bluuebunny/crossref_metadata_2025 huggingface dataset:
Matching of an Overhung Volute to a Centrifugal Compressor at Varied Operating Conditions
Authors: Thiyagarajan Janakiraman , Fredriksson Carl , Anton Nicholas , Genrup Magnus , Fridh Jens
Published: August 2024

Centrifugal compressors are widely used in turbocharged powertrains for Heavy-Duty applications. The volute of the centrifugal compressors is generally of the overhung type. The design of volutes is often neglected, and the shape of the volute is dictated by the packaging requirements of the engine. However, with the advent of Hydrogen-based propulsion systems, the efficiency of all the components of the centrifugal compressor stage is important in order to achieve a higher efficiency at the stage level and also to understand the contribution of the volute towards stage performance. Measuring static pressure and total pressure inside and at the exit of the volute is a challenging task due to the complex nature of the flow inside an overhung volute. This study involves an experimental campaign to quantify the volute performance using static and total pressure measurements at different locations on the volute.

The total pressure measurements were carried out using calibrated rotating Kiel probes to quantify the flow angles and the corresponding total pressure values. This enabled the measurement of the maximum total pressure value at a location for a given operating condition. These total pressures and static pressures were measured for a variety of operating conditions across the entire compressor map at the inlet and exit of the volute. In addition, two new parameters were introduced, a fictive area ratio and uniformity index that could be used to quantify volute performance and also help match the volute to a given diffuser and impeller configuration.
Prediction of Lean Blowout Limits for Bluff Body Stabilized Flame Using a Gradient Method of Damköhler Number and Temperature
Authors: Jia Xin , Hu Bin , Sui Xiuming , Zeng Wen , Yu Xin , Zhao Qingjun
Published: August 2024

The prediction of the lean blowout for bluff body stabilized flame is of great significance for the design of a combustion chamber. In this paper, a lean blowout experiment was conducted on the bluff body stabilizer, and the CH* chemiluminescence was used to illustrate the impact of different equivalence ratios on the flame structure. The realizable k-ε turbulence model and flamelet generated manifolds combustion model were used to simulate the non-premixed bluff body stabilized flame. The characteristic region was determined based on the CO mass fraction, and the relative change rate of the average Damköhler number and temperature relative to the global equivalence ratio within the characteristic region was used as indicators for predicting lean blowout. The results show that as the equivalence ratio decreases, the flame intensity in the recirculation zone decreases, however, the flame intensity within the shear layer remains almost constant. When the equivalence ratio decreases to near blowout, there is a significant decrease in the flame intensity within the shear layer. CO is an important product in combustion and is directly related to the amount of heat released by combustion. The variation pattern of the characteristic region determined based on CO mass fraction with equivalence ratio is consistent with the actual flame variation. The relative rate of change of Damköhler number and temperature within the characteristic region is used to predict lean blowout. The lean blowout limits predicted by these two indicators are compared with experimental results and showed good consistency at different airflow rates and temperature. In general, within the range of examined parameters, the lean blowout limits predicted by Damköhler number are more accurate than the one based on temperature.
Large Eddy Simulations of a High-Speed Low-Pressure Turbine Cascade at Subsonic and Transonic Mach Numbers
Authors: Tene Hedje Patrick , Bricteux Laurent , Bechane Yacine , Lavagnoli Sergio
Published: August 2024

High-Speed Low-Pressure Turbines are one key turbomachinery component in ultra-high bypass ratio geared turbofan engines. The High-Speed Low-Pressure Turbine (HS-LPT) typically operates at transonic exit Mach numbers and low Reynolds numbers. These flow regimes are prone to boundary layer instabilities such as separations on the suction side, leading to a significant increase in losses. It is therefore essential to understand the operation of LPTs and, more specifically, the behaviour of the boundary layer on the blades in such environments.

We present a numerical investigation of a high-speed low-Reynolds turbine cascade simulated at nominal and off-design Mach numbers. The study case is the SPLEEN C1 cascade tested in the transonic linear cascade rig S-1/C of the von Karman Institute. The cascade is numerically operated at the nominal test exit Reynolds number Re2,is = 70k, over a range of subsonic and transonic exit Mach numbers: M2,is = 0.70 ; 0.80 ; 0.90 and 0.95. All simulations are performed with the Explicit Compressible Solver of the massively parallel code YALES2, using a Wall Resolved Large-Eddy Simulations (WRLES) approach, and featuring a fourth-order finite volume spatial discretization. This scale-resolving approach allows to capture the turbine flow physics with high accuracy at an acceptable computational cost. The test case offers the possibility to assess the Mach and compressibility effects on the profile aerodynamics of HS-LPT : separation, transition mechanisms, unsteadiness and passage choking as well as trailing edge unsteady flows.

The flow predictions show a substantial agreement with the available high-fidelity experimental data. Furthermore, the calculations suggest that the wake thins, and loss increase with the Mach number. The experiments support this evidence, although discrepancies are observed in peak losses for Mach numbers above 0.70. The root cause is likely found in the laminar inflow used in the LES simulations compared to the free-stream turbulence intensity level of 2.5% of the experimental test case. Compressibility effects are observed. In particular, a weak compression wave stands in the region of the cascade throat for the case M2,is = 0.90, whereas a shock appears for M2,is = 0.95 with the cascade choked. The role of the shock on the separation and transition on the blade suction side is discussed.
The Influence of Inlet Distortion on Combustion Performance in a Recirculation Combustor
Authors: Luo Shaowen , Shi Yunjiao , Zhao Ningbo , Yang Ren , Zheng Hongtao
Published: August 2024

The mismatching phenomenon between compressor and combustor in gas turbines may cause inlet distortion at combustor entrance, which has an influence on combustion performances. An experimental investigation was carried out in the prevent study to reveal the relationship between inlet distortion and combustion performances. During the experimental work, inlet distortions were introduced by locating orifice plates at the combustor inlet, including mid-peak, upper-biased peak, lower-biased peak. The exhaust gas were measured by the outlet thermal-couple and gas analyzer. Results show that the distortion form and operating conditions have a minor impact on combustion efficiency, whereas they significantly affect the total pressure loss coefficient and the outlet temperature distribution factor (OTDF). In particular, under conditions of higher distortion, the total pressure loss coefficient increases significantly. When the inlet non-uniformity increases from 4.15% to 51.37% (upper-biased peak), the total pressure loss coefficient increases by 2.65% (a 63% increase compared to the previous value), and the OTDF increases by 13.3% (a 67.5% increase compared to the previous value). Additionally, the impact of the upper-biased peak distortion on OTDF is greater than that of the lower-biased peak distortion.
Numerical Investigation and Multi-Objective Structure Optimization of Transpiration Cooling on the Leading Edge of Turbine Blade
Authors: Liu Taolue , He Fei , Wu Xiaorong , Zhou Zhizhao , He Yang , Wang Jianhua
Published: August 2024

Transpiration cooling, utilizing the micro-hole channel of the porous matrix, is regarded as highly promising turbine blade cooling applications. This study comprehensively investigates the cooling performance of transpiration cooling on the leading edge of C3X turbine blade. The numerical investigation is conducted by comparing the uniform and gradient porous matrix. Various influence factors such as coolant mass rate, porosity and average pore diameter are taken into discussion. The simulation results suggest that the gradient porous matrix scheme can improve cooling efficiency by altering the permeability distribution and adjusting coolant flow accordingly. Additionally, the average total pressure loss coefficient is primarily influenced by the region directly facing the mainstream and the new structure can also reduce this coefficient. To optimize the transpiration cooling performance with a gradient design, a novel optimization process is proposed, which combines Computational Fluid Dynamics (CFD), Artificial Neural Network (ANN) and Multi-Objective Genetic Algorithm (MOGA). The optimization process is implemented through the coupling simulation of ANSYS FLUENT and MATLAB via Text User Interface (TUI) and User Defined Function (UDF). The configuration parameters of the porous matrix are set as design variables, with the average cooling efficiency and average total pressure loss coefficient serving as optimization objectives. The simulation results demonstrate an improvement in the former (increases by 11.35%) and a reduction in the latter (decreases by 36.23%) respectively compared with the uniform porous matrix. This optimization process provides a straightforward and reliable method for addressing a range of similar structural issues.
Numerical Analysis of Multi-Stage Impingement Cooling Structure: Flow and Heat Transfer Characteristics
Authors: Wang Pengfei , Wang Pei , Liu Jun , Liu Jiajie , Du Qiang , Liu Haoyang , Wang Zhiguo , Wang Haohan
Published: August 2024

Impingement cooling is widely employed for thermal regulation of high-temperature components in gas turbine engines, owing to its high local convective heat transfer coefficients. However, the effectiveness of this method is compromised by the external crossflow caused by spent air from upstream jets, particularly in single-stage narrow channels with significant external crossflow. This study explores the flow and heat transfer characteristics of an innovative multi-stage impingement cooling structure. Our numerical analysis reveals that this multi-stage configuration significantly reduces the adverse effects of external crossflow, while also improving coolant utilization efficiency. Compared to the single-stage configuration, the multi-stage structure achieves higher Nusselt numbers on the target surface with only half the coolant consumption at an equivalent Reynolds number. The analysis indicates that single-stage configuration is inferior in terms of coolant mass flow rate and Nusselt number distribution, especially at minimal jet-to-target distances. In contrast, the multi-stage configuration effectively manages external crossflow, leading to a more uniform distribution of coolant and Nusselt number on the target surface. The superiority of the multi-stage configuration is further evidenced by its overall thermal efficiency, which considers both flow resistance and heat transfer. Moreover, a small transition chamber height in the second-stage can induce strong internal crossflow, potentially affecting optimal impingement cooling performance.
Vibration and Acoustic Emission Assessment of a SiCf/SiC Ceramic Matrix Composite With Damage
Authors: Jeffs Spencer P. , Stephen Jordan , Quiney Zak , García Luna Gonzalo
Published: August 2024

SiCf/SiC Ceramic Matrix Composites (CMCs) offer considerable advantages over existing metallic systems employed in hot section components in the gas turbine engine. However, due to their complex structure there are a number of damage modes that can occur under mechanical loading, such as matrix cracking, interfacial cracking and fibre failure. Therefore, there is a requirement for test methods, that are in-situ and ex-situ, to help understand these damage modes, in terms of how and when they take place and what they mean relative to material condition.

The article investigates the use of vibration testing as a means of condition assessment through analysing the vibration response of undamaged and damaged SiCf/SiC CMC material. Cantilever beam vibration experiments were conducted before and after a series of mechanical loading conditions. Resonant frequency values were extracted using the Fast Fourier Transform (FFT) and compared, revealing a correlation between changes in natural frequency relative to the undamaged material, and the mechanical loading level, thus a correlation with the level of damage in the CMC. In addition, acoustic emission (AE) testing was carried to support the understanding of the damage mechanisms taking place in the CMC. The results reveal that vibration testing could potentially offer an alternate nondestructive evaluation (NDE) technique to assess the condition of CMC material.
Predicting Gas Turbine NOx Emissions With Machine Learning
Authors: Eller Harrison , Singh Sanjana , Soni Sumit
Published: August 2024

Gas Turbine operations result in production of Nitrogen Oxides (NOx) and Carbon Monoxide (CO), both of which are pollutants that are to be strictly monitored and controlled. To control NOx within permissible limits, Combustion Emissions Monitoring System (CEMS) readings are to be continuously monitored and flagged for any anomaly in NOx emissions. This paper covers the method for developing a proof of concept of a Machine Learning (ML) model that predicts NOx from a selected pair of General Electric 7FA (7FA) and Siemens Westinghouse 501F (SW501F) gas turbines that are actively monitored in real time. The Keras library and the open-source machine learning framework TensorFlow are used for constructing, developing, testing, and tuning all respective models in Python. The authors show that working with quantitative, time-series data, a deep neural network (DNN) using a rectified linear unit activation function is deemed the most appropriate for the given issue at hand. Using this framework in conjunction with the domain knowledge from a monitoring and diagnostic team and gas turbine experts, a DNN for each frame type is successfully constructed. The 7FA test site and SW501F test site produced NOx predictions with a mean absolute error of 0.55 and 0.7 ppm respectively, hence demonstrating the capability of a machine learning model to accurately predict NOx emission for any typically trained scenario.
Numerical Study on Unsteady Flow of a Supersonic Partial Admission Impulse Turbine
Authors: Li Tongxi , Wang Jiakang , Wang Zhiheng , Xi Guang
Published: August 2024

Partial admission is an essential method to ensure the effective operation of turbines in various operating conditions. The transition section of partial admission turbines is pivotal in governing the unsteadiness and non-uniformity, yet its flow dynamics remain somewhat elusive. To enhance the comprehension of the flow characteristics within supersonic partial admission impulse (SPAI) turbines, this study employs a three-dimensional unsteady numerical simulation on a singlestage SPAI turbine equipped with four circular nozzles. The findings reveal that shock waves are produced at the leading edge of the admission area, and flow separation occurs twice on the suction surface. In the non-admission area, the fluid is in a turbulent state and predominantly static. Particularly in the transition section, processes of emptying and filling are evident. An intense shock wave forms at the entrance to the channel in the transition section leaving the admission area, as the high- and low-energy fluids mix in the subsequent channels, resulting in significant energy losses. During the rotor rotation, the blades experience fluctuating aerodynamic forces, which are pronounced in the admission area, while negligible in the non-admission area. These forces are mainly dominated by the intake passage frequency and other frequencies associated with nozzle spacing. Phenomena of under-shoot and over-shoot are observed as the blades enter or exit the admission area, potentially impeding turbine performance or providing additional torque.
Workflow for Fast and Efficient Forced Response Analysis of Turbomachinery
Authors: Patil Sunil , Sabatier Laurent , Madden Andrew , Bronson Jeff , Zori Laith
Published: August 2024

The advances in turbomachinery methods over the last decade have led to unsurpassed simulation fidelity. Computational Fluid Dynamics (CFD) methods for turbomachinery, including multistage blade rows, have become reliable and robust. Finite Element Methods (FEM) in the area of mistuning have become established throughout the industry.

However, current day-to-day aerodynamic methodology still relies heavily on simplifications, reduced methods, and low-fidelity analyses. One impediment is the workflow bottlenecks: taking data from one system, transforming it, and using it another.

This paper lays out a streamlined workflow for forced response of bladed turbomachinery components, linking CFD with FEM for tuned or mistuned forced response. At each stage, high fidelity solutions are used eliminating the need for simplifying assumptions and limiting methods. Additionally, manual steps are replaced with automated and verifiable steps. Both the CFD and FEM rely on making use of the cyclic symmetric nature of the solution fields, leading to fast and accurate solutions. Technologies such as phase lag approach on CFD side, and mode superposition on FEA side are explained to speed up overall time to solution significantly.

Lastly, the forced response workflow includes built-in utility to quickly extract the vibrational stresses and strains, especially equivalent (von Mises) and principal values, required for high-cycle fatigue and lifing calculations.

Forced response of the NASA Rotor 67 fan subjected to inlet distortion is used in this work to highlight the streamlined workflow.
Performance Comparison of Gas Turbine Layouts With Pressure Gain Combustion for Propulsion Applications
Authors: Purushothaman Sreenath , Sorce Alessandro , Traverso Alberto , Gaillard Thomas
Published: August 2024

Different pressure gain combustion methods such as Constant Volume Combustion (CVC), Pulse Detonation Combustion (PDC), Rotating Detonation Combustion (RDC) and Oblique Detonation Wave Combustion (ODWC) are being explored for aerospace propulsion applications in recent years. In order to fully utilize the benefits of pressure gain combustion, it is necessary to analyze the propulsion engine from a system level. This includes the study of integrating pressure gain combustor with other components such as compressors and turbines, investigating the effects of combustor and turbine cooling, as well as engine performance under different operating conditions. In this paper, the performance of different engine layouts employing pressure gain combustion is studied. An RDC chamber is chosen as reference combustor technology, interacting dynamically with compressors, turbines, ejectors, and other engine components. All layouts are designed to provide a maximum design thrust of 100 kN, which is typical of a high bypass commercial turbofan engine. The combustor dynamic model is based on theoretical pressure gain combustion maps with a wide operational envelope, while the compressors and turbines are based on actual engine data, scaled to match the combustor operation. The results show the benefits and limitations of using pressure gain combustion in propulsion system in the most promising engine layouts.
Energy and Cost Analysis of Concentrated Solar Thermal Plants Integrated With Latent Heat Thermal Energy Storage for the Decarbonization of Industrial Processes
Authors: Giampietro Davide , Stefanizzi Michele , Fornarelli Francesco , Dambrosio Lorenzo , Nicolini Daniele , Miliozzi Adio , Camporeale Sergio Mario
Published: August 2024

Industrial energy demand in the EU is driven by the thermal energy share, which accounts for the most part of the total energy demand. A large part, about one-third, is at medium temperatures, between 100 and 200 °C, and it is still produced by fossil fuels, mainly natural gas. This energy demand could be met by solar thermal energy by using Concentrated Solar Thermal (CST) technologies, suitably combined with thermal energy storage systems.

This paper presents a study of CST plant composed by Parabolic Trough Collectors (PTC) combined with Latent Heat Thermal Energy Storage (LHTES) system in shell-and-tubes configuration for the supply of heat for industrial processes. Firstly, the criteria adopted for the sizing and the quasi-static simulation of the system are described. Significant attention is given to evaluate the variation of the Solar Fraction (SF) with the typical parameters of thermal storage, such as the maximum capacity and exchange surface, given a specific location and the Solar Multiple (SM). The methodology has been applied to a dairy processing facility within the agri-food sector with a thermal load of 500 kWth. Then, an economic analysis has been carried out by evaluating the impact of the component’s costs, such as the linear parabolic collectors, thermal storage materials and landscape preparation. Finally, the Levelized Cost of Heat (LCOH) has been computed for different thermal storage sizes in order to find the best combination that minimizes it. As a result, despite the overall increase of the SF with the thermal storage capacity, the proposed work shows how the minimum value of the LCOH (7.24 c€/kWh) corresponds to low storage capacity (1 MWh).
Propelling Education: Introducing and Examining the “English-to-Engineering” Multi-Year Undergraduate Research Program
Authors: Martinez Soto Karen , Haldeman Charles , Teolis Samuel , Gray David , Lowe Todd
Published: August 2024

A student-led, industry-affiliated, extracurricular undergraduate program has been developed at Virginia Tech which is entering its third year. The program was developed with an umbrella theme of sustainability in aerospace propulsion under which the original students “auditioning” for the program proposed a range of research topics. The original program structure was focused on addressing some shortfalls observed both by academia and industry relative to traditional undergraduate engineering education over many years. Broadly speaking, these issues can be separated into topics related to encouraging earlier exposure to open ended problems and the ability to practice a wide range of teaming exercises earlier in the student’s career, both of which are of high value to industry. Discussion around these challenges has been ongoing, but often curriculum constraints have made incremental solutions hard to generate. The current incarnation of this program is as an extracurricular activity, focused on student-owned, multi-year projects. At the time of the program creation, it was not clear if such a program would be of interest to the students, or if industry and faculty could provide the required support. Three years into the program it is clear that this approach is widely accepted and valued by all parties, but most fully by the students. The program is addressing part of the needs outlined originally, but as the program enters its next phase, the ability to address the successes and challenges of the current system needs a more formal educational framework. This paper focuses on describing the current program, and some of the limitations that having a multi-year, student-owned project provides in frameworks such as Fink’s Taxonomy of Significant Learning. This is important as the lessons of this experience are considered by other academic institutions with a goal of fully leveraging the student experiences and capabilities provided by this approach. Academic and industry perspectives are critical as the next phase of the program need to generate greater and different industry involvement and fuller integration into the existing curriculum to provide maximum value to the students, faculty, and industry.
Steam Turbine Low Pressure 75in Last Stage Blade for Nuclear Half Speed Applications
Authors: Kostyuchenko Sergey , McBean Ivan , Masserey Pierre-Alain , Casu Christian , Noirot Vivian , Lemaire Julien , Berquier Christophe
Published: August 2024

The impact of global warming is driving the current trend in the power industry to transition away from employing fossil fuels for power production. Nuclear energy has been demonstrated to be a safe, reliable, and dispatchable way of generating either base load power or to balance fluctuations in renewable power. General Electric has further developed its Arabelle steam turbine platform to address the growing demand for nuclear power. This included the development of one of the longest low pressure steam turbine last stage blades, at 75 inches. Due to the sheer size of the turbine components, the development of this turbine posed several challenges, from both mechanical integrity and design perspectives. This paper documents the design development, validation, and manufacturing processes of the low-pressure turbine last stage blade.
Mechanical Behavior of Nozzle Guide Vane Bushing in Absence of Lubrication by Means of Novel Endurance Test Rig
Authors: Bucciarelli Federico , Tomasello Stella Grazia , Bellacci Michelangelo , Checcacci Damaso , Ghiara Antonio , Maestrale Francesco , Manconi Salvatore
Published: August 2024

Nowadays, Variable Guide Vanes such as Inlet Guide Vanes (IGVs) and Nozzle Guide Vane (NGVs) are key components in the design of axial expanders and gas turbines, which are now required to work with an ever-increasing flexibility due to the frequent shutdowns, start-ups and load changes to which they are subject. Such severe service conditions, due to the ever-increasing introduction of the renewable energies in the energy market, are particularly challenging for such components, which were already intrinsic complex in order to obtain higher availability performances. For this reason, a deeper understanding of the mechanical behavior of such components by means of experimental characterizations has become mandatory for the design process, especially when high loads are involved.

Under such premises, the present work, starting from the recently presented novel design of an experimental test rig, aims at showing the results of a testing campaign performed on standard and coated bushing. The test article manufacturing technology selected for the campaign will be presented. Then results of static testing, aimed at measuring friction coefficients of the whole kinematic assembly, will be summarized both at room and operating temperature both for new and worn geometries. Also, the outcomes from accelerated endurance tests, lasting 200h and performed with peak temperature of 525°C in absence of lubrication, will be reported giving insights on the design of these kinematic couples. Inspections of analyzed specimens are also included in the postprocessing. These results are a key element for the improvement of the life prediction of these components enabling progressively more challenging operating conditions for the next generation of expanders.
Impact of Different Equations of State in the Turboexpander Design for Allam Cycle
Authors: Alfarano Emanuela , Michelassi Vittorio , Fantozzi Francesco
Published: August 2024

Clean, affordable, and reliable power generation is at the very center of our present and future needs. While renewable power sources are increasing their penetration in the energy mix, natural gas with carbon capture will still play a key role. Oxyfuel combustion is a promising technology that combines power generation and carbon capture without the need for a dedicated carbon dioxide capture plant. In particular, the Allam cycle employs natural gas oxy-fuel combustion in a supercritical carbon dioxide environment with a turbine expansion. The design process of such a turbo-expander comes with significant challenges due the unique aero-thermal operating conditions. Moreover, the evolving fluid mixture properties are still largely unknown.

The present paper investigates the impact of uncertainties in supercritical carbon dioxide mixtures thermodynamic models on the design and performance of the turboexpander in an oxycombustion power cycle. After providing a review on the current equations of state available for supercritical carbon dioxide mixtures with steam, the paper quantifies the influence of equations of state differences in the turboexpander unit design and operation. The paper also addresses the importance of the equation of state on the Allam cycle thermodynamic model in view of its application to industry relevant sizes.
In-Situ and Ex-Situ Measurement of Stresses in Environmental Barrier Coatings
Authors: Hudyncia Hans , Shi Jun , Li Weizhou , Li Xiaodong
Published: August 2024

Ceramic Matrix Composites (CMCs) offer a step improvement in temperature capability over the current best high temperature super alloys for gas turbine applications. Silicon Carbide (SiC) based CMCs react with water vapor at temperature and therefore need an Environmental Barrier Coating (EBC) for protection against the water vapor attack. EBC is typically deposited on a CMC component through Air Plasma Spray (APS) process, which involves melting and fast quenching of molten ceramic powders (such as ytterbium disilicate and ytterbium monosilicate). The fast quenching and subsequent cool down to room temperature introduce residual stress in the EBC. In addition, EBC coated CMC components often go through a heat treatment process afterwards. For Yb-silicates, this both stabilizes/crystalizes the EBC and increases hermiticity by healing cracks and pores. This heat treatment at elevated temperature changes the coating residual stress state. It is important to be able to measure the coating stresses during deposition and heat treatment so that APS process improvement and EBC coating life assessment can be made. This paper describes novel methods to measure coating stresses continuously during APS and during heat treatment up to 1400°C, using an optical deformation and curvature-based approach.
Adaptation of Air Centrifugal Compressor Stages for Hydrogen-Based Economy: Impact on the Design Point and its Corresponding Flow Coefficient
Authors: Kienzle Norman , Al Arafa Mushfiq , di Mare Francesca , Budt Marcus
Published: August 2024

One approach to saving time and R&D capacity in providing a compressor stage portfolio for a hydrogen-based economy is to adapt established air centrifugal compressor stages for operation with hydrogen. However, this shift from air to hydrogen operation in air-ready centrifugal compressor stages results in notable changes in the design point and its corresponding flow coefficient. These alterations arise due to distinct gas properties, differences in pressure ratio, and outlet temperature.

The design point flow coefficients for the analyzed air-driven centrifugal compressor stages spanned from 0.04 to 0.1. To predict the hydrogen operation of these stages there is an urge to predict the flow coefficient range for the new gas. Therefore, this paper aims to comprehensively investigate the impact of shifting from air to hydrogen mode on the design point and its corresponding flow coefficient. The transition has been analyzed by developing a comprehensive methodology that integrates a prediction method, 1D mean line calculation, computational fluid dynamics (CFD) analysis, and a corrector method. The investigation has been conducted on five different centrifugal compressor stages at a wide range of flow coefficients. The maximum speed of the individual stages has not been exceeded to ensure that the machines remain structurally feasible.

The findings derived from the simulation results suggest that air-ready centrifugal compressor stages, when operated with hydrogen, experience a shift in the peak efficiency point flow coefficient. This mode shift leads to a reduction in the peak efficiency flow coefficient; hence the hydrogen design point flow coefficient of air-designed stages is in the range of 0.02–0.08. An investigation to analyze the flow coefficient dependency on gas molecular mass and other factors is carried out to explain the findings. Then, the hydrogen peak efficiency flow coefficient can be used for the 1D mean line calculation of air-ready centrifugal compressor stages for hydrogen mode.
Heat Transfer and Flow Field Characteristics of Variable Aspect Ratio, Serpentine Passages
Authors: Wang Hanlin , Klein Denali , Wright Lesley M.
Published: August 2024

This study investigates the effect of acceleration and deceleration in the turn region of a two-pass, serpentine channel. Channel aspect ratios of 2:1 and 4:1 are considered in three combinations to investigate the effect of acceleration and deceleration through the turn region in a smooth, two-pass channel. The length of the inlet section enables the flow entering the first pass to approach fully developed. For each aspect ratio combination, the experiments include nominal Reynolds numbers ranging from 15,000 to 45,000 in the first passage. The Reynolds numbers in the second pass range approximately from 9,000 to 75,000. A transient thermochromic liquid crystal technique is used to measure the detailed surface heat transfer coefficient distributions, and the flow field characteristics are measured by tomographic PIV. Enhanced heat transfer from the impinging flow on the side wall and downstream in the second pass is observed for all cases. On the basis of the first pass Nusselt number ratio, the accelerating case provides the best overall heat transfer enhancement. However, on the basis of the second pass Nusselt number ratio, the decelerating case is a promising arrangement. If the Reynolds number is controlled, the constant cross-section case has the highest Nusselt number and heat transfer coefficient in the turn, and if the mass flow is controlled, the accelerating case exhibits the lowest overall average Nusselt numbers and heat transfer coefficients. The flow field results suggest the secondary flow induced by the turn is weakened when the flow accelerates after the turn for the accelerating channel. The opposite is observed for the decelerating channel. The strength of the counter-rotating vortex pair, turbulence level, and local heat transfer enhancements are closely correlated in a serpentine channel.
Meanline Design and Aerodynamic 3D RANS Investigations of a Multistage Helium Axial Compressor
Authors: Prabhakar Arvind
Published: August 2024

A mean line aerodynamic design and analysis of a multistage helium gas axial flow compressor is presented for a High-Temperature Gas Reactor (HTGR) application. The multistage axial flow compressor design geometry from mean line design is based on a free vortex design method and targeted for achieving high loading, high polytropic efficiency, and is further tuned and investigated for optimum performance by performing three-dimensional Reynolds Averaged Navier Stokes (3D RANS) CFD studies. Performance of the axial compressor and key design quantities are compared with similar previous designs to highlight robustness of the presented design methodology. The design studies also discuss the impact of selecting optimum parameters like thickness to chord length of rotor blades in spanwise direction from hub of the blades to shroud of the blades. Key loss-causing phenomena are identified through 3D RANS CFD analysis, with the intent to improve the final design.

Further, The presented designs are verified by 3D RANS CFD analysis for achieving high aerodynamic polytropic efficiency, targeted design pressure ratio while maintaining high blade loading, and negligible flow separation at the design point. Such a design can also reduce the number of stages for typical HTGR applications, thereby lowering the overall weight of the large multistage axial flow compressor.
Effect of Rotation on 45-Degree Broken V-Ribs in a 2 Pass Square Channel
Authors: Thirumalai Madhusudan Pallikaranai , Ekkad Srinath V.
Published: August 2024

The demand for elevated turbine inlet temperatures in gas turbine airfoils requires the innovation of advanced internal cooling designs to enhance turbine durability and performance. The internal cooling passages in gas turbine blades typically feature ribs that are designed to induce turbulent mixing consequently increasing heat transfer. As the turbine blades rotate, the Coriolis and Buoyancy forces affect the fluid flowing through these channels, thereby causing a non-uniformity in heat transfer distribution between the pressure side and suction side of the turbine blade internal cooling channels. Prior studies have explored various geometries of ribs under stationary and rotating conditions. The present study investigates the heat transfer characteristics of a two-pass channel (AR = 1) featuring 60 degree broken-V ribs which has not been studied in detail under rotation. The rib-height to hydraulic diameter ratio is 0.125 and rib-pitch to height ratio of 16. The heat transfer coefficient was measured using transient liquid crystal thermography technique and detailed Nusselt numbers have been reported. The experiments were carried out for varying Reynolds number (35000, 45000 & 60000) to cover a typical range of operating conditions found in air-breathing engines.
A Study on Average Eigenvalue Sensitivity for the Improvement of Rotordynamic Stability of Integrally Geared Centrifugal Compressors
Authors: Luo Zhusan , Schwarz Carl L.
Published: August 2024

This paper presents a study on the average eigenvalue sensitivity to design variables of an integrally geared centrifugal compressor pinion-bearing system and its application to the improvement of the rotordynamic stability. The average eigenvalue sensitivity is the approximation of the eigenvalue sensitivity, i.e., the central difference of eigenvalue is substituted for the partial derivative of eigenvalue with respect to a design variable. Hence, the average sensitivity coefficients can be calculated using a rotordynamic analysis program integrated with a bearing analysis program. The results are presented in a new frequency versus logarithmic decrement diagram, which is designed for multiple analysis cases.

The average eigenvalue sensitivity to the mass properties of an impeller can not only predict how much an eigenvalue of interest varies with the mass properties, but also indicate where the impeller should be modified. The average eigenvalue sensitivity to a bearing design variable strongly depends upon pad length, bearing load and pivot offset. The sensitivity study tells what design variables should be changed for satisfactory rotordynamic stability and bearing performance. The effects of main shaft dimensions on the average eigenvalue sensitivity are examined to select and tune certain dimensions for the rotordynamic stability. This numerical method has been implemented to improve the rotordynamic stability of two compressor pinions.
High Speed Rotating HPT Blade Thermal Imaging of a Full Scale Cooled 1+1/2 Stage Turbine in a Short Duration Transient Test Facility
Authors: Anthony Richard J. , Vanasse Neil , McClaren Scott
Published: August 2024

This paper presents results from original development of a long wavelength infrared (LWIR) high pressure turbine (HPT) blade thermal imaging system on a Full Scale Cooled 1+1/2 Stage Rotating Turbine in the Air Force Research Laboratory Turbine Research Facility (TRF) at WPAFB, OH. The TRF is a short duration transient turbine blowdown rig capable of matching relevant non-dimensional parameters such as Reynolds Number, Prandtl Number, corrected speed, along with cooling pressure ratios. A LWIR HPT blade thermal imaging camera and custom optical probe are carefully designed and installed to capture transient surface temperatures across a 46-blade rotor arranged in a rainbow wheel of cooled and uncooled airfoils. Over ten transient rotating turbine tests were run acquiring rotating HPT blade images from four different rotor blade views at full RPM. Lessons are shared regarding signal-to-noise challenges of fast transient rotor IR measurements. Together, data from these views show different transient thermal gradients across cooled and uncooled airfoils, revealing insight into cooling flow circumferential platform leakage, and film cooling variations under varying backflow margin. Transient thermal images are also captured showing the effects of momentary hot gas ingestion and film cooling recovery. Furthermore, this paper demonstrates the ability to locate individual subsurface blocked cooling hole passages that do not appear in borescope inspection. This experiment is the first to show such behavior on a full-scale rotor at full RPM in the TRF.
Practical Application of ARMA Model Method for Blade Tip Timing
Authors: Chai Pengfei , Wang Shang , Meng Yiming , Chen Yong , Tian Jie , Ouyang Hua
Published: August 2024

Blade tip timing (BTT) is a non-contact measurement technology for rotating blade vibration. However, BTT often has nonuniform undersampling. Building a response mode is an efficient method for BTT signal analysis. The autoregressive moving-average (ARMA) model is famous for modelling a linear stationary time series in discrete time. We modified the classical Yule-Walker equation-based ARMA solving method to adapt to BTT measurement. The ARMA model method is applied in compressor field tests. The tests are conducted in stable states with different rotational speeds. The ARMA models with different order and probe arrangements are performed on the measured data. The results show that the identified natural frequency is credible and has close results for most ARMA models. The identified natural frequency increased as the rotational speed increased, which confirmed the rationality of the results. The results of different probe arrangements indicated that at least four probes are recommended in our test.
An Active Turbulence Grid for Turbomachinery Flow Experiments
Authors: Bertelli Federico , Okada Mizuki , Lavagnoli Sergio , Hillewaert Koen
Published: August 2024

Quantifying and predicting free-stream turbulence effects on the aerodynamic performance of turbomachinery flows continue to be of primary interest to advance the physical understanding and the modeling of the loss mechanisms. This work is motivated by the need to expose turbine flows to a wide class of inlet turbulence fields, characterized by the peculiarity of setting the turbulence intensity levels and yet tuning the turbulence scales independently. This paper describes the development and the experimental characterization of an active turbulence generator concept that provides the authority for enabling future experimental measurements in turbine cascade rigs. The study has been conducted in an auxiliary low-speed test bench with a small cross-sectional area, testing at low Mach numbers (∼ 0.05) and ambient conditions. Pressure, hot-wire anemometry and particle image velocimetry (PIV) measurements are presented. The results indicate that the active turbulence generator is capable of generating a wide range of homogeneous and isotropic free-stream turbulence. Values from low to high turbulence levels (1.5–13%) with minimum pressure losses and a low degree of non-uniformity (< 5%) have been obtained with the ability to independently control the integral length scale within the range of 6–25 mm.
Multi-Disciplinary Optimization of Gyroid Topologies for a Cold Plate Heat Exchanger Design
Authors: Daifalla Elhusseiny , Shahpar Shahrokh , Tristanto Indi , Carta Mario
Published: August 2024

The strive to reduce the environmental impact of aviation has led to electrification and increasing demand for powerful onboard power electronic systems. These high-performance electrical components are bound to produce significant amounts of low-quality heat waste that, if not dissipated properly, will lead to malfunctioning and even permanent damage. For this reason, high performance heat exchangers represent a key enabler for future advances in aircraft systems electrification and are vital to meet net zero goals and reduce the aviation’s carbon footprint. For a given volume of the exchanger, the heat flow rate can be increased by adopting more sophisticated fluid domains. However, excessive geometrical complexity will lead to an increase in pressure losses, often resulting in inhomogeneous temperature distributions. In this paper, a novel optimization procedure is employed to maximize the efficiency of a high-performance heat exchanger, while minimizing overall pressure loss and temperature gradients. The optimization is performed with full-3D high-fidelity computational flow simulations. The geometry of the fluid domain is constituted by triply periodic minimal surfaces, with a parametrization based on thickness and aspect ratios, done by using the nTopology suite. To assess the performance gain, the topology-optimized design is compared against the datum case and a conventional serpentine design.
Numerical Simulation and Experimental Study of a Full-Scale Mild Combustion Chamber
Authors: Xiong Yan , Ben Yali , Yang Ningjing , Liu Zhigang , Zhang Zhedian , Shao Weiwei , Xu Xiang
Published: August 2024

Over the past four decades, gas turbine combustion has been dedicated to achieving low emissions, resulting in numerous advancements in combustion technologies. MILD combustion, a relatively promising new technology with unique characteristics, has garnered extensive research and attention in the last twenty years. However, applying MILD combustion to gas turbines remains a significant challenge due to limited space and high heat release rates per unit. Currently, most MILD combustion experiments are conducted on a laboratory scale. To address this issue, we conducted full-scale MILD combustion experiments under pressure test conditions in this study. NOx data were obtained at different outlet temperatures (1473 K–1773 K) under experimental conditions of 1.5 bar pressure and air inlet temperature at about 423K and 510K. These results were compared with previous lab-scale research data. The findings indicate that while the NOx emission data for full-scale experiments increased relative to lab-scale studies, it still remained below 10 ppm@15%O2 during operating conditions, demonstrating the low NOx emission potential of MILD combustion. This outcome can be attributed primarily to the adiabatic state of the full-scale combustion chamber’s process and relatively poor mixing effects between fuel and air as well as flue gas and unburned reactants due to size enlargement. These findings have significant implications for designing full-scale MILD combustion chambers in gas turbine engines.