Performance Testing of Axial Compressors

Performance testing is a key part of the design and development process of advanced axial compressors.  These are widely used in the modern world and can be found in nearly every industry, and include the core compressor for aeropropulsion turbofan engines, as well as aeroderivative gas turbine engines for power generation.  An example of this are the turbine engines shown in Figure 1 and 2, which feature an industrial gas turbine and a high bypass ratio turbofan engine with a multistage high-pressure core compressor. The development time of these machines can involve numerous expensive design-build-test iterations before they can become an efficient and competitive product. This places a great importance on the accuracy of the data taken during the performance tests during the development of the compressor since the test data taken is often used to anchor the loss models within the design tools. Modern axial compressors typically have high aerodynamic loadings per stage for improved system efficiency and requires precise aerodynamic matching of the stages to achieve the required pressure ratio with high efficiency. Variable geometry inlet guide vanes and stators in the first few stages are typically required to provide acceptable operability while maintaining high efficiency and adequate stall margin.

Industrial gas turbine for power generation.
Figure 1. Industrial gas turbine for power generation. Source
Figure 2. Turbofan engine for aeropropulsion.
Figure 2. Turbofan engine for aeropropulsion. Source

Performance Testing of Axial Compressors

Axial compressors all undergo a thorough design and development phase in which performance testing is vital to their ultimate success as a product. Performance testing during the development phase of these high-power density machines can ensure that the design meets the specified requirements or can identify a component within the turbomachine which falls short of its expected performance, and may require further development, and possible redesign. Performance testing can also ensure that the unit can meet all the conditions specified and not merely the guaranteed condition. Aerodynamic performance testing multistage axial compressors during the early part of development is often done in phases. The development test program is planned and executed with a design of experiments approach and includes varying the air flow and shaft rotational speed as well as the variable geometry schedule in order to fully characterize the compressor. In the first phase, the front block of the compressor is built and tested at corrected (referenced) air flow rate, inlet pressure, temperature and shaft rotational speed. Instrumentation includes utilizing traditional rakes and surveys at the exit, to obtain spanwise distributions of pressure, temperature, and flow angles. Testing in phases is typically done for two reasons. Read More

To Infinity and Beyond – A New Era of Space Exploration and the CAE Software to Get Us There

There’s nothing quite like rocket science, is there? It’s as fascinating as it is complicated. It’s not enough to just get a design right anymore – you have to get it right on the first go-around or very soon thereafter. Enter AxSTREAM.SPACE and all the functionality upgrades introduced in 2021.

AxSTREAM.SPACE was created by experienced mechanical and turbomachinery engineers to level the playing field when it comes to turbomachine-based liquid rocket engine design. By giving propulsion and system engineers a comprehensive tool that can connect with other proprietary or commercial software packages, the sky is, in fact, not the limit for innovation. It covers everything from flow path aerodynamic and hydrodynamic design to rotor dynamics, secondary flow/thermal network simulation, and system power balance calculations. This year, we are proud to unveil some new features that enhance each of these capabilities, which were developed at the request of our customers.

 

AxSTREAM SPACE - CAE
AxSTREAM.SPACE Software bundle

Power Balance

A critical part of any rocket engine development, as pointed out in a NASA blog, is engine power balance, also known as thermodynamic cycle simulation. AxCYCLE, SoftInWay’s own thermodynamic cycle solver that has been widely used in power generation and aviation is now helping companies build rocket engines from scratch, as well as expand their engine lineup based on an existing system. There are some goodies, however, which make it the perfect tool for power balance, and an asset of AxSTREAM.SPACE.

One of the first upgrades in AxCYCLE for rocket engine design was the integration with NASA’s Chemical Equilibrium with Applications, or CEA, tool. Considered the gold standard when it comes to incorporating accurate chemical properties in your working fluid, CEA was developed by NASA and is widely used throughout the industry, so it makes sense that we’d incorporate it into AxCYCLE for your convenience. Another new feature is the incorporation of burners for rocket engines specifically, and these were validated against NASA’s CEA tool as well.

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Turbomachinery and Rockets – a Historical/Technical Evolution

Introduction

Quite surprisingly, rockets in their primal form were invented before turbomachinery, even though turbines and pumps are both present in modern launcher engines. However, it is interesting to note that  both can be traced to the same ancestor. In this post we will discuss some of the history and technical evolution of rockets and turbomachinery – and this all starts with an old pigeon.

Figure 1. Steam Turbine and Rocket

Rockets

Circa 400BCE, a Greek philosopher and mathematician named Archytas designed a pigeon-like shape made out of wood that was suspended with wires and propelled along these guides using steam demonstrating the action-reaction principle long before Newton formalized it as a rule in Physics. As we know today, the faster and the more steam escapes the pigeon, the faster it goes. Turn this 90 degrees to have the bird face upward, and you have a very basic rocket concept. However, rockets are a lot more complex than this, and do not typically use steam (except in the case of liquid hydrogen + liquid oxygen propellants) as the propelling fluid.  Read More

Saving the Planet, One Turbine Simulation at a Time

This is an excerpt from the Siemens Blog. You can read the full version here.

Originally written By Erik Munktell  on January 14, 2021

 

Listening to the turbine experts: a review of 2020

Can a turbine simulation save the planet? One simulation alone is not enough. But one simulation with that intent can inspire other engineers and researchers to do the same. This butterfly effect is happening today in turbine design.

I live in Sweden, the same country as Greta Thunberg. Her message is that we must act now to save the planet. For a long time, Sweden’s electricity has come mainly from Hydropower and Nuclear power. But lately a lot of focus has still been on building wind and solar power plants. Here in Sweden we also have more trees being grown than being cut down. As a result we are close to being carbon negative, transportation and industry included.

With this country-wide energy focus friends often ask me why I work with gas turbines. Surely, they are not needed?  I rarely get them to listen to my answer for more than a few minutes, as in my enthusiasm it quickly gets technical! But in short – I do it to save the planet. Or rather, we do it to save the planet. Because I am not alone in this effort. Many people work on making turbines run more efficiently, with fewer – or even no – polluting emissions. We can’t do everything by ourselves, but our work can inspire others and together we can create a clean energy future.

My small part in this plan is to make sure the actual makers of gas turbines have the best tools in the world for designing new and better electricity generating or flight enabling propulsion products. In this blog, I take a look at the many ways we saw in 2020 that turbine companies are using our simulation tools to do just that.

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Combined Cycles – A Brief History and Evolution of Cycles

Combined power cycles are a common source of energy, since they offer higher energy efficiency while also making use of common technology. The idea of combining two different heat-engine cycles, however, has been around longer than you think. Today’s blog is going to cover the basics of combined cycle power plants, and their history of how they went from experiments to one of the most common sources of energy in the United States, for example. But how did this come to be, and what really is a combined cycle?

An animated exterior of a combined cycle power plant, image courtesy of General Electric
An animated exterior of a combined cycle power plant, image courtesy of General Electric

Basics

At its most basic form, a combined cycle is the synthesis of two independent cycles into one, which allows them to transfer thermal energy into mechanical energy, or work. On land, this is typically seen in power-generation, so the heat of these two cycles makes electricity. At sea, many ships operate using combined power cycles, but instead of just electricity, the mechanical energy is put to work by propelling the ship as well as providing onboard power.

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Gas Turbine CFD – Driving Innovation with Data and Insight

This is an excerpt from the Siemens Blog. You can read the full version here.

Originally Written By Chad Custer – February 2, 2021

Once upon a time in a world without gas turbine CFD simulation.

Manager: The design team came up with a new blade concept, but they need to know the maximum possible temperature in the machine.

Test engineer: Anywhere in the whole machine?

Manager: Yes. And for any operating condition the machine might get used for. How long until you can have those results to the team?

Test engineer: Uhh

Terms like “virtual prototype”, “simulation testbed” and “digital twin” have become so common that you may dismiss them as buzzwords. However, to me, these terms not only still have meaning. These words do drive how I look at simulation. Read More

Waste Heat Recovery

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”.

Waste heat losses and work potential of different process exhaust gases - Image 1
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

Design of Waste Heat Recovery System based on ORC for a Locomotive Gas Turbine

This is an excerpt from a technical paper, presented at the Asian Congress on Gas Turbines (ACGT) and written by Abdul Nassar, Nishit Mehta, Oleksii Rudenko, Leonid Moroz, and Gaurav Giri. Follow the link at the end of the post to read the full study!

INTRODUCTION

Gas turbines find applications in aerospace, marine, power generation and many other fields. Recently there has been a renewed interest in gas turbines for locomotives. (Herbst et al., 2003) Though gas turbines were first used in locomotives in 1950 – 1960’s, the rising fuel cost made them uneconomical for commercial operation and almost all of them were taken out of service. The diesel locomotives gained popularity and presently locomotives are operated by diesel engines and electric motors. The emission levels in diesel locomotives have raised concerns among the environmentalists, leading to stringent emission norms in recent years. One of the solutions to reduce emission for these locomotives is to switch to LNG fuel which requires huge investment in upgrading the engines to operate with LNG. The other alternative is Gas Turbine based locomotives and this has gained renewed interest with RZD and Sinara Group of Russia successfully operating LNG based Gas Turbine-electric locomotives. Fig. 1 shows the GT1-001 freight GTEL from Russia, introduced in 2007. It runs on liquefied natural gas and has a maximum power output of 8,300 kW (11,100 hp). Presently, this locomotive holds the Guinness record for being the largest gas turbine electric locomotive (Source: http://www.guinnessworldrecords.com). Though there have been a lot of improvements in gas turbines, the thermal efficiency is still not very high unless the exhaust heat is efficiently utilized by a bottoming cycle.

Fig. 1 Russian GT1_001 gas turbine locomotive

Converting the gas turbine into a combined cycle unit, with a bottoming steam cycle, is employed in case of several land-based and marine applications; however, such an option is not practical in a locomotive gas turbine due to the requirements of steam generators, steam turbines and other auxiliaries. The next best alternatives are to utilize either an organic Rankine cycle (ORC) or a supercritical carbon dioxide cycle (sCO2) to extract heat from the exhaust of the gas turbine and convert it into useable energy in the bottoming cycle (Rudenko et al., 2015; Moroz et al., 2015a; Moroz et al., 2015b; Nassar et al., 2014; Moroz et al., 2014). Supercritical carbon dioxide cycles, operating in a closed-loop Brayton cycle, are still in research phase. There is not much practical experience in deploying an sCO2 unit for propulsion gas turbines even though there is considerable research currently in progress. Hence, the obvious choice is to incorporate an ORC based system which is compact, modular and easy to operate. The same concept can also be implemented in any gas turbine application, be it a land-based, power generation, or marine application. Read More

Combined Power Cycles: What Are They and How Are They Pushing the Efficiency Envelope?

Combined cycle power plants have introduced a significant increase in efficiency compared to simple cycle power plants. But what is a combined cycle power plant and how does it work?

What is a Combined Cycle Power Plant?

In simple terms, a combined cycle power plant is a combination of more than one type of cycle to produce energy. A combined cycle plant consists of a topping and bottoming cycle with the objective to maximize the energy utilization of the fuel. The topping cycle normally is a Brayton cycle based gas turbine while the bottoming cycle is a Rankine cycle based steam turbine.

Gas turbines are used because this equipment can very efficiently convert gas fuels to electricity with the choice of using different fuels. Recently, the simple cycle efficiencies of gas turbines have improved considerably. As an example, standard fossil fired Rankine cycles with conventional boilers have an efficiency in the range 40–47% depending on whether they are based on supercritical or ultra-supercritical technology. By utilizing waste heat from the heat recovery of the steam generators to produce additional electricity, the combined efficiency of the example power plant would increase to 60% or more. Combined cycles are the first choice if the goal is to generate maximal energy for a unit amount of fuel that is burnt.

Why Don’t all Power Plants Use Combined Cycles

You might be wondering why not all plants are based on the combined cycle. The primary reason is fuel availability. Not all regions are blessed with the availability of gas that can be easily utilized in a gas turbine. Transporting gas from one location to another, or converting a fuel to gas specifically for operating a gas turbine, may not be the best economic decision. The technological expertise required in maintaining a gas turbine is another challenge faced by gas turbine operators. A typical combined cycle plant is presented in Figure 1.

Schematic of a combined cycle power plant created in AxCYCLE
Figure 1. Schematic of a Combined Cycle Power Plant Created in AxCYCLE

The key component of the combined cycle power plant apart from the turbines is heat recovery steam generator (HRSG). The major objective is to convert maximal heat from the exhaust gas of the gas turbine into steam for the steam turbine. The HRSG, unlike the conventional boiler, will operate at a lower temperature and is not subject to the same temperature as the boiler furnace. The exhaust gas from the gas turbine is directed through the tubes of the HRSG wherein water flowing through these tubes, observes heat and converts into steam. The temperature of the live steam is in the range of 420 to 580 C with exhaust gas temperatures from the gas turbine in the range of 450 to 650 C. A supplementary burner could be included in the HRSG, but adding a supplementary burner reduces the overall cycle efficiency. Read More

Turbomachinery CFD Simulation: Art in Motion

This is an excerpt from the Siemens Blog. You can read the full version here.

Originally Written By Justin Hodges - July 14, 2020  

Turbine blade simulation juxtaposed with turbine blade art. The resemblance is uncanny! 

Believe it or not, there is some true art in turbomachinery CFD simulation. From the creamer in your coffee to the tumbling of flow through a small waterway. There is something palpable with intrigue when observing fluid flows in our everyday routines. As computational fluid dynamics practitioners, we are fortunate to have a unique opportunity. That is to simulate and observe these same curious fundamentals of turbulence and fluid flow until our heart is content.

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