SoftInWay Inc. delivers time and cost saving turbomachinery solutions through industry-leading consulting services, fully in-house developed software, and customizable training courses.
Gas turbines have a rich history and play a key role in many of the modern-day technology we rely on. Welcome to part 1 of this blog where we’ll look at the history and evolution of gas turbines and don’t forget to join us for part 2 (next week) which will take a deeper look into hydrogen energy and where these machines are headed.
The First Industrial Gas Turbines
Gas turbines are unique in many respects. First, they are among the most ancient turbomachines in their idea (approximately the 15th century) and at the same time, quite young in terms of practical implementation (the turn of the 19th–20th centuries).
Prototypes of gas turbines, which included the so-called smoke machines, began surfacing as early as the 17th century. However, the starting point in the development of gas turbines can be considered to have taken place in 1791 when Englishman John Barber filed an application for a heat engine patent.[1]. The turbine was equipped with a chain-driven reciprocating compressor and had a combustor and turbine. Barber proposed the use of charcoal, gas, or other suitable fuels to produce inflammable gas. The gas from the producer went into a common receiver and then into the combustion chamber where it mixed with compressor air and was ignited. The resulting hot gasses were allowed to impose on a turbine wheel. To prevent overheating of the turbine parts, provisions to cool the gas by means of water injection were incorporated. There is no record of this engine being built but, in any event, it is unlikely that it would have self-sustained because of the large power requirements of the reciprocating compressor. A patent drawing of Barber’s device is shown in Figure 1 [2].
Figure 1 John Barber’s Gas Turbine. English Patent 1791 [2]In 1872, Franz Stolze designed an engine with an axial compressor, an axial turbine on the same shaft, a heat exchanger, a gas producer, and a combustion chamber. The gas turbine unit (Figure 2) was created and designed to produce 200 hp at a speed of 2000 rpm. However, the tests were not successful and instead only produced 20 hp. [1] Read More
One of the important factors affecting compressor performance is the distribution of work between compressor stages.
There can be many different axial compressors with the same design point value for efficiency, airflow and pressure ratio and all of these compressors will meet the required parameters at the design point. Compressors operate in a variety of modes. Many compressors are equipped with a turning inlet guide vane (IGV) or guide vane (GV). At the same time, the question of the number of stages with a turning IGV or GV, at what angle to turn them, and whether the maximum efficiency will be the same remains unresolved. To answer this, designers need to compare the impact of the distribution of work between compressor stages at the design point on the compressor characteristic. This allows you to choose the form of work distribution to achieve the specified parameters of the compressor in off-design modes of operation. This also allows you to obtain the required degree of pressure ratio and airflow at a given frequency of rotation of the compressor rotor. This analysis is necessary for jet engines since the compressor works in conjunction with the combustion chamber, turbine, and nozzle. This can also be carried out for other applications of multistage compressors.
With the help of AxSTREAM and ION, studies were carried out on multistage compressors with various shapes of the flow path, a different number of stages, and a different distribution of work among the stages.
Figure 1. Calculated typical characteristics of a multi-stage, variable compressor.
The problem is considered in the following formulation:
Influencing factor:
Distribution of work on compressor stages.
Variable parameter:
Compressor operating mode.
Axial compressor type:
With fixed IGV or GV.
With turn of IGV or GV.
Additional task for the compressor with turn IGV or GV:
Develop a criterion for the required number of compressor stages with restagger angle of the blades IGV or GV.
The compressor is taken from the article sourced at the end of this post Read More
Update – March 1, 2023: AxSTREAM NET is our legacy software replaced by AxSTREAM System Simulation. System Simulation was born out of the union of the legacy AxCYCLE and AxSTREAM NET software packages.
It is impossible to imagine the design of any rocket engine without a nozzle – a technical device that serves to accelerate gas flow passing through it to speeds exceeding the speed of sound. The main types of nozzle profiles are shown in Figure 1.
Rotating machines have huge and important roles in our daily life although we may rarely think about them. Steam turbines at electrical power plants rotate the electrical generator shafts which produce electricity coming into our homes and offices. Driving to or from work, the reciprocating cycle in your vehicle’s internal combustion engine results in rotation of the transmission and the wheels of vehicles, while the electric car wheel operation is a result of induction motor rotation. If you get on an airplane, rotation of the turbo reactive gas turbine engine produces the effective thrust to sustain flight by moving, compressing and throwing the gas behind the plane. We can even find the useful effects of rotation in our kitchens when we are blending the food or washing our closes.
Although these rotating machines are different, the approaches to modelling their rotor dynamics are pretty much the same, since similar processes occur in rotating parts which differ in their vibrations from the non-rotating machines.
Do you remember the example of rotating washing machine? Have you ever seen it jumping on the floor trying to squeeze out your closet? We bet you have. This is the simplest example of the increased unbalance affecting the amplitudes of machine vibrations. Washing machines are designed to experience these noticeable vibrations during their operation without breaking. But the steam turbine or compressor rotors which have the tight clearances between the impellers and the casing can not boast of that leeway. In addition to that, the excessive vibrations significantly influence the machine’s useful life due to the increased fatigue.
This is why the rotor dynamics predictions are one of the most important parts of rotating machine analyses. And although they may seem easier than comprehensive stress-strain investigations of machine components, in some cases the rotor dynamics analysis can be trickiest part.
Usually, the rotor dynamics analyses are divided into lateral and torsional stages depending on the nature of rotor response to be used. They are discussed in different types of standards (API [1], ISO [2], etc.). Let’s consider the example of the lateral vibrations of a 4 stage compressor rotor with an operational speed of 8856 rpm.
Fig. 1 – 4 Stage Compressor Rotor
This rotor rotates in the 4 pad tilting, pad oil film journal bearings. The characteristics of these bearings should be determined carefully to ensure that there will not be an excessive wear, heat generation or friction in them. Read More
Update – February 28, 2023: AxCYCLE is our legacy software and is replaced by AxSTREAM System Simulation. System Simulation was born out of the union of the legacy AxCYCLE and AxSTREAM NET software packages.
During industrial processes, an estimated 20 to 50% of the supplied energy is lost, i.e., by dumping the exhaust gas into the environment [1]. The waste heat losses and the potential work output based on different processes including but not limited to the ones shown in Figure 1. Does it REALLY have to be thrown away? Sometimes yes, other times no. In this blog post, we will focus on the “no” through a process called “Waste Heat Recovery”.
Figure 1: Waste heat losses and work potential of different process exhaust gases [US Department of Energy [2]]Some well-known examples of waste heat recovery processes are found in turbochargers in cars or a heat recovery steam generator. One simple structure of application is when a heat exchanger is fed with the exhaust gas of a turbine, therefore being cooled down before being released into the air. This heat exchanger is part of a secondary (bottoming) cycle where another turbine provides additional power output without having to burn additional fuel. This heat exchanger is part of a secondary cycle where another turbine provides additional power output. Read More
In the age of green energy and increased efforts to minimize our carbon footprint, the design of a turbocharger plays an important role in reducing engine fuel consumption and emissions while increasing the performance. When developing an engine with a turbocharger, the general approach is to select a turbocharger design from a product list. The primary issue with this approach is that it does not cover 100% of the requirements of engine characteristics, i.e. it has non-optimal construction for the engine being developed. The operational characteristics of an engine directly depends on the interactions between the system components. This non-optimal construction will always lead to a decrease in the engine’s performance. In addition, the iteration process of turbocharger selection is time and resource consuming.
That is why the most optimal way to develop an engine with turbocharging is to design a turbocharger from scratch; wherein the operational points of compressor needed to satisfy the engine’s optimal operation are known, i.e. compressor map (Figure 1). But how do we quickly get a compressor map? Even at the preliminary design level, the design of turbocharger flow path requires dozens of hours for high-level engineers. And what about less experienced engineers?
Incorporating a digital engineering approach with a turbomachinery design platform such as AxSTREAM® allows designers to find the compressor design with all the required constraints which correspond to the specified compressor map needed. The design process is presented in Figure 2. Read More
Update – February 28, 2023: AxCYCLE is our legacy software and is replaced by AxSTREAM System Simulation. System Simulation was born out of the union of the legacy AxCYCLE and AxSTREAM NET software packages.
And just like that, we’re wrapping up 2021! I feel as though I just wrote our 2020 year-in-review, but here we are getting ready for 2022. So just what did we get up to in the last 12 months here at SoftInWay?
AxSTREAM Continues to be at the Cutting Edge
Like any other industry and discipline, engineers and managers are always looking to design turbomachinery components and systems better, faster, and at a lower cost. After all, who says you can’t pursue all 3 points of the triangle of truth?
Users can now design and simulate a wide range of rocket engine cycles, from gas generator and staged combustion cycles to expander cycles and even simple pressure-fed systems.
AxSTREAM.SPACE wasn’t the only area of attention for our development engineers, however. Here is an overview of some key capabilities added inside the AxSTREAM platform, which include:
AxCYCLE
Features new capabilities in hydrogen/fuel cell cycle design and simulation, in addition to the above-mentioned new capabilities in rocket engine cycle modeling.
AxCFD
Received improvements to facilitate easier startup, meshing, and postprocessing. That means more results in less time, in a CFD solver already known for its fast solve times.
AxSTREAM For Turbines
Is now capable of incorporating drilled nozzles in turbine designs, which opens the door for supersonic turbines to be designed and analyzed with precision and accuracy.
AxSTREAM RotorDynamics
Received several features and capabilities in 2021. These include, but are not limited to:
The potential to model the position of the static moment acting on the shaft to correctly represent the moment along the rotor.
The ability to account for crank inertia only, the piston pressure only, or both these effects in tandem.
The ability to investigate the moments and stresses in torsional couplings of reciprocating machines.
Refined results for angular displacement, velocity, torque, and torsional stresses
Drilled nozzles in an axial turbine in AxSTREAM
New Seminars!
One of our favorite new events we took part in this year were the Sustainable Energy Seminar workshop and our new training course we hosted in conjunction with the American Institute of Aeronautics and Astronautics (AIAA). In both cases, our focus was on the future!
For the Sustainable Energy focused workshop, our training team introduced engineers to how the AxSTREAM platform is used for creating sustainable energy turbomachinery systems, such as waste heat recovery, nuclear, systems utilizing supercritical carbon dioxide (sCO2), hydrogen, and heat pumps.
Attendees got to see how the AxSTREAM platform offers solutions for a wide array of engineering challenges in sustainable energy. Everything from pump, compressor, and turbine aerodynamics and hydrodynamics to rotor dynamics, to thermal-fluid network models were used to show engineers how entire sustainable energy systems can be built from scratch, and how having all these engineering disciplines contained in one program ensure results can be received in just a few hours.
In sum, this seminar offered engineers a great chance to learn more about how AxSTREAM can be an end-to-end solution for sustainable energy system design, analysis, and simulation!
In partnership with AIAA, SoftInWay hosted 12 lectures over 6 weeks, for a total of 24 hours which covered turbomachinery for emerging space applications, specifically in liquid rocket propulsion.
This course covered the entire design process from determining missions’ requirements and their influences on system design, to turbopump component design as well as explored the benefits of using a flexible, integrated, multi-disciplinary design platform such as AxSTREAM.
Course students were taught the value of having a program like AxSTREAM to “push the envelope” when it comes to rocket engine design, and how having an integrated and automation-capable set of tools in one platform can significantly shorten design cycles and lead times.
As a result, engineers from every kind of space exploration company imaginable attended the AIAA course, with many of them looking for ways to incorporate AxSTREAM into their workflow and shorten their product development times.
Smashing Webinar Records for the Second Year in a Row!
2021 was a good year for our webinar team, as the continuous developments to AxSTREAM meant that more challenging engineering topics could be taken on. After all, we want to keep things interesting!
Each of these topics covered an area of concern for turbomachinery engineers.
In the aftermarket industry, reverse engineering can be critical to conducting failure analysis on a turbomachine or to create spare parts on a machine where part availability ranges from scarce to none. Additionally, reverse engineering is invaluable when a company that makes use of turbomachines, such as a refinery or power plant, is looking to digitize their fleet of machines and predict maintenance and prevent downtime. Read More
In today’s intensely competitive global market, product enterprises are constantly seeking new ways to shorten lead times for new product developments that meet all customer expectations. In general, product enterprise has invested in CAD/CAM, rapid prototyping, and a range of new technologies that provide business benefits. Nowadays, reverse engineering (RE) is considered one of the technologies that provide business benefits by shortening the product development cycle [1]. Figure 1, shows how reverse engineering can close the gap between what is “as designed” and what is “actually manufactured” [1].
Figure 1. Product Development Cycle. SOURCE: : [1]
Reverse engineering (RE) is now recognized as an important factor in the product design process which highlights inverse methods, deduction and discovery in design. In mechanical engineering, RE has evolved from capturing technical product data, and initiating the manual redesign procedure while enabling efficient concurrency benchmarking into a more elaborated process based on advanced computational models and modern digitizing technologies [2]. Today the application of RE is used to produce 3D digital models of various mechanical worn or broken parts. The main steps in any reverse engineering procedure are: sensing the geometry of the existing object; creating a 3D model; and manufacturing by using an appropriate CAD/CAM system [2]. Read More
Suppose you want to build a turbopump to increase the pressure of your working fluid. However, you find that the fluid that you are working with keeps vaporizing in the impellers you design, causing all sorts of performance issues. What can you do in this case? One solution is to design an inducer for your turbopump.
Axial inducers are used in turbopumps upstream of the impeller to avoid cavitation, reduce the inlet pressure requirement, and/or allow for operation at higher turbopump rotational speeds for a given inlet pressure [1]. For a turbopump to function properly, the inlet pressure of the pump must be high enough to avoid cavitation. Cavitation is a phenomenon where vapor bubbles which form in the flowing fluid collapse suddenly – potentially causing surface damage of the impeller, performance degradation, as well as catastrophic failure.
The cavitation phenomenon can be visualized in the below image. The inlet flow (flowing from the left side of the image) hits a blunt body in the fluid channel. This causes the pressure to locally drop and vapor bubbles to form. As the fluid continues to flow (towards the right side of the image), the vapor bubbles collapse once the fluid pressure has sufficiently increased.
Figure 1: Formation of vapor bubbles in cavitating fluid flow
Now that we understand the problem, how can we make sure these cavitation effects won’t happen in our pump? To predict when cavitation will occur, two parameters are commonly used. The available net positive suction head (NPSHa) describes how much greater the local inlet static pressure is relative to the local inlet vapor pressure. Essentially, NPSHa indicates whether the conditions for cavitation to occur are met. The required net positive suction head (NPSHr) describes the inlet head corresponding to a certain drop in performance capability. A typical NPSHr parameter is the standard 3% NPSH (NPSH3) which describes the inlet pressure corresponding to a 3% drop in head rise capability of the pump at a particular flow rate. Generally, NPSHr is measuring whether there is enough cavitation present to cause a noticeable decrease in the pump’s performance. If the NPSHr is much greater than NPSHa, then significant performance decreases due to cavitation may occur. That is to say, when the available net positive suction head is insufficient, bad things can happen, ranging from performance degradation to outright damage and failure.
Update – February 28, 2023: AxCYCLE and AxSTREAM NET are our legacy software packages replaced by AxSTREAM System Simulation. System Simulation was born out of the union of the legacy AxCYCLE and AxSTREAM NET.
Today’s simulation and analysis (S&A) tools allow engineers to study and verify system/machine properties and visualize the aerodynamic, thermodynamic, structural, and other physical properties without having to build a physical prototype. We can perform cooling secondary flow systems analysis in a gas turbine; a detailed performance study for a supercritical CO2 turbine/compressor; predict cavitation for industry a water pump/rocket turbopump; and so many more. Products and machines are becoming more and more complex. Unfortunately, engineers only run a handful of designs through the S&A process, due to the cost associated with limited computer resources and the time required to run simulations and to create complex 3D models of designs. Furthermore, verification and certification of system designs are often done using actual hardware—a costly and time-consuming endeavor. Considering these aspects, 1D and 3D simulations are significantly important. However, engineers need to determine the trade-off between 1D and 3D simulation.
Figure 1 AxSTREAM Platform with Modules from 0D to 3D including seamless geometry import into STAR-CCM+
1D Simulation
Imagine what’s required to generate one 3D design for a gas turbine secondary cooling flow system, and multiply it by 1,000 design alternatives. Even if we were to only use conceptual CAD models, this project would require extraordinary computing power and data storage—not to mention simulation and design expertise.
And so, even with the movement to bring more cloud-based S&A tools to market, resources required for 3D modeling will still result in very few designs being extensively explored, thanks to their complexity. Detailed low-dimensional models of system behavior can provide valuable insights into system performance and function thus guiding the design process. Read More
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