Performance Testing of Axial Compressors

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

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

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

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

Rotor Dynamics Challenges in High-Speed Turbomachinery for HVAC Applications

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

An Overview of Axial Fans

Axial fans have become indispensable in everyday applications starting from ceiling fans to industrial applications and aerospace fans.  The fan has become a part of every application where ventilation and cooling is required, like in a condenser, radiator, electronics, etc., and they are available in a wide range of sizes from few millimeters to several meters. Fans generate pressure to move air/gases against the resistance caused by ducts, dampers, or other components in a fan system. Axial-flow fans are better suited for low-resistance, high-flow applications and can have widely varied operating characteristics depending on blade width and shape, a number of blades, and tip speed.

Fan Types

The major types of axial flow fans are propeller, tube axial, and vane axial.

  • – Propellers usually run at low speeds and handle large volumes of gas at low pressure. Often used as exhaust fans these have an efficiency of around 50% or less.
  • – Tube-axial fans turn faster than propeller fans, enabling operation under high-pressures 2500 – 4000 Pa with an efficiency of up to 65%.
  • – Vane-axial fans have guide vanes that improve the efficiency and operate at pressures up to 5000 Pa. Efficiency is up to 85%.
Types of Fans
Figure 1 Different Types of Axial Fans
Aerodynamic Design of an Axial Fan

The aerodynamic design of an axial fan depends on its applications. For example, axial fans for industrial cooling applications operate at low speeds and require simple profile shapes. When it comes to aircraft applications however, the fan must operate at very high speeds, and the aerodynamic design requirements become significantly different from more traditional fan designs. Read More

An Introduction to Accurate HVAC System Modeling

HVAC (Heat, Ventilation and Air Conditioning) is all about comfort, and comfort is a subjective feeling associated with many parameters like air quality, air temperature, surrounding surface temperature, air flow and relative humidity. For example, while it is easy to understand how the temperature of the air in your living impacts how good you feel, the surfaces with which you are in contact also strongly affect your comfort. For example, last night I got out of bed to clean up after my dog who thought it would be a good idea to swallow (and give back) her chew toy. If I was wearing my slippers, it would have been much easier to go back to sleep between the warm bed sheets without the discomfort of waiting my cold feet warm up to normal temperature.

Speaking of sleep discomfort, many stem from HVAC imbalances.  If you wake up in the middle of the night quite thirsty, then you should probably check how dry your bedroom is. The recommended range is 40-60% relative humidity. A higher humidity puts you at risk for mold while lower humidity can lead to respiratory infections, asthma, etc.

Now that we know how HVAC contributes to our comfort, let’s look at the HVAC unit as a system and see its role, functioning and simulation at a high level. The following examples provided are for a house, but similar concepts apply to residential buildings, offices, and so on.

Controlling Temperature

The easiest parameter to control is the air temperature. It can be set by a thermostat and regulated according to a heating or cooling flow distributed from the HVAC unit to the different rooms through ducting. Without the introduction of thermally-different-than-ambient air, the house will heat or cool itself based on a combination of outside conditions and how well the building is insulated. Therefore, to keep a constant temperature a certain amount of energy must be used to provide heating (or cooling) at the same rate the house is losing (or gaining) heat.  This is a match of the house load and heating/cooling capacity. Figure 1 provides a graph of the energy needed.

Illustration of dependency of house load and heating capacity on outside temperature
Figure 1 Illustration of dependency of house load and heating capacity on outside temperature

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A Century of Chiller Technology

A convergence of technologies had to occur to make the modern, high-efficiency centrifugal chiller a reality. To appreciate the technology fully, we must go back in history and understand the origins of the air conditioning and refrigeration industry. Along the way, we will find an important diversion in aerospace and the critically important centrifugal compressor. Ultimately, we will find that the modern chiller is a testament to advanced technology that was developed in multiple fields.

Some of the first advances in and applications of modern industrial refrigeration were in the United States. In May 1922, Willis Carrier revealed the “Centrifugal Refrigeration Machine” – a very early incarnation of what we now call a chiller [1]. The first installation went to a Philadelphia candy manufacturer; it’s interesting to know that the birth of modern refrigeration and air conditioning started on a large scale. Back in those days, economy of scale enabled the technology to be developed. It was not until a decade later that the core technology began to be adopted into compact units that could be used in smaller businesses such as boutique shops. It took several more decades for smaller residential air conditioners to take off commercially.

Shown in the photograph below is Carrier’s first centrifugal chiller in his New Jersey factory [1].

First Centrifugal Chiller
Photo from [1]
The size of this machine is evident, as is the fact that its design, at the time, necessitated components be spread out in space for assembly and maintenance. By modern standards, the same footprint space could be used to accommodate a modern chiller with over 500 refrigeration tons in capacity. By comparison the original design has less than 100 refrigeration tons of capacity.

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Combined Cycles – A Brief History and Evolution of Cycles

Combined power cycles are a common source of energy, since they offer higher energy efficiency while also making use of common technology. The idea of combining two different heat-engine cycles, however, has been around longer than you think. Today’s blog is going to cover the basics of combined cycle power plants, and their history of how they went from experiments to one of the most common sources of energy in the United States, for example. But how did this come to be, and what really is a combined cycle?

An animated exterior of a combined cycle power plant, image courtesy of General Electric
An animated exterior of a combined cycle power plant, image courtesy of General Electric

Basics

At its most basic form, a combined cycle is the synthesis of two independent cycles into one, which allows them to transfer thermal energy into mechanical energy, or work. On land, this is typically seen in power-generation, so the heat of these two cycles makes electricity. At sea, many ships operate using combined power cycles, but instead of just electricity, the mechanical energy is put to work by propelling the ship as well as providing onboard power.

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Hydrogen in Combined Cycles

Hydrogen is a clean and carbon-free fuel and is considered a key element for energy transition. Renewable power generation by solar and wind is increasing, which requires flexible operation to balance the load on the energy grid with the ability to rapidly adjust the output. Gas turbines with a combustion system for hydrogen operation offers a low carbon solution to support the stability of the energy grid. This provides a solution to the need for energy storage, in the form of hydrogen, and flexible power generation.

Discharging green-house gases and particulates into the atmosphere has an impact on the global climate. With this current trend of increasing awareness towards the environment, alternative fuels are again being examined to reduce the impact of emissions. Hydrogen is perceived as the only long-term solution to global warming concerns. It is also the only fuel that can create large reductions in carbon emissions. There are zero CO2 emissions produced in hydrogen combustion. Hence, NOx emissions are the only remaining concern. Micro-mix combustion is used to implement miniaturized diffusive combustion to combust hydrogen with low emissions. With miniaturized diffusive combustion, local flame hot spots, which are caused by arising stoichiometric conditions of hydrogen, are reduced substantially with an increase in the local mixing intensity. Improvements in the mixing quality provide reduced emissions of NOx with a more balanced flame profile. Micro-mix combustion was also studied with different mixtures of fuels including hydrogen, kerosene and methane establishing an adaptive combustors [1,2].

Power generation systems based on hydrogen could be an important alternative to conventional power systems based on the combustion of fossil fuels. The main effort in the field is oriented towards the use of hydrogen in fuel cells and combustion with gas turbines. Consider the main options for combined cycles based on a hydrogen-fueled gas turbine unit shown in Figure 1.

Basic Simple and Combined Co-generation Cycles

Figure 1. Brayton - Rankine combined cycle
Figure 1. Brayton – Rankine combined cycle

One of the most widely used combined cogeneration cycles is the Brayton – Rankine cycle. This cycle is a symbiosis of the Brayton (simple cycle gas turbine) cycle and the Rankine (steam turbine) cycle.

Figure 2. Typical efficiencies of various types of plants
Figure 2. Typical efficiencies of various types of plants [3]
Figure 2, above, shows the efficiency of the power plant depending on the type of cycle. The power plants referenced are: the simple cycle gas turbine (SCGT) plants with firing temperatures of 2400°F (1315°C); recuperative gas turbine (RGT) plants, where the exhaust gases from the turbine are used to heat the incoming air to the combustion chamber; the steam turbine plants; the CCPPs; and the advanced combined cycle power plants (ACCPs), such as CCPPs using advanced gas turbine cycles. Read More