Critical Speed Maps in Turbomachinery

Posted by Yana Solomonova

For many years, one of the primary analysis techniques has been undamped critical speed analysis, and this technique is still performed today for the preliminary estimation of critical speeds and mode shape characteristics. First, let’s take a look at what this kind of analysis technique is and what it involves.

Critical speeds and their associated mode shapes are most influenced by the support (bearing and pedestal structure) stiffness magnitudes, the support locations, and the rotor’s mass and stiffness properties. Based on this, the following definition can be given. A critical speed map is a graph representing the effect of rotor support stiffness on the critical speed of the rotor. A general view of the critical speed map is shown in Figures 1-2.

Figure 1 Undamped Critical Speed Map [1]
Figure 2 Undamped Critical Speed Map in AxSTREAM RotorDynamics
Figure 2 Undamped Critical Speed Map in AxSTREAM RotorDynamics™

With this definition in hand, the next question would be what is critical speed? Critical speed is the rotational speed that corresponds with a structure’s resonance frequency (or frequencies). A critical speed appears when the natural frequency is equal to the excitation frequency. The excitation may come from unbalance that is synchronous with the rotational velocity or from any asynchronous excitation. Read More

Turbomachinery Design Strategies & Tips: How to Choose Between an Axial or Radial Configuration

Posted by Fengting Du

From the electricity that charges our phones to the jet engines that propel airplanes across the sky, turbines can be found powering our modern world in various forms and configurations.  These mighty machines are the silent heroes of our energy infrastructure, found in everything from locomotives and power plants to industrial machinery and rocket engines. But what distinguishes one turbine from another? How do engineers decide on the design and configuration of these mechanical marvels? This intricate task requires an understanding of turbomachinery design, including axial and radial configurations. So, let’s dive into the differences between an axial and radial configuration.

Fig.1 Example of an axial turbine used in a jet engine. Source

In an axial turbine, the fluid (such as steam, gas, or water) flows along the rotation axis, similar to a windmill where the fluid enters and exits in the same direction. The turbine blades are arranged in stages along the rotor, with each stage converting the fluid’s energy into mechanical energy. Read More

Bearing Optimization: Enhancing Reliability and Performance in High-Speed Machines

Posted by Andrew Tanchenko

Introduction: Bearing Optimization Approach

Hydrodynamic plain bearings play a crucial role in the overall reliability, vibration, and performance of rotary bearing systems. High-performance rotating machines operate at high speeds and subject bearings to significant static and dynamic loads. Consequently, bearing modeling must accurately simulate physical effects. However, the increasing complexity and demanding applications of bearings pose challenges for engineers striving to develop reliable designs.

One critical aspect of bearing design is optimizing the bearing clearance to prevent metal-to-metal contact, especially under heavy loading. This optimization is closely linked to the selection of the minimum oil film thickness (MOFT), which becomes a limiting factor during the process. Another limitation to consider is the maximum allowable level of bearing loading (eccentricity).

The variable parameters that can be considered in the optimization process are as follows:

Figure 1: Plain Cylindrical Bearing
Figure 1: Plain Cylindrical Bearing
  • Bearing clearance (Cb)
  • Radius (R)
  • Bearing length (L)
  • Bearing grooves positions
  • Oil supply temperature (Tin)
  • Oil viscosity (Visc)
  • Load factor (Load_f)

 

­Objective functions and constraints:

  • Minimum Power loss (Nfr)
  • Minimal allowable oil film thickness (MOFT)
  • Maximum allowable level of bearing loading (E)

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Since bearings are integral to the rotor system, the next optimization step involves analyzing the rotor dynamics simulation for a rotor-bearing system. This analysis ensures that resonances are avoided, and sufficient margins are provided to separate critical speeds from the operating speed. (more…)

Coupled Digital Engineering Solutions in Podracing: More Bang for your Republic Credits!

Posted by Clement Joly

Authors note:  While I have the utmost respect for die-hard Star Wars fans, I must confess that growing up, Episode I was my favorite. Perhaps it was the allure of Darth Maul’s dual lightsaber, the adrenaline-pumping Podracing on Tatooine, or Natalie Portman (no elaboration needed) that captivated my young mind. Although May 4th has already passed this year, my love of Episode I combined with my upcoming presentation at JANNAF had me thinking that perhaps it’s time to revisit the engineering behind Podracers.

In a previous blog post, we explored the possibilities of redesigning Anakin’s Podracer. Back then, we discovered that the movie’s turbine and compressor design fell far below the mark. However, poor Ani didn’t have access to the advanced AxSTREAM® software platform for designing turbomachinery systems and components, nor did he possess the financial means to acquire top-of-the-line hardware (let’s be honest, Watto’s junkshop hardly exuded luxury).

Figure 1 Watto’s junkshop in Mos Espa, Tatooine
Figure 1 Watto’s junkshop in Mos Espa, Tatooine. Source

Today, we revisit the exhilarating world of Podracing, determined to avoid the disastrous fate that befell Ben Quadinaros’ craft.

Ben Quadinaros' unfortanate start
Figure 2 Ben Quadinaros’ unfortunate start. Source 

Now, many factors could have contributed to that unfortunate incident. For example, frustration-induced control slamming is never advisable… However, the most plausible explanation is a failure at one of the subsystem interfaces. Why do I think so? Simply because this is a common issue with modern systems, including vehicles. Everyone involved means well and possesses the necessary technical prowess to perform their individual tasks. However, problems often arise when these meticulously designed parts and subsystems attempt to interface seamlessly. This is precisely where a coupled digital engineering solution comes into play! Close your eyes (then reopen them to keep reading) and imagine a place where all critical propulsion and auxiliary components can be modeled together, accommodating any desired conditions (including those we cannot run with physical hardware on a test bench).

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Calculation Methods for Dynamic Parameters of Rolling Element Bearings and Their Prediction Accuracy

Posted by Yana Solomonova

Rolling element bearings are essential components in a vast range of rotating mechanical systems, providing rotational support and a wide range of methods for friction control. The performance of these bearings is crucial to the overall functionality of the machine. Therefore, predicting the dynamic behavior of rolling bearings accurately is vital to ensure their reliable operation. Figure 1 shows a general view of angular contact ball bearings.

Figure 1 Angular contact ball bearings, [1]
Figure 1 Angular contact ball bearings, [1]
Dynamic parameter calculation is the process of determining the bearing’s dynamic response under specific operating conditions, including load, speed, and lubrication. The calculation of these parameters is crucial for designing and selecting bearings and predicting their operating life. The main dynamic parameters are:

  • Radial and axial stiffness, which is the ability of a bearing to resist deformation when subjected to radial and axial loads. This parameter is essential in ensuring that the bearing maintains its shape and does not deform excessively under the applied load.
  • Damping, which is the ability of a bearing to absorb energy and dissipate it in the form of heat. This parameter is crucial in ensuring that the bearing does not overheat, leading to premature failure.

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Moreover, bearing stiffness and damping are used for the rotor dynamic calculations of the machine supported by rolling element bearings for the accurate prediction of the rotor response under static and dynamic loads, taking into account the correct bearing characteristics. Read More

Nuclear Power Reactors: A Vital Energy Source Part 2

Posted by Suheab Thamizullah

Part 1 

Now that we understand what a nuclear reactor is, why it is used, and how it works (covered in part 1), let’s take a deeper dive into the different types of nuclear reactors, their benefits and limitations, and strategies to design and model nuclear reactor cycles using AxSTREAM System Simulation.

Types of most commonly used nuclear reactors:

There are several types of nuclear power reactors available worldwide. Based on their design, they use uranium with different concentrations as fuel, moderators to delay the fission process, and coolants for heat transfer. However, the most commonly used nuclear reactors are pressurized water reactors (PWRs) and boiling water reactors (BWRs). PWRs dominate the global nuclear fleet with 301 units comprising 66% of all nuclear power plants in operation [6], followed by BWRs at 16% with 72 units, and all other types of reactors accounting for the remaining 18%.

Pressurized water reactors (PWRs):

PWRs were designed and implemented commercially sooner than BWRs due to the earlier notion that pressurized liquid water would be much safer to handle than steam in the reactor core and would add to the stability of the core during operation. That is why the first commercial reactor in Shippingport was a PWR. Figure 4 shows a schematic design of a typical PWR plant.

Figure 4. Schematic Diagram of a Pressurized Water Reactor Power Plant. SOURCE
Figure 4. Schematic Diagram of a Pressurized Water Reactor Power Plant. SOURCE: [7]
A PWR plant consists of two separate light water (coolant) loops, primary (nuclear part) and secondary (conventional portion) as shown in Figure 4. PWRs use ordinary water as both coolant and moderator. The PWR primary loop works at an average pressure of 15 to 16 MPa, with the help of a set of pressurizers, so the water does not boil even at a temperature of 320 to 350 ℃ in the reactor. The heat from the primary water (nuclear part) transfers to the secondary water (conventional part) in the steam generator (Figure 4). There, secondary water converts into steam which drives the turbine to generate electricity. The core water cycles back to the reactor to reheat, repeating the process. Read More

Nuclear Power Reactors: A Vital Energy Source Part 1

Posted by Suheab Thamizullah

Part 2 

Introduction:

There is no doubt that energy has been driving and will drive the technological progress of human civilization. It is a vital component for economic development and growth, and thus our modern way of life. Researchers project that the world energy demand will almost double by 2040 (based on energy usage)[3], which must be met by utilizing energy sources other than fossil fuels such as coal and oil. Fossil fuel power generation contributes to significant greenhouse gas emissions into the atmosphere and influences the climate change trend. Although several research and development programs (for example, carbon sequestration and ultra-supercritical steam turbine programs) have been initiated to make fossil power generation much cleaner, more is needed to fend off the bigger problem. Therefore, many countries worldwide have recognized the importance of clean (i.e., emission-free) nuclear energy, and there are proven technologies that are more than ready for deployment. Nuclear power can solve the energy trilemma of supplying clean and affordable base-load power.

Figure 1. Nuclear Power Plant Cooling Tower
Figure 1. Nuclear Power Plant Cooling Tower

The use of nuclear energy for power generation varies widely in different parts of the world.  About 454 nuclear power reactors currently supply more than 10% of the world’s electricity, operating at a high capacity factor of 81% (world average)[1]. Thirty-one countries use nuclear power plants, with 70% of the world’s nuclear electricity generated in five countries – the USA, France, China, Russia, and South Korea. As such, many other countries have tremendous opportunities for nuclear energy growth. Today the average age of the operational power reactors stands at 30 years, with over 60% of all nuclear power plants having operated for more than 31 years[1]. Hence, nuclear power reactors are an essential energy source that has been providing electricity to millions of people worldwide. Despite the controversy surrounding nuclear power due to the risk of radiation exposure, nuclear reactors have proven to be a reliable, efficient, and emission-free source of electricity generation. Nuclear reactors have been built for the primary purpose of electricity production, although they are used for other applications such as desalination, radioisotope production, rocket propulsion, and much more. A view inside the Olkiluoto 2 nuclear reactor vessel is shown in Figure 2. Read More

Modifying Gas Turbines to Burn Hydrogen Fuel

Posted by Mykhailo Shevchenko

Hydrogen fuel and renewable energy are becoming increasingly relevant in the gas turbine industry as the world shifts towards decarbonization. Hydrogen fuel, in particular, is seen as a promising alternative to traditional fossil fuels due to its clean-burning properties. As a result, many gas turbine manufacturers are exploring ways to modify existing engines to run on hydrogen or hydrogen mixtures. Additionally, the use of renewable energy sources such as wind and solar power to generate hydrogen fuel is gaining traction, providing a sustainable solution for the gas turbine industry. These developments are crucial in reducing carbon emissions and meeting climate goals, making hydrogen and renewable energy an essential focus for the future of the gas turbine industry.

In light of these developments, one of the key methods to achieve decarbonization is to use a mixed renewable gas (e.g., green hydrogen, biogas, syngas) or pure hydrogen (in the future) as a fuel for stationary gas turbine engines (GTE) that generate electricity.

Figure 1: Heavy Duty Gas Turbine, AE94.3A (Ansaldo Energia) [1]
The main advantage of this method is that companies need not design and manufacture fundamentally new engines for hydrogen combustion. Instead, modifying the existing GTE fleet is sufficient. Another benefit of introducing hydrogen gas turbine technology is the possibility of using idle or underutilized equipment, thereby providing a new lifecycle. Read More

An Overview of Brayton Cycles

Posted by Jack Massih

The open Brayton cycle is commonly used in gas turbine engines for power generation, aircraft propulsion, and industrial processes. The Brayton cycle, named after American engineer George Brayton, who proposed it in 1872, converts fuel energy into mechanical work. The Brayton cycle became widely used in practical applications following the development of the gas turbine in the 1930s. Gas turbines were used extensively during World War II, and their efficiency and reliability improved significantly.

The Brayton cycle has numerous advantages for energy applications. For one, engineers can design it compactly, making it a strong fit for tight enclosures. With gas turbines being a common engine driver, the Brayton cycle is popular in modern applications. Since Brayton cycle engines are particularly efficient in gas turbine engines, they are useful for power generation, aircraft and marine propulsion, industrial processes, and more.

Additionally, Brayton cycle motors produce few emissions thanks to their efficient exhaust gas treatment systems, making them a greener choice than other fossil fuel systems. Coupled with their high efficiency from the isentropic compression and expansion processes that minimize energy loss, engineers continue to develop Brayton thermodynamic cycle systems to this day.

There are two main types of a Brayton cycle: open and closed. In an open Brayton cycle, the working fluid is continuously supplied to and exhausted from the system, and the process operates in an open loop. On the other hand, in a closed Brayton cycle, the working fluid is contained within the system and circulates in a closed loop. The schematics of a simple open-cycle gas turbine utilizing an internal-combustion process and a simple closed-cycle gas turbine using heat transfer processes are both shown in figure 1.

Figure 1 - Open cycle (left) and closed cycle (right) for operating a Brayton cycle
Figure 1: Open cycle (left) and closed cycle (right) for operating a Brayton cycle (https://web.mit.edu).

An ideal Brayton cycle consists of the following four processes:

  1. Isentropic compression: air is compressed to high pressure and temperature via an isentropic process that is adiabatic and reversible.
  2. Constant pressure heat addition: high-pressure air is fed into a combustion chamber where fuel is added and ignited.
  3. Isentropic expansion: high-temperature gases from the combustion chamber expand in the turbine in an isentropic process, producing mechanical work.
  4. Constant pressure heat rejection: the exhaust gases are expelled into the atmosphere.

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Common Design Challenges in Compressed Air Energy Storage Systems

Posted by Vladyslav Kotechenkov

Renewable energy is a topic which has gained significant traction in recent years. Unlike fossil fuels, which are finite and contribute to environmental degradation, renewable energy provides a cleaner, healthier, and more sustainable path forward for meeting our energy needs. Energy storage systems refer to technologies that store energy for later use, allowing for a more flexible and reliable energy supply from renewable sources such as solar and wind.

There are a wide variety of energy storage systems that enhance the power generation capabilities of renewable power plants. The most familiar system may be hydropower, with over 95% of today’s energy grid storage being held by pumped hydropower. When electric demand is low, “turbines pump water to an elevated reservoir using excess electricity. When electricity demand is high, the reservoir opens to allow the retained water to flow through turbines and produce electricity” [5]. Thanks to its performance, pumped hydropower has dominated the energy grid storage market for years. However, other emerging technologies are gaining notoriety, including compressed air energy storage, which will be the topic of today’s blog.

Have you ever wondered what happens to the air when you blow up a balloon? Well, some clever people have figured out how to use that air to store electricity. It’s called compressed air energy storage (CAES), and it’s basically like having a giant balloon underground that you can fill up with air when you have extra electricity and let it out when you need more. Sounds simple, right? Well, not quite. Some challenges are involved, like keeping the air from getting too hot or cold, and making sure it doesn’t leak or explode. But if done right, CAES systems can help us use more renewable energy sources like wind and solar, and reduce our dependence on fossil fuels.

Fig – 1. Green Energy Conservation
Fig – 1. Green Energy Conservation [4]
Compressed air energy storage is a technology that stores excess electricity as compressed air in underground reservoirs or containers. When electricity is needed, the compressed air is heated and expanded to drive a turbine and generate power. CAES can help balance the supply and demand of electricity, especially from intermittent renewable sources like wind and solar. There are two main types of CAES: diabatic and adiabatic. Diabatic CAES dissipates some of the heat generated during compression to the atmosphere and uses natural gas or other fuels to reheat the air before expansion. Adiabatic CAES stores the heat of compression in a thermal storage system and uses it to reheat the air without additional fuel. Adiabatic CAES has higher efficiency and lower emissions than diabatic CAES but also higher costs and technical challenges.
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