bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and Computational Study on the Impact of Aerodynamic Load Distribution on Aerodynamic Performance of Variable-Speed Turbine Blade
Authors: Fan Du , Zhou Zhihong , Liu Huoxing
Published: September 2023

Improving the adaptability of variable speed turbine blades to incidence angle by optimizing blade aerodynamic load design is one of the effective technical means to realize the efficient operation of variable-speed turbine blades in a wide range of incidence angle and improve the performance of variable speed turbine. In this paper, cascade experiments and numerical simulation study are carried out under a wide range of incidence angles for three variable-speed turbine blades with different aerodynamic load distributions. The results show that, under the positive incidence angle, the sharp increase of loss mainly occurs in the front part of the suction surface, while the loss increase in other areas is not obvious. Under the negative incidence angle, the sharp increase of loss mainly occurs in the middle and rear parts of the pressure surface. Under the extreme negative incident angle, the increase of loss caused by the middle and rear part of the pressure surface accounted for more than 90% of the total loss increment, while the loss caused by the middle part of the suction surface affecting the flow at the rear of the suction surface accounts for less than 10%. The suitable fore-loaded blades design can greatly broaden the working range at negative incidence angle, while aft-loaded blades can slightly reduce the blade loss at positive incidence angle.
Numerical Analysis of Flame Shape Impact on the Performance of Fuel Staging in a Lean-Burn Aeronautical Burner
Authors: Cunha Caldeira Mesquita Léo , Vié Aymeric , Ducruix Sébastien
Published: September 2023

The BIMER combustor is a lab-scale burner investigating fuel staging techniques as a stabilisation strategy for lean premixed prevaporized combustion for aeronautical applications. Two stages compose its injection system: the pilot and the multipoint stages. The staging factor is defined as the ratio of fuel mass flowrate injected through the pilot stage over the total one. As three flame shapes were found experimentally, Large-Eddy Simulations are performed in this study to assess the impact of the flame shape on the combustion regime and stability of the burner. Two operating conditions were explored experimentally (pilot-only and multipoint-dominated) to validate the simulations and compare the three flames. An additional multipoint-only condition is also investigated for the V flame. The burning regimes (premixed and non-premixed) and noise signatures (as a function of fuel staging) were compared to check whether these flames could benefit from the staging strategy. The M and Tulip flame combustion regimes are little affected by fuel staging, remaining mostly premixed and non-premixed, respectively, regardless of fuel staging. In opposition, the V flame changes from being mostly non-premixed to completely premixed, when the injection is changed from pilot-only to multipoint-only. For the same staging evolution, the V flame also emits less noise for the investigated points. These results show that the V flame shape is the only one that allows this burner to benefit from an efficient fuel staging strategy.
Conjugate Heat Transfer and Thermal Stress in an Impingement Cooling Unit for Gas Turbine Vane
Authors: Wang Shanyou , Li Xueying , Ren Jing
Published: September 2023

Impingement cooling is widely used in gas turbines because of its excellent local heat transfer capability, and it plays an important role in the next generation of double-wall cooling technology. However, it induces inhomogeneous temperature fields as well as thermal stress fields. In this paper, the conjugate heat transfer and thermal stress characteristics are investigated for an impingement unit including a single round nozzle and solid plate with uniform heat flux on the heated surface through an experimentally validated numerical approach. The studied operating parameter are Reynolds number (from 10000 to 30000), nozzle-to-plate distance ratio (from 2 to 10), and thickness of solid plate (108 mm and 50 mm). The results show that the Nusselt number distribution along radius may have two maxima at a small impingement distance which is driven by the mismatch of maximum wall shear stress location and maximum near-wall turbulence kinetic energy location. Considering the uneven heat transfer distribution as a boundary condition of solid thermal conduction, thermal conduction would reform the heat flux which makes the uniform heat flux boundary condition on the heated surface into uneven heat flux distribution on the impinged surface. The temperature can be lowered and distributed more evenly by increasing the thermal conductivity of the plate. In contrast, the temperature can be lowered but distributed more unevenly by reducing the thickness of the plate. The flat plate expands into a shape with a thin center and thick edges due to the uneven temperature field. This research illuminates the coupling mechanism between convective heat transfer, solid heat conduction, and thermal stress, which has significance for the prediction of gas turbine vane metal fatigue life.
Structural Assessment of Instrumented Parts for Gas Turbine Flange to Flange
Authors: Satheesh Aparna , Soman Abhimanyu , Santhanagopala Krishnan Babu , Reddy Peddi Mallikarjuna , Manoharan Sambandam
Published: September 2023

Market demands new gas turbines or enhancement of an existing gas turbines to fulfill its demand from time to time. These demands are due to changing environmental regulations, market competition, energy efficiency, technological advancements, change in fuel type. Any new GT product enhancement requires validation to understand capability of subsystem behavior and to gain more confidence on performance improvement. Several instrumentations are required to measure these responses at identified locations from different subsystems in gas turbine during prototype testing. Gas turbine is tested with all these instrumentations with several variations in operating parameters to gather actual responses from gas turbine performance and its subsystem. These instruments require modification in subsystem components to gather data and cable routing to send these data to acquisition system. Pressure probes, thermocouples, strain gages, accelerometers, clearance probes, etc. are placed at the identified locations after necessary modifications in subsystem components. These modified features are validated through appropriate analytical assessments to ensure design robustness ensuring successful test campaign and data acquisition. This paper describes those analytical assessments ensuring design robustness.
Steam Turbine Development for Small Modular Reactors
Authors: Ray Suman
Published: September 2023

Introduction of Small Modular Reactor (SMR) technology is likely to play a significant role in energy transition over the next decades by delivering safe, reliable, and sustainable power when required. There are currently more than ninety different types of SMRs in development employing various fuel and cooling solutions. The nearest to market SMR designs are based on state-of-the-art boiling water reactor (BWR) or pressurized water reactor (PWR) technologies and will generate electrical power using steam turbine generator sets operated using an optimized Rankine cycle.

This paper will provide an insight on developments of new steam turbine modules for various inlet volumetric sizes suitable for the 50 MW to 500 MW power range focused on the major design considerations. Even though the steam expansions for the near to market SMRs vary significantly they all have wet steam expansions. The wetness significantly influences the performance and swallowing capacity of the modules. Like industrial or utility power plant of these sizes, steam turbines for SMRs will operate at full speed i.e., 3000 rpm for 50 Hz grids or 3600 rpm for 60 Hz grids although the smallest SMR may have high speed turbines. While the geometric features could be scaled from large nuclear machines with proven operating experience, nucleation effect and water droplet sizes does not scale in the same proportion and hence the impact of wetness needs special consideration. The design features need to reduce water erosion to the largest extent possible by suitably extracting water and hence improving performance and reliability.

All SMR plants are expected to have significantly shorter lead times to commercial operation than today’s large nuclear plant. This being achieved by modularizing the design, constructing in a factory environment, and consequently reducing the erection time and project cost. To achieve a high degree of construction schedule certainty, standardization of plant design across the different site locations is a strong consideration. Selection of a common steam turbine footprint without compromising performance at different cold end conditions is an important contributing factor.
Investigation on the Unsteady Surge Flow Behavior of an Axial-Centrifugal Compressor
Authors: Li Jiaan , Wen Mengyang , Wang Baotong , Zheng Xinqian
Published: September 2023

Compressor aerodynamic instability, such as surge, has been attracting a broad interest in research because of its severe damage to engine performance and structural integrity. Therefore, the knowledge concerning surge flow mechanism and characteristics plays an essential role in taking effective measures of surge recovery. This paper aims to investigate the surge characteristics and distinct instability evolution process of an axial-centrifugal compressor using URANS simulation. Firstly, the CFD model of a combined compressor consisting of one axial and one centrifugal stage was established and validated by experimental data, then the transient characteristics of the surge were obtained. It was found that when the surge occurs, the reverse flow firstly occurs at the diffuser, and an obvious surge cycle was observed at the outlet of the centrifugal stage. In contrast, the pressure at the outlet of axial stage varied linearly with the mass flow without hysteresis phenomenon. When the reverse flow fully developed, the area with reverse flow showed an S-shaped meridional distribution, and higher reverse flow velocity existed at the regions near rotor hub, stator tip, and impeller tip. As a result, these regions were at risk to the detrimental effects of reverse flow and thus, suffer unsteady aerodynamic forces. Furthermore, a full-annulus model was established to study the development of the flow field during the surge inception process. The results showed that rotating stall was first observed near the axial stator hub, while the flow inside the centrifugal stage, worked normally. It indicated that the strong pressurization effect of the downstream centrifugal stage stabilized the operation of the combined compressor even though the upstream axial stage operated at rotating stall.
Continual Adaptation of Compressor Maps During Operation on Measurement Data For Increased Performance of Model-Based Applications in Turbomachinery
Authors: Lorenzen Finn , Schönig Felix , Grote-Ramm Wolfgang , Oliveira Brito Marcel , Neuberger Heiko , Sobolyev Alexander
Published: September 2023

Higher control engineering concepts, including artificial intelligence and model-based control, are recently becoming more popular in complex industrial applications because they enable a significant increase in efficiency. E.g., a model-based approach can be used to enhance the control and monitoring of several coupled components of a larger turbomachinery train. This requires dynamic models of the components, including all machine characteristics, which may experience a shift in their behavior over the course of their lifetime. Such changes occur due to natural fouling, wear of sub-components or external effects induced by maintenance measures. To overcome this problem, we model machine-characteristic maps with artificial neural networks, which may be used as part of prediction models in a model predictive control unit. If an appropriate data set is available, this allows us to adapt the model to the current behavior of the machine without requiring in-depth knowledge about the underlying physics of this “concept drift”, as it is known in literature. However, the training of neural networks is usually connected with high computational effort while the task needs to be executed in real-time during operation. Furthermore, in real operating conditions, machine sensors can only provide labeled data from the current operating point of the machine, which can be stationary for long operation periods of up to several months. In general, this yields only an unrepresentative data subset of the machine-characteristics, which is not sufficient to retrain the whole model to a new state. To solve these problems, we firstly reduce the model adaptation to a convex optimization problem, which can be efficiently solved in real-time conditions. Secondly, we use a specialized data management system with which we can integrate historical data to supplement the unrepresentative data subset. In this paper we show the application of the outlined method on a compressor map and discuss the advantages and requirements of the method in the context of modeling applications for industrial turbomachinery.
Reacting Flow Prediction of the Low-Swirl Lifted Flame in an Aeronautical Combustor With Angular Air Supply
Authors: Hoffmann Sven , Koch Rainer , Bauer Hans-Jörg
Published: September 2023

The development of lean-burn combustion systems is of paramount importance for reducing the pollutant emissions of future aero engine generations. By tilting the burners of an annular combustor in circumferential direction relative to the rotational axis of the engine, the potential of increased combustion stability is opened up due to an enhanced exhaust gas recirculation between adjacent flames. The innovative gas turbine combustor concept, called the Short Helical Combustor (SHC), allows the main reaction zone to be operated at low equivalence ratios. To exploit the higher stability of the fuel-lean combustion, a low-swirl lifted flame is implemented in the staggered SHC burner arrangement. The objective is to reach ultra-low NOx emissions by complete evaporation and extensive premixing of fuel and air upstream of the lean reaction zone.

In the present work, a modeling approach is developed to investigate the characteristics of the lifted flame in an enclosed single-burner configuration, using the gaseous fuel methane. It is demonstrated that by using the Large Eddy Simulation method, the shape and lift-off height of the flame is adequately reproduced by means of the finite-rate chemistry approach.

For the numerical prediction of the lean lifted flame in the SHC arrangement, the focus is on the interaction of adjacent burners. It is shown that the swirling jet flow is deflected towards the sidewall of the staggered combustor dome, which is attributed to the asymmetrical confinement. Since the stabilization mechanism of the low-swirl flame relies on outer recirculation zones, the upstream transport of hot combustion products back to the flame base is studied by the variation of the combustor confinement ratio. It turns out that increasing the combustor size amplifies the exhaust gas recirculation along the sidewall, and increases the temperature of recirculating burned gases. The present study emphasizes the capability of the proposed lean-burn combustor concept for future aero engine applications.
Impact of Flow Unsteadiness on Turbine Airfoil Heat Transfer via Streaming
Authors: Agarwal Tapish , Jacobi Ian , Cukurel Beni
Published: September 2023

Thermal management of turbine airfoils is a critical design consideration, but the impact of unsteadiness on heat transfer of attached flow regions has received less attention in the literature. When turbine surfaces are subjected to unsteady zero-mean flow fluctuations, either naturally or artificially, the mean velocity around them is modified due to a non-linear interaction of fluctuations, known as streaming. In this numerical study, we examine the effect of streaming on heat transfer and skin friction in a simplified model of the flow over a turbine blade. Both heat transfer and skin friction modifications were found to strongly depend on the amplitude and wave speed of the unsteady flow perturbations. Over a wide range of disturbance parameters, skin friction modification was negligible, but a significant effect on heat transfer due to streaming was identified. Moreover, the impact of favorable pressure gradients, which are typical for turbine airfoils, on the streaming phenomena was also considered, and it was found that flow regions of zero-pressure gradient produced the strongest amplification of heat transfer, although the effect of the pressure gradient varied with Strouhal number. Due to its significant effect on wall heat transfer, the streaming phenomenon should be taken into account during the design and measurement of the thermal properties of unsteady systems.
GT36 First Stage Development Enabling Load and Fuel (H2) Flexibility With Low Emissions
Authors: Pennell Douglas , Tay-Wo-Chong Luis , Smith Richard , Sierra Sanchez Patricia , Ciani Andrea
Published: September 2023

In this paper the multi-burner first stage (MBFS) premix system design of Ansaldo’s GT36 constant pressure sequential combustion system (CPSC) is presented. This first stage generates the required inlet temperature to the sequential burner (a parameter essential to regulate for fuel reactivity and stoichiometry): In addition, the first stage maintains optimal NOx and CO emissions and provides for dynamic stability control within the CPSC.

The 8 slot BEV premix burner is introduced, showing its integration into the MBFS and in the overall layout for the CPSC can system. The BEV and MBFS is the culmination of a 10-year development made in tandem with the GT36 can system. The burner is a successor to mature EV and AEV premix burner technologies established in many other methane-based gas turbines. It operates with all necessary fuel blends of methane and hydrogen and creates the inlet conditions with those fuels for the center-body sequential burner to function optimally as the second stage of the can system. The unique use of fuel stages within the BEV burner itself provides the flexibility to overcome the inherent limitations of premix only systems when running with highly reactive fuels. Full pressure can and GT combustion emissions and dynamic data are presented for various loads and fuel compositions, demonstrating the operation, and allowing for tailored solutions in today’s varying GT environment. The system ensures Ansaldo approaches zero CO2 emissions capability for gas turbines in an increasingly hydrogen dominated market.
Analysis of Combustor-Turbine Interaction by Using Coupled and Decoupled Scale-Resolving Simulations Under Representative Operating Conditions
Authors: Tomasello Stella Grazia , Andreini Antonio , Meloni Roberto , Cubeda Simone , Andrei Luca , Michelassi Vittorio
Published: September 2023

The physical phenomena due to the interaction between the combustor chamber and the first stage nozzle arouse an ever-increasing interest. In fact, a complex and unsteady flow field, characterized by a high level of turbulence and temperature distortions, usually can be found at the interface plane between the two hot gas path components, especially with the implementation of lean-burn combustors that allow the reduction of NOx emissions, but at the cost of requiring highly swirled and turbulent flows to stabilize the flame. Such severe conditions at the inlet of the first stage nozzle can have a potential impact on the performance of the component, resulting in a perturbation of the heat transfer, the aerodynamics and the effectiveness of the cooling system. To highlight the risks and uncertainties associated with carrying out decoupled simulations, scale-resolving simulations have been carried out to guarantee an accurate resolution of most of the flow structures while keeping the computational cost low. Firstly, a fully integrated combustor-nozzle setup, including a realistic turbine nozzle cooling system has been investigated under realistic operating conditions. The results have then been compared with those coming from a SBES decoupled simulation of the first stage nozzle alone. In this case, the prescribed time-varying inlet boundary conditions have been extracted from a SBES of the stand-alone combustor where the nozzle has been replaced with a discharge convergent that preserves the Mach number of the NGV while guaranteeing the same throat area. Moreover, in order to assess the discrepancies between different CFD approaches, the results coming from the correspondent preliminary RANS S1N simulation are here also included, by imposing as inlet boundary conditions two-dimensional maps from the time-averaged solution of the precursor SBES of the stand-alone combustor. Thus, the present work concentrates on the comparison and the analysis of numerical SBES simulations of an integrated combustor-NGV configuration and isolated NGV RANS and SBES simulations to assess the impact of the presence of the combustor under realistic operating conditions and realistic annular geometry.
Impact of the Purge Flow Density Ratio on the Rim Sealing Effectiveness in Hot Gas Ingestion Measurements
Authors: Orsini Lorenzo , Picchi Alessio , Facchini Bruno , Bonini Alessio , Innocenti Luca
Published: September 2023

The rim seals of gas turbines are used to control the ingestion of hot mainstream gas into the wheel space between the rotor disk and the stationary casing. Sealing air, which is generally used to pressurize the cavity space, flows through the seal clearance and then mixes with the flow path in the annulus. Predicting the correct quantity of purge flow necessary to prevent excessive ingestion of hot gases while, at the same time, minimizing the penalties in terms of engine efficiency and stage aerodynamics represents a great challenge for the designers and a crucial point for the design of reliable engines. Such estimate is governed by unsteady phenomena and CFD approaches are still expensive and time-consuming, especially if 3D domains and unsteady conditions have to be simulated. Fundamental test cases, replicating actual engines geometries, are still a valid approach to calibrate correlations or simplified models such as the so-called Orifice Model. However, most of the experimental studies deal with test rigs at room temperature and do not take into account the effect of the density ratio between purge and main flows.

To fill this gap, the present paper reports the impact of the density ratio on the rim sealing effectiveness by performing a non-intrusive diagnostic based on the Pressure Sensitive Paint (PSP) technique on both the stator and rotor side. The analysis was performed on a cold Rotating Cavity Rig, developed for the study of hot gas ingestion, where two different values of density ratio were tested by using N2 (DR = 1) and CO2 (DR = 1.52) as purge flow. The data extracted from the PSP seal effectiveness maps allowed to calibrate the Orifice Model for the stator side and to fit the coefficients of the Buffer Ratio model for the rotor surface at different flow conditions where the Externally-Induced ingress is the dominant mechanism for gas ingestion. The results highlighted the impact of the DR on the seal effectiveness and on the low-order models considered for the data analysis. In the end, it is shown that the obtained results can be used to scale experimental data, generally collected at DR close to one, towards more representative engine values where the difference between the density of purge and main flows cannot be neglected.
High Speed Rotary Atomizer Supported on Porous Type Gas Bearings: Challenges Faced, Operability Demonstration and Load Testing
Authors: Wadhvani Vishal , Bazergui Claude , Mehan Paul , Smith Michael , Michael Anthony
Published: September 2023

A novel “patent-pending” high speed rotary atomizer supported on porous gas bearing technology was designed, fabricated and tested in response to challenges with an existing product on active magnetic bearing (AMB) technology and the desire to keep the design oil-free due to its inherent maintenance/operation benefits. The lessons learnt on the magnetic bearing atomizer system especially in regards to the periodic rotor imbalances the atomizing process imposes on the system, scaling/ cost complexity of the design and the customer complaints/ feedback were at the heart of this new design endeavor on gas bearing technology. This paper describes all these issues in detail and the testing data on this new design is presented along with the challenges/ setbacks faced during the initial stages of prototype testing. Some of the failures experienced during the early stages of prototype testing will be described in detail (especially due to the temperature rise seen inside the machine at high operating speeds) and how some novel design improvements/ measures were undertaken to overcome them. Lastly, the benefits of this new design will be discussed in comparison to other bearing technologies and how they are being leveraged for use in multiple sizes so it can be a truly scalable platform.
Second Edition: Assessment of Current Capabilities and Near-Term Availability of Hydrogen-Fired Gas Turbines Considering a Low-Carbon Future
Authors: Webb Bobby M. , Harper Jim , Steele Robert , Noble David R. , Emerson Benjamin , Wu David , Lieuwen Tim
Published: September 2023

Gas turbines continue to play a vital role in the global push for decarbonization, both for near-term reductions as coal phases out for natural gas operation and long-term transitions to carbon-free fuels. While decarbonization presents a threat to traditional combustion-based power generation, it offers an opportunity for a renewed role of the existing and future gas turbine fleet in a carbon-free future. This renewed role positions gas turbines to help stabilize power grids with large portfolios of intermittent renewable generation sources, with the gas turbines operating on low-carbon fuels such as hydrogen. Historical approaches to decarbonization of gas turbine combustion face hydrogen fuel content limitations, while simultaneously implementing dry, low-NOx (DLN) technologies. In 2020, we presented a review of the current state-of-the-art, and we projected the emerging technologies for DLN, high hydrogen combustion capabilities. In this paper, we revisit those projections and update the current state-of-the-art combustion capabilities through the last three years of development along with new initiatives to push capabilities further. Readers of this paper will take away an understanding of where the field is on low-NOx, high hydrogen combustion. Additionally, an overview takeaway will be understanding of the current capabilities of each of the OEMs and other major players, including the developing technologies and targets that each is working towards for a carbon-free, dispatchable power generation source.
High Altitude Relight Performance of Hydrogen-Air Micromix Combustion Systems
Authors: Treleaven Nicholas C. W. , Puggelli Stefano , Mercier Renaud , Leparoux Julien , Sun Xiaoxiao , Sethi Bobby
Published: September 2023

In order to reduce the environmental impact of commercial aviation, hydrogen is being considered as a replacement fuel for kerosene in commercial aircraft. Due to the significantly different physical properties as compared to kerosene, this change in fuel promotes a potential revolution in the design of the combustion chamber. One of the alternative combustion systems recently proposed for hydrogen is micromix. The micromix injection consists of replacing a single air and fuel injector with many hundreds or thousands of small-scale simplified jet in crossflow type injectors. These simple injectors consists of an air gate that generates a small axial jet and a hydrogen injection hole that introduces the fuel perpendicularly into the path of the injected air. This configuration then leads to a large number of relatively rich partially-premixed flamelets in an otherwise globally lean combustor. The high local mixture fraction enhances flame stability, while the size of the flamelets enhances mixing and reduces the residence time of hot products, leading to low production of nitrous oxides. This relatively revolutionary approach has still to be tested thoroughly over the full range of engine conditions and operability specifications. One such requirement is high altitude relight: the low temperature and pressure of the combustion chamber reduce the laminar fuel speed and turbulence levels up to conditions where ignition using conventional methods may not succeed. This study used high fidelity Large Eddy Simulation to investigate high altitude relight for a micromix system. In particular, two approaches for chemistry description are compared: tabulated chemistry based on premixed flamelets and transported chemistry. Flame kernels of different sizes are computed with both approaches to determine the minimum kernel size required for ignition and a probability of ignition. Results show that due to the small recirculation zones downstream of these injectors, ignition must take place close to the injector face. Tabulated chemistry methods fail to predict ignition and a detailed analysis is proposed to better understand the differences with transported chemistry. A simplified model is also presented that links the probability of ignition with the flame speed and radius of the initial flame kernel.
Effects of Surface Roughness on Three-Dimensional Flow Structure Within Shaped Film Cooling Holes
Authors: Banko Andrew J. , Benson Michael J. , Davidson F. Todd , Zia Wasif , Bordbar Alireza , Boyce Christopher , Veley Emma M. , Thole Karen A.
Published: September 2023

Additive manufacturing (AM) techniques are expanding what is possible for designing and constructing gas turbine components that can handle increasingly harsh operating conditions. However, AM techniques can also introduce surface roughness that is more prominent than conventional manufacturing methods. The influence of this roughness could have an important effect on the performance of film cooling holes. However, little is known experimentally on what happens inside of a film cooling hole since this region is challenging to access with traditional measurement techniques. This study uses magnetic resonance velocimetry (MRV) to observe the in-hole flow structure of a scaled version of a baseline diffuser-shaped hole configuration with and without surface roughness at two blowing ratio conditions. The roughness geometry is derived from computed tomography (CT) scans of a metal-AM diffuser hole. The three-component, three-dimensional, time-averaged velocity field is measured by MRV and includes the flow from the plenum, within the hole, and in the vicinity of the hole exit. The momentum distribution within the diffuser differs between the smooth and rough holes, with peak velocities and flow asymmetry influenced by the surface roughness. Flow along the leeward wall of the diffuser is nearly separated, and the size of this separated flow region is smaller in the roughened cases. These effects are accentuated at larger blowing ratio. These data provide explanatory evidence of how the momentum distribution within smooth and rough holes may impact surface effectiveness results downstream of the shaped holes. CT scans of the surface roughness coupled with the MRV measurements provide non-optical means to characterize the hole geometry and as-built performance of additively manufactured test coupons with important implications for the field.
Test Rig Concept for Evaluating the Performance of a CO2 Immersed Electro-Mechanical Rotor System Utilizing Gas Bearings: Part-1 Mechanical and Electric Machine Design
Authors: Ertas Bugra , Powers John , Gary Keith , Torrey Dave , Zierer Joseph , Baehmann Peggy , Rallabandi Vandana , Adcock Tom , Anandika Nevin , Bidkar Rahul A.
Published: September 2023

This paper presents the mechanical and electric machine design of a 27krpm rotating test rig aimed at reducing technical risks with hermetic oil-free super-critical carbon dioxide (sCO2) turbomachinery. The test rig rotor system is based on a conceptual turbomachine design discussed in a companion paper that evaluates a sCO2 waste heat recovery (WHR) unit for land-based gas turbines at natural gas (NG) compressor stations. The key novelty of the hermetic sCO2 turbomachine concept is the utilization of additively manufactured CO2 gas bearings and a CO2-immersed direct-drive permanent magnet (PM) electric machine. The previous effort on conceptual design identified 3 main technical risks, which included thrust bearing load capacity, rotordynamics, and thermal performance of the system. Therefore, key requirements of the test vehicle include the ability to test the rotor system in a 400psi (27.6 bar) hermetic CO2 operating environment, apply up to 1,500 lbs (6.7 kN) of rotor thrust loads, capability to assess rotordynamics with radial gas bearings, inclusion of instrumentation to assess thrust bearing load capability, and flexibility for varying secondary cooling flows to confirm thermal model predictions. Design topics such as rotordynamics, bearing design, and electric machine design are addressed in the paper, while highlighting critical elements. In addition, additive build trials for Inconel 718 radial and thrust bearings were performed to prove the manufacturability of the bearing design concepts. The results of the design efforts yield a test rig concept with ability to operate at 27,000 rpm, apply thrust loads to 1,500 lbs, deliver CO2 up to 800psi, and modulate cooling flows.
Enhancements to Impingement Heat Transfer Through Nozzle Geometry Modifications
Authors: Ortiz Laura-Cebrian , Acharya Sumanta
Published: September 2023

Jet impingement heat transfer is commonly employed in turbine cooling. The current paper aims to experimentally analyze the enhancement of the heat transfer rate when using a turbulent impinging jet with different nozzle geometries that alter the nozzle exit flow condition and/or enhance unsteadiness/turbulence and induce it into the jet-flow. The nozzle geometry is altered by adding annular trips or axial trips or swirl trips on the internal surface of the nozzle. The measurements are based on a steady state approach with a uniform heat flux boundary condition and infra-red imaging to determine surface temperatures. Data on the local and average Nusselt number are reported for different jet-to-target spacings (H/D = 1.5–12) and Reynolds numbers (Re = 10000–97000). These results are compared with the corresponding baseline round jet geometry. It is observed that nozzles with swirl turbulators provide the greatest enhancement in surface heat transfer.
Evaluation of Pressure Drop and Cooling Effectiveness of Serpentine Channels With Varying Internal Rib Configurations
Authors: Yoon Christopher , Ellinger Molly E. , Bogard David G.
Published: September 2023

Gas turbine airfoils commonly use serpentine passages for internal cooling. To enhance the heat transfer in this internal passage, rib turbulators are often used. There have been many studies of rib turbulators to determine the optimum height, spacing, and angle; but almost all of these studies have been conducted using straight ducts. In this study, computational RANS predictions using the Realizable k-ϵ model and wind tunnel experimentation were used in conjunction to determine the optimum rib turbulator configuration for use in serpentine channels. The serpentine passage configuration had three U-bends and L/DH = 10 for each leg. The channel was placed below a simulated turbine airfoil wall which was flat, and the ribs in the channel were placed on this wall. Computations and experiments were completed with a smooth channel and with ribs at angles of −60°, 90°, and +60°, rib heights of e/H = 0.125 and 0.25, and spacing between ribs of P/e = 4 and 8. Studies were also done using turning vanes in the U-bends to reduce separation regions downstream of the U-bend. A key result from this study was that ribs oriented at −60° would produce similar pressure drops to the smooth serpentine channel. Flow field visualization showed that large separation regions after each U-bend of the serpentine channels were responsible for increased pressure drop, and the −60° ribs helped to redistribute the biased flow. Rib orientations of 90° and +60° experienced larger pressure drops than the −60° ribs both computationally and experimentally. Compared to the smooth channel, the channels with rib turbulators had only a small increase in heat transfer rates, ranging from 4% to 16% for varying rib angles. This small enhancement of heat transfer was attributed to the large heat transfer for the smooth serpentine channel caused by strong vortical flow generated downstream of the U-bends.
Analytical Study on Hybrid Thrust Foil Bearing, Structural Characterization and Measurement of Static Performance
Authors: Ebewele Ehiremen , Kim Daejong , Ki Jeongpill
Published: September 2023

This work presents a novel design of a hybrid thrust foil bearing (HTFB) with an outer diameter of 154mm, along with simulation and test results. The HTFB incorporates a high-pressure air/gas injection to the taper portion of the thrust foil bearing, boosting the hydrodynamic effect on the main bearing surface and hydrostatic load capacity at zero speed. As a result, this bearing has high load capacity, low power loss, and no friction/wear during startup and shutdown. Firstly, push-pull tests were conducted on a double-acting HTFB configuration to evaluate the nonlinear structural stiffness of the bump foil structure. The measured nonlinear stiffness model was adopted to predict the overall bearing performance under various speeds and external loads. The bearing performance was predicted at 40krpm, 3000N axial load, and 6 bar absolute hydrostatic pressure in both hydrodynamic and hybrid modes. The simulation uses an advanced model which predicts the 2D plate top foil deflection with physical bump locations mapped from the actual hardware. The simulation confirms that the hybrid operation significantly increases the minimum film thickness compared to hydrodynamic bearing due to the boost effect of hydrodynamic pressure in the main film. The preliminary experimental measurements on load capacity at zero speed agree with the prediction. Rotational tests were conducted at 10krpm, 15krpm and 20krpm. Ultimately, the novel HTFB shows excellent static performance with potential for use in Organic Rankine Cycle (ORC) generators and other large oil-free turbomachines.
3D Printing-Enabled Layer Hierarchies
Authors: Song Kenan , Ravichandran Dharneedar , Jambhulkar Sayli , Xu Weiheng
Published: September 2023

Advanced composite materials (ACMs), especially nanoparticle-reinforced polymer composites (NpRPCs), exhibit desirable physical and chemical properties that include low density coupled with directed high stiffness and strength, optimal dimensional stability, superior temperature, and chemical resistance, as well as relatively cost-efficient manufacturing. Successful manufacturing of high-performance nanocomposites depends on the precise control of processing factors, including (i) uniform dispersion of the nanoparticles, (ii) effective matrix-filler interfacial interactions at the molecular level, and (iii) alignment/orientation of the nanoparticle and/or polymer chains. This study highlights a newly designed nozzle for multilayer composite structure fabrication using thermoplastic and thermoset polymers, as well as nanoparticles of various morphologies (e.g., 1D and 2D), which have been used for the scalable fabrication of 1D fibers, 2D coatings, and 3D architectures via 3D printing. Discussion of the nozzle design, layer formation mechanism, and fabrication of functional structures of 1D, 2D, and 3D morphologies will be the focus of this talk. The demonstrations in structural supports, thermal dissipations, electrical conductors, plastics recycling, stimuli-responsive systems, and tissue scaffolds show massive potential in national defense, space exploration, energy storage, and human health.
Print Speed Optimization for UV-Assisted 3D Printing of Lunar Regolith Simulants Composite Inks
Authors: Marnot Alexandra , Cho Jaehyun , Brettmann Blair
Published: September 2023

Direct-ink-write (DIW) 3D printing of dense composite inks is an attractive method of additive manufacturing for Lunar missions using in-situ derived resources. DIW offers a wide degree of freedom for formulation design with multiple methods for solidifying the inks post-extrusion. The use of UV-curing, however, poses certain complications when the loading of particles in the ink reaches levels above 50 vol% due to light scattering, absorption, and reflection. Herein, we investigate the curability of two Lunar regolith simulants, compared against a model system of glass microspheres, as particles in UV-curable inks. Photo-DSC is utilized to assess the degree of cure of the inks at a range of timescales. These results are tied to depth of cure experiments following the ISO 4049 method to verify cure depths meeting a target print layer height and to optimize the speed of printing while maintaining structural integrity. The extent of cure is verified both qualitatively through print shape fidelity and quantitatively through ATR-FTIR. This work not only highlights the importance of particle mineralogy for achievable UV-assisted solidification post-extrusion, but also presents test methods easily adapted to a design of experiment framework that require very little sample volume to identify successful formulations and printing parameters.
The Effect of Voltage on the Initiation of Natural Pulsation in Electrohydrodynamic Jet Printing
Authors: Hawa Angelo , Bahrami Ali , Barton Kira
Published: September 2023

Electrohydrodynamic jet (e-jet) printing is a high-resolution additive manufacturing process that uses an electric field to extract polarizable ink from a nozzle. The high-resolution capabilities of e-jet printing are very favorable for the fabrication of printed electronics and biosensors, which is typically achieved using a highly controllable pulsating jet. In this regime, high voltage pulses are superimposed over a baseline DC voltage, which primes the meniscus for the subsequent pulse. While a higher baseline voltage reduces the response time of the system, values above a certain threshold can cause the printing to transition toward an uncontrollable jetting regime in which the natural dynamics of the ink instigate pulsating jet behavior. To characterize the effect of these unwanted transitions on the final print, key parameters of the natural pulsating jet mode must be identified. This work presents findings on the relevant time constants and volume measurements of jet printing at various subcritical voltages. While the impingement time of the jet was found to be proportional to the applied voltage, the volume of the initial droplet increasingly varied. Conclusions regarding permissible pulse widths and system predictability as a function of voltage were made.
Optimization of Process Parameters and Variability Study in Friction Stir Welding of 6061-T6 Aluminum Alloy and Ti64 Alloy With Interlayer
Authors: Mustafa Saed Enam , Rai Rajiv Nandan
Published: September 2023

Friction stir welding (FSW) of Aluminum (AA6061-T6) and Titanium (Ti64) dissimilar alloys have been carried out in the presence of a 2 microns Copper interlayer. Three levels of tool rotation speed and traverse speed have been selected as variable input parameters. The output parameters considered response variables were the temperature on the Ti side, temperature difference, microhardness, and tensile strength. Taguchi’s L9 array has been used for the experimental design. The Taguchi’s L9 orthogonal array is used in order to estimate the factors that influence the performance criteria and also which factors are more important than others. From the response table, the tool rotation speed has been found as the most influential factor affecting the quality of the welded joint. The signal-to-noise (S/N) ratio indicated that the welded joint’s optimal quality was achieved at 500 rpm and 14 mm/min. The ANOVA analysis found that the p-values of all the response variables are less than the significance level α (0.05). The variability study indicated that the process was under statistical control, and no assignable causes of variability were present. However, the ways and means to reduce inherent variability can be further explored using an improved experimental setup.
Forecasting the Range of Possible Human Hand Movement in Consumer Electronics Disassembly Using Machine Learning
Authors: Liao Hao-Yu , Chen Yuhao , Hu Boyi , Liang Xiao , Behdad Sara
Published: September 2023

Robotic technology can benefit disassembly operations by reducing human operators’ workload and assisting them with handling hazardous materials. Safety consideration and predicting human movement is a priority in human-robot close collaboration. The point-by-point forecasting of human hand motion which forecasts one point at each time does not provide enough information on human movement due to errors between the actual movement and predicted value. This study provides a range of possible hand movements to enhance safety. It applies three machine learning techniques including Long Short-Term Memory (LSTM), Gated Recurrent Unit (GRU), and Bayesian Neural Network (BNN) combined with Bagging and Monte Carlo Dropout (MCD), namely LSTM-Bagging, GRU-Bagging, and BNN-MCD to predict the possible movement range. The study uses an Inertial Measurement Units (IMU) dataset collected from the disassembly of desktop computers to show the application of the proposed method. The findings reveal that BNN-MCD outperforms other models in forecasting the range of possible hand movement.
Online Cost-Effective Classification of Mixed Tool and Material Conditions in Ultrasonic Metal Welding: Towards Integrated Monitoring and Control
Authors: Lu Kuan-Chieh , Meng Yuquan , Dong Zhiqiao , Shao Chenhui
Published: September 2023

Ultrasonic metal welding (UMW) is widely used in industrial applications such as electric vehicle battery manufacturing and automotive body assembly. The joint quality of UMW is sensitive to a variety of undesired yet inevitable process disturbances such as tool condition and material surface condition. Online monitoring and control capabilities are critically needed to quickly detect process anomalies and adaptively adjust process parameters, thus ensuring satisfactory joint quality and reducing process variability. While existing research has developed online quality monitoring methods for UMW, the cost-effectiveness of hardware (sensors, data acquisition equipment, and edge-computing devices) and software (computational efficiency) in a monitoring system has not been investigated systematically. The cost-effectiveness of monitoring also decides the window during which control actions can be executed, thus ultimately influencing the joint quality. This paper presents a systematic study on three factors related to cost-effectiveness: (1) sensor selection, (2) sampling rate of data acquisition, and (3) signal fraction. A method based on discrete wavelet transformation (DWT) is used for automatic feature extraction due to its effectiveness in extracting both time-domain and frequency-domain information with varying signal lengths. We develop a multi-layer perceptron (MLP) classifier to process DWT-generated features and recognize two types of welding disturbances including tool condition and material surface condition. Case studies demonstrate that combining a suitable signal fraction with a subset of sensors leads to comparable performance to using all sensors at full length. Moreover, the interaction between the sampling rate and the signal fraction is investigated. Results confirm the feasibility of building an accurate monitoring system with limited sampling rate and signal fraction, which increases the window for real-time control.