generator to produce electricity.

A compressor works in the opposite way and is driven by a motor. Air is drawn in by the rotating blades and forced through the compressor. Each set of blades/valves is slightly smaller, which gives the air more energy and compression.

GAS TURBINES - BOTH WORLDS COMBINED

Aircraft turbines have both a compressor and a turbine, and between them is the combustion chamber. Air is drawn into the turbine, compressed and mixed with the fuel so that combustion takes place, resulting in thrust. In addition, a turbine in the exhaust stream is activated by the exhaust flow. The turbine's impeller is connected to the compressor and thus acts like a mechanical connecting motor to the compressor, driving the compressor. However, the main energy of the hot exhaust gas is used to generate thrust by increasing its velocity through the nozzle.

This basic principle is also found in turbojet/jet engines, the simplest types of aircraft gas turbines.

The turbofan gas turbine is the most common type of turbine engine used in aircraft today. The basic principle is the same, but the components are more complex. In addition, there is a fan and a bypass system to further increase the efficiency and stability of the turbine.

Turboshaft engines are widely used in applications requiring sustained high power, high reliability, small size and light weight. They find this application in helicopters, auxiliary power units, boats and ships, tanks, hovercrafts and stationary equipment.

THE STRUCTURE OF THE SHEET

The blade and vane have different functions, but share similar geometric elements. The blade redirects the flow path, while the vane transfers energy between the gas and the rotor. The blades must operate at high speeds and temperatures, while the vanes direct the flow driven by the rotating blades to the next turbine stage with optimum efficiency. Both the blades and the guide vanes must be resistant to oxidation, corrosion and wear and have a long service life.

This is one of the most important aspects that companies consider when improving their blades to increase performance and extend blade life.

MEASUREMENT INCREASES EFFICIENCY

The structure and function of the blade consists of three aspects:

1) The root is used to fix the blade to the rotor or casing. Depending on the mechanical load, required fastening precision and manufacturing costs, the roots can be different. We will discuss this topic in more detail in the future.

2) The blade, functionally shaped to ensure proper interaction with the gas flow, is designed to redirect the flow path while the blade transfers energy between the gas and the rotor. The airfoil transitions into the root and shroud via a transition radius and curved platform surface. The airfoil consists of a pressure side and a suction side with a leading edge and a trailing edge, which will be part of our detailed blog.

3) The shroud is optional and depends on the turbine application. Shrouded blades are used to control and minimize leakage currents between blade tips and blades and to limit vibration amplitudes to ensure the creation of a stable outer ring.

WENZEL MEASURES #MOREPARTSFASTER

In the manufacture of blades there is a wide variety of shapes, dimensions and requirements for any desired application. The profiles are designed to maximize the required performance. Regardless of the size, surface or lead time, there are no limitations for CORE . The high-speed optical scanning system is designed for the harsh conditions of a direct production environment. CORE M features temperature stability, dirt and vibration resistance. Highly dynamic linear drives and the robust base machine of the 6-axis measuring system enable measurements at high speed.

The innovative optical high-intensity photoelectric proximity switch from WENZEL ensures fast point detection, even on hard-to-reach components and highly reflective surfaces, without time-consuming repositioning of the component or pretreatment of surfaces.

The CORE M has a measuring volume of 500 mm x 500 mm x 2,500 mm, making it ideal for measuring large components. Inside the machine housing is a system of dynamic counterbalance weights that counteract the forces generated by the high-speed movement of the scanner, so there is no loss of accuracy even at remarkably high measuring speeds. The comprehensive software package from WENZEL enables simple and fast evaluations on blades using the WM | Blade Analyzer blade analysis software developed in cooperation with industry partners.

As you may have noticed, we love measuring turbine blades with their gunmetal gray and smooth, graceful design. These little pieces have a significant impact that allows us to travel the world, build our economies, and protect our countries and our loved ones - all of which are great reasons to do so. I encourage you to enjoy a relaxing river cruise on an old steamboat, marvel at the size of the big wind turbines, visit Niagara Falls, and think about how far we've come over the centuries. Remember that improvements have been made through measurement and technology has evolved.

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