An unsteady flow is one where the parameters change with respect to time. In general, any liquid flow is unsteady. But if a hydraulic system is working at constant boundary conditions, then the parameters of the fluid flow change slowly; thus this flow is considered steady. At the same time, if the parameters of the fluid flow oscillate over time relative to some constant value, then it called quasi-steady flow 1.
In practice, most fluid flows are steady or quasi-steady. Examples of the three flows are presented in Figure 1. Steady flow is presented by a simple pipe. The quasi-steady flow is represented by a sharpened edge channel. The unsteady flow is presented by an outflow from a reservoir.
Different Cases of Unsteady Flow
During operations, hydraulic systems act for long intervals at steady conditions which are called operating modes. Change between two different operating modes occurs over a short time interval (called a transient mode). If any hydraulic system works more than 95% of the time at these operating modes though, why is the unsteady flow is so important? Because the loads depend on time intervals. If the load is less, then the maximum system pressure is higher. Read More
Reduction in CO2 emissions is driving the development of different electric, turbo-electric and hybrid electric propulsion systems for various applications and industries including space, aviation, automotive and marine. Electric propulsion (EP) is not a new concept, having been studied in parallel with chemical propulsion for many years. EP is a generic name encompassing all the ways of accelerating a propellant using electric power by different possible electric and/or magnetic means. The simplest way to achieve electric propulsion is to replace the heat generated by combustion in conventional chemical engines with electrical heating.
Electric propulsion systems offer several advantages compared to other conventional propulsion systems. It not only helps reduce the environmental emissions but also helps reduce fuel consumption and increases safety levels. Electric propulsion has become a cost effective and sound engineering solutions for many applications. Electric propulsion engines are also more efficient than others. It is proven to be one of the most energy saving technologies as we can use more renewable sources of energy (due to the versatility of electricity generation) instead of non-renewable sources of energy like gasoline. The major limitation of electric propulsion, when compared with conventional propulsion is limited by the available electric power capacity on board, this may be the reason, it is not the default propulsion system.
Generally, electric propulsion architectures vary depending on the application. Figure 1, above, shows the EP architectures for an aviation application. These architectures rely on different electric technologies (batteries, motors, generators, and so on). Typical aircrafts use gas turbine engines as the source of propulsion power, but all electric aircraft systems use batteries as the only source of propulsion power as shown in Figure 1 on the right. The hybrid systems use gas turbine engines for propulsion and to charge batteries which also provide energy for propulsion and accessories during one or more phases of flight as shown in Figure 1 on the left. Read More
Turbo Compressors are used to increase the pressure of a gas, which are required in propulsion systems like a gas turbine, as well as many production processes in the energy sectors, and various other important industries such as the oil and gas, chemical industries, and many more.
Such compressors are highly specific to the working fluid used (gas) and the specific operating conditions of the processes for which they are designed. This makes them very expensive. Thus, such turbo compressors should be designed and operate with high level of care and accuracy to avoid any failure and to extract the best performance possible from the machine.
Turbo Compressor Characteristic Curves
The characteristic curves of any turbo compressor define the operating zone for the compressor at different speed lines and is limited by the two phenomenon called choke and surge. These two opposing constraints can be seen in Figure 2.
Choke conditions occurs when a compressor operates at the maximum mass flow rate. Maximum flow happens as the Mach number reaches to unity at some part of the compressor, i.e. as it reaches sonic velocity, the flow is said to be choked. In other words, the maximum volume flow rate in compressor passage is limited by limited size of the throat region. Generally, this calculation is important for applications where high molecular weight fluids are involved in the compression process.
Surge is the characteristic behavior of a turbo compressor at low flow rate conditions where a complete breakdown of steady flow occurs. Due to a surge, the outlet pressure of the compressor is reduced drastically, and results in flow reversal from discharge to suction. It is an undesirable phenomenon that can create high vibrations, damage the rotor bearings, rotor seals, compressor driver and affect the entire cycle operation.
Preventing Choke and Surge Conditions
Both choke conditions and surge conditions are undesirable for optimal operation of a turbo compressor. Each condition must be considered during design to ensure these conditions are prevented. Read More
The following is an excerpt from Exceptional People Magazine, conducted by Monica Davis and focused on profiling SoftInWay’s CEO, Dr. Leonid Moroz. The article appeared in the September/October 2019 issue. A link to the full interview can be found here
Turbomachinery design is critical in industries like aerospace, oil and gas, defense, and clean technology. Dr. Leonid Moroz’s company, SoftInWay Inc., also helps some of the world’s largest manufacturers of turbines, turbochargers, pumps, and fans. But Moroz is happy to explain that his company’s innovations also impact the car you drive, the vacuum cleaner you use, the air conditioning in which you work, and the electricity needed to power your mobile phone.
A lover of music and athletics as a child, Moroz knew early on that engineering held promise as a lifelong career. So he started his career as a Group Leader at TurboAtom. TurboAtom, while a state-owned entity, is one of the world’s top thermal, nuclear, and hydropower plant turbine construction companies. It’s a company that operates at the level of companies like General Electric and Siemens.
Moroz designed both gas and steam turbines during his eight years at TurboAtom. While he was there, he also earned his Ph.D. in Turbomachinery from the Kharkiv Polytechnic Institute in Ukraine.
When he founded global aerospace engineering leader SoftInWay, Inc. in 1999, he intended to assist turbomachinery manufacturers needing his expertise. What evolved from that intent has revolutionized engineering design and allowed improved efficiencies for multiple system types: Its flagship software, AxSTREAM.
AxSTREAM helps engineers develop efficient turbomachinery flow path design, redesign, analysis, and optimization. Under Moroz’ direction, AxSTREAM itself has also evolved into a design platform supporting rapid development of a new generation of liquid rocket engines.
Still a relatively small company, SoftInWay supports over 400 companies worldwide and works closely with universities, research laboratories, and government organizations. The company takes its educational responsibilities seriously, continually offering webinars, training sessions, educational blogs, and online workshops on topics like When To Upgrade Your Pump, The Pros and Cons of Wind Energy, and Radial Outflow Turbine Design.
Moroz loves to talk about his work, his company, its innovations, and his team. He’s proud to have had the same group of engineers for 30 years, so SoftInWay feels more like a family than a workplace. As the company has become a leading global R&D engineering company, it has expanded to encompass locations in Boston, Massachusetts; Zug, Switzerland; Ukraine; and India.
Yes, Moroz’ specialty is indeed a bit technical for people who aren’t in turbomachinery engineering design. But Moroz and his team clearly enjoy what they’re doing because it benefits society and makes life easier and more comfortable in myriad ways.
Next time you switch on that ShopVac or Hoover, be sure to thank Dr. Leonid Moroz.
Monica: We often take for granted how engineering plays a huge role in our daily lives. How much of the world depends on the kind of technology and engineering capabilities you produce?
Dr. Moroz: Quite substantially. For example, society produces a lot of waste and heat. If you have options, it utilizes waste and heat to produce power, or it is thrown away. We’ve helped companies to utilize this energy and to produce power to heat or cool our houses, to prepare food, and to help our businesses survive.
Another example again would be launchers design. Launchers are important for turbomachinery. A significant part of space development depends on turbomachinery inside those launchers.
It’s important to understand two directions where people can utilize turbomachinery with power consumption and power generation. Power generation is when you produce power, so we need to be more efficient, but the second part, when we get this power, we need to cool our houses, we need to cool our cars, and so on, and again, it’s turbomachinery.
You can be sure that you utilize turbomachinery to develop an air conditioning system that is efficient and is quite substantially in large buildings.
Power consumption for air conditioning is like 30 or 40 percent of the overall power consumption. Can you imagine if you were to decrease this by 10 to 20 percent? It would be a considerable saving…Read the full interview here
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
Radial turbines are quite popular for turbochargers and micro-gas turbines. They can also be found in compact power sources like in auxiliary power units of aircrafts. In short, they are suitable in power generation applications where expansion ratios are high and mass flow rates are relatively small. In a radial turbine, the flow enters radially and exits either axially or radially depending on whether it is an inflow or outflow type radial turbine. The most commonly used type of radial turbine is a radial-inflow turbine, in which the working fluid flows from a larger radius to a smaller radius. A centripetal turbine is very similar in appearance to the centrifugal compressor, but the flow direction is reverse. Figure 1 shows the radial-inflow turbine on the left and radial-outflow turbine on the right.
Nowadays, the popularity of radial-outflow turbines, in which the flow moves in the opposite direction (from the center to the periphery), is growing. With recent advancement in waste heat recovery applications, there has been a renewed interest in this type of turbines. These radial-outflow turbines are most commonly used in applications based on organic Rankine cycles (ORC).
The radial-outflow turbine design was first invented by the Ljungström brothers in 1912, however it was rarely used for a number of reasons. One of which was related to the decrease of turbine-specific work due to the increase of the peripheral velocity from inlet to outlet while expanding the vapor. Another reason was the usage of steam as a working fluid. It is known from thermodynamics that the expansion of steam is characterized by high enthalpy drops, high volumetric flows and high volumetric ratios. Thus, a significant number of stages are needed to convert the enthalpy drop of the fluid into mechanical energy.
The lubrication system is one of the most important systems of an engine.
This system should ensure:
Delivery of the required oil amount to the moving parts (e.g.-Bearings);
Dissipation of the heat generated due to friction by circulation of lubricant throughout the system; and
Cleaning of the oil from contamination and impurities introduced during engine operation.
To meet the above requirements, the lubricant circulation (lubricant reaching each component) should happen at appropriate pressure and mass flow rate throughout the system. This is also required in order to avoid cavitation caused by adverse pressure, and excessive heat generation due to less mass flow rate, at any place or particularly at any component. However, sometimes lubricant does not circulate properly to each corner of the system or to the rotating components. In some cases, the rotation of the crankshaft can actually starve the bearings and increase the internal heat due to insufficient supply of lubrication.
To avoid such problems, simulation engineers must model the whole system at all operating modes. They can predict the best system by varying flow rates (volumetric or mass flow rates), system pressures, temperatures, heat flows, as well as by changing the system geometry itself. Such modelling can be performed easily and with sufficient accuracy in a 1D Thermal Fluid analysis tool, such as AxSTREAM NET™ developed by SoftInWay.
It is worthwhile to use a 1D-Analysis tool in this case, because it can be used at any stage of the system design process to explore more options for improving the final design and to reduce development cycle time. The simulation engineer can easily create a model of automotive engine lubrication system, using different elements (components) which are available in the element database of AxSTREAM NET™. The system configuration can also be easily changed at any stage in the design process without rebuilding the complex 3D models.
Let us try to understand how to build a 1D scheme for an automotive engine lubrication system in a 1D tool (AxSTREAM NET™). First, we need to identify the major elements (components) which are part of the automotive engine lubrication system as per their order or sequence in the scheme. A typical engine lubrication system involves components like Oil – sump, strainer, pump and filter, all of which are parts of the initial oil suction line. In addition, the main gallery involves components like flow passages within the connecting rods, crankshaft, and bearings. The typical connections among these elements are shown in Figure 1.
Now let’s see the arrangement of a few components with their specific purposes towards the construction of the whole model.
We as human kind have always aimed at achieving something better, something bigger. This led to the research on gas turbines, which was mainly inspired due to the immediate requirement in the aerospace and power generation industry, to also look beyond the scope of aeronautics.
Today gas turbine technology is often used when dealing with aerospace and power generation industries, but believe it or not, gas turbine technology has been used in ground transportation too; notably locomotives.
The Early Applications
After the first world war, several countries had the expertise and the finances to invest in achieving the technological edge in the new post war era. The gas turbine technology was one such technological endeavor, and by the mid-20th century the gas turbine could be found in several applications. Birth of gas turbine locomotives can be credited to two distinct characteristics of these locomotives versus the contemporary diesel locomotives. First, there are fewer moving parts in a gas turbine, decreasing the need for lubrication. This can also potentially reduce the maintenance costs. Second, the power-to-weight ratio is much higher for such locomotives which makes a turbine of a given power output physically smaller than an equally powerful piston engine, allowing a locomotive to be powerful enough without being too bulky.
The concept of using gas turbines to power a car is not new. In fact, for many decades now, various car manufacturers have experimented with the idea of using either axial or radial gas turbines as the main propulsion of concept vehicles. In the 50’s and 60’s it was Fiat and Chrysler who introduced such concept cars. In those cases, the gas turbine was directly powering the wheels for propulsion. Toyota followed the same concept in the 80’s (Figure 1) . Their concept car utilized a radial turbine in order to propel the vehicle using an advanced electronically controlled transmission system.
The main advantage of a gas turbine compared with conventional reciprocating (or even rotary) car engines is the fact that it has a much higher power-to-weight ratio. This means that for the same engine weight, a gas turbine is able to deliver much higher power output. This is why aviation was one of the biggest adopters of this technology.
Looking to solve the problem of range anxiety in electric vehicles, many companies have started exploring the business model of recharging electric batteries in automotive vehicles with a parallel turbine engine driving a generator – coined under the term ‘micro-turbine range extender’ (or MTRE). As seen in the turbine-powered car programs initiated in the 50s and 60s, issues with low efficiencies, slow throttle response, and capital cost of the powertrain rendered all of these programs futile shortly after their inception. However, the revolution of electric vehicles and hybrid technologies has allowed this technology to resurface from a different direction. With battery-driven electric motors designated as the main driver, these cars are equipped with a technology that has both energy efficient low-end torque as well as groundbreaking throttle response and many of the former drawbacks during its initial iterations are solved using an electric drivetrain. The turbine-engine, instead of operating as the main driver, will now only operate at its most efficient power output mode and work to simply drive electricity through the generator, recharging the vehicle’s battery packs. Acting as an isolated thermo-mechanical system, a micro-turbine range extender can be designed and optimized without having to worry about the varying duty cycles and idling that is inherent in the vehicle’s drivetrain. The thermodynamic model of a typical micro-turbine range extender can be seen below in Figure 1.
One application within commercial vehicles that has benefitted from this technology utilizes a MTRE system developed by Wrightspeed. The specific application lies within retrofitting refuse trucks with this electric powertrain in order to help them save an estimated $35,000 a year on fuel and maintenance costs. In such heavy-duty applications, it is obvious that the potential for fuel cost and maintenance savings is much higher due to the large fuel burning needed for these vehicles as well as the harsh drive cycle a refuse truck goes through. The question in the expansion of this technology generally comes in two forms: What makes the micro-gas turbine range extender a better alternative than a normal ICE hybrid option? – and – What is the viability of scaling this for consumer vehicles given the capital cost of the drivetrain?