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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SuperTruck II Program and Waste Heat Recovery Systems

Familiar to many, the 2011 SuperTruck program was a five-year challenge set by the U.S. Department of Energy to create a Class-8 truck that improves fuel efficiency by 50 percent.  Hoping for even more groundbreaking achievements this time around, the Department of Energy has initiated a second five-year program to bring further fuel-efficiency advancements and near closer to eventual commercialization.  Cummins, Peterbilt, Daimler Trucks North America, Navistar, and Volvo Group remain the five teams involved in this R&D endeavor.  Michael Berube, head of the Energy Department’s vehicle technology office mentioned “SuperTruck II has set goals beyond where the companies think they can be.”  SuperTruck II is looking for a 100 percent increase in freight-hauling efficiency and a new engine efficiency standard of 55 percent.  With such lofty goals, the SuperTruck II development teams will need to tackle improvements in freight efficiencies from all sides.

Figure 1 - Daimler SuperTruck
Figure 1 – Daimler SuperTruck

Material considerations, body aerodynamics, low-resistance tires, predictive torque management using GPS and terrain information, combustion efficiency, and several other improvements methods on the first iteration have demonstrated how the SuperTruck II will require a multi-phase and integrated systems approach to achieve equally successful numbers. However, with an engine efficiency target that is 31 percent above the SuperTruck’s first go around, special attention will be required on engine advancement to achieve an efficiency standard of 55 percent.

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Foil Air Bearings for High-Temperature Turbocharger Applications

Within the realm of turbocharging, there are a number of different design challenges that influence the design process on both large-scale marine applications and smaller-scale commercial automobile applications.  From aerodynamic loads to dynamic control systems to rotor dynamics and bearing challenges, turbochargers represent a special subset of turbomachinery that requires complex and integrated solutions.  Turbocharger rotors specifically, have unique characteristics due to the dynamics of having a heavy turbine and compressor wheel located at the overhang ends of the rotor. The majority of turbocharger rotors are supported within a couple floating-ring oil film bearings.  In general, these bearings provide the damping necessary to support the high gyroscopic moments of the impeller wheels.  However, there are several disadvantages of working with these oil systems that have allowed different technologies to start to surface for these turbomachines.  With the floating-ring oil models, varying ring speed ratios and oil viscosity changes significantly influence the performance of the rotor dynamic model.

Dan blog bearing for turbochargers
Figure 1 – Floating-Ring Bearing Model for a Turbocharger

The application of oil-free bearings have started to emanate due to the overall consistency of their performance and the minimized heat loss associated with air as the damping fluid. Studies on these bearing types for turbomachinery applications are neither trivial nor unique, as they have seen plenty of exposure within the commercial and military aircraft industries within turbo compressors and turboexpanders. However, the success of these specific applications are due to the fact that these turbomachines operate with light loads and relatively low temperatures. The main design challenges with foil air bearings are a result of poor rotor dynamic performance, material capabilities, and inadequate load capacities at high temperature/high load applications.

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Simultaneous Design for Turbocharger Compressors and Turbine Wheels

AxSTREAM Blade Profiling
Figure 1- AxSTREAM 3D Blade Profiler for Radial Designs

Increasing regulation for reducing emissions has forced the automotive industry to accept different technologies over the years in order to stay ahead of the market. In an industry that is so accustomed to internal combustion engines, new solutions such as electric motors and turbocharger systems have allowed experts in other industries to cultivate an influence in the automotive market. Specifically in the realm of turbomachinery, increased development has gone into designing turbochargers in order to minimize the effect and size of internal combustion engines. Design challenges are inherent in the fact that an engine is a positive displacement device whereas the turbocharger falls under aerodynamic turbomachinery. The two separate machine types have distinctly different flow characteristics, and the proper sizing of a turbocharger for its parent engine requires proper modeling of the engineering system as a whole.

In general, initial turbocharger sizing becomes a matter of obtaining the necessary boundary conditions required for a preliminary design. A thermodynamic cycle analysis of an ICE-Turbocharger system will allow the designer to obtain an initial idea of the bounds

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Axial Compressor Challenges in Hyperloop Designs

Back when the California high-speed rail project was announced, Elon Musk (CEO of SpaceX and Tesla Inc. and perhaps the most admired tech leader of present day) was not only disappointed with this project, but also introduced an alternative to this system called the Hyperloop in 2012.  Since the abstract of this project was introduced, many engineers around the world have started to evaluate the feasibility of this “5th Mode of Transportation”.

Hyperloop Alpha Conceptual Design Sketch
Hyperloop Alpha Conceptual Design Sketch

The general idea for the Hyperloop consists of a passenger pod operating within a low-pressure environment suspended by air bearings.  At the realistic speeds estimated by NASA of 620 mph, the pod will be operating in the transonic region.  While Japan’s mag-lev bullet train has succeeded at achieving speeds of up to 374 mph, the scale and complexity of a ground transportation system rising above 600 mph bring to surface an unusual number of engineering challenges. As well, brand new designs such as the one proposed by Musk have a certain amount of risk involved due to this technology inherently having no previous run history on a large scale.

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Surge Conditions of Centrifugal and Axial Compressors

Centrifugal and axial compressors must operate within certain parameters dictated by both the constraints of the given application as well as a number of mechanical factors.  In general, integrated control systems allow compressors to navigate dynamically within their stable operating range.   Typical operating ranges for compressors are represented on a plot of volumetric flow rate versus compression ratio.  Compressors have a wide number of applications, from household vacuum cleaners to large 500 MW gas turbine units.  Compression ratios found in refrigeration applications are typically around 10:1, while in air conditioners they are usually between 3:1 and 4:1.  Of course, multiple compressors can be arranged in series to increase the ratio dramatically to upwards of 40:1 in gas turbine engines.  While compressors in different applications range dramatically in their pressure ratios, similar incidents require engineers to carefully evaluate what is the proper operating range for the particular compressor design.

Dan Post 10
Figure 1- Typical Performance Map Limits – Compressor Ratio (Rc) vs. Volumetric Flow Rate (Qs)

For intensive applications of centrifugal and axial compressors, the phenomenon of surge resides as one of the limiting boundary conditions for the operation of the turbomachine. Essentially, surge is regarded as the phenomena when the energy contained in the gas being compressed exceeds the energy imparted by the rotating blades of the compressor. As a result of the energetic gas overcoming the backpressure, a rapid flow reversal will occur as the gas expands back through the compressor. Once this gas expands back through to the suction of the compressor, the operation of the compressor returns back to normal. However, if preventative measures are not taken by the appropriate controls system or any implemented mechanical interruptions, the compressor will return to a state of surge. This cyclic event is referred to as surge cycling and can result in serious damage to the rotor seals, rotor bearings, driver mechanisms, and overall cycle operation.

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Component Matching of Industrial Gas Turbines

An important first step in understanding the gas turbine design process is the knowledge of how individual components act given their particular boundary conditions. However, in order to effectively leverage these individual design processes, a basic knowledge of how these components interact with each other is essential to the overall performance of a gas turbine unit. The power and efficiency outputs of a gas turbine are the result of a complex interaction between different turbomachines and a combustion system. Therefore, performance metrics for a gas turbine are not only based on the respective performances of each turbine, compressor, and combustion system, but also on their interactions. The concept of component matching becomes crucial in understanding how to deal with these systems simultaneously.

two-shaft-gas-turbine
Figure 2 – Simplified Two-Shaft Gas Turbine Arrangement Modeled in AxCYCLE

In general, gas turbines for industrial applications consist of a compressor, a power turbine, and a gas generator turbine designed into one of two arrangements. The first arrangement invokes the use of the gas generator turbine to drive the air compressor, and a power turbine to load the generator on a separate shaft. This two-shaft arrangement allows the speed of the gas generator turbine to only depend on the load applied to the engine. On a single-shaft arrangement, the system obviously cannot exist at varied speeds and the power turbine coupled with the gas generator turbine would be responsible for driving both the generator and the compressor. A simplified diagram of each arrangement is displayed in Figures 1 and 2.

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Utilization of Supercritical CO2 Bottoming Cycles

In the ever-expanding market for waste-heat recovery methods, different approaches have been established in order to combat the latest environmental restrictions while achieving more attractive power plant efficiencies.  As gas turbine cycles continue to expand within the energy market, one particular technology has seen a significant upsurge due to a number of its beneficial contributions.  Supercritical CO2 (S-CO2) bottoming cycles have allowed low power units to utilize waste heat recovery economically.  For many years, the standard for increasing the efficiency level of a GTU (Gas Turbine Unit) was to set up a steam turbine Rankine cycle to recycle the gas turbine exhaust heat.  However, the scalability constraints of the steam system restrict its application to only units above 120MW.

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Feasibility of Mixed Flow Compressors in Aero Engines

The term, “mixed flow compressor”, refers to a type of compressor that combines axial and radial flow paths. This phenomenon produces a fluid outflow angle somewhere between 0 and 90 degrees with respect to the inlet path.  Referred to as the meridional exit angle, the angled outflow of this mixed flow configuration possesses the advantages of both axial and centrifugal compressors.  Axial compressors can produce higher order efficiencies for gas engines, but they have relatively low-pressure ratios unless compounded into several stages.  Centrifugal compressors can produce high-pressure ratios in a single stage, but they suffer from a drop in efficiency.  The geometrical distinction of mixed flow compressors allows for higher efficiencies while maintaining a limited cross-sectional area.  The trade-off for a mixed flow compressor when introduced to aero gas turbines is that there is an associated weight increase due to the longer impellers needed to cover this diagonal surface.  However, when related to smaller gas turbines, the weight increase becomes less significant to the overall performance of the engine.

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Achieving Successful 3-Dimensional Hand Tracking Using Quasi-Random Sequences

With the advent of emerging technologies in the space of human-computer interaction (HCI), a prevalent challenge has been finding methods that can accurately represent these motions in real time.  Applications using RGB-D cameras to track movements for consumer-based systems has already been employed by Microsoft in the space of tracking silhouette movements in video games as well as app navigation in the Microsoft Kinect system.  However, tracking methods must evolve in order to successfully represent the complexity of human hand motion.  The two main categories of 3D hand articulation tracking methods consist of appearance-based and model-based tracking.  Appearance-based tracking methods are efficient in the limited space of comparing the present model to a number of already defined hand configurations.  Model-based tracking methods allow the computational configuration to explore a continuous space in which the hand motions are optimized at a high dimensional space in near real time.

scatter-plot
Figure 1 – 256 Points from a Pseudorandom Number Source (Left) Compared to a Quasi-Random Low-Discrepancy Source (Right)

If the computer tracks the human wrist with six degrees of freedom and the other joints accordingly, the ensuing dimensional analysis occurs at a high dimensional space.  A saddle joint (2 DOF) at the base of the each finger plus the additional hinge joints (1 DOF each) at the middle of the finger describes each finger with four degrees of freedom.  In turn, the problem of tracking the articulation of a single hand is performed in a dimensional space of 27.  This highly dimensional problem formulation requires an optimization technique specific to the problem that can provide a uniform coverage of the sampled space.  Quasi-random sequences are known to exhibit a more uniform coverage of a high dimensional compared to random samples taken from a uniform distribution.  The Sobol sequence, developed by Russian mathematician Ilya Sobol, describes a quasi-random low-discrepancy sequence that more evenly distributes a number of points in a higher dimensional space.  Figure 1 represents the distribution discrepancy between a pseudorandom number generation and a quasi-random low-discrepancy Sobol sequence generation.

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