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.
In pumps, compressors, gas turbines, and powertrains with rotating parts, there are typically cavities between the spinning rotor and the fixed stator elements. The flow’s behavior at those cavities can significantly affect a machine’s temperatures, structural loads, vibrations, and overall efficiency. Similar radial cavities, where the flow is restricted between a rotating part and a non-rotating wall, are ubiquitous in the secondary flow channels of gas turbine engines (Figure 1).
Careful planning of secondary flows can be extremely useful. For example, since secondary flows influence the pressure in cavities, flows can be designed to compensate for axial loads acting on the rotor. Additionally, flow rotation in secondary flow channels critically impacts blade cooling design. For these reasons, a solid understanding of the processes occurring in radial channels is vital for high-quality design and optimization. Read More
As human-beings, our differences are what makes us unique (if I may quote the Seek Discomfort crew – “What makes you different is what makes you beautiful”). For turbomachines, this sentiment also rings true. We design different turbomachines because we have varied roles, needs and constraints for them. To that effect, there is no universally best turbine, compressor, or pump. Therefore, figuring out which set of “skills” a turbomachine should have is the key role of a design engineer so that they may effectively capture and estimate performances of the machine they will work on early on while having the certitude this is the best that can be done.
Generative design is one of these recent buzzwords that characterizes an approach to the design of components (or systems) that has been around for quite some time already. Rather than producing one geometry for one value of each input (such as boundary conditions, flow coefficients, number of stages, etc.), generative design allows you to create thousands of designs within minutes that you can review, compare, and filter to select the one that best suits your needs. Let’s look at an example of an axial turbine design process comparing traditional preliminary design vs. generative design.
Approach 1 or what most companies call Traditional Preliminary Design, is to look in textbooks and previous examples of what a given turbine for that application “should” look like. It may involve things like using Ns-Ds diagrams, load-to-flow diagrams, blade speed ratio vs. isentropic velocity ratio correlations, scaling/trimming existing designs, etc. These have served their purpose well enough, but they have their limitations which make them fairly challenging to really innovate. Such limitations include previous experience/data being restricted to a given fluid, relative clearance size, given configuration, lack of secondary flows, etc. A summary of a traditional preliminary design workflow (familiar to too many engineers) is presented below.
Now, we know that changing (ahem, improving) your workflow is not always easy. But growth happens through discomfort and switching to a generative design approach does NOT mean rebuilding everything your team has done in the past. What it effectively gives you is the confidence that the input parameters you finalized will provide not only the desired performance but the best ones that can be achieved (and it saves time too…a lot of time). From there, you can use these inputs in your current design software or you can continue the design process in our design platform, AxSTREAM® (meaning you can add generative design capabilities upstream of your existing workflow or replace parts/all of that workflow depending on what makes the most sense for you). You can pay your engineers to do engineering work, instead of visiting online libraries and guessing input parameters in hope they will find the needle in the haystack. Or, with generative design, you kind of look for haystacks and shake them until the needle falls off.
So, how does this work in AxSTREAM, you may ask? Very well, I may reply :D. Read More
Rotating machines have huge and important roles in our daily life although we may rarely think about them. Steam turbines at electrical power plants rotate the electrical generator shafts which produce electricity coming into our homes and offices. Driving to or from work, the reciprocating cycle in your vehicle’s internal combustion engine results in rotation of the transmission and the wheels of vehicles, while the electric car wheel operation is a result of induction motor rotation. If you get on an airplane, rotation of the turbo reactive gas turbine engine produces the effective thrust to sustain flight by moving, compressing and throwing the gas behind the plane. We can even find the useful effects of rotation in our kitchens when we are blending the food or washing our closes.
Although these rotating machines are different, the approaches to modelling their rotor dynamics are pretty much the same, since similar processes occur in rotating parts which differ in their vibrations from the non-rotating machines.
Do you remember the example of rotating washing machine? Have you ever seen it jumping on the floor trying to squeeze out your closet? We bet you have. This is the simplest example of the increased unbalance affecting the amplitudes of machine vibrations. Washing machines are designed to experience these noticeable vibrations during their operation without breaking. But the steam turbine or compressor rotors which have the tight clearances between the impellers and the casing can not boast of that leeway. In addition to that, the excessive vibrations significantly influence the machine’s useful life due to the increased fatigue.
This is why the rotor dynamics predictions are one of the most important parts of rotating machine analyses. And although they may seem easier than comprehensive stress-strain investigations of machine components, in some cases the rotor dynamics analysis can be trickiest part.
Usually, the rotor dynamics analyses are divided into lateral and torsional stages depending on the nature of rotor response to be used. They are discussed in different types of standards (API , ISO , etc.). Let’s consider the example of the lateral vibrations of a 4 stage compressor rotor with an operational speed of 8856 rpm.
This rotor rotates in the 4 pad tilting, pad oil film journal bearings. The characteristics of these bearings should be determined carefully to ensure that there will not be an excessive wear, heat generation or friction in them. Read More
Update – February 28, 2023: AxCYCLE is our legacy software and is replaced by AxSTREAM System Simulation. System Simulation was born out of the union of the legacy AxCYCLE and AxSTREAM NET software packages.
During industrial processes, an estimated 20 to 50% of the supplied energy is lost, i.e., by dumping the exhaust gas into the environment . 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”.
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
In the age of green energy and increased efforts to minimize our carbon footprint, the design of a turbocharger plays an important role in reducing engine fuel consumption and emissions while increasing the performance. When developing an engine with a turbocharger, the general approach is to select a turbocharger design from a product list. The primary issue with this approach is that it does not cover 100% of the requirements of engine characteristics, i.e. it has non-optimal construction for the engine being developed. The operational characteristics of an engine directly depends on the interactions between the system components. This non-optimal construction will always lead to a decrease in the engine’s performance. In addition, the iteration process of turbocharger selection is time and resource consuming.
That is why the most optimal way to develop an engine with turbocharging is to design a turbocharger from scratch; wherein the operational points of compressor needed to satisfy the engine’s optimal operation are known, i.e. compressor map (Figure 1). But how do we quickly get a compressor map? Even at the preliminary design level, the design of turbocharger flow path requires dozens of hours for high-level engineers. And what about less experienced engineers?
Incorporating a digital engineering approach with a turbomachinery design platform such as AxSTREAM® allows designers to find the compressor design with all the required constraints which correspond to the specified compressor map needed. The design process is presented in Figure 2. Read More
The Achilles heel of turbochargers has always been the time between pressing your foot to the gas pedal and waiting for the engine to respond with the desired power. This lapse in engine response, commonly termed turbo lag, is what has hindered turbochargers from delivering optimal performance. The aim of a turbocharger is to provide more power, better efficiency and less lag in power delivery. Engine efficiency is becoming more important than ever before, leading to the development of smaller engines. However, the power requirements are not decreasing which means the loss in engine displacement from small designs must be picked up with alternative technologies, such as turbochargers, which can help improve power delivery and fuel economy.
Electric turbochargers (e-turbos) provide a solution to eliminating turbo lag while adding additional performance benefits. This allows for larger turbocharger designs which can provide larger power and efficiency gains, stay cooler over longer periods of use, and drastically improve engine responsiveness. Garrett Motion are developing e-turbos for mass market passenger vehicles set for launch in 2021, with a claimed fuel efficiency improvement of up to 10%. When used on diesel engines, this e-turbo could be up to a 20% reduction in NOx emissions. In most cases, fuel efficiency will be improved by about 2 – 4%. Other manufacturers such as Mitsubishi and BorgWarner are already developing their own electric turbos and are expected to have announcements in the near future matching the trend in e-turbo development.
As we covered in our previous blog about fuel cell systems, a large contributor to their efficiency is the compressor that is selected for it. But what are the different kinds of compressors, and which one is best for a specific system?
Compressors have a wide variety of designs and types, which differ in pressure and performance, depending on the kind of compressed fluid. Compressors are also classified according to the type of work: dynamic and positive displacement. Figure 1 shows the types and classification of compressors.
Figure 2 shows a comparison of various types of compressors according to several criteria: generated pressures, occupied volume, lubrication requirements, compressor weight, and pressure ripples at the outlet.
As can be seen from the comparison above, we can conclude that centrifugal compressors offer a number of advantages over its positive displacement counterparts:
Only the bearings require lubrication;
Creates a sufficiently high pressure (1.5…6 bar);
Has high efficiency (80…82%); and
Has a fairly wide performance range.
Next, we will consider the application of the centrifugal compressor in the fuel cell system. Read More
Alternative energy based on the use of fuel cells is gaining more and more popularity and is increasingly being used in the automotive, aerospace, and energy industries as well as other sectors of the economy.
What is a Fuel Cell?
Fuel cells (FC) are electrochemical devices which convert the chemical energy of a fuel directly into usable energy – electricity and heat – without combustion. This is quite different from most electricity-generating devices (e.g., steam turbines, gas turbines, reciprocating engines), which first convert the chemical energy of a fuel to thermal energy via combustion, then into mechanical energy, and finally to electricity.
Fuel cells are similar to batteries containing electrodes and electrolytic materials to accomplish the electrochemical production of electricity. Batteries store chemical energy in an electrolyte and convert it to electricity on demand until the chemical energy has been depleted.
Fuel cells do not store chemical energy. Rather, they convert the chemical energy of a fuel into electricity. Thus fuel cells do not need recharging, and can continuously produce electricity as long as fuel and an oxidizer are supplied.
A prototype fuel cell is shown below in Figure 1.
What is the operating principle of a fuel cell?
Today, there are two types of electrolytes used in fuel cells: acid or alkali. The type also depends on the chemical reactions that take place in the element itself. Read More
Update – February 28, 2023: AxCYCLE is our legacy software and is depreciated by AxSTREAM System Simulation. System Simulation was born out of the union of the legacy AxCYCLE and AxSTREAM NET software packages.
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!
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.
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
Update – March 1, 2023: AxSTREAM NET is our legacy software depreciated by AxSTREAM System Simulation. System Simulation was born out of the union of the legacy AxCYCLE and AxSTREAM NET software packages.
Even in today’s age of underwater nuclear power, the majority of the world’s submarines still use diesel engines as their main source of mechanical power, as they have done since the turn of the century. A diesel engine must operate at its optimum performance to ensure a long and reliable life of engine components and to achieve peak efficiency. To operate or keep running a diesel engine at its optimum performance, the correct lubrication is required. General motors V16-278A type engine is normally found on fleet type submarines and is shown in Figure 1. This engine has two banks of 8 cylinders, each arranged in a V-design with 40 degree between banks. It is rated at 1600 bhp at 750 rpm and equipped with mechanical or solid type injection and has a uniform valve and port system of scavenging.
Lubrication system failure is the most expensive and frequent cause of damage, followed by incorrect maintenance and poor fuel management. Improper lubrication oil management combined with abrasive particle contamination cause the majority of damage. Therefore, an efficient lubrication system is essential to minimize risk of engine damage.
The purpose of an efficient lubrication system in a submarine’s diesel engine is to:
Prevent metal to metal contact between moving parts in the engine;
Aid in engine cooling by removing heat generated due to friction;
Form a seal between the piston rings and the cylinder walls; and
Aid in keeping the inside of the engine free of any debris or impurities which are introduced during engine operation.
All of these requirements should be met for an efficient lubrication system. To achieve this, the necessary amount of lubricant oil flow rate with appropriate pressure should circulate throughout the entire system, which includes each component such as bearings, gears, piston cooling, and lubrication. If the required amount of flow rate does not flow or circulate properly to each corner of the system or rotating components, then cavitation will occur due to adverse pressure and excessive heat will be generated due to less mass flow rate. This will lead to major damage of engine components and reduced lifetime. Read More