Beyond the Clouds in No Time

We can all agree that airplanes are cool, and rockets are awesome, but when combined, the result is even better! Besides getting engineers to jump up and down for this revolutionary concept, Reaction Engines Ltd applied it to an actual SABRE engine concept.

SABRE stands for Synergistic Air-Breathing Rocket Engine and one typically does not associate “Air-Breathing” with “Rocket.” which makes this engine a one of a kind to reach new heights (literally). Let’s dig into the geeky technical specs of the engine while going through some quick history of this revolutionary single stage to orbit propulsion system.

SABRE Engine
Source: Reaction Engines

SABRE is an evolution of Alan Bond’s series of liquid air cycle engine (LACE) and LACE-like designs that started in the early/mid-1980s under the HOTOL project. Upon termination of HOTOL funding, Bond formed Reaction Engines Ltd. SABRE is currently being developed for hypersonic flights and runs on a combined cycle; the precooled jet engine configuration is used in the air-breathing phase of the flight until air becomes scarce and speed critical. From this moment on the engine switches to its close cycle rocket mode to bring the Skylon airplane to orbit (2 engines are mounted on the aerospace plane).

The air-breathing mode (below Mach ~5 and about 25 km altitude which is about 20% of the orbital velocity and altitude, respectively) works almost like a regular jet with one major difference being the apparition of a new component, first discussed in 1955; the air precooler which is placed behind the translating axisymmetric shock inlet cone that slows the air to subsonic speeds inside the air-breathing engine using 2 shock reflections. The precooler is “capable of cooling incoming air (without liquefying it, from around 1000°C) to −150°C (−238°F), to provide liquid oxygen (LOX) for mixing with hydrogen to provide jet thrust during atmospheric flight before switching to tanked LOX when in space.” This precooler also allows a considerable reduction of the thermal constraints of the engine which then requires “weaker” and much lighter materials that are a necessity when reaching orbital velocities and altitudes. With compressors working more efficiently with a colder fluid, and the incoming air already highly compressed from the flight speed and shock waves, the fed pressure in the combustion chamber is around 140 atm. When in rocket mode, the inlet cone is closed and liquid oxygen and liquid hydrogen are burned from on-board fuel tanks for the remaining 80% of velocity and climb required to reach orbit.

Source: Reaction Engines

On a very recent note, feasibility studies conducted by the U.S. Air Force Research Laboratory were successfully passed in 2015.

Although the application of the SABRE engine is destined for orbital use, its cousin (Scimitar) has been designed for the environmental-friendly A2 hypersonic (top speed higher than Mach 5) passenger jet for 300 rushed passengers (about 3 times more than the Concorde) under the LAPCAT (Long-Term Advanced Propulsion Concepts and Technologies) study founded by the European Union.

When dealing with such high speeds, noise becomes a real constraint and flying above inhabited areas is restricted, which is why specific aerial routes are designed. According to Alan Bond, the A2 design could fly subsonically from Brussels International Airport into the North Atlantic, reaching Mach 5 across the North Pole and over the Pacific to Australia in about 4.6 hours, with a price tag similar to what you would pay for business class these days. This speed would heat the body of the craft so that windows are not an option because the appropriate thickness would represent a considerable weight. It is therefore thanks to flat panel displays showing images that you would be able to enjoy the scenery.

Blog - plane 2
Source: www.salon-de-l-aviation.com

 

When one talks about high-velocity flight it is difficult not to think of the French Concorde that operated between 1976 and 2003 and could travel at Mach 2.04 (limited by thermal constraints due to the material used) using the Scramjet technology; scramjet standing for “supersonic combustion ramjet”. This allowed a New York City to Paris flight in less than 3.5 hours instead of 8 hours with a conventional jet.

Blog -220px-Concorde_Ramp
Source: http://www.concordesst.com/powerplant.html

The principle of this technology is to compress air with shock waves under the body of the aircraft before injecting the fuel (the Concorde’s intake ramp system can be seen on the figure on the right).

Due to the high inefficiency of this technology at low speeds, afterburners are used from take-off until reaching the upper transonic regime.

Keeping in mind that the heating of the Concorde’s body due to friction could make it expand by as much as close to a foot, it becomes easy to understand one of the reasons why high altitudes (scarcer air and therefore lesser aerodynamic resistance) are chosen for such high flight velocities; the Concorde cruising altitude was around 56,000 ft and would be decreased when sun radiation levels were becoming too high. On a side note you can keep an eye out at Charles de Gaulle airport in Paris (France) for a Concorde displayed outside.

Oh and did I forget to mention that the turbomachinery parts on the SABRE engine are currently being designed in the AxSTREAM suite??

SoftInWay Case Study

New Release: AxCYCLE v. 4.0

We have just released the newest version of AxCYCLE, our software tool for thermodynamic cycle design and analysis. AxCYCLE 4.0 has some brand new features that will inevitably aid you in designing optimal Gas, Steam, Combined, Turbocharger, Supercritical CO2, Organic Rankine, and Waste Heat Recovery Cycles.

Take a look at the latest updates and additions:

Turbine Efficiency Calculation
In previous versions of AxCYCLE, efficiency was an input parameter that needed to be changed manually for each off-design condition. The Calculated Efficiency option will automatically recalculate the efficiency for off-design conditions.

blog - axcycle 4.0

New Components
Several new components were added to the AxCYCLE library for more sophisticated and customizable cycles.

Bearing: Used to simulate mechanical energy losses in bearings. The estimated mechanical losses are assigned as a power value and are accounted for in the total energy balance

Gearbox: Used to simulate the mechanical energy transfer between two shafts considering mechanical energy losses in the gearbox. These losses are measured using a gearbox efficiency value.

End Seal: Used to simulate seal leakage. The value of the leakage depends on the difference between the upstream and downstream pressure.

Steam Cycle Builder
AxCYCLE’s new wizard for the creation of basic steam cycles. It can be used for steam cycles with regenerative heating, optional moisture separators, and re-heaters. The Builder creates a cycle diagram with the correct fixed conditions and initial values, meaning the generated cycle is ready for calculation! It does all of the work for you!

Learn more about AxSTREAM and AxCYCLE on our website, or email us at info@softinway.com to find out exactly how we can help with your next turbomachinery project.

How much more can I get with what I have?

Gas turbines are continuing their trend in becoming more efficient with each generation. However, the rate at which their efficiency increases is not significant enough to match more and more constraining environmental goals and regulations. New technologies like combined cycles therefore need to be used to increase cycle-specific power (more power produced without burning additional fuel).

The first generation of combined cycles featured a bottoming steam cycle that uses the heat from the gas turbine exhausts to boil off water in order to power a turbine and generate power. This traditional approach has been around since about 1970 and nowadays allows obtaining an additional 20% in cycle thermal efficiency (40% in simple gas turbine cycle configuration vs. 60% as a combined gas-steam cycle).

Figure 1: General efficiency increases over time for simple and combined cycle gas turbines
Figure 1: General efficiency increases over time for simple and combined cycle gas turbines
Figure 2: Example of a simple, recuperated Brayton, supercritical CO2 cycle that uses the exhaust flow of a gas turbine to heat its working fluid
Figure 2: Example of a simple, recuperated Brayton, supercritical CO2 cycle that uses the exhaust flow of a gas turbine to heat its working fluid

While this traditional approach is definitely effective, it does have some drawbacks; the equipment usually takes a significant amount of 3D space, there is always the risk of corrosion and substantial structural damage when working with 2-phase fluids, and so on. This, therefore, allows for different technologies to emerge, like supercritical CO2 cycles.

A supercritical fluid is a fluid that is used above its critical pressure and temperature and therefore behaves as neither a liquid nor a gas but as a different state (high density vs gas, absence of surface tensions, etc.). As a working fluid, supercritical CO2 has numerous advantages over some other fluids, including a high safety usage, non-flammability/toxicity, high density, inexpensiveness and absence of 2-phase fluid.

 

Figure 3: Example of difference in power density between supercritical carbon dioxide (left) and steam (right) for a 10 MW power turbine
Figure 3: Example of difference in power density between supercritical carbon dioxide (left) and steam (right) for a 10 MW power turbine

Moreover, steam turbines are usually difficultly scalable to small capacities which mean that they are mostly used in a bottoming cycle configuration for high power gas turbines. On the other hand supercritical CO2 (Rankine) cycles can be used for smaller machines as well as the bigger units while featuring an efficiency comparable to the one of a typical Rankine cycle and estimated lower installation, operation and maintenance costs.

Figure 4 Cycle efficiency comparison of advanced power cycles (source: A Supercritical Carbon Dioxide Cycle for Next Generation Nuclear Reactors. Dostal, V., 2004
Figure 4 Cycle efficiency comparison of advanced power cycles (source: A Supercritical Carbon Dioxide Cycle for Next Generation Nuclear Reactors. Dostal, V., 2004

The paper I presented at the ASME Power & Energy 2015 compares different configurations of SCO2 bottoming cycles for an arbitrary case for different boundary conditions before applying the selected cycle to a wide range of existing gas turbine units. This allowed determining how much additional power could be generated without needing to burn additional fuel and the results were far from insignificant! For the machines studied the potential for power increase ranges from 15% to 40% of the gas turbine unit power. Want to know how much more power you can get with your existing machines? Contact us to get a quote for a feasibility study before designing the waste heat recovery system yourself or with our help.

Demystifying “Pushbutton” Approaches for CFD & FEA Turbomachine Design

Demystifying “Pushbutton” Approaches for CFD & FEA Design, Analysis, Redesign, & Optimization of Turbomachines

centrifugalcompressordesignAlthough there is not just one way to design a turbomachine there sure is one way not to do it; blindly.

A misconception that I commonly see when teaching engineers about fundamentals of turbomachines, as well as when leading design workshops, is that some engineers (mostly the younger generations) envision themselves plugging numbers, pushing buttons and getting results immediately without any real brain power behind their actions.

Nowadays, software packages are an integral part of an engineer’s toolkit, but in the same way that a mechanic would not (or should not) use a screwdriver as a hammer, each software has its own applications and ways to use it.

Continue reading “Demystifying “Pushbutton” Approaches for CFD & FEA Turbomachine Design”

Innovation in Aerospace: Aircraft Compressor Design

Aerospace - croppedOur next webinar is on Thursday, April 30th! Are you an engineer involved in the Aerospace Industry and its latest development, a manager interested in improving the performance of your aircraft engines, or a student interested in the future of aerospace and the current climate of the industry? You should attend! During the webinar we will be taking a close look at the most recent trends and developments of compressors in aircraft engines with a focus on the key factors for the successful development of aircraft engines.

Key factors for successful development of aircraft engines include technological viability, performance, and re-usability. As one of the industry’s most high-technology products, aircraft engines require innovation in manufacturing and especially in design. They also face the need for continuous development in its technical capabilities in terms of achieving not only higher efficiencies and reliability but also safety and environmental legislations.

Continue reading “Innovation in Aerospace: Aircraft Compressor Design”

Preliminary Design Explained

Thinker- 2-26-2015Companies utilize different principles to design new turbomachinery. A design exercise is an extremely complex task and requires knowledge of many design trade-offs. This article is intended to reveal preliminary design philosophy and clarify some mysteries in this fast solution method.

Let’s define a few terms first. Boundary conditions (BCs) are the inlet and outlet states of a working fluid. Design inputs are small number of variables that are necessary to begin the design exercise. SoftInWay identifies BCs, design mass flow rate, rotational speed, and a few dimensions as the design inputs. The Preliminary design is a tool for quickly assessing design outputs giving many sets of design inputs. The algorithm utilized in the Preliminary design tool is an inverse solver. Inverse solution in this context implies finding geometry of interest knowing a very few design inputs.

How stuff works? The whole process comes down to estimating losses in each component and then calculating fluid states and component geometry applying simple kinematics and conservation equations. Calculated geometry and states are used to find real losses from loss models. This loss model results are compared with the guessed values and the algorithm repeats until they agree. In a practical implementation, however, the solution scheme will be more comprehensive but underlying principle remains the same — design output heavily relies on the models.

Loss models are extremely important and they determine the range of applicability for an industrial code. The models are collective work of many scientists and designers. Usually, they are some empirical correlations serving large family of components and predicting real machine performance quite well. Can we trust the results? That raises a lot of concerns and skepticism. The predictions are as good as the models that describe the physical processes. Verification and validation plays vital role in the developing of the code. The industry trend is to rely on published scientific data as a first iteration and calibrate models while working on real projects. Range of applicability is determined for each empirical correlation. For example, the veteran of compressor design Ronald Aungier shows that his loss model with respect to return channel in centrifugal stage has good agreement with experiment (Figure 1). Therefore, Aungier’s model can be used for similar machines.

Figure 1 -- Loss in optimized return system design

Figure 1 — Loss in optimized return system design

Preliminary design space study — know your limits! When an aerodynamicist is given specification on a new piece of machinery, he/she does not know anything about all the details of the design. Preliminary design can quickly show achievable performance for the machine, estimate critical relationship between design inputs and outputs, and facilitate in determining trends and trade-offs. Design space is a set of many preliminary designs. Because inverse solver is fast, a designer can generate thousands of designs in the matter of eye blink. Moreover, set of mathematical statements and state-of-the art aerodynamic reasoning allows outputting three dimensional geometry for each preliminary design with properly sized components. Ultimately, exploring the design space will eliminate costly mistakes prior to detailed design is carried on.

Myths and misconceptions about preliminary design. Inverse solver does not solve potential flow problem. Inverse task does not perform boundary layer analysis. Preliminary design is not a Navier-Stoks solver. Inverse design is not a table look-up but utilizes empirical loss model in the tested and verified domain. At the same time, preliminary design is not a blade-to-blade analysis tool. Preliminary design is a good starting point for further detailed design and analysis including blade profiling, performance map generation, impeller design, structural analysis, and CFD. All the above can be accomplished within one integrated design environment such AxSTREAM.

Good luck with your challenge!

IvK

References:

  • http://www.dreamstime.com/
  • Aungier R. Centrifugal Compressors. The strategy for aerodynamic design and analysis. ASME Press. New York. 2000

SoftInWay Launches STU – An Online Turbomachinery Training Resource

This week marks the official launch of SoftInWay Turbomachinery University – a new online resource for turbomachinery design training. The site, affectionately referred to as ‘STU’, was created after the SoftInWay Learning Center received high demand and positive feedback.

SoftInWay_Turbomachinery_Universtiy_-_2015-01-27_09.19.14

The site was reconstructed and redesigned into a cohesive learning portal, packed with webinars, courses, and software trials. Users can take courses on demand and earn certifications specific to certain topics. The first course focuses on axial turbines, beginning at the basics and continuing on to streamline design and optimization. Continue reading “SoftInWay Launches STU – An Online Turbomachinery Training Resource”

TBT Webinar – Developing Reliable, High Performance, Advanced 3D Blades

It’s Throwback Thursday which means we have another one of our favorite past webinars! This week’s is called Developing Reliable, High Performance, Advanced 3D Blades. It was the first of three in a special Steam Turbine Series

Since 1884, steam turbines have been exemplary turbomachines that have improved throughout the years with modern design advances. As steam turbines became common, the competition heated up and today efficiency continues to be a hot topic. One trending technique that makes steam turbines most efficient is advanced 3D blading. Continue reading “TBT Webinar – Developing Reliable, High Performance, Advanced 3D Blades”

TBT Webinar – Design of Impulse and Reaction Turbines

This week’s TBT webinar, Design of Impulse and Reaction Turbines Webinar #2: Applications for Supercritical CO2 Cycle, discusses important considerations for using high-density working fluids with small turbine sizes. Structural constraints and performance are considered and the full design process is demonstrated.

video2This webinar covers:

  • Supercritical CO2 cycle overview
  • Estimation of impulse and reaction turbine application rationality in modern supercritical CO2 cycles taking into consideration structural requirements and performance goals
  • Comparison of CO2 and steam turbines (impulse and reaction) for the same boundary conditions
  • Detailed flow path design with AxSTREAM

Who should watch:

  • Mechanical and aerospace engineers working on conceptual turbine design
  • Operation/Overhaul/Engineering managers seeking to increase energy efficiency
  • Everyone interested in how SoftInWay Inc., and AxSTREAM can help them with creating more efficient Turbomachinery

You can find the recording here, in our video center. Not registered for our center? Not a problem, just register and you’ll be emailed access info for all of our free learning materials.

Throwback Thursday Webinar – Green Energy and ORC

It’s #ThrowbackThursday and we’re sharing one of our past webinars called “Green Energy – Turbomachinery for Organic Rankine Cycles.”iStock_000015544357Medium

Growing global demand for energy coupled with environmental concerns from the prevalence of fossil fuel usage has created a strong demand for new sources of clean energy. This demand has inspired scientists and engineers to search for and propose new solutions to generate greener, cleaner energy. One of the new methodologies which has been proposed is generating electricity from low temperature heat sources, the Organic Rankine Cycle being among the most widely used. Such popularity encouraged innovation in the area, and inspiring various design modifications in conjunction with low temperature heat sources and with a wide range of power rates. Continue reading “Throwback Thursday Webinar – Green Energy and ORC”

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