Turbomachines

Turbomachines

What is a turbomachine?

A turbomachine is a rotating mechanical machine in which energy is transferred between the device and the fluid due to the dynamic movement of the machine, and it is widely used in the science of mechanics and aerodynamics. In these machines, energy may be taken from the working fluid (such as turbines) or given to the working fluid (such as pumps). The design and construction of these machines for industrial applications are very complex, but all of them follow the simple and basic principles governing turbomachines.

As mentioned, a turbomachine is a machine that transfers mechanical energy between the working fluid and its rotating vanes through the dynamic movement of these vanes. The word turbo in the naming of turbomachines shows the rotating movement of these machines, and as mentioned, the basic principles governing all turbomachines are the same.

An important point to note is that energy transfer in turbomachines is done through a change in the enthalpy of the working fluid of the turbomachine. Finally, this energy in fluid mechanics problems is known as shaft work, either given to the working fluid like compressors or received from the working fluid like turbines. The figure below shows a view of a jet engine, including the turbine (number 7, the part that receives energy from the working fluid) and the compressor (number 3, the part that gives energy to the working fluid).

cfd analysis of turbomachinery

In summary, turbomachines can be divided into two groups energizing and energy receiving in terms of energy transfer between the working fluid and the machine. Another point is that the interaction between the fluid and the blades of the turbomachine produces a force called (Lift Force). This force is considered one of the main parameters for designing wind power plants in some turbomachines, such as wind turbines.

Turbomachines are essential components in industrial sectors. Turbomachines are used for various applications, such as propulsion systems for airplanes, turbines for electricity generation, compressors for air conditioning systems, and pumps for water supply systems.

Turbomachines have increased significantly over the years due to their versatility and ability to adapt to different working conditions. They are used in various industries such as power generation, aerospace engineering, automobile manufacturing, oil and gas production, etc. In addition, they offer several advantages, including cost savings in various industrial applications in terms of energy consumption and maintenance costs in different industrial sectors.

When the first turbomachine was invented, it was primarily used to generate electricity. Turbomachines are used to drive the shafts of steam turbines. These turbines generate electricity, which is then transmitted to domestic and industrial consumption sectors through the electricity distribution network. Turbomachines are also used in gas turbine engines and jet engine compressors, as well as in other types of power generation, such as nuclear and thermal power plants. A turboprop engine is an internal combustion engine that uses a propeller driven by a turbine powered by an auxiliary fuel source. Turboprop engines have many applications, including in helicopters and small airplanes.

cfd analysis of turbomachinery

A turbofan engine is an internal combustion engine that uses a fan driven by a turbine powered by an auxiliary fuel source. A turbofan engine can achieve high bypass ratios, enabling high thrust levels at low rotational speeds. They are commonly used to power air vehicles such as large military jets, commercial transport, and cargo aircraft, or even some models of civilian aircraft such as the Boeing 747 or the Airbus A380. The Rolls-Royce Trent 800 is an example of a turbofan jet engine in a civil aircraft.

cfd analysis of turbomachinery

Advantages of turbomachine simulation using CFD

The use of CFD in turbomachines helps engineers to understand the performance of these machines better. It also allows them to optimize their design for better efficiency and power output. With the help of a software based on CFD methods such as FLUENT, engineers can analyze the behavior of different components in a turbomachine and predict their performance in other operating conditions. There are many advantages of using CFD because they provide accurate results with minimal effort and cost. Another benefit of using CFD analysis is that engineers can analyze their initial design models before construction, design more precisely, and choose the most optimal design mode for construction.

These basic models are created with the help of software such as SolidWorks, Autodesk Inventor, and Catia.

  This allows them to test different designs without having to build anything physically. In addition, it will enable engineers to analyze their strategies early to identify potential problems before investing and wasting too much time on the project. CFD is critical in the optimization process that involves reducing energy consumption and increasing efficiency in a turbomachine. Fluent software helps engineers create computer simulations in different modes that can be used to compare different designs.

The disadvantages of using this software are that they require powerful computing computers. If powerful computing computers are not available, these simulations can be very time-consuming. In addition, engineers must predict how their design will work and create their initial design with the help of software such as SolidWorks and Catia. To save computational costs. These predictions can be very difficult because there is no way for them to know what will happen before the project is finalized.

Application of CFD in the design and development of fans

Fans are electric machine that converts electrical energy into kinetic energy. The operating fluid of these types of devices is gas, mainly air. This device is generally used for cooling and air circulation for air conditioning. It should be noted that the propellers of all piston and turboprop airplanes and the first rotating part of the air inlet (fan) for turbofan motors can also be classified as fans. Fans consist of a rotating part with different titles such as propeller, impeller, rotor, etc.; depending on their application, they can be axial, radial, or combined.

type of fan

Compressibility, turbulence, rotation, and single phase are the most important characteristics of the fan governing flow. However, in some cases, the compressibility of the flow in fans (such as the flow passing through the airplane propeller and the fan of turbofan engines) is also added to these characteristics, and the stability of the flow is usually an acceptable assumption. In general, the most important CFD applications in flow design and development are:

– Simulating and studying the behavior of turbulent circulation flows passing through fans using various turbulence models and methods

-Using periodic boundary conditions to reduce the volume of calculations for axial fans (if they are axially symmetric)

– Studying, checking, and optimizing the design of the cross-section (airfoil) of fan blades

– Studying, checking, and optimizing the design of the blade shape along with the installation angles (Incidence Angle) and Twist Angle

– Studying, checking, and optimizing the entire shape of the fan, such as the number of blades and their dimensions

– Studying and investigating the effects of the fan on the fluid behavior of the whole system

Application of CFD in the design and development of

pumps

A pump is a device that converts energy, usually electrical energy and, in exceptional cases, mechanical energy (such as piston pumps), into fluid energy (its pressure change). The working fluid of pumps is liquid.

pump

Turbulent, incompressible, rotating flows are the most important flows in pumps. Of course, we do not see the circular flow for reciprocating pumps. The important point is the phenomenon of cavitation in the flow of liquids in pumps like water pumps, which greatly impacts the corrosion of impellers. With the above explanations, it can be said that the uses of CFD in the design and development of pumps are:

– Calculation of flow rate, velocity, and pressure fields in the entire pump space, including the outlet boundaries

-Studying and checking the qualitative and quantitative performance of impellers

– Simulating the two-phase flow (cavitation) and investigating its effects on the corrosion and service life of impellers

Extraction of performance curves of pumps under different operating conditions

– Optimizing the performance of impellers

Application of CFD in the design and development of compressors

Compressors use mechanical energy to increase the pressure and temperature of gases and reduce their volume. Unlike pumps, the working fluid of compressors is gas and mainly air. Jet engines, pressurized airplane cabins, natural gas transmission through pipelines, storage of pure gases in small volumes, heat transfer in refrigeration systems, air storage in submarines, and provision of compressed air for brakes that work with air are among the most important things that The role of compressors is vital in them.

Compressibility, turbulence, rotation, and instability are prominent flow characteristics in compressors. It should be noted that compressibility itself causes heat transfer and fluid temperature changes. Using different CFD methods, all regimes governing compressor flow can be simulated. But the most important goals of using CFD in these types of devices are:

– Simulating and solving the flow field along with the calculation of speed, pressure, temperature, and enthalpy in the entire compressor

– Predicting the amount of pressure increase for each stage and estimating the ratio of the total pressure of the compressor

-Studying, checking the performance, and improving the design of the blades (airfoils) of different rows of the compressor

– Studying, checking the performance, and optimizing the design of the blades, including the angle of installation and twisting

– Investigating the interaction of the rotor and stator in each row of axial compressors

– Optimizing the design of each row of axial compressors (number and shape of rotor and stator blades)

– Optimizing the shape of the shell, outlets, and row of blades to reach the maximum pressure ratio in radial compressors.

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