Design of Inlet Guide Vane (IGV) for Centrifugal Compressors

All centrifugal compressor designers want to achieve the highest efficiency as well as wide operating range. With this in mind, the inlet guide vane (IGV) is a convenient and economic option for various applications.

IGVs are a series of blades circumferentially arranged at the inlet of compressor, driven electronically or pneumatically.By adjusting the orientation of IGVs, the air flow enters the impeller at a different direction therefore changing the flow behavior while affecting the passing mass flow rate (throttling). This can effectively reduce the power consumption to increase the compressor’s overall efficiency while avoiding surge to provide a better off design working range.

The designer needs to optimize blade profile and positioning of the IGV for efficient operation of a compressor, which can be a tedious job if one does not have a handy tool. Figure 1 shows an example of IGV working on different angles.

Example IGV Characteristic Curve
Figure 1. Example IGV Characteristic Curve

In AxSTREAM, people are able to add IGV component before the centrifugal compressor impeller which can provide different ways to edit its profile such as:

  1. Directly accessing variables in the project (grid)
  2. Meridional coordinates (in viewer, 1D/2D streamline module)
  3. Axial profiler and blade design

Figure 2 shows the interface of adding an axial IGV to your compressor.

Figure 2 How to Insert Axial IGV in AxSTREAM

After setting all data information like tip/hub diameters, number of blades, clearance, stacking mode for 3D blade, etc., you will be able to see the flow path and 3D models in a graphic interface, as shown in Figure 3.

Figure 3 Flow Path and 3D Model of Centrifugal Compressor with Axial IGV

Then you can include  theIGV into the calculation both in a 1D/2D module or 3D CFD module. You can also create numerical experiments, comparing design and off-design performance with different IGV profiles and angle setting.

If you want to also take into account of diffuser design, you can do so with different combination of IGV/diffuser parameters. You could also run several tens of design simultaneously in batch mode and automatically obtain the optimized design.

Contact us at Sales@Softinway.com for a demo of more AxSTREAM features for centrifugal compressor design.

References:

http://manualarchive.ingersollrandproducts.com/manuals/manuals/instructionbook/Misc_Manuals/principles_operation.pdf

http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=2718&context=icec

http://manualarchive.ingersollrandproducts.com/manuals/manuals/instructionbook/Misc_Manuals/principles_operation.pdf

Overcoming the Use of ICEs in Hybrid Electric Vehicles with Turbomachinery – Micro-Turbine Range Extenders – Part 2

As introduced in the last blog regarding Micro-Turbine Range Extenders, we will continue the discussion of turbine engine applications in the automotive sector in this blog.

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.

Figure 1 – Thermodynamic Formulation of a Micro-Turbine Range Extender Model in AxCYCLE™

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?

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

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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Importance of Preliminary Design for Centrifugal Compressors

prelim-design
Preliminary Design in AxSTREAM

Centrifugal compressors span a number of applications including oil compression systems, gas shift systems, HVAC, refrigeration, and turbochargers. It works by using energy from the flow to raise pressure, using gas to enter the primary suction eye (impeller). As the impeller rotates, the blades on the impeller push the gas outwards from the center to the open end of impeller to form a compression. Compressors are commonly used for combustion air supplies on cooling and drying systems. In HVAC system application, fans produce air movement to the space that is being conditioned. As a key component of an energy cycle, design/performance requirement must be met. While a design can easily be scaled from an existing design through appropriate parameters, a tailored design from scratch to confirm with design requirement for the specific cycle would give a better match and improve overall cycle performance.

There are variants of non-aerodynamic constraints in centrifugal compressor design practice, from frame size to durability and ultimately cost. An optimized impeller design should also ensure that aerodynamic problems associated with the all compressor components are minimized. With all of these (aerodynamic and non-aerodynamic) design constraints, there is no better way to optimize your compressor design than starting from the preliminary step, making sure that your compressor meets your criteria from a one dimensional basis ( a step that is often overlooked in practice).
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Overcoming the Use of ICEs in Hybrid Electric Vehicles with Turbomachinery – Micro-Turbine Range Extenders

The concept of turbine-powered automotive vehicles is not necessarily an unfamiliar idea or a technology that has yet to be explored.  In fact, several prominent automakers explored this concept as early as the 1950s and 60s – with real, functional prototypes.  Notably, Rover-BRM in the UK as well as Chrysler and General Motors in the US employed turbine engine programs to test the viability of such engines in the commercial market.  The Chrysler turbine engine program began its research back in the late 1930s and eventually ran a public user program from September 1964 to January 1966 where a total of 55 cars were built.   General Motors had tested gas turbine-powered cars with its many iterations of the Firebird in the 50s and 60s.  Rover and British Racing Motors developed several prototypes of their Rover-BRM concept that actually participated in the Le Mans race three years in a row, from 1963 through 1965.  However, even Chrysler, which was considered the leader of gas turbine research in automobiles, had to eventually abandon their program in 1979 after seven iterations of the turbine engine.  Many of the initial issues with heat control and acceleration-lag were improved during the program’s lifetime, but the program had never paid off in the retail automotive sector, and its continued development was deemed too risky for Chrysler at the time.

Chrysler Turbine Car
Figure 1- Chrysler Turbine Car – Now at Display in the Walter P. Chrysler Museum

Several decades later, we are seeing a resurgence of turbine motors in automobiles, but now serving as a range extender generator for electric vehicles instead.  As with many upcoming technologies, learning from past research and failed historical attempts can bring light to the most elegant and innovative solutions for today’s modern challenges.  This revolution of an old concept shares many of the qualities that made turbine engines attractive back in its initial development phase.  Such advantages include the ability to run on any flammable liquid and the high power density that results in a significantly lower weight and size contribution than its piston engine counterpart.

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SoftInWay’s Role in Meeting the Future Needs of Steam Turbine Industry

Steam turbine technology has advanced significantly since it was first developed by Sir Charles Parson in 1884 [1]. The concept of impulse steam turbines was first demonstrated by Karl Gustaf Patrik de Laval in 1887. A pressure compounded steam turbine based on in de laval principle was developed by Auguste Rateau in 1896. Westinghouse was one of the earliest licensee for manufacturing steam turbines obtained from Sir Charles Parson and became one of the earliest Original Equipment Manufacturers (OEM) in power generation and transmission.

Over the years, as steam turbine technology advanced, the design principles were based on either impulse type or reaction type with reaction type being more efficient. Though impulse was not as efficient as reaction type, it gained popularity due to lower cost and compact size. With advances in design and optimization methods being employed, the efficiency levels between these two types are not very distant, ranging between 2 – 5% based on the size and application. Read More

The Use of SCO2 in Power Generation

Lab imageGlobal warming and the growing demand for energy are two primary problems rising in the power generation industry. A simple solution to these problems has been researched for a number of years. The SCO2 Brayton cycle is often looked into as an alternative working fluid for power generation cycles due to its compactness, high efficiency and small environmental footprint. The usage of SCO2 in nuclear reactors has been studied since the early 2000s in development of Generation IV nuclear reactors, but the idea itself can be traced back to the 1940s. During this time however, no one really looked into the potential of supercritical CO2 since steam was found to be efficient enough, not to mention it was the more understood technology when compared to SCO2. In modern times though, demand of more efficient energy continues to rise and with it, the need for SCO2.

The potential of supercritical CO2 implementation is vast across power generation applications spanning nuclear, geothermal and even fossil fuel.  The cycle envisioned is a non-condensing closed loop Brayton cycle with heat addition and rejection inside the expander to indirectly heat up the carbon dioxide working fluid.
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Gas Turbine Cooling Technology

Turbine Cooling Scheme Designed in AxSTREAM NET
Figure 1. Turbine Cooling Scheme Designed in AxSTREAM NET

People are pushing turbine inlet temperature to extremes to achieve higher power and efficiency. Material scientists have contributed a lot to developing the most durable material under high temperatures such as special steels, titanium alloys and superalloys. However, turbine inlet temperature can be as high as 1700˚C [1] and cooling has to be integrated to the system to prolong blade life, secure operation and achieve economic viability.

A high pressure turbine can use up to 30% of the compressor air for cooling, purge, and leakage flows, which is a huge loss for efficiency. It is worth it only if the gain of turbine inlet temperature can outweigh the loss of cooling. This applies to both aviation engines and land based gas turbines.

The history of turbine cooling goes back 50 years and has evolved to fit different environments. The diversity of turbine cooling technology we see today is just the tip of the iceberg. As time goes on and technology advances, people are able to achieve higher cooling efficiency at lower coolant usages. For different goals and needs, different constructs can be applied but the detailed cooling design must balance with the whole system and make the most of technological advances in the areas. For example, if the flow path is optimized, mechanical design is modified, or if new material is employed, the cooling design needs to change accordingly. One thing worth mentioning is that manufacturing of hot section components and turbine cooling design have an interdependent cause and effect, outpacing and leading each other to new levels. Merging of disciplines and additive manufacturing will, in the future, bring more flexibility to turbine cooling design.

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Leveraging AxSLICE for Centrifugal Pump Upgrades and Retrofits

Often, service companies are faced with the challenge of redesigning existing pumps that have failed in the field with extremely quick turnaround times. While there are quick-fix methods to return these pumps into operation, other more complex problems may require taking a step back and analyzing how this particular pump could be redesigned based on its current operation.  These engineering upgrades could solve recurring issues with failure modes of a certain machine, and they could also solve new capacity demands that are imposed by a customer based on their system’s upstream or downstream changes. While efficiency increases could be beneficial to the overall system, many times it is more important to solve capacity requirements and increase the life of the pump by decreasing the Net Positive Suction Head Required (NPSHr).

In this blog post, we will investigate how to move an existing centrifugal pump through the AxSTREAM platform in order to solve engineering challenges seen on common OEM pump upgrades.  With the use of AxSTREAM’s integrated platform and reverse engineering module, many of the CAE tasks that are common in an analysis such as this one can be realized in record speed. The first step of the reverse engineering process occurs in obtaining the necessary geometrical information for the desired pump. Through AxSLICE, the user can take an STL, IGES, CURVE file, or a generated cloud of points and properly transform this 3D profile into a workable geometry inside the AxSTREAM platform. In a matter of minutes, the user can outline the hub and shroud and transform a blank 3D profile into a profile defined by a series of segments.  Seen in Figure 1, the centrifugal pump is now defined by a hub, shroud, and intermediate section.

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Identifying Compressor Problems

Centrifugal Compressor for Refrigeration Because the most vital part of a refrigeration and HVAC system is to function optimally, compressors are used to raise the temperature and pressure of the low superheated gas to move fluid into the condenser. Consequently, refrigeration compressors must be properly maintained through regular maintenance, testing and inspection. There are a couple conditions which would indicate compressor problem or failures. However, with the right supervision it is possible to avoid further damage. Through this post we will identify and discuss some of these conditions:
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