Is CFD Evolving Fast Enough for the Technologic World?

It is common knowledge that CFD analyses are more of a “see you tomorrow” affair than an “I’ll grab a coffee and I’ll be back”.

Although the fairly recent developments in electronics allow for more computing power while being more affordable, it can still take a significant amount of time to run a good CFD case.

AxCFD
The AxCFD module in SoftInWay’s AxSTREAM

One of the main advantages of running CFD is that there is no need to have an actual, manufactured prototype in order to run an experiment. Prototypes have been known to be mainly restricted to companies/individuals that had manufacturing capabilities and quite a lot of money on their hands. However, with recent advancements like 3D printing, this prototyping is not only possible but is also relatively fast (and getting faster everyday with new techniques being developed).

It comes to a point where it is worth evaluating, qualitatively, each method, however different they actually are.

Although CFD is an extremely common practice in modern day engineering and is immensely useful, it tends to sometimes completely replace actual prototyping and this can create some issues… Indeed, CFD is neither an exact science nor it is always “cheap” (some complex problems can easily cost several thousand dollars in computing costs) but either way it sure has its perks. These two arguments are unfortunately largely part of a general misconception of CFD that decision makers and the younger generation of engineers are often victims of. When managers are given the choice between purchasing a software that can supposedly simulate any physical problem (CFD case) and a machine that can physically build components (manufacturing case) the upfront cost strongly leads these decision makers to adopt the first option.

However, CFD does not always suffice.  Results of CFD analyses are influenced by numerical and modeling errors, unknown boundary conditions or geometry and more. Refining your mesh is becoming easier and ultimately leads to reduced numerical errors while, at the same time, increasing your calculation time. Modeling errors can come from misuse or inaccuracy of certain models when trying to simulate real, complex physics like turbulence. And so on to the point that different codes and even different engineers can find some minor discrepancies in the final results of the same case.

This means that less experienced engineers tend to over-trust their results, thinking of CFD as the universal answer to every physical problem. To place (smartly) more confidence in CFD results the codes should be calibrated and corrected based on experimental results that do require prototyping at some point unless a product is wrongly put on the market without proper physical testing – which can happen, unfortunately. Comparing both an original and an optimized geometry in CFD is perfectly possible and realistic but as for any solver a baseline should be created. One cannot simply say he has improved the efficiency of a machine by 2% if the original machine was not analyzed beforehand.

Calibration of the CFD models is based on available data from experiments and this data is often very limited compared to the results that CFD can provide. While a physical test would provide values like power as well as some pressures and temperatures in most cases, CFD analyses can go way beyond this by providing parameters distributions, flow recirculation areas, representation of the boundary layer appearing on the surfaces, etc. that allow getting a good understanding of what is happening to the flow within the machine, which is something that definitely cannot be appreciated in most experimental runs. Beside the mentioned disadvantages that 3D printing has, an important one that is shared with CFD is that the time needed to build a geometry strongly depends on its size. However, CFD can deal with the repetition of an element in a row fairly accurately while the entire wheel has to be manufactured to be analyzed. This sort of restrains rapid prototyping to smaller machines, at the moment.

For these reasons and despite all these “warnings”, CFD remains and will remain an essential engineering tool that provides a good comparison of cases rather than a truly accurate representation of the reality we live in. As a conclusion, CFD still continues to evolve with the recent technological developments and should be supplemented with experimental testing instead of substituting it.

Innovative Boost of Larger Internal Combustion Engines

The last few decades have brought with them a dramatic increase in the development and use of turbochargers in automobiles, trains, boats, ships, and aircrafts. There are several reasons for this growth, including rising demand for fuel efficiency, stricter regulations on emissions, and advancements in turbomachinery design. Turbochargers are appearing more and more and are replacing superchargers.

turbocharger
Turbocharger

 

Turbochargers are not the only turbomachinery technology growing in popularity in the marine, automobile, and railroad industries. Organic Rankine Cycles are being applied to take advantage of the exhaust gas energy and boost engine power output. ORCs, a system for Waste Heat Recovery, improve the overall efficiency of the vehicle, train, or boat, and reduce specific emissions.

As the size of the engines we consider increases, there is more heat available to recuperate, and more potential WHR systems to use. For instance, we can consider different combinations of these systems with both non-turbocharged and turbocharged engines. We are able to design and compare engine boost system combinations, with and without a turbocharger, with and without a blowdown turbine, and with and without a WHR system, at the cycle and turbine design levels.

In our upcoming webinar, we will do just that. We will design different combinations for larger ICEs and compare the results. This webinar will also cover introductions to these systems and application examples for supplementary power production systems in the automotive and marine industries.

We hope you can attend! Register by following the link below.

Register

 

Challenges and Opportunities in the Turbomachinery Industry

Steam turbines have been around for more than a century, and some say the Turbomachinery industry is rather mature. So how does a company decide between competing Turbomachinery producers? Do they go to Siemens or GE? How about Rolls Royce vs. Pratt?

Manufacturers invest millions, if not billions, of dollars (depending on their size) into their sales & marketing to create a perception of having the better technology and lower prices in order to beat the competition. They do so, however, by sacrificing quality and margins.

Last week, we had a very nice dinner with some of our colleagues from a large Japanese manufacturer. They explained to us that, in addition to pricing pressure and brand pressure, the “cost of goods” landscape is changing rapidly with fierce competition from Chinese and Indian companies from the manufacturing perspective. But there exists a “risk” to outsource manufacturing to a cheaper location and lose the quality, or at least the perception of quality, of the turbomachine.

So what is the solution?

At SoftInWay, we are an R&D engineering company and thus consistently feel that the differentiation of our clients from the rest of the market should not just be in price, but rather in truly creating better machines from the perspective of performance, durability, environmental footprint, etc.

However even “R&D” and the design aspects of something as mature as “the steam path” can be a challenge.

Companies have several approaches to designing new machines:

  1. Complete design from scratch based on a new concept: example SCO2 Cycle Technology.
  2. Redesign or improve on existing technologies ( this can often be considered the safest by the larger OEMs with a high level of risk aversion and investor pressure).
  3. Not changing the flow path but adding to the overall machine.

The only approach of these three which can really give a new or existing company any real advantage is the first.

We have also taken a look at another interesting idea: Every “major” manufacturer has at some point taken their designs, models and often software code from academia. The result is that, since they have something that works and has been tested, the engineering R&D teams are often crippled by lack of budget for new tools that will allow them to effectively take approach 1 or even sometimes 2.

Alternatively, some engineering managers upon first meeting us and learning about AxSTREAM ™, our software for design, analysis and optimization, have asked us – why do we need a new approach if we know ours works?

We feel that the answer is quite simple: Although the industry is quite mature, every player does something a little bit different. Our software has been developed and improved over the last 15 years by working with over 200 major players in the Turbomachinery Industry. Because we started as a consulting company, our mission in the beginning was never to be a software player, but rather to make our engineers’ lives easier.  Accomplishing this led us to develop new, innovative software features that would further our capabilities with consulting projects. In 2005, we released our software into the market.

The result became quite interesting: Today in 2015, over 50% of our new feature developments come from our clients’ ideas and requests. What does this mean for a user of software like AxSTREAM as well as for the industry? They can benefit not only from their experience and ours, but also from the experience of the industry as a whole. From a figurative perspective, AxSTREAM has been built and added to by those in the Aerospace, Automotive, Defense, and Power Generation industries, just to name a few. Its capabilities stretch beyond a single field. The ability to innovate using a new approach, such as AxSTREAM, becomes less risky and more attainable. Some might even say the biggest risk in developing new technology is doing so alone, in a room, shut off from the outside world (without AxSTREAM).

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

Gas Turbine Technology in Aircraft Propulsion

It is very interesting to take a look at how gas turbine technology has made its way into aircraft propulsion and improved over time. When the idea of a turbojet was introduced by Frank Whittle and others in the 1920s, no one could have guessed that it would change the future of air propulsion. The Committee on Gas Turbines from the National Academy of Sciences reported (1940): “In its present state … the gas turbine engine could hardly be considered a feasible application to airplanes mainly because of the difficulty in complying with stringent weight requirements imposed by aeronautics” [1]. This puts into perspective the immense advancement that gas turbine development has made to be an integrated part of aircraft propulsion today.

genx-1b engine
GEnx-1B engine (first run, 2006) for the Boeing 787 Dreamliner, from Airline Reporter [3].
Rolls-royce avon engine
Rolls-Royce Avon Engine (first run, 1946), from Wikipedia [2].
 

 

 

 

 

 

 

A quick look at the engine characteristics reveals the great advancement in design and manufacturing of jet engines from the early turbojets to the most advanced turbofans today. For instance, General Electric’s J31, with an overall pressure ratio of 3.8:1 and maximum thrust of 1,650 lbf, was one of the first manufactured jet engines in the United States [2]. Nowadays, Rolls-Royce Trent 1000 has achieved a maximum thrust of 78,000 lbf with an overall pressure ratio of more than 50:1 [4]. Without a doubt, gas turbine technology has made a huge impact on aircraft propulsion and there will be more to come in future.

Trent 1000 engine, from Rolls-Royce [4].
Trent 1000 engine, from Rolls-Royce [4].
[1] www.MIT.edu
[2] www.Wikipedia.org
[3] www.AirlineReporter.com
[4] www.Rolls-Royce.com

 

 

Power Production Does Not Have To Be So Wasteful

Whether it’s to drive you to work, power up your electronic devices, fly you to your holiday destination (extraterrestrial or not), or even set up the perfect lighting for this Valentine’s Day, your daily life requires power production. Although renewable energies are gaining popularity, many people remain unprepared to make the complete switch to these innovative power sources (except Iceland). Making the things we have more “energy efficient” or “green” has become an attractive marketing tool for many of businesses.

Presentation of the boundary conditions, unrecuperated and recuperated waste heat recovery cycles in AxCYCLE™
Presentation of the boundary conditions, unrecuperated and recuperated waste heat recovery cycles in AxCYCLE™

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Optimizing Your Power Plant Redesign

Our next webinar will be held on February 26th and cover the best industry practices when it comes to power plant redesign. The constant increase of global energy consumption and rising cost of fuel require higher energy generating capacity with a simultaneous improvement of the efficiency of energy conversion processes. The greatest effect of improving the performance of existing power plants and other energy systems can be obtained by modifying the thermodynamic cycles of these plants.

The Kendall Cogeneration Station in Cambridge, MA

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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. (more…)

TBT Webinar: Centrifugal Compressor Design: Can You Really Avoid Choke and Surge?

It’s Throwback Thursday and we are sharing another of our past webinars! This week’s is called Centrifugal Compressor Design: Can You Really Avoid Choke and Surge?

video2

Surge and choke are inherent, sophisticated phenomena in centrifugal compressor operation. They limit the operational range of any centrifugal compressor and cause severe damage to the machine if it is in surge condition. Several books cover the development of centrifugal compressor surge and choke models that can be applied in compressor control systems in order to avoid surge and choke; while these methods focus retroactively, there are some proactive methods that can be applied during the design phase of the machine. (more…)