Category: General – Turbomachinery

Any blog post pertaining turbomachinery-related information: questions about turbomachinery, software, turbomachinery best practice and more.

The Simultaneous Simplicity and Complexity of Supersonic Turbines and their Modern Application

Posted by Maksym Burlaka

Supersonic axial turbines have attracted interest in the industry since the 1950s due to the high power they  provide, allowing a reduction in the number of low-pressure stages, and thus leading to lighter turbines as well as lower manufacturing and operational costs. Due to these valuable features, supersonic axial turbines are currently widely used in different power generation and mechanical drive fields such as rocket engine turbopumps [1, 2, 3, 4], control stages in high pressure multi-stage steam turbines, standalone single stage and 2-row velocity compound steam turbines [5, 6], ORC turbo-generator including geothermal binary power stations [7, 8, 9, 10], turbochargers for large diesel engines [11] and other applications. Therefore it is not forgotten, but instead a very important field in turbomachinery when highest specific power, compactness, low weight, low cost and ease of maintenance are dominant requirements. Especially nowadays, when development of small capacity reusable low-cost rocket launchers, compact and powerful waste heat recovery (WHR) units in the automotive industry, distributed power generation, and other fields are in extreme demand.

Meanline Results of Supersonic Turbine in AxSTREAM
Meanline Results of Supersonic Turbine in AxSTREAM

Typically, supersonic turbine consists of supersonic nozzles with a subsonic inlet and one or two rows of rotating blades. The turbine usually has partial arc admission. The total flow could go through either a single partial arc or several ones. The latter is typical for a steam turbine control stage or standalone applications. The inlet manifold or nozzles chests, as well as exhaust duct, are critical parts of the turbine as well. Due to the very frequent application of partial admission, it is not possible to implement any significant reaction degree. Thus, this kind of turbine is almost always an impulse type. However, some reaction degree could still be applied to full admission turbines. The influence of  the rotor blades profile designed for high reaction degree on rotor-stator supersonic interaction and turbine performance is not well studied at the moment.

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Compressors in Fuel Cell Systems

Posted by Taras Hryshchenko

Previous Blog

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 1 Compressor Types
Figure 1: Compressor Types. Source: Dongdong Zhao, “Control of an ultrahigh-speed centrifugal compressor for the air management of fuel cell systems” 5 Jun 2014, p. 8.

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.

Comparisons of Compressors
Figure 2: Comparison of Compressors. Source: Dongdong Zhao, “Control of an ultrahigh-speed centrifugal compressor for the air management of fuel cell systems” 5 June 2014, p. 13.

As can be seen from the comparison above, we can conclude that centrifugal compressors offer a number of advantages over its positive displacement counterparts:

  1. Lightweight;
  2. Small volume;
  3. Only the bearings require lubrication;
  4. Creates a sufficiently high pressure (1.5…6 bar);
  5. Has high efficiency (80…82%); and
  6. Has a fairly wide performance range.

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Next, we will consider the application of the centrifugal compressor in the fuel cell system. Read More

An Introduction to Fuel Cells: What Are They, How Do They Work, and How Can We Improve Their Efficiency?

Posted by Taras Hryshchenko

Next Blog

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.

Fuel Cell
Figure 1: Fuel Cell. Source

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

Performance Testing of Axial Compressors

Posted by Joseph Veres

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

Common Challenges in Rocket Engine Rotor/Bearing Systems

Posted by Volodymyr Martynenko

Rocket engines are the perfect creation of the human mind, incorporating our existing knowledge in aerodynamics, thermodynamics, solid and fluid mechanics, and rotor dynamics. Believe it or not, rocket engines designs contain turbopumps that move fuel and the oxidizer into a combustion chamber creating the perfect conditions for their burning and high-efficiency rocket motion. The word “turbopump” means that the pump is driven by the turbine installed on the same shaft or connected to it through a gearbox. This thrilling tandem results in a bunch of rotor dynamics effects inherent in pumps, turbines, high-speed rotors, cryogenic temperature materials, etc. And all these effects must be carefully taken into account during rotor dynamics studies.

A standard schematic of an internally geared turbopump consists of the liquid hydrogen (LH2, fuel) and liquid oxygen (LO2, oxidizer) rotors.

Fig. 1 - Internally geared turbopump model
Fig. 1 – Internally geared turbopump model

Although the rotor dynamics model is usually simpler than the CAD models, it looks quite complicated in the case of the turbopump. The rotors contain sections that are hollow and sections with some elements inside the hollow space. Read More

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

Posted by Daniel Green

Update – February 28, 2023: AxCYCLE and AxSTREAM NET are our legacy software packages replaced by AxSTREAM System Simulation. System Simulation was born out of the union of the legacy AxCYCLE and AxSTREAM NET.

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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Modern Approaches and Significance of Multiphase Flow Modeling

Posted by Mark.Adams

Update – February 28, 2023: AxCYCLE and AxSTREAM NET are our legacy software packages, replaced by AxSTREAM System Simulation. System Simulation was born out of the union of the legacy AxCYCLE and AxSTREAM NET.

Introduction

Corresponding with the development of industrial technology in the middle of the nineteenth century, people dealt with multiphase flows but the decision to describe them in a rigorous mathematical form was first made only 70 years ago. As the years progressed, development of computers and computation technologies led to the revolution in mathematical modeling of mixing and multiphase flows. There are a few periods, which could describe the development of this computation:

«Empirical Period» (1950-1975)

There were a lot of experiments that were done during this period. All models were obtained from experimental or industrial facilities which is why using them was difficult for different cases.

«Awakening Period» (1975-1985)

Because of sophisticated, expensive, and not universal experiments, the researchers’ attention was directed to the physical processes in multiphase flows.

«Modeling Period» (1985-Present)

Today, the models for multi-flow calculation using the equations of continuity together with equations of energy conservation are obtained, which allow describing phase’s interaction for different flow regimes. (A.V. Babenko, L. B. Korelshtein – Hydraulic calculation two-phase gas-liquid course: modern approach // Calculations and modeling journal. – 2016. – TPА 2 (83) 2016. – P.38-42.)

Technology Development

Since the time of industrial development, installation designs have undergone great changes. For example, there are shell and tube evaporators for freeze systems where the heat transfer coefficient has increased 10 times over during the last 50 years. These results are a consequence of different innovation decisions. Developments led to research into mini-channels systems, which is the one of the methods to increase intensification of phase transition. Research has shown that heat exchange systems with micro and nano dimensions have a much greater effect than the macrosystems with channels dimensions ≤3-200 mm.

In order to organize fundamental research, it is very important to understand hydro, gas dynamics, and heat changes in two-phase systems with the phase transition. At present, the number of researchers using advanced CFD programs has increased. Our team is one of the lead developers of these program complexes.
Mathematical modeling of compressible multiphase fluid flows is interesting with a lot of scientific directions and has big potential for practical use in many different engineering fields. Today it is no secret that environmental issues are some of the most commonly discussed questions in the world. People are trying to reduce the emissions of combustion products. One of the methods to decrease emissions is the organization of an environmentally acceptable process of fuel-burning with reduced yields of nitrogen and sulfur. The last blog (https://blog.softinway.com/en/modern-approach-to-liquid-rocket-engine-development-for-microsatellite-launchers/) discussed numerical methods, which can calculate these tasks with minimal time and cost in CFD applications.

Waste Heat Boiler
Picture 1 – Waste heat boiler http://tesiaes.ru/?p=6291

For more effective use of energy resources and low-potential heat utilization, the choice of the Organic Rankine Cycle (ORC) is justified. Due to the fact that heat is used and converted to mechanical work, it is important to use a fluid with a boiling temperature lower than the boiling temperature of water at atmospheric pressure (with working flow-boiling temperature about 100⁰C). The usage of freons and hydrocarbons in these systems makes a solution impossible without taking into account the changes of working fluid phases. Read More

Turbomachinery and Rockets – a Historical/Technical Evolution

Posted by Clement Joly

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

Willis Carrier, Air Conditioning, and His Contribution to Mechanical Engineering and HVAC Systems

Posted by Daniel Green

Welcome to this special edition of the SoftInWay blog! While we at SoftInWay are known for helpful articles about designing various machines, retrofitting, and rotor dynamics, we believe it is also important to examine the lives of some of the men and women behind these great machines.

Commonly listed among the greatest mechanical engineering inventions of the 20th Century, the air conditioning system has gone from basic use in refrigeration to a staple of living in many countries. Locales that were previously borderline uninhabitable for people sensitive to heat or poorer air quality, became available, thanks to this device that could be installed in homes and businesses. But who invented the air conditioning system?

A portrait photograph of Willis Carrier in 1915

Willis Haviland Carrier (1876-1950) was born on November 26th, 1876 in Angola, a small town in Upstate New York just outside of Buffalo. Carrier was the inventor of modern air conditioning as we know it. While other forms of air conditioning had been around for millennia, what Carrier invented was utterly life-changing for those who were able to use it, and work/live in air-conditioned environments.  His work has been so influential on modern HVAC engineering and the world in general, that his legacy company has a website in his honor.

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Rotor Dynamics Challenges in High-Speed Turbomachinery for HVAC Applications

Posted by Volodymyr Martynenko

In comparison to large steam and gas turbines, the rotating equipment found in heat ventilation and air conditioning (HVAC) applications is often seen as more simplistic in design. However, sometimes a simpler model of a rotating machine does not mean a simpler approach can be used to accurately investigate its rotor dynamics behavior. For example, a large number of effects should be taken into account for single-stage compressors used in HVAC applications. Three important ones include:

  1. High values of rotational speeds above the first critical speed;
  2. Rigid rolling element bearing used in the design and therefore a relatively flexible foundation which should be modeled properly;
  3. Aerodynamic cross-coupling adding additional destabilizing forces to the structure.

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All these effects should be modeled properly when performing lateral rotor dynamics analyses of HVAC machines. And, in some cases, this simpler model can prove a much more challenging task than building the complex model of a steam turbine rotor.

Let’s consider a seemingly simple example of a high-speed single-shaft compressor for HVAC application (Figure 1). It consists of the compressor and motor rotors, the flexible coupling connecting them, the ball bearings connecting the rotors to the bearing housing joined with the compressor volute, and the structural support.

Fig. 1 - Single stage compressor model
Fig. 1 – Single-stage compressor model [1]
The compressor rotor is connected with the motor through a flexible coupling. Its lateral vibrations can be considered uncoupled from the motor rotor vibrations, and the lateral rotor dynamics model appears pretty straightforward (Figure 2).

Fig. 2 - Rotor dynamics model of the single stage compressor rotor
Fig. 2 – Rotor dynamics model of the single-stage compressor rotor

However, additional factors are discovered if you include the mechanical properties of the supporting structure when considering the lateral rotor dynamics calculations. These factors are very important to an accurate model. Read More