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).
Today, we revisit the exhilarating world of Podracing, determined to avoid the disastrous fate that befell Ben Quadinaros’ craft.
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).
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 , 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.
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
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), 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.
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). 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. 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
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.
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
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.
An ideal Brayton cycle consists of the following four processes:
Isentropic compression: air is compressed to high pressure and temperature via an isentropic process that is adiabatic and reversible.
Constant pressure heat addition: high-pressure air is fed into a combustion chamber where fuel is added and ignited.
Isentropic expansion: high-temperature gases from the combustion chamber expand in the turbine in an isentropic process, producing mechanical work.
Constant pressure heat rejection: the exhaust gases are expelled into the atmosphere.
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” . 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.
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. Read More
– Look! Up in the sky! – It’s a Bird! – It’s a Plane! – No! It’s… Oh it’s drones again…
If you hear a bzzzz annoying you, do not rush to look for the unfortunate fly to finish it off. Perhaps it is also troubled by the sound that this flying aluminium box makes.
Drones come in many forms, some harmless and some dangerous. Let’s look at which is which and discuss some of their unique features.
Drones are flying robots, including unmanned aerial vehicles (UAVs) that can fly thousands of kilometers, as well as small drones designed for confined spaces. Aerial vehicles that do not carry a human operator, fly either remotely or autonomously, and carry either lethal (non-friendly) or nonlethal (likely friendly) payloads are considered drones.
Depending on the flight missions of the drones, the size and type of installed equipment are different. Considerable advantages of drones have led to a myriad of studies focusing on the optimization and enhancement of the performances of these drones. According to the mentioned characteristics, drones benefit from the potential to carry out a variety of operations, including reconnaissance, patrolling, protection, transportation of loads, and aerology. Read More
Turbomachines are undoubtedly complex. While designing them from scratch has the best potential to maximize performance, it is not always the best route.
With the help of similarity concepts and the associated nondimensional parameters, the preliminary design of a new machine can be based on features of an existing machine, even one which may have been designed for a different fluid, other flow conditions, or a different rotational speed.
Let’s say we have a turbomachine, in this case, a one-stage Centrifugal Compressor. It was designed for a specific mass flow rate and rotational speed value to achieve a certain pressure ratio at the best efficiency possible.
One would be able to get the same performance at any value of mass flow rate or rotational speed required just by scaling the machine (scaling is the process of changing a geometry while preserving similarity between the prototype and the model). And not just this specific point, but the whole performance map could be moved either to lower or higher mass flow rates. This is possible thanks to the concept of “Similarity”. Read More
As human beings, we are very vulnerable to environmental conditions, especially those in the stratosphere. Unlike cockroaches (which seem oddly equipped for pretty much anything), humans cannot survive in extremely low or extremely high ambient pressures or temperatures. Perhaps the best minds of our generation didn’t immediately think “how can I be more like this indestructible insect”, but nevertheless technological advancements have helped us get one step closer to their tenacity…at least in stratospheric conditions. Technology does not stand still though and is constantly improving and with it, we’re given more choices and variety in environmental control systems.
When designing environmental control systems (ECS), it is very important to understand that the top priority of these systems is to provide safety and comfort under absolutely any conditions, whether flying over the Sahara Desert or Alaska. We are talking about a minimum of 75 kPa and 20-24 °C. Relative humidity should range from 15 to 60% .
The ECS is usually split in one air conditioning machine (ACM) pack per engine. The ACM size is dictated by the ventilation requirement of 6 (g/s)/pax minimum (e.g. 1.2 kg/s minimum for the 200 pax capacity of A320; some 2 kg/s is the typical design value). This air can be taken both from the engine and through separate air intakes (but that’s a completely different story). Read More
This blog discusses tip clearance loss models in centrifugal compressor impellers with large relative clearances
In the flow path of turbomachines, there is a clearance between the tip of the rotor blades and the housing parts of the machine. This clearance is necessary in order to prevent the rotor from touching the stator during rotation of the impeller. The tip clearance value depends on the following features:
Deformation of the rotor under the action of gas, thermal and centrifugal loads
Housing deformations under the influence of air pressure and uneven heating
Clearance in bearings
There is a pressure gradient between the suction side and the pressure side, which results in a flow from one side of the blade to the other through the clearance. Studies of the flow in the tip clearance of the blades of turbomachines indicate its complex nature. The flow through the tip clearance affects the flow in the shroud section of the blade and has a significant impact on performance and efficiency. According to the results of the studies, an increase in the relative clearance by 1% reduces efficiency by 2%. Known methods for evaluating the effect of tip clearance on efficiency are most often reduced to a linear dependence of the reduction in efficiency on the relative clearance. This provides acceptable accuracy for engineering calculations with a relative clearance of no more than 3%.
The typical value of the tip clearance for the centrifugal compressor impeller is 0.2-0.5 mm. However, in some cases, the clearance is significantly higher and reaches 1-3 mm. An example would be the impellers of low-pressure compressors, which are made of plastic. Plastic is not a sufficiently rigid material, which requires the designer to significantly increase the tip clearance in order to avoid the impeller touching the housing part of the compressor in operation.
A feature of centrifugal compressors is the low blade height at the outlet of the impeller. Figure 1 shows the impeller of the compressor designed for pressure ratio ptr=2.4 with the diameter and height of the blades at the outlet, respectively, 220 mm and 15.1 mm. For such an impeller, with an absolute clearance of 0.5 mm, the relative clearance will be 3.3%. This means that simple clearance loss estimation methods will have a large margin of error for such an impeller. It should be taken into account that an impeller designed for the same outlet diameter, but at pressure ratio ptr=5, will have approximately half the blade height, respectively, and the relative clearance is twice as large.
Recently, there has been strong interest in small turbomachines. The impeller diameter of such compressors ranges between 50-70mm. The real estimation of clearance losses for this kind of compressor is a problem due to the large relative tip clearance. Read More