Category: General – Turbomachinery

Any blog post pertaining turbomachinery-related information: questions about turbomachinery, software, turbomachinery best practice and 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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Drones Among Us!

Posted by Vladyslav Kotechenkov

– 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.

Figure 1 - An MQ-9 Reaper on a training mission in Nevada
Figure 1. An MQ-9 Reaper on a training mission in Nevada [3]
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

A Comparison of Different Rocket Engine Cycles Throughout the Years

Posted by Mykhailo Vasin

Introduction

Throughout history, humans have had an insatiable desire to understand the world around them, including the stars. The science of rocketry has been developing for centuries, even predating our current era. Today’s rockets are the result of numerous experiments and the combination of many different areas of engineering. Few things can withstand the extreme conditions that rockets must endure, including the intense loads during launch and drastic temperature changes caused by cryogenic components and combustion chambers. Successful launches depend heavily on well-informed design decisions. The complexity and interdependence of the systems that must work together seamlessly in rocket design are unparalleled by any other engineering discipline. It is no coincidence that they say “rocket science” when it comes to something incredibly complex. Figure 1 displays numerous advanced rocketry systems over several decades.

 

Different Rocket
Figure 1 – Different Rocket Types. Source

Rocketry’s origins trace back to ancient China, where the first rockets were created around 100 AD. These early rockets were used during religious celebrations and produced colorful sparks, smoke, and explosions using gunpowder and bamboo tubes that were closed on one end. The first recorded use of rockets in warfare occurred during the Battle of Kai-Keng in 1232, where the Chinese used a primitive solid-fuel rocket to repel the Mongols. The rocket consisted of a closed tube filled with gunpowder attached to a long stick. Ignition of the gunpowder increased pressure inside the empty tube, and the hot gas and smoke had to escape through the open end. By the law of conservation of momentum, this creates thrust to propel the rocket towards the closed end of the tube, with the long rod as a primitive control system. Read More

Scaling Laws in Turbomachinery Design and Operational Optimization

Posted by Fernando Pelcastre

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.

Table 1. Specification for Baseline Compressor
Table 1. Specification for Baseline Compressor
Figure 1. Baseline Centrifugal Compressor
Figure 1. Baseline Centrifugal Compressor

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

SoftInWay Year End Review – 2022 Edition

Posted by Kimberley Squillante

In what feels like two shakes of a lamb’s tail, we’re wrapping up 2022! The year has been both challenging and rewarding, largely due to our incredible team, customers, and partners. So, what did SoftInWay get up to this year, and what is on the horizon for 2023?

New AxSTREAM Developments

Since the very first version of AxSTREAM, our development strategy has always been centered around the needs of our clients. After all, in an industry undergoing rapid technological advancements, it’s critical to have the tools and support needed to hit your project goals and keep up with the growing demand

2D view of pipe diffuser in AxSTREAM (left) & 3D view of pipe diffuser in AxSTREAM (right)
2D view of pipe diffuser in AxSTREAM (left) & 3D view of pipe diffuser in AxSTREAM (right)

Here is an overview of some key capabilities added inside the AxSTREAM platform, which include:

AxSTREAM for Turbines

  • Features expanded capabilities in incorporating both drilled and milled nozzles in turbine designs

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AxSTREAM for Compressors

  • Is now capable of incorporating pipe diffusers into centrifugal compressor designs, enabling higher efficiency and performance in gas turbine engines

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­AxSTREAM RotorDynamics & Bearing

  • Has several new features including but not limited to the:
    • Addition of finite element method for steady-state isothermal analysis of herringbone grooved gas journal bearings
    • Addition of finite element method for steady-state isothermal analysis of spiral grooved gas thrust bearings
    • Automated calculation of stiffness required to model the rigid connection between rotors
    • Ability to apply custom stress concentration factors during torsional harmonic analysis for both reciprocating and turbo machines.
AxSTREAM System Simulation

While the official launch of our newest product, AxSTREAM System Simulation, is set for next year, we showed off the beta version of this product in September during a webinar on environmental control systems (more on that later).

  • AxSTREAM System Simulation brings together legacy 0D and 1D solvers into a new and intuitive interface for a powerful solution. Through the integrated reduced-order modeling of dependent multidisciplinary systems, AxSTREAM System Simulation can eliminate the interface gap that exists between siloed software or sub-systems, thus speeding up development and reducing associated costs. More to come next year so stay tuned for the official release!
New Partnership with Ansys

In the summer of this year, we announced a technological partnership with Ansys to enable seamless integration between our AxSTREAM Platform and Ansys’ simulation software. The Ansys-SoftInWay partnership supports further digitization of a very streamlined workflow, from the initial design in AxSTREAM to analysis using Ansys’ 3D physics solvers Ansys® CFX®, Ansys® Fluent®, and Ansys® Mechanical™. The new workflow enables the integration of the high-fidelity simulations and optimization studies needed through Ansys Workbench to automate the entire development process in one continuous chain. Through this partnership, companies can fully automate the development process from the initial stages all the way to the completed design in one environment; a must-have for any engineering team developing turbomachinery and propulsion technology. Read More

Choosing the Best Environmental Control System When Designing an Aircraft

Posted by Vladyslav Kotechenkov

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.

Figure 1 – Environmental Control System in an aircraft [2]
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% [1].

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

Tip Clearance Loss Models in Centrifugal Compressors

Posted by Evgen Rublevskiy

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
  • Design features

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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.

Figure 1 - Scheme of a Centrifugal Compressor
Figure 1 – Scheme of a Centrifugal Compressor

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

Stage Number Selection in Axial Aircraft Turbines

Posted by Mykhailo Shevchenko

Choosing the number of stages during the development of axial turbines is one of the most controversial design tasks because it has many options to consider. This task does not have an exact solution, since it depends on the total turbine work, circumferential velocity and is determined by a combination of gas-dynamic, strength, construction, and technological factors. This blog will discuss some of the considerations for stage number selection of an axial turbine.

Using Stage Loading vs Parson’s Parameter

Designing turbines requires the use of complex parameters to simultaneously consider the influence of various factors on the characteristics of the turbine. Thus, the stage loading (mostly aircraft turbines) or the Parson’s parameter (stationary turbines and aircraft turbines) have been used for wide applications in turbines theory.

  • Stage loading is the ratio of the theoretical turbine work LU and the square of the circumferential velocity U.

­Stage loading Formula

  • Parson’s parameter y is the ratio of the circumferential speed to the speed equivalent to the isentropic heat drop.

­Parson's Parameter

High turbine efficiency is achieved, when these parameters are in the range μT = 1.2…1.6 (y=0.45…0.6), which can be seen in Figures 1 and 2 [1], respectively.

Figure 1 total to total turbine

Figure 2 Turbine Stage Hydraulic efficiency

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An Introduction to Electric Motor Cooling Systems

Posted by Suheab Thamizullah

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.

Electric motors are all around us. They feature prominently in every major industry, and in many of the devices we use daily. For instance, this author’s personal morning routine relies on electric motors when using a coffee grinder, when turning on a desktop computer to read the news, and even when setting up an automatic cat feeder. Electric motors convert electrical energy into mechanical energy through interaction between the magnetic fields generated in the motor’s stator and rotor windings. To meet the power requirements of different industries and applications, electric motors are available in a variety of strengths and sizes.

Electric Motor
Figure 1. Electric Motor. SOURCE: [1]
Electric motors can have remarkably high efficiency ratings of over 90 percent. In other words, a large portion of the electrical energy that is supplied to the motor is successfully converted into mechanical output. The approximately 10 percent remaining is lost in the form of heat. Regardless of the application, one of the main challenges that motor designers face is that of thermal management.

Selection of the right electric motor is often based on a particular work or load requirement. When an electric motor is in operation and high performance is needed, the motor’s load can be increased (letting the motor draw more current), and greater heat is generated due to increases in rotor and stator losses. Since the heat flux in a system influences its thermal behavior, the motor’s temperature evolution depends on these losses. Read More