bluuebunny/crossref_metadata_2025 huggingface dataset:
Searching for the Optimal Arrangement of Mistuned Blades Based on Solving the Traveling Salesman Problem for Simple Mass-Spring Linear System
Authors: Serebriakov Nikolay , Selivanov Alexander
Published: September 2021

The article presents an approach to finding the optimal arrangement of blades in a bladed disk based on solving the traveling salesman problem using the ant colony algorithm. The solution to the problem is presented for an equivalent model of the bladed disk. The mistuning parameters are assumed as known — for example, from the data of geometric measurements for each blade from the set used for assembling the bladed disk — considering the influence of the rotation on the investigated resonance mode.

Approaches have already been published for the construction of equivalent models and the use of combinatorial optimization methods, including solving the traveling salesman problem, to find the optimal arrangement of the blades. Therefore, this article focuses on demonstrating a simple program implementation of this method.

This approach allows a quick assessment of the effect of the blade assembly in the bladed disk on the amplitudes of alternating stresses. It even considers several restarts of the algorithm to determine other possible configurations of the system.
Modelling Conjugate Heat Transfer Within a Gas Turbine Secondary Air System Using 1D and 2-3D Solid Models in Thermo-Fluid System Simulation
Authors: Hunt David , Yuan Youming , Gardner Ian
Published: September 2021

This paper presents an implicit conjugate heat transfer (CHT) model designed for 1D systems of both solids and fluids. It demonstrates that this approach can be extended to include 2D and 3D elements being co-solved in a 2D or 3D thermal product. The approach is applied to a simple analytical problem and then to a Secondary Air Cavity within a Gas Turbine to illustrate the potential of this technique to be applied to more complex thermo-fluid simulations. Such simulations are important in trade off studies to balance minimizing engine bleed whilst ensuring sufficient cooling. The benefits of this CHT model are presented by comparison with the traditional approach of explicit co-simulation in which the temperature from the fluid domain is applied as a boundary condition to the thermal simulation and heat flux from the thermal simulation is applied as a boundary condition to the fluid domain (or vice versa). The ability to replace 1D elements with 2D or 3D elements allows model continuity from conceptual to detailed design and the reverse process potentially offers a route for model reduction later in lifecycle to support operation and maintenance through the use of an executable digital twin.
Approximation Method of the Gas Turbine Engine Compressor Characteristics
Authors: Avdeev Sergey , Tkachenko Andrey
Published: September 2021

A technique of representing and approximating of gas turbine engine (GTE) compressor maps is given. The aims of this study are to improve the efficiency of processing GTE test results and the reliability of GTE mathematical model.

The paper analyzes various approaches of approximating, presenting, and generalizing the characteristics of compressors. The advantages and limitations of the existing compressor maps approximation methods are summarized in the paper. A comparison of the obtained approximating method is carried out against previously developed methods.

Based on the performed analysis, a method is proposed for approximating of compressor maps, considering the requirements of identification of the GTE model. The resulting approximation method is based on the use of equations in a polar coordinate system. The study also analyzed the possibility of using the developed method in the system of thermodynamic calculations and analysis “ASTRA” (the program was developed at Samara University).

The developed approximation technique was tested on the experimental characteristics of the low- and high-pressure axial compressor. The estimation of the quality of the approximation was carried out using the standard deviation. It has been demonstrated that the obtained approximating functions describe the experimental data quite well. The obtained values of the standard deviation in the polar coordinate system were less than 10%.
Survey of Calculation Methods for Polytropic Efficiencies
Authors: Wettstein Hans E.
Published: September 2021

Calculating polytropic efficiencies is a basic task used for quantifying performance of power cycles involving compression and/or expansion. The incremental definition of a “polytropic curve” of gases by Gustav Zeuner in 1905 may be the oldest mention of the word “polytropic” in a thermodynamic context [1].

In Turbomachinery blading, the typical changes of state are nearly adiabatic and polytropic. L. S. Dzung was probably the first defining an incremental polytropic efficiency in 1944 [3]. Recursive integration of this has become the best thermodynamic quality measure of a blading.

Both Zeuner and Dzung started their consideration with an incremental definition. However, they integrated analytically assuming ideal gas data. This resulted in the well-known formula (1) p v n = constant Most thermodynamic textbooks declare this the definition of a polytropic change of state. However, the incremental definition survived too. Stodola [2], Dzung and later scientists established it as another definition of a polytropic change of state.

Thus, we face now two definitions of a polytropic change of state, which are theoretically identical for ideal gases but different for real gases and vapors. In educational context, this is disturbing and forcing to a logical detour. We trace the historic roots and show that the initial incremental definition is the physically healthier one. Recursive integration allows direct application to turbomachinery with any finite pressure ratio and to any real fluid.
Multi-Parameter Optimization to Improve the Erosion Resistance of Coating by FE Simulation
Authors: Li Fang , Wang Shunsen , Cai Liuxi , Feng Zhenping
Published: September 2021

Finite element method (FEM) was used to study the stress peak of stress S11 (Radial stress component in X-axis) on the steam turbine blade surface of four typical erosion-resistant coatings (Fe2B, CrN, Cr3C2-NiCr and Al2O3-13%TiO2). The effect of four parameters, such as impact velocity, coating thickness, Young’s modulus and Poisson’s ratio on the stress peak of stress S11 were analyzed. Results show that: the position of tensile stress peak and compressive stress peak of stress S11 are far away from the impact center point with the increase of impact velocity. When coating thickness is equal to or greater than 10μm, the magnitude of tensile stress peak of stress S11 on the four coating surfaces does not change with the coating thickness at different impact velocities. When coating thickness is equal to or greater than 2μm, the magnitude of tensile stress peak of stress S11 of four coatings show a trend of increasing first and then decreasing with the increase of Young’s modulus. Meanwhile, the larger the Poisson’s ratio, the smaller the tensile stress peak of stress S11. After optimization, When coating thickness is 2μm, Poisson’s ratio is 0.35 and Young’s modulus is 800 GPa, the Fe2B coating has the strongest erosion resistance under the same impact conditions, followed by Cr3C2-NiCr, CrN, and the Al2O3-13%TiO2 coating, Al2O3-13%TiO2 coating has the worst erosion resistance.
Centrifugal Compressor Stage Efficiency and Rotor Stiffness Augmentation via Artificial Neural Networks
Authors: Agnolucci Andrea , Marconcini Michele , Arnone Andrea , Toni Lorenzo , Grimaldi Angelo , Giachi Marco
Published: September 2021

Centrifugal compressor stages with high rotor stiffness (i.e. impeller hub-to-outer-diameter ratio) may represent a crucial element to cope with tight rotordynamic requirements and constraints that are needed for certain applications. On the other hand, high-stiffness has a detrimental effect on the aerodynamic performance. Thus, an accurate design and optimization are required to minimize the performance gap with respect to low-stiffness stages. This paper shows a redesign and optimization procedure of a centrifugal compressor stage aimed at increasing the impeller stiffness while keeping high aerodynamic performance. Two different optimization steps are employed to consider a wide design space while keeping the computational cost as low as possible. At first the attention is focused on the impeller only, then the diffuser and the return channel are taken into account. The multi-objective and multi-operating point optimization makes use of artificial neural networks (ANNs) as a surrogate model to obtain the response surfaces. RANS calculations are carried out using the TRAF code and are employed to create the training dataset. Once the ANN has been trained, an optimization strategy is used to find the constrained optimum geometries for the impeller and the static components. The optimized high-stiffness stage is finally compared to the low-stiffness one to assess its applicability.
Dynamical Characterization of Thermoacoustic Oscillations in a Hydrogen-Enriched Partially Premixed Swirl-Stabilized Methane/Air Combustor
Authors: Kushwaha Abhishek , Kasthuri Praveen , Pawar Samadhan A. , Sujith R. I. , Chterev Ianko , Boxx Isaac
Published: September 2021

In this study, we systematically analyze the effects of hydrogen enrichment in the well-known PRECCINSTA burner, a partially premixed swirl-stabilized methane/air combustor. Keeping the equivalence ratio and thermal power constant, we vary the hydrogen percentage in the fuel. Successive increments in hydrogen fuel fraction increase the adiabatic flame temperature and also shift the dominant frequencies of acoustic pressure fluctuations to higher values. Under hydrogen enrichment, we observe the emergence of periodicity in the combustor resulting from the interaction between acoustic modes. As a result of the interaction between these modes, the combustor exhibits a variety of dynamical states, including period-1 limit cycle oscillations (LCO), period-2 LCO, chaotic oscillations, and intermittency. The flame and flow behavior is found to be significantly different for each dynamical state. Analyzing the coupled behavior of the acoustic pressure and the heat release rate oscillations during the states of thermoacoustic instability, we report the occurrence of 2:1 frequency-locking during period-2 LCO, where two cycles of acoustic pressure lock with one cycle of the heat release rate. During period-1 LCO, we notice 1:1 frequency-locking, where both acoustic pressure and heat release rate repeat their behavior in every cycle.
Compressor Maps and Coupling: Symmetry, Paradox, and Clarity
Authors: Iwrey Benjamin
Published: September 2021

The most common compressor map framework, referred to here as the β-framework, will be shown to suffer from limitations that grow more troublesome in the multiple-map environment.

When maps are coupled in series in the β-framework, it is very common to find operating points that are physically unrealizable, but these cannot generally be avoided without first generating them. A feasible situation is described in which the β-framework leads to an apparent physical paradox.

In the proposed S-framework, the map itself is recast in terms of independent variables (corrected speed and exit corrected flow) and dependent variables (inlet corrected flow and temperature ratio). The propagation of information in map coupling is split into an upstream-marching corrected flow ‘flux’ and a downstream-marching temperature ‘flux’. Finding the equilibrium operating point requires only finding a simple intersection between curves.

The S-framework is then developed further into a more compact S’-framework that exhibits a natural set of qualitative symmetries. The S- and S’-frameworks are shown to simplify compressor map expression, resolve the problems shown with the β-framework, and aid intuition with regard to off-design phenomena. The resolution of the paradox using the S’-framework is a new description of multistage compressor performance hysteresis.
Development of Turbulent Quantities Inside an Axial Turbine Vane
Authors: Behre Stephan , Kožulović Dragan , Hösgen Christian , Jeschke Peter
Published: September 2021

The paper presents experimental and numerical investigations of the three components of turbulent kinetic energy and its development upstream and downstream of the first vane of 1.5 stage axial flow turbine. The experimental data has been recorded using a miniature hot wire probe, equipped with three 9μm platinized tungsten wires, allowing the determination of the kinetic energy in all three spatial directions. By means of turbulent grids, a total of three different inlet turbulence levels, varying from 0.4 to 4.5%, was created. Extensive field traverses up- and downstream of the first stator have been conducted, covering more than one stator pitch and including both the free stream and the wake. For one inlet condition, a total of three axial positions between the stator and the rotor have been measured to evaluate the development of the composition of the turbulence. The type of turbulence is visualized by making use of the barycentric color map. Detailed investigations of all three fluctuation components reveal that, depending on the anisotropy level and the distribution of energy along the three spatial directions at the stator’s inlet, the velocity gradients within the first stator either promote a production or destruction of turbulent kinetic energy. As a consequence, the distribution of turbulent energy along the three spatial directions is at the stator’s outlet almost identical for the three configurations. Finally, the measurements with focus on the turbulence composition are compared to unsteady CFD simulations using, the, in industrial application, most commonly applied k-w turbulence model. In addition, an Explicit Algebraic Reynolds Stress Model (EARSM) is also applied and compared to numerical and experimental data. However, the paper is focused on the interpretation of the experimental data.
Testing and Acceptance of Semi-Machined Turbine Rotor Forging Elements
Authors: Ingistov Steve , Nagy Douglas
Published: September 2021

Turbine wheels are critical elements and the integrity of their forgings is extremely important. The procurement of wheel forgings utilized oversized outside diameters in order to provide ample amount of material from which test material was cut out. Test specimens were produced in accordance with relevant ASTM standards. Test specimens were divided into three groups; tension, impact and hardness / metallography. Tension and impact tests at sub-zero, room and elevated temperatures were conducted in presence of owner’s inspectors at an independent certified laboratory. Once all specimens passed the tests, the semi-machined forgings were released to the machining facility. Machined forgings were then sent for over-speed tests at sub-zero and elevated temperatures. Over-speed testing under sub-zero temperature was the ultimate test of the forgings. Over-speed testing of the forgings under elevated temperatures served to minimize residual tensile stresses at the bore of the wheel and convert them to beneficial compressive stresses. The above described tests of turbine Elements forging are critical when the owner selects third party producers to reverse engineer and manufacture these elements. This paper details the selection of the tests, the execution of the owner’s acceptance testing program, especially the over-speed tests, and how this helps to ensure the high integrity of critical rotating elements for a mid-size heavy industrial frame gas turbine.
High-Temperature Ignition Kinetics of Gas Turbine Lubricating Oils
Authors: Cooper Sean P. , Petersen Eric L.
Published: September 2021

Lubricant ignition is a highly undesirable event in any mechanical system, and surprisingly minimal work has been conducted to investigate the auto-ignition properties of gas turbine lubricants. To this end, using a recently established spray injection scheme in a shock tube, two gas turbine lubricants (Mobil DTE 732 and Lubricant A from Cooper et al. 2020) were subjected to high-temperature, post-reflected-shock conditions, and OH* chemiluminescence was monitored at the sidewall location of the shock tube to measure ignition delay time (τign). A combination of an extended shock-tube driver and driver-gas tailoring were utilized to observe ignition between 1183 K and 1385 K at near-atmospheric pressures. A clear, two-stage-ignition process was observed for all tests with Mobil DTE 732, and both first and second stage τign are compared. Second stage ignition was found to be more indicative of lubricant ignition and was used to compare τign values with lubricant A. Both lubricants exhibit three ignition regimes: a high-temperature, Arrhenius-like regime (> 1275 K); an intermediate, negative-temperature-coefficient-like regime (1230–1275 K); and a low-temperature ignition regime (< 1230 K). Similar τign behavior in the high-temperature regime was seen for both lubricants, and a regression analysis using τign data from both lubricants in this region produced the Arrhenius expression τign(μs) = 4.4 × 10−14exp(96.7(kcal/mol)/RT). While lubricant A was found to be less reactive in the intermediate-temperature regime, Mobil DTE 732 was less reactive in the low-temperature regime. As the low-temperature regime is more relevant to gas turbine conditions, Mobil DTE 732 is considered more desirable for system implementation. Chemical kinetic modeling was also performed using n-hexadecane models (a lubricant surrogate suggested in the literature). The current models are unable to reproduce the three regimes observed and predict activation energies much lower than those observed in the high-temperature regime, suggesting n-hexadecane is a poor surrogate for lubricant ignition. Additionally, experiments were conducted with Jet-A for temperatures between 1145 and 1419 K around 1 atm. Good agreement is seen with both literature data and model predictions, anchoring the experiment with previously established τign measurement methods and calculations. A linear regression analysis of the Jet-A data produced the Arrhenius expression: τign(μs) = 6.39 × 10−5exp(41.4(kcal/mol)/RT).
Multi-Parameter Prediction for Steam Turbine Based on Real-Time Data Using Deep Learning Approaches
Authors: Sun Lei , Liu Tianyuan , Xie Yonghui , Xia Xinlei
Published: September 2021

Accurate and real-time parameters forecasting is of great importance to the turbine control and predictive maintenance which can help the improvement of power system. In this study, deep-learning models including recurrent neural network (RNN) and convolutional neural network (CNN) for multi-parameter prediction are proposed, and are applied to predict real-time parameters of steam turbine based on data from a power plant. Firstly, the prediction results of RNN and CNN models are compared by the overall performance. The two models show good performance on forecasting of six state parameters while RNN performs better. Moreover, the detailed performance on a certain day show that the relative error of two models are both less than 2%. Finally, the influence of model designs including loss function, training size and input time-steps on the performance of RNN model are also explored. The effects of the above parameters on the prediction performance, training and prediction time of the models are studied. The results can provide a reference for model deployment in the power plant. It is convinced that the proposed method has a high potential for dynamic process prediction in actual industrial scenarios through the above research.
Acoustic-Convective Interference In Transfer Functions of Methane/Hydrogen and Pure Hydrogen Flames
Authors: Æsøy Eirik , Aguilar José G. , Bothien Mirko R. , Worth Nicholas A. , Dawson James R.
Published: September 2021

We investigate the occurrence and source of modulations in the gain and phase of flame transfer functions (FTF) measured in perfectly premixed, bluff body stabilised CH4/H2 and pure H2 flames. The modulations are shown to be caused by flow disturbances originating from the upstream geometry, in particular the grub screws used to centre the bluffbody, indicative of a more generalised phenomenon of convective wave propagation. Velocity measurements are performed at various locations around the injector dump plane, inside the injector pipe, and in the wake of the bluffbody to provide detailed insight into the flow. Peaks corresponding to natural shedding frequencies of the grub screws appear in the unforced velocity spectra and it is found that the magnitude of these convective modes depends on their location. Flame imaging and PIV measurements show that these disturbances do not show up in the mean velocity and flame shape which appear approximately axisymmetric. However, the urms and vrms fields capture a strong asymmetry due to convective disturbances. To further quantify the role of these convective disturbances, hydrodynamic transfer functions are constructed from the forced cold flow, and similar modulations observed in the FTFs are found. A strong correlation is obtained between the two transfer functions, subsequently, the modulations are shown to be centered on the vortex shedding frequency corresponding to the first convective mode. The reason behind the excitation of the first mode is due to a condition that states that for acoustic-convective interaction to be possible, the shedding (convective) frequency needs to be lower than the cut-off frequency of the flame response. This condition is shown to be more relevant for hydrogen flames compared to methane flames due to their shorter flame lengths and thus increased cut-off frequency.
A Novel Deep Learning Model for the Flow Field Reconstruction of An Oscillating Airfoil
Authors: Li Yunzhu , Liu Tianyuan , You Jiarui , Xie Yonghui
Published: September 2021

In this paper, a novel model is presented for reconstructing unsteady periodic fields of velocity vector and pressure scalar over an oscillating foil. This data-driven method based on convolutional neural network can be utilized to accomplish two objections: fields reconstruction from limited measurements and transient aerodynamic characteristics prediction. The verification results of an oscillating foil under low Reynolds number show that this method can accurately reconstruct all the fields only by limited pressure information at probes on the foil surface. The evaluation on aerodynamic characteristics prediction illustrates that our model outperforms four classical machine learning methods. Meanwhile, a well-trained CNN model can almost achieve real-time flow field prediction by leveraging the GPU acceleration. Finally, the exploration of the robustness for the CNN model is conducted on several aspects, including training size, probe layouts, probe numbers and measurement noises.
Reaction Model Development of Selected Aromatics as Relevant Molecules of a Kerosene Surrogate – The Importance of M-Xylene Within the Combustion of 1,3,5-Trimethylbenzene
Authors: Ramirez Hernandez Astrid , Kathrotia Trupti , Methling Torsten , Braun-Unkhoff Marina , Riedel Uwe
Published: September 2021

The development of advanced reaction models to predict pollutant emissions in aero-engine combustors usually relies on surrogate formulations of a specific jet fuel for mimicking its chemical composition. 1,3,5-trimethylbenzene is one of the suitable components to represent aromatics species in those surrogates. However, a comprehensive reaction model for 1,3,5-trimethylbenzene combustion requires a mechanism to describe the m-xylene oxidation.

In this work, the development of a chemical kinetic mechanism for describing the m-xylene combustion in a wide parameter range (i.e. temperature, pressure, and fuel equivalence ratios) is presented. The m-xylene reaction submodel was developed based on existing reaction mechanisms of similar species such as toluene and reaction pathways adapted from literature. The sub-model was integrated into an existing detailed mechanism that contains the kinetics of a wide range of n-paraffins, iso-paraffins, cyclo-paraffins, and aromatics.

Simulation results for m-xylene were validated against experimental data available in literature. Results show that the presented m-xylene mechanism correctly predicts ignition delay times at different pressures and temperatures as well as laminar burning velocities at atmospheric pressure and various fuel equivalence ratios. At high pressure, some deviations of the calculated laminar burning velocity and the measured values are obtained at stoichiometric to rich equivalence ratios. Additionally, the model predicts reasonably well concentration profiles of major and intermediate species at different temperatures and atmospheric pressure.
Grid Plate Flame Stabilizer for High Intensity Gas Turbine Combustion: The Influence of the Method of Fuel Injection on Mixing, Flame Development and NOx Emissions
Authors: Quiñonez Arce José Ramón , Andrews Gordon E. , Burns Alan D. , Al-Dabbagh Naman
Published: September 2021

Grid plate flame stabilizers for low NOx emissions have renewed interest in recent years due to their use in low NOx hydrogen gas turbine combustors. For non-premixed grid plate combustion, the difference in flame stabilizer design is in how the grid plate air flow is fueled. In the present work a simple four hole grid plate is investigated using CFD with three methods of fueling the air holes: radially inward fuel injection using 8 fuel nozzles per air hole (Grid Mix, GM 1 and Micromix); central fuel injection (FLOX method); and through a fuel annulus around each air hole (GM2). ANSYS FLUENT CFD predictions for GM2 are compared with axial gas composition traverses inside the combustor and with the mean combustor exit plane emissions. The three methods of fuel injection are also compared using isothermal CFD to determine which of the three methods offer the best mixing quality, which controls the relative NOx emissions. The predictions were for an equivalence ratio of 0.624 for the combustion stage and 0.5 for the isothermal study, using industrial propane. CFD modelling used RANS simulation with Realizable k-epsilon turbulence model, non-premixed combustion with the Steady Laminar Flamelet model. The temperature and mixing profiles obtained for GM2 were in reasonable agreement with the experiments and the other two fuel injection methods were then compared with GM2.
Development of a 25 MWth Flameless Pressurized Oxy-Combustion Pilot
Authors: Schmitt Joshua , Malavasi Massimo
Published: September 2021

The Flameless Pressurized Oxy-Combustion (FPO) cycle, a novel flexible fuel technology, is being developed into a large pilot. This effort seeks to complete the preliminary engineering and planning of a 25 MWth Pilot Plant that will demonstrate the technology for scale-up to a commercial unit. The technology, pioneered by ITEA at the 5 MWth scale, must be brought to a higher technology readiness level (TRL) to be viable at the commercial scale.

The 25 MWth pilot cycle was optimized for cost and technology development and demonstration. Preliminary drawings, layouts, and plans were defined. Process flow diagrams were used to describe the pilot configuration in greater detail. A heat and mass balance with stream data was created. A master equipment list specified the operating conditions for major pieces of equipment within the pilot using this heat and mass balance.

The 25 MWth FPO pilot is assessed for environmental performance. A test campaign is developed to assess the type of test and number of hours required for pilot demonstration. The environmental performance is compared against projected performance at the commercial scale.

This project builds upon extensive evaluation of the techno-economic performance of the FPO technology already performed by ITEA. This includes system improvements, such as the addition of a turbo-expander to the flue gas stream. Some of the performance-enhancing components are not as well defined as others. The primary goal of this effort was to bring all of the core cycle components to the same level of design maturity.

A techno-economic assessment (TEA) evaluated the FPO technology at the commercial scale in comparison to the NETL baseline cases. The reference plants were used in combination with proprietary equipment estimates to build a plant capital cost and cost of electricity evaluation. FPO performed better than the sub-bituminous post-combustion capture cases. Further preliminary estimates of improvements to the FPO cycle show even further gains when compared to conventional carbon capture methods.
Experimental Investigation of a High Velocity Gaseous Jet Injection Into an Oscillating Crossflow
Authors: Song Jinkwan , Wilson Johnathan , Lee Jong Guen
Published: September 2021

This paper presents the experimental results of a gaseous jet injected into an oscillating-air crossflow. The jet to crossflow momentum flux ratios are chosen as 19, 30 and 58, and the mean air crossflow velocities are chosen as 10m/s, 25 m/s, and 60 m/s. The crossflow is modulated at frequencies up to 280 Hz with a maximum crossflow velocity fluctuation of 30% of its mean velocity. Acetone planar laser-induced fluorescence is used to record the instantaneous jet concentration field. Three distinct regions are observed near the injection location (x/d < 18); the jet core, the fast bending zone, and the fully developed plume zone. The location of the end of potential core can be determined primarily by the momentum flux ratio. Based on observations of these three regions, a set of correlations for the trajectory of maximum jet concentration is proposed for the potential core region and for the fully developed plume zone. The potential core responds quasi-steadily to the crossflow oscillation and the fluctuation of penetration of the potential core zone linearly increases with respect to the crossflow velocity fluctuation level. The jet penetration under oscillating crossflow is slightly lower than that under steady crossflow, especially when the mean crossflow velocity is low (10–25 m/s). However, the differences of trajectories between the oscillating and the steady crossflow cases become almost negligible as the mean crossflow velocity increases further. The axial decay of jet concentration under oscillating crossflow occurs at faster rate than that under steady crossflow, indicating that the oscillating air crossflow enhances the mixing between the jet and the crossflow. The vertical jet concentration profile at different axial location confirms that the main effect of crossflow modulation is enhanced mixing of jet with crossflow. However, no noticeable effect of modulation frequency of crossflow on the jet penetration is found.
The Development of Turboexpander-Generators for Gas Pressure Letdown Part I: Design and Analysis
Authors: Khatri Rasish , Liu Jeremy , Sarhan Freddie , Najeeb Ovais , Kajita Hiroshi , Kozuka Mitsuru
Published: September 2021

This paper describes the design and development of an innovative 280 kW and a 125 kW Turboexpander Generator (TEG) for natural gas pressure letdown (PLD) applications. The flange-to-flange TEG is supported by active magnetic bearings (AMB) and uses an advanced thrust balancing scheme to minimize the net load on the thrust bearing. The machine designs for the two TEG frame sizes are very similar to maintain commonality between parts. A review of the high-speed generator (HSG) and AMB design is provided. A complete AMB closed-loop dynamics study is presented, including a comprehensive rotordynamics and controls analysis. The touchdown bearing design is shown and discussed, and design details of the touchdown bearing resilient mount are presented. The touchdown bearings are given resilience with a tolerance ring. A detailed simulation of a rotor touchdown event at full speed is shown. The magnetic bearing controller (MBC) and variable speed drive (VSD) are located approximately 35 m from the TEG, exposed to the outside environment, and are not required to be explosion-proof. The prototype TEGs are intended to be manufactured and tested in Q1 2021. They will be commissioned, and field tested in Q2 2021. A follow-up paper detailing the mechanical testing and field testing of the units will follow in 2022.
Optimization of an Oil Film Journal Bearing for Temperature Reduction
Authors: Chatterton Steven , Pennacchi Paolo , Vania Andrea , Dang Phuoc Vinh
Published: September 2021

Rotating machines are generally equipped with tilting-pad journal bearings. In general, during the design phase, the aspects that are most taken into account are the dynamic performances in terms of stiffness and damping and the minimum thickness of the oil film to avoid mixed lubrication conditions that can lead to white metal wear phenomena. The thermal aspect, on the other hand, is often underestimated and can be critical for machines operating at high speed and high load. Thermal heating is caused by shear stresses in the lubricating film. In general, an increase in lubricant temperature corresponds to a reduction in oil viscosity followed by a reduction in lubricant film thickness. This has a beneficial effect on bearing stiffness. On the contrary, a high temperature in the oil film is detrimental to the mechanical characteristics of the white metal which is characterized by a low melting temperature and subject to thermal creep phenomena.

The article analyzes, by means of numerical simulations, the influence of the bearing geometry on the thermal behavior of the bearing. The bearing geometry will then be optimized to reduce the maximum temperature in the bearing.
Off-Design of a Pumped Thermal Energy Storage Based on Closed Brayton Cycles
Authors: Frate Guido Francesco , Paternostro Luigia , Ferrari Lorenzo , Desideri Umberto
Published: September 2021

The growth of renewable energy source requires reliable, durable and cheap storage technologies. In this field, the Pumped Thermal Energy Storage (PTES), is drawing some interest as it appears not to be affected by geographical limitations and use very cheap materials. PTES is less efficient than pumped hydro and batteries, but it could achieve satisfactory efficiencies, show better economic performance and be characterized by negligible environmental impacts. A PTES stores the electric energy as thermal exergy in solid packed beds, by operating two closed Brayton cycles, one for charging and the other one for discharging. Although PTES thermodynamical behavior is well understood, the interaction between the components is rarely investigated. This study investigates the impact of packed-bed behavior on turbomachines operating conditions. In this way, PTES off-design and part-load performance are estimated. A control strategy especially suited for closed Brayton cycles, i.e. the inventory control, is used to control the system. As it resulted, PTES is characterized by an excellent part-load performance, which might be a significant advantage over the competing technologies. However, the off-design operation induced by the packed-bed thermal behavior might significantly reduce the system performance and, in particular, that of the discharge phase.
Proper Orthogonal Decomposition Analysis and Braking Control on Hydrodynamic Retarders by Bionic Iris Effective Diameter Regulation
Authors: Chen Xiuqi , Wei Wei , Liu Tangzhu , Xie Wenhao , Li Yifei , Zhuo Wang , Ruolin Wang , Yan Qindong
Published: September 2021

AIris, a flat circular membrane in the middle layer of human eyeball, is controlled by sympathetic nerve and can automatically adjust pupil size according to light intensity to limit the amount of light entering the eyeball. This paper attempts to introduce the artificial iris diameter changing mechanism into hydrodynamic machinery, that is, to control the hydrodynamic retarder without filling fluid by changing the inner diameter of iris and changing the flow path of retarder. Through the decomposition and reconstruction of the intrinsic flow field, the flow field characteristics of the iris retarder are deeply understood, and the fast prediction of the braking torque is realized. At the same time, the close-loop controller is designed to control the iris opening that realizing the adaptive adjustment of the output torque of the retarder, thus overcoming the difficulty on-line observation of actual filling rate of oil problem and the inaccurate tracking of braking torque on traditional hydrodynamic retarder with filling rate control. Our work prove that the nonlinear controller can achieve fast and accurate torque closed-loop torque control in various braking conditions compared with the hydrodynamic rate control retarder, and the potential of iris mechanism for adaptive control of hydrodynamic retarder is verified.
Control Strategy Development for Optimized Operational Flexibility From Humidified Micro Gas Turbine: Saturation Tower Performance Assessment
Authors: De Paepe Ward , Pappa Alessio , Coppitters Diederik , Montero Carrero Marina , Tsirikoglou Panagiotis , Contino Francesco
Published: September 2021

Waste heat recovery through cycle humidification is considered as an effective tool to increase the operational flexibility of micro Gas Turbines (mGTs) in cogeneration in a Decentralized Energy System (DES) context. Indeed, during periods with low heat demand, the excess thermal power can be reintroduced in the cycle under the form of heated water/steam, leading to improved electrical performance. The micro Humid Air Turbine (mHAT) has been proven to be the most effective route for cycle humidification; however, so far, all research efforts focused on optimizing the mHAT performance at nominal electrical load, and no thermal load. Nevertheless, in a DES context, the thermal and electrical load of the mGT needs to be changed depending on the demand, requiring both optimal nominal and part load performances. To address this need, in this paper, we present the first step towards the development of a control strategy for a Turbec T100 mGT-mHAT test rig. First, using experimental data, the global performance, depending on the operating point as well as the humidity level, has been assessed. Second, the performance of the saturation tower, i.e. the degree of saturation (relative humidity) of the working fluid leaving this saturator, is analyzed to assess the optimal water injection system control parameter settings. Results show that optimal mHAT performance can only be obtained when the working fluid leaving the saturation tower is fully saturated, but does not contain a remaining liquid fraction. Under these conditions, a maximal amount of waste heat is transferred from the water to the mGT working fluid in the saturation tower. From these data, some general observations can be made to optimize the performance; being maximizing injection pressure and aiming for a water flow rate of ≈5 m3/h. However, having a specific control matrix, that allows setting the saturation tower control parameters for any set of operational setpoint and the inlet conditions would be of more interest. Therefore, future work involves the development of a control matrix, using advanced data post-processing for noise reduction and accuracy improvement, as well as an experimental validation of this methodology on the actual test rig.
Gaussian Stochastic Process Modeling of Blend Repaired Airfoil Modal Response Using Reduced Basis Mode Shape Approach
Authors: Brown Jeffrey M. , Kaszynski Alex A. , Gillaugh Daniel L. , Carper Emily B. , Beck Joseph A.
Published: September 2021

A machine learning (ML) approach is developed to predict the effect of blend repairs on airfoil frequency, modal assurance criterion (MAC), and modal displacement vectors. The method is demonstrated on a transonic research rig compressor rotor airfoil. A parametric definition of blend geometry is developed and shown to be capable of encompassing a large range of blend geometry. This blend repair geometry is used to modify the airfoil surface definition and a mesh morphing process transforms the nominal finite element model (FEM) to the repaired configuration. A multi-level full factorial sampling of the blend repair design space provides training data to a Guassian stochastic process (GSP) regressor. The frequency and MAC results create a vector of training data for GSP calibration, but the airfoil mode shapes require further mathematical manipulation to avoid creating GSP models for each nodal displacement. This paper develops a method to significantly reduce blended airfoil mode shape emulation cost by transforming the mode shape training data into a reduced basis space using principal component analysis (PCA). The coefficients of this reduced basis are used to train a GSP that can then predict the values for new blended airfoils. The emulated coefficients are used with the reduced basis vectors in a reconstruction of blended airfoil mode shape. Validation data is computed at a full-factorial design that maximizes the distance from training points. It is found that large variations in modal properties from large blend repairs can be accurately emulated with a reasonable number of training points. The reduced basis approach of mode shape variation is shown to more accurately predict MAC variation when compared to direct MAC emulation. The added benefit of having the full modal displacement field also allows determination of other influences such as tip-timing limits and modal force values.
Investigation on the Effects of Field Emission Plasma on the Performance of a Micro-Combustor
Authors: De Giorgi Maria Grazia , Cinieri Giacomo , Fontanarosa Donato , Ficarella Antonio
Published: September 2021

This work provides a numerical investigation of the effects of micro field emission dielectric barrier discharge (FE-DBD) plasma actuation on the performance of a micro-combustion system composed of two straights perpendicular microchannels for propellant injection followed by a rectangular micro-combustion chamber in a T-shaped planar configuration.

Concerning the modeling, a novel two-step approach has been developed. The first step consisted in solving the chemistry of a sinusoidal plasma discharge in a zero-dimensional modeling. To this purpose, the collisional processes involved in the plasma discharge have been solved using a Boltzmann-equation approach, which permits to predict the electron impact reactions based on a two-temperature model. Furthermore, the zero-dimensional hypothesis used for computations assumed uniform plasma during the overall discharge duration. Concerning the plasma chemistry, excitation and de-excitation processes, electron-ion recombination reactions, attachment and detachment for electrons and neutral species have been considered in order to improve the prediction accuracy.

This step allowed to quantify the body force, the heat source and the propellant composition modification induced by sinusoidal plasma actuation operating at 10 MHz of repetition rate, atmospheric pressure and 300 K temperature. Therefore, the predicted cycle averaged plasma effects have been used in 2D steady-state simulations of the laminar, compressible, reactive micro flow, based on a continuum Navier-Stokes approach. SIMPLE pressure-velocity coupling scheme was chosen with a second order pressure spatial discretization. A second-order upwind scheme was applied. The hydrogen-oxygen combustion has been modeled using the Connaire mechanism. The comparison between the results of the reference case without plasma actuation, and those retrieved in presence of plasma actuation at different supplied voltages, highlighted the performance enhancement due to plasma discharge.
Compressor Map Corrections for Highly Non-Linear Fluid Properties
Authors: Anderson Mark
Published: September 2021

Turbomachinery systems are often subject to variations in ambient conditions and applied loads in operation. Standard maps (perhaps the most common being pressure ratio verses mass flow for compressors) are usually presented in terms of fixed inflow conditions. To account for changes in performance due to varying inlet conditions, compressors maps are often presented in standardized form where the mass flow and rotational speeds are normalized as a function of the reference condition total pressure and temperature. These methods are very widely used, particularly in the turbo charger industry. With these normalized maps, the actual performance of a compressor in a given environment can be deduced simply and easily with very reasonable accuracy in most cases.

The underlaying assumption of this conventional normalization process is that the fluid behaves as a perfect gas. While this is usually sufficient for air compressors, the method is not viable where the fluid properties are not near perfect gas conditions, which is certainly the case for supercritical applications. The highly variable fluid properties near the critical point, and the challenges they present in design, have been well documented in the literature. The two most critical properties to consider in the design process are the density and the speed of sound. The density determines the volumetric flow for a given mass flow and this in turn determines the incidence angle, a primary driver of performance. The speed of sound directly affects the range of the compressor via choking. Choking range can be further complicated by the fact that under certain conditions, the choked state can be reached at Mach numbers less than one. While rare, this situation can occur when the inflow conditions are found close to the liquid side of the saturation dome.

To account for these effects, a new method is proposed to generate normalized maps of performance that can be used to determine actual performance of a wide range of inlet conditions for highly non-linear thermodynamic properties. Although not as simple as the conventional perfect gas method that can be applied in a “back-of-the-envelope” style, the new method can be applied very rapidly using a spreadsheet-based method directly calling high fidelity NIST thermodynamic models. The end result of this tool is that a compressor map that has been painstakingly generated with testing or CFD can be applied to any inlet condition and the range and performance predicted very rapidly with high accuracy.
Design of 1 MW Direct-Fired Combustor for an sCO2 Power Cycle
Authors: Delimont Jacob , White Steve , Andrews Nathan
Published: September 2021

Direct-fired super-critical carbon dioxide (sCO2) power cycles, are a potential method for efficiently capturing nearly all of the CO2 emissions from burning fossil fuels. Direct-fired sCO2 cycles require a very high degree of recuperation, which in turn means that the inlet temperature to the combustor is significantly higher than would typically be seen in a similar gas turbine combustors. Previous efforts have shown that combustor inlet temperatures of around 700 °C are to be expected for a cycle with around 1200 °C combustor exit temperatures [1]. This high inlet temperature means that bypass gasses are extremely hot, which poses some difficulties for the design of the combustion system, especially thermal management of the combustor liner and injectors in the 200 bar sCO2 environment.

The project team led by Southwest Research Institute (SwRI) is in the process of building a 1 MW scale direct-fired combustor. This paper will detail some of the design challenges and obstacles associated with designing a direct-fired sCO2 combustor. These obstacles include thermal management of fuel and oxygen streams, oxygen safety, and combustor cooling. This paper will focus on many of the design questions necessary for the design of a direct-fired sCO2 combustor. This work presents computational modeling details of the actual 1 MW geometry currently being built.