bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Conical Cavity on the Load Capacity of Externally Pressurized Steam-Lubricated Journal Bearing
Authors: Liu Zhansheng , Qi Jinlei , Yu Xiangyu
Published: September 2023

Motivated by the urgent need for the development of oil-free and closed-loop turbomachinery in deep-space and deep-sea exploration missions, process-gas lubricated bearing has seen the recent surge of interest due to its numerous advantages. Particularly, externally pressurized steam-lubricated bearing plays an important role in closed-cycle steam turbine, which significantly influences the machine reliability and operating characteristics. In order to achieve effective lubrication and obtain high load capacity, a full understanding of how bearing geometrical parameters and gas properties affect the bearing overall performance is required.

This study mainly proposes a novel design to increase the load capacity of the externally pressurized steam-lubricated journal bearing. Firstly, the correctness of simulation is verified based on a simple bearing model. And with the help of the computational fluid dynamics numerical tool, this paper conducts a detailed fluid flow and heat transfer analysis for inherently compensated steam journal bearing. The computations have been performed for two different gases — air and steam. The bearing diameter is 110mm and it has single-row 8 orifices. Flow field parameters such as pressure distribution, mass flow rate, velocity distribution are presented. Results also reveal the classical pressure depression in the gas film entrance and transonic flow phenomenon in the bearing clearance. Second, based on the lubrication flow analysis, a new conical cavity concept is presented. The study compares the static load capacity performance and flow characteristics of the steam journal bearing with and without the conical cavity. We find that the conical cavity structure can actually improve the static load capacity of the inherently compensated bearing. Finally, the influence of conical cavity angle on the load capacity and mass flow rate is investigated. There are 11 different conical cavity angles which vary from 20 degrees to 70 degrees. The numerical results show that the conical cavity angle almost has no influence on the static load capacity but reduces the mass flow rate when the angle value rises. This study demonstrates that how to design the high load capacity externally pressurized steam-lubricated journal bearing for closed-cycle steam turbine.
Transient Heat Flux Budgeting on a High-Pressure Turbine
Authors: Saavedra Jorge , Lozano Francisco , Paniagua Guillermo
Published: September 2023

This research is focused on the temporal heat flux budgeting on a high-pressure turbine exposed to periodic upstream total flow temperature variations using computational fluid dynamics simulations. A high-pressure turbine vane is exposed to sinusoidal upstream total flow temperature oscillations with peak-to-peak variations around 50K at various frequencies. Transient Unsteady Reynolds Average Navier-Stokes simulations (URANS) are performed, taking advantage of the k-w SST transitional turbulent closure. The transitional kw SST model identifies the transient stagnant conditions’ impact on the velocity and temperature boundary layers, considering its influence on turbulent production and dissipation and thermal convection while minimizing the computational burden. The proposed numerical set-up is verified against experimental pressure and heat flux distributions over a high-pressure turbine vane.

The evolution of the near wall velocity and thermal profiles are described along the periodic operation, identifying the temporal dynamics governing the heat flux distribution. The velocity and static temperature development are also analyzed based on spectral proper orthogonal decomposition to identify the dominant structures responsible for the transient thermal and momentum response. The temporal characterization of the thermal boundary layer and heat flux distribution over the turbine vane enables the design of more efficient flow control and cooling strategies that mitigate heat loading while minimizing the amount of coolant.
Towards an Improved Description of Film-Cooling Heat Transfer Through Anisotropic RANS Modeling: A Combined LES/RANS Contribution
Authors: Laroche Emmanuel , Dupuy Dorian , Duchaine Florent , Gicquel Laurent
Published: September 2023

This study focuses on the physics and the modeling of the heat transfer taking place within the Penn State 777 shaped hole flow configuration. To do so, a dedicated Large-Eddy Simulation conducted with the AVBP solver is carried out and shows good reproduction of the main flow characteristics observed in terms of features and adiabatic effectiveness. This simulation is then more deeply analyzed to conduct an a priori evaluation of the most current heat flux assumptions used in RANS modeling, being the Prandtl analogy and the Daly Harlow hypothesis. Results obtained for this shaped hole configuration confirm previous ones obtained for cylindrical holes, showing the deficiencies of classical RANS models. In particular, it is shown that the equivalent Turbulent Prandtl number usually fixed at 0.9 is here largely overestimated. The most representative value is indeed around 0.5 in most regions of interest. It is also showed that the diffusion process is not the same in all directions, namely the wall normal and transverse directions turbulent diffusion processes differ. A Reynolds-Stress model simulation using the Elliptic Blending Reynolds-Stress Model developed by Manceau is then conducted, combined with different advanced heat flux models. With this new and more advanced model, obtained results show major improvements compared to state of the art RANS simulation using the k-ω SST along with the Prandtl analogy. In particular, the centerline and the lateral effectiveness profiles are considerably enhanced, exhibiting a more representative lateral spreading. The respective contributions issued by the improved Reynolds-stress description and the heat flux models are eventually analyzed. A modified model for the heat flux formulation is hence suggested in an attempt to provide extra improvement compared to Daly-Harlow formulation. In conclusion, this work strongly advocates for the use of anisotropic models either for turbulent stress modeling or turbulent heat flux modeling for the description of film cooling phenomena at stake.
Review and Development of Natural Gas/Hydrogen Fuel Flexible Reduced Chemical Mechanism for High-Order Modeling of Gas Turbines
Authors: Valles Miguel A. , Kessler Iris , Windom Bret C.
Published: September 2023

Green hydrogen produced from water electrolysis is a promising carbon-free energy storage medium that, when blended with natural gas, can be transported in existing natural gas pipeline infrastructure, and utilized in associated power plants to reduce the carbon intensity of existing natural gas-powered systems. However, hydrogen’s high reactivity presents unique challenges related to maintaining stable combustion while balancing low NOx emissions in traditional dry low-NOx combustion systems designed for natural gas fuel. Therefore, there is a need to develop retrofittable combustion technologies that can be adapted to existing gas turbine engines to permit high hydrogen fuel blend ratios. State-of-the-art Computer-Aid Engineering (CAE) tools are needed to study the impact of hydrogen within these devices and to design next-generation novel combustor designs strategies to enable high hydrogen/low NOx combustion. At the heart of these CAE tools is a chemical mechanism to model the combustion reactions and species generated throughout the engine; however, the size of the mechanism is strongly tied to the computational expense. For this reason, it is critical to have a high-fidelity and validated yet tractable mechanism that can be used in advanced computational fluid dynamic modeling approaches while also capturing the key reactions responsible for flame stability and NOx emissions. Many chemical mechanisms exist, each designed for and validated with combustion applications/data under unique conditions. Here we quantitatively compare several of the most common small species chemical mechanisms for suitability in modeling gas turbine engine relevant conditions.

In doing so, we report the results of an extensive literature review comparing existing hydrogen and natural gas chemical mechanisms to a wide range of laminar flame speeds and ignition delay time experimental data. The predictability of existing chemical mechanisms and deficiencies in the validation dataset are discussed. These deficiencies vary from case to case but are noticeable at high pressures (>10 bar) and for blended fuels (natural gas and hydrogen). A large gap was found in current laminar flame speed experimental data at high pressure and temperatures which is also where the largest discrepancies are noticed between existing chemical mechanisms. Preliminary NOx modeling validation for several common NOx chemistry sub-mechanisms was also performed using hydrogen diffusion flame experimental data. Future work will evaluate NOx in natural gas species diffusion flame experiments and laminar flame speed experiments.
Static Characteristics Analysis of Textured Thrust Bearing Based on the Multigrid Algorithm
Authors: Xu Kefan , Zhang Guanghui , Sun Wenlong , Han Jiazhen
Published: September 2023

Carefully designed compliant foil structure or surface texturing can both help improve bearings’ performance. However, little research has been done on their combination: textured gas foil bearing. This paper adopted the modified compressible Reynolds equation as the pressure governing equation of bump-type foil thrust bearing, and the influence of different slip models was discussed. The predicted load capacity agrees with the literature data. This paper further presented the execution time differences between various numerical methods, including the direct, iterative, and multigrid algorithms, when handling the significant discretization effort introduced by texture. The results indicate that the multigrid algorithm performs best, and the execution time is generally reduced by 50% compared to the traditional direct method under the same operating parameters. Besides, further analysis of the textures’ effect on bearings’ performance was carried out based on three distribution types. The results indicate that textures affect all static characteristic parameters more when the relative texture depth increases. For the #1 texture distribution type, the maximum increment of load capacity could exceed 10% when the textures are assumed to be manufactured in the ramp of the top foil. In conclusion, the multigrid is an excellent solution that can balance computational accuracy and efficiency for textured foil thrust bearings. Furthermore, an appropriate arrangement of textures could improve foil thrust bearings’ performance.
The Development and Use of a Natural Gas / Oxygen Burner Rig for Environmental Barrier Coating and Ceramic Matrix Composite Technology Maturation
Authors: Presby Michael J. , Endo Makoto , Fox Dennis S. , Harder Bryan J. , Lee Kang N. , Hoffman Leland C. , Cuy Michael D.
Published: September 2023

This work outlines the development of a new natural gas/oxygen (NG/O2) fueled combustion rig located at the NASA Glenn Research Center for high-temperature environmental durability studies of advanced materials and components at atmospheric pressure. The NG/O2 burner rig can simulate the high-temperature, high-heat flux, and high-velocity thermal environments encountered in gas turbine engines. It also provides the capability to study environmental effects such as water vapor and other foreign contaminants relevant to these applications. The rig is anticipated to bridge the gap between other laboratory methods such as furnaces, jet-fueled burner rigs, high-heat flux lasers, and more expensive engine rig testing. The NG/O2 rig is expected to have maximum sample temperature capabilities over 3,000°F (1,649°C) and result in higher water vapor content compared to our Mach 0.3 to Mach 1.0 jet-A burner rigs which is important for characterizing current and next-generation environmental barrier coatings. This paper will provide an overview of the development of the NG/O2 burner rig, initial characterization, and current research and development efforts on environmental barrier coated ceramic matrix composites.
Simulation of Methane Oxycombustion in Supercritical Carbon Dioxide
Authors: Henry De Frahan Marc T. , Rahimi Mohammad J. , Doronina Olga , Perry Bruce A. , Yellapantula Shashank , Cormier Ian , Day Marc , Martin Michael James
Published: September 2023

The Allam-Fetvedt Cycle (AFC) offers the potential for electricity generation with minimal or even negative carbon emissions by using oxycombustion in supercritical carbon dioxide (sCO2). Because of the extreme high temperatures and pressures encountered in these systems, simulation of oxycombustion requires use of a complex equation of state such as the modified Soave-Redlich-Kwong (SRK) equation, coupled with equally complex correlations for transport properties. The current work simulates a model combustor using both an ideal gas equation of state and the SRK equation of state. The model combustor features a jet of CH4 mixing with and reacting with O2 in the sCO2 ambient. Two jet configurations are considered: one of pure CH4, and one of CH4 mixed with sCO2. Comparison of results shows that key output properties such as combustor temperature and flow distribution are impacted by the choice of equations of state. Inspection of simulation results shows that mixing and reaction rates, as well as the uniformity of the flow, are impacted by the choice of equation of state. These results show that even though use of a complex equation of state greatly increases the computational costs of these simulations, it is critical to accurately capturing the physics of these systems.
Investigation of Water Film Behavior on the Surface of an Airfoil in a High-Speed Flow and Subsequent Ligament Formation and Breakup From the Trailing Edge
Authors: Safiullah S. , Esquivias Brandon , Hickey Brendan , McDonell Vincent , Tabata Soichiro , Senoo Shigeki
Published: September 2023

The breakup of liquid films in high-speed flows are found in many applications. These include pre-filming air blast atomization found in fuel injectors and shedding from airfoils. In this work, the behavior of a liquid film on the surface of a NACA 0012 airfoil placed in a high-speed air flow is investigated. The results complement previous results obtained on time averaged ligament behavior and droplet sizes generated by the same airfoil. A combination of computational fluid dynamic (CFD) simulations and experimental studies were carried out to assess features of water films, including the film thickness, wave speed, droplet shedding, and the dynamics of the sheet. In the present work, air velocities up to 175 m/s were used with water films flows between 1.4 and 2.6 cm2/s. The water film was introduced onto one side of the airfoil surface through a series of 0.5 mm holes separated by 1mm at a location 35 mm downstream of the leading edge of the vane. Experimental results were obtained using four primary tools. The first is a point measurement of the dynamic film thickness using a confocal laser induced fluorescence method. This spatially resolved measurement provides time resolved measurement of the instantaneous liquid film thickness at specific points on the vane surface. This is complimented by time averaged images of the film thickness on the entire vane surface. Third, high speed videos are obtained to study the accumulation and breakup of the liquid at the trailing edge of vane. Finally, laser diffraction is used to document the spray dynamics downstream of the vane. In addition to the experimental results, CFD simulations of the film behavior are also carried out using ANSYS Fluent. The results illustrate that the average film thickness decreases with air velocity and increases with the water flow rate. The results are consistent with the previous study and the current CFD analysis. Frequency analysis suggests that the dominant frequency of liquid film wave, ligament breakup length, drop size and spray concentration increase with the air velocity and is modestly affected by water flow rate. Finally, design tools are provided to predict the average film thickness and dominant frequencies of the film thickness, ligament breakup, spray concentration and droplet average size.
Performance and Emissions Benefits of Cooled Ceramic Matrix Composite Vanes for High Pressure Turbines
Authors: Wehrel Patrick , Schöffler Robin , Grunwitz Clemens , Carvalho Francisco , Plohr Martin , Häßy Jannik , Petersen Anna
Published: September 2023

Ceramic Matrix Composites (CMCs) offer great potential for developing lighter and more efficient aero-engines. Due to their high temperature capability, CMCs are mainly used in the hot gas section in order to replace cooled metallic components and thus save cooling air. Especially CMC vanes for high pressure turbines (HPTs) have been researched and tested in the past. A realistic design approach for cooled CMC vanes is the so-called shell and spar concept. The application of such vanes in HPTs as inlet guide vanes (IGVs) at constant rotor inlet temperature (T41) enables performance and emissions benefits which are assessed by means of a reference engine in this paper. Compared to metallic IGVs, more temperature-resistant CMC IGVs require significantly less cooling air and generate lower cooling losses. A quantitative comparison will be presented. Consequently, the redesign of the reference engine to the setting of a hybrid HPT leads to a reduction in thrust specific fuel consumption (TSFC) by 0.23 % at cruise conditions. Additionally, there is potential to extract the IGV cooling air at a lower pressure level, increasing the cruise TSFC gain to 0.41 %. In the course of the redesign process, the turbine inlet temperature (T4) is reduced by 50 K in order to reach the same T41 with a lower IGV coolant mass flow. Regarding emissions, this leads to a decreased production of nitrogen oxides (NOx). Hence, several NOx emissions parameters can be reduced by more than 4 %.
Effects of Supercritical CO2 Fluid Properties on Heat Exchanger Design
Authors: Lugo Afonso , Turunen-Saaresti Teemu , Tiainen Jonna
Published: September 2023

Supercritical CO2 (sCO2) in industrial applications is a promising solution for the reduction of equipment size and for the potential increasement of overall efficiency. The characteristics of CO2 near the critical point are advantageous for the heat transfer, with high specific heat capacity when compared to conventional liquid or gas coolants. Moreover, dopants can be mixed to CO2, in a blend, to further increase the heat transfer and elevate the critical point of the fluid. Under the framework of the Horizon 2020 DESOLINATION (DEmonstration of concentrated SOLar power coupled wIth advaNced desAlinaTion system in the gulf regION) project, a heat exchanger was designed using CO2 and blend as working fluids in an innovative power cycle bank of a concentrated solar power (CSP) plant coupled to a water desalination system. In this paper, the innovative heat exchanger is evaluated in terms of the geometry, focusing on heat transfer and turbulence, using computational fluid dynamic (CFD) simulations with SST k-ω turbulence model and real-gas models with REFPROP library for thermodynamic and transport properties. Within each fluid, the diameter of the channels varied from 1.8–2.2 mm and the results are compared to analytical models. The geometry with 1.8 showed a larger pressure drop, but also larger overall heat transfer coefficient. It is observed that both pressure drop and heat transfer decrease with the diameter. Blend as the hot fluid resulted in higher average temperature and heat transfer coefficient, but in lower pressure drop than pure CO2. Nusselt number correlations were compared, showing the decrease of its values with the diameter for pure CO2, while for the blend it was observed higher values for 2.0 mm of diameter, except for Fang and Xu correlation that showed the same trend as the CO2.
Calculation of Thermodynamic Wetness Loss in Steam Turbines Using CFD Simulation
Authors: Hoznedl Michal , Kolovratník Michal , Jun Gukchol
Published: September 2023

In the paper the behavior of wet steam flow is described in three different steam turbines. The first one is the 1100 MW turbine in the nuclear power plant with the pressurized water reactor. The second one is the 660 MW turbine in the fossil fuel power plant with ultra-supercritical steam parameters at the turbine inlet. The last turbine has a nominal output of 34 MW and operates in the municipal waste incinerator. However, this turbine can often also operate even at 2 MW or higher. In all three turbines in the last stage area passages are made for an optical probe to measure steam wetness and primary droplets size, and for a pneumatic probe to determine the pressures, velocities and flow directions. On the basis of experimentally obtained data analyses of thermodynamic wetness loss for all three turbines are performed using numerical flow simulations considering equilibrium and non-equilibrium steam. The condensation model that includes the nucleation rate and droplet growth velocity used in ANSYS CFX is calibrated based on experimentally obtained data. It is evident that the obtained loss patterns depend fundamentally on the turbine type and operating parameters.
Understanding Thermal Unsteadiness in Engine Representative Flows and Improved Methodologies for Derived Heat Transfer Calculations Using Thin-Film Gauges
Authors: Singh Deepanshu , Beard Paul F. , Cardwell David , Chana Kam S.
Published: September 2023

The Oxford Turbine Research Facility (OTRF) is a high-speed rotating transient test facility, that allows unsteady aerodynamic and heat transfer measurements at engine representative conditions. In addition, a variety of inlet temperature profiles can be simulated in the rig including radial distortion, circumferential distortion, and swirl. However, the engine representative flows cause complications in the processing of heat transfer data. The unsteadiness in temperature data was found to significantly rise as temperature distortions were introduced in the NGV inlet profile, to model a lean burn combustor exit. Using the NGV inlet temperature profile survey data, the thermal unsteadiness has been quantified and compared with a Uniform inlet. The experiments with a radially varying NGV inlet temperature profile showed up to nine times higher thermal unsteadiness, compared to the Uniform inlet. The second part of the paper is a continuation of the work presented in a previous paper by Singh et al. [1] and describes improved methodologies for derived heat transfer calculations using thin-film gauges. In addition, the uncertainty associated with the derived heat transfer parameters, such as the heat transfer coefficient and adiabatic wall temperature has been quantified. The refined processing techniques have been demonstrated on casing heat transfer measurements, acquired in the OTRF with two inlet temperature profiles.
Investigation of the Stability and Surge Limit in an Industrial Centrifugal Compressor With Variable Inlet Guide Vanes
Authors: Stemmermann Julian , Reymond Loïc Marc , Geilich Marius , Jeschke Peter
Published: September 2023

The instability phenomena of an industrial centrifugal compressor are experimentally investigated under various pre-swirl settings and rotational speeds, ranging from subsonic to transonic inflow. The compressor under consideration was installed in an open-loop test rig and consists of variable inlet guide vanes (IGV), a non-splittered impeller, a vaneless diffuser and a volute. The IGV allows pre-swirl angles of −15° (counter-rotating pre-swirl) to +60° (co-rotating pre-swirl). The compressor map measurement in the off-design region at different IGV pre-swirl angles shows that co-rotating pre-swirl facilitates rotating stall. A nominal non-integer stall cell number of 2.4 to 4.6 and a rotational speed of 10 to 25% of the impeller rotational speed characterize the rotating stall phenomena observed. In contrast, mild surge is observed on speed lines without pre-swirl and with counter-rotating pre-swirl at a low rotational speed. At some operating points rotating stall occurs in addition to the mild surge, whereby the rotating stall shows a broadband signal rather than a distinct frequency. The surge limit mass flow rate of the speed lines without pre-swirl stagnates at an approximate isentropic relative Mach number at the leading edge of 0.69 and then rapidly increases at a Mach number of 0.78. As such, the operating range of the compressor stage significantly decreases and the stability and surge limit coincide. In summary, the results presented in this paper show that the IGV has a major impact on the type of instability preceding the deep surge of the compressor stage. The surge limit does not follow any obvious pattern and therefore its prediction during the pre-design remains challenging.
Development of a Chemical Looping Combustor Fed With Natural Gas and Its Integration With a Gas Turbine in ASPEN Plus
Authors: Bartocci Pietro , Abad Alberto , Cabello Arturo , de Las Obras Loscertales Margarita , Zampilli Mauro , Taiana Andrea , Serra Angela , Fantozzi Francesco
Published: September 2023

The lowest cost solution for carbon capture and storage in power plants at the moment is represented by chemical looping combustion. This technology nevertheless has not yet met the market due to scale up needs and also to the fact that to be coupled to a gas turbines a chemical looping combustor has to be operated at high pressure and high temperature. While high pressurization of the reactor can imply problems in the management of the circulation rate and the sealing between the air reactor and the fuel reactor; operation at high temperature can imply agglomeration, sintering and also attrition problems for the oxygen carriers. To analyze those problems a Mari Curie project has been funded under the Horizon2020 EU program. This paper presents the analysis of two configurations of the chemical looping combustor and of the coupled gas turbine. Both configurations are examples of possible bioenergy with carbon capture and storage (BECCS) technologies. The aim is to compare BECCS efficiency with that of combined cycles fed with natural gas and using post-combustion carbon capture and storage, which seem to be the competing technologies. A methodology for the dimensioning of the pressurized chemical looping combustor to be coupled to a gas turbine of the power of about 12 MW mechanical power, is presented and applied also based on the results of experimental campaigns previously performed at the Spanish National Research Council (CSIC), Instituto de Carboquimica of Zaragoza, Spain.
A Conceptual Model for the Flutter Mechanism in Interlocked Turbine Blades
Authors: Gallardo Juan Manuel , Pérez Escobar Óscar
Published: September 2023

Many turbine rotor blades adopt the interlock configuration; among its advantages, there is a large increase in the natural frequencies with respect to the simpler cantilever configuration. Most widespread assessment methods estimate that this frequency increase should lead to a large improvement to the flutter stability of the interlocked rotor rows; some well-known approaches, such as the Panovsky-Kielb stability maps, suggest that flutter should be very unlikely for interlock configurations. Nevertheless, both the experience and detailed simulations indicate that it is possible to find flutter in interlocked blades, even with moderate aspect ratio.

In this paper, the authors study the underlying physics behind flutter for interlocked blades, and present a very simplified model that is able to reproduce the main modal characteristics of interlocked blades, including the frequency increase and change in mode-shape as a function of the nodal diameter. This model also identifies a flutter mechanism, which is dependent on the aerodynamic interaction between the bending and torsion motion of the blade; even if both basic motions are individually stable, their interaction may lead to a coupled aeroelastic instability. The results from this simplified model are fully consistent with detailed 3D linearized unsteady CFD simulations of representative turbine rotor blades, and should be of application in many realistic cases of interlock flutter. Finally, the authors present a study on the influence of the main parameters of the simplified model on the flutter stability, and derive some conclusions about the implications on flutter-free interlock design.
Wind Turbine Drivetrain Fault Detection Using Multi-Variate Deep Learning Combined With Signal Processing
Authors: Jamil Faras , Jara Avila Francisco , Vratsinis Konstantinos , Peeters Cédric , Helsen Jan
Published: September 2023

The maintenance of wind turbines is essential to reduce wind energy levelized costs. Earlier detection of potential faults in the rotating subcomponents, such as the drivetrain, helps to plan maintenance actions. Several vibration processing methods, e.g., short-time Fourier analysis, are available in the literature to detect faults, however, they require domain expertise. Moreover, many researchers are focusing on machine learning methods to complement such techniques. This paper combines deep learning methods, more specifically auto-encoders, with more than 400 indicators based on advanced signal processing techniques. It is impractical to train a deep-learning model for each indicator, and significant manual effort is required to investigate all indicators. This paper focuses on a multivariate deep learning model to explore the potential to learn the underlying relationships among the signal processing indicators for healthy datasets and compress them into one health status. The reconstruction error of this model is then used to identify changes in the condition of the system. The output directly illustrates the high-level health state of the system for early fault detection. This proposed method is demonstrated on real-life offshore wind turbine data from several years. Further analysis can be done to pinpoint specific fault types using frequency spectrum analysis.
Optimization of an HPT Blade and Sector-Based Annular Rig Design for Supercritical CO2 Power Cycle Representative Testing
Authors: Tuite Logan , Braun James , Paniagua Guillermo
Published: September 2023

As part of the ongoing research into the design of hardware for zero emission cycles, a first stage high-pressure turbine (HPT) blade is optimized for a 350 MWe supercritical CO2 (sCO2) power cycle using the surrogate-assisted genetic algorithm optimizer in Numeca FINE/Design 3D with objectives of increasing efficiency and decreasing heat load to the blade. Supercritical CO2 property tables are constructed from NIST REFPROP data, and a bicubic interpolation is used to create polynomial expressions for the condensable gas simulation in FINE/Turbo. A detailed mesh sensitivity study is performed for a baseline design to identify the proper grid refinement and efficiently allocate resources for the optimization. Seventy design variables are selected for the initial population generation. Self-organizing maps are then used to reduce the number of design variables, focusing on the most important ones affecting the objective functions. The optimization results in approximately 3000 three-dimensional Reynolds Averaged Navier Stokes simulations of different blade shapes with increases in efficiency of up to 0.85 percentage points and decreases in heat load of 14%. Families of blade shapes are identified for experimental testing in an annular rig at the Purdue Experimental Turbine Aerothermal Laboratory. A design to adapt the Big Rig for Aerothermal Stationary Turbine Analysis test section for testing optimized geometries is introduced, which features eccentric radius sectors allowing for scaled-up geometries of sCO2 optimized blade profiles to be tested at design cycle representative conditions at high Reynolds numbers in dry air. Analysis into the effects of Reynolds number, working fluid, and geometric relations are presented to prove the efficacy of the test method.
Model Predictive Control Strategies for Turbine Electrified Energy Management
Authors: Hill Elyse D. , Amthor Aria E. , Soloway Donald I. , Simon Donald L. , Connolly Joseph W.
Published: September 2023

The increasing electrification of aircraft propulsion systems is leading to new control architectures being developed to address integration between electric machines and gas-based turbine engines. For hybrid-electric propulsion systems, current conceptual architectures often couple electric machines with the shafts of gas turbine engines and introduce energy storage. Leveraging the electrical power system of hybridized engines, Turbine Electrified Energy Management (TEEM) is a recent control approach that improves transient operability in an effort to enable more efficient and lighter weight turbomachinery. This study seeks to expand TEEM’s application beyond traditional proportional-integral (PI) control by presenting linear model predictive control (MPC) schemes to execute the TEEM concept. Through constraint selection and cost function design, transient operability goals for TEEM are considered with no external logic or saturation. Unique to the designs are the use of a washout filter, which simplifies transient detection and motor activation logic. The proposed architectures are implemented with both centralized MPC and distributed MPC approaches, and comparisons are drawn to a benchmark PI controller simulated on a nonlinear turbofan engine model at one ground condition and one cruise condition. Performance is evaluated using compressor maps, stall margin performance, and two novel metrics: transient stack usage and transient excursion integral. Results reveal the linear MPC scheme performs comparably to the baseline controller and can be implemented in at least two distinct configurations with potential for further modifications, thus establishing the groundwork for future investigations.
Pressure Characteristic Rollover of a Transonic Centrifugal Impeller
Authors: Cao Teng , Hayashi Yoshihiro , Tomita Isao
Published: September 2023

This paper presents a detailed numerical investigation of a transonic centrifugal compressor to understand the mechanism causing its pressure rise characteristic rollover, which fundamentally impacts compressor stability. Distinct characteristic rollover behaviors at different compressor speeds are predicted and studied. It is found that the impeller characteristic rollover occurs at high blade tip Mach number (> 1) conditions. It is the result of a combination of the inducer and exducer performance. The inducer is found to stall early, while the exducer is mostly a stable part maintaining the overall impeller stability. The overall impeller characteristic rolls over when the exducer’s performance deteriorates significantly, which happens at higher flow conditions towards high speed. This is due to the flow compressibility effect (density change). It shows the flow density across the impeller increases with the blade tip Mach number. The increased density leads to a reduced exducer exit flow coefficient with higher workload and aerodynamic losses. Detailed analysis is carried out to understand the 1D and 3D flow mechanisms governing the inducer and exducer, hence the impeller characteristic.
Active Fluidic Control of a Nozzle Guide Vane Throat
Authors: Spens Alexander , Bons Jeffrey P.
Published: September 2023

Experiments were conducted to validate the building blocks of a fluidically controlled variable area turbine concept that uses injected high-pressure air to effectively reduce the choke area of the turbine inlet. Preliminary results from a simple quasi-1D converging-diverging nozzle, with an injection flow slot upstream of the throat, showed a 2.2:1 ratio between throttled mass flow rate and injected mass flow rate at a constant nozzle pressure ratio. The penetration of the injection flow and corresponding reduction in the primary flow streamtube were successfully visualized using a shadowgraph technique. Building on this success, a representative single passage nozzle guide vane transonic flowpath was constructed to demonstrate feasibility beyond the quasi-1D converging-diverging nozzle. Both secondary slot blowing from the vane pressure surface and vane suction surface just upstream of the passage throat again successfully reduced primary flow. In addition, fluidic vortex generators were used on the adjacent suction surface to reduce total pressure loss and further throttle the primary flow. Implications for application of this active flow control technology to a variable area turbine are considered.
Distortion Transfer in Multi-Stage Compressor and Modeling of Spool-Coupling Problem With Circumferentially Distorted Inflow
Authors: Okada Ryuichi , Murooka Takeshi , Kato Dai
Published: September 2023

Among various types of total pressure distortion, circumferential distortion is well known to reduce the operability range of the aero engine. The effect of the circumferential total pressure distortion on single-stage fans have been studied by various researchers. There are, however, few studies about the effect of the circumferential total pressure distortion on multistage compressors. It is also known that in the case of turbojet engines or low bypass ratio turbofan engines, not only the LPC (fan) but also the HPC is influenced by the circumferential distortion. This is called spool coupling effect. However, no method has been fully established to assess the effect of the circumferential distortion on each component and eventually on the whole engine.

In the first part of the present study, the flow field of a multistage research compressor, the front six stages of the Energy Efficient Engine, under circumferentially distorted inflow is analyzed using the Body Force Method, whose coefficients are tuned using the steady RANS solution of the compressor with clean inlet flow. The computed results show that, while the rear stage operates much like in the way described by the parallel compressor model, the front stage experiences circumferential aero loading fluctuations due to the static pressure field formed at the boundaries of the distortion. Consistency of the results is qualitatively confirmed based on comparisons with theory.

In the second part of the study, a new engine performance model including spool coupling effect is proposed. It is a so-called “Parallel Engine” model, in which all the components are divided into distorted and undistorted sectors. The spool coupling effect is represented by a single parameter, namely the normalized axial gap between LPC and HPC. Change in the performance of a notional turbojet engine with circumferential distortion due to the spool coupling effect is presented. Outlook to combine the two methods is briefly summarized at the end.
Impact of Tip Clearance Variation of Highly Loaded Tandem Blades in Axial Compressors
Authors: Konrath Liesbeth , Peitsch Dieter
Published: September 2023

Tandem blades are a means to achieve highly loaded compressor stages. The resulting secondary flow structures around tandem blades, however, are very complex and the source of unwanted losses reducing the potential of tandem blades. Especially for tandem blades with tip clearance, the complexity of the flow increases significantly due to the two imminent clearance vortices. Experimental campaigns were conducted to analyze the development of secondary flows in the tip region of tandem blades for different clearance sizes and incidence angles. For comparison, a conventional single airfoil blade of similar turning serves as reference. Furthermore, the tandem blades feature a highly enlarged pitch-to-chord ratio in comparison to the reference blade. By analyzing the flow topology around the tandem blades, the potential to reduce the blade count within the cascade can be assessed as well. Five-hole probe pressure measurements in the wake of the blades as well as oil flow visualizations of the blade surfaces and the tip clearance end wall have been carried out. Generally, the five-hole probe measurements show a similar development for both, tandem and reference blade, when increasing clearance height and incidence. Differences emerge, when the analysis of the measurements is split up into gap and non-gap side. Going deeper into the flow topology, oil flow visualizations show similar developments for the front blade tip clearance vortex and the reference blade with increased clearance heights and incidences. The tandem rear blade clearance vortex seems largely unaffected, confirming previous observations. The rear blade tip clearance vortex seems to have a stabilizing effect on the flow field.
A Numerical Test Rig for Turbomachinery Flows Based on Large Eddy Simulations With a High-Order Discontinuous Galerkin Scheme - Part 2: Shock-Capturing and Transonic Flows
Authors: Klose Björn F. , Morsbach Christian , Bergmann Michael , Hergt Alexander , Klinner Joachim , Grund Sebastian , Kügeler Edmund
Published: September 2023

In the second paper of this three part series, we focus on the simulation of transonic test cases for turbomachinery applications using a high-order discontinuous Galerkin spectral element method (DGSEM). High-fidelity simulations of transonic compressors and turbines are particularly challenging, as they typically occur at high Reynolds number and require additional treatment to reliably capture the shock waves characterizing such flows. A recently developed finite-volume subcell shock capturing scheme tailored for the DGSEM is applied and evaluated with regard to the shock sensor. To this end, we conduct implicit large-eddy simulations of a high-pressure turbine cascade from public literature and a transonic compressor cascade measured at the German Aerospace Center, both at a high Reynolds number above 106. Based on the results, we examine modal-energy and flow-feature based shock indicator functions, compare the simulation data to experimental and numerical studies and present an analysis of the unsteady features of the flows.
Development of a Reduced Order Model Based on Aerodynamic Influence Coefficients to Simulate Aeroelastic Phenomena in Axial Compressor Blades
Authors: Casoni Marco , Benini Ernesto , Magrini Andrea
Published: September 2023

A reduced order model (ROM) is proposed to simulate the aeroelasticity of compressor blades in both coupled and uncoupled mode at low computational cost. The ROM describes the structural dynamics of blades using the mode superposition technique, while effective aerodynamic forces are modeled using various system identification methods. The ROM takes advantage of the aerodynamic influence coefficients (AIC) to model the aerodynamic loads of vibrating blades. System identification of unsteady aerodynamic forces is performed using ARX polynomial models, nonlinear ARX polynomials, Hammerstein-Wiener models and recurrent neural networks. Two different training signals are tested, and their performance is compared. The uncoupled results are validated against traditional Fourier method, showing good agreement in estimated aerodynamic damping. The different formulations of the coupled ROM are then compared to the coupled full order model (FOM) of reference: consistent predictions for the damping ratio are achieved, with a substantial reduction of the computational cost with respect to full order models of reference.
Influence of Casting Defects on the Low Cycle Fatigue Performance of MAR-M247 – A Path Towards a Probabilistic Model
Authors: Radners Jan , Schweizer Christoph , Eckmann Stefan , Al-Ameri Malek , Amann Christian , Gumbsch Peter , Kadau Kai
Published: September 2023

Intermittent renewable energy sources are becoming increasingly important. This creates a demand for more flexible gas turbine operation conditions, to fill supply gaps and manage peak loads. As a result, the number of startup and shutdown cycles — the low cycle fatigue (LCF) loading of a gas turbine component — increases substantially. This work investigates the LCF performance of a common rotor blade material, to support the future transition towards more flexible power plant operation. One of the goals of this multi-year government funded project is the development of a probabilistic life model of cast material including defects such as porosity. The focus of this work is the investigation of the influence of casting defects on the LCF performance of cast MAR-M247. A comprehensive test program on defective and defect-free specimens at realistic engine conditions, i.e., temperature and stress was conducted. A first deterministic fatigue life model that accounts for material defects is proposed.
A Data-Centric Approach to Loss Mechanisms
Authors: Senior Alistair C. , Miller Robert J.
Published: September 2023

Breaking down the total loss in a turbomachine into a number of low order physical models is a powerful way of developing loss models. A problem, however, is that in complex flows it is often not clear how to put together these physical models in the correct way. An additional problem is that the designer often doesn’t know whether all of the underlying low order physical models are correct or whether a more general, and accurate, physical model is yet to be discovered. In practice this problem often leads to loss models of low accuracy, which only work in a limited part of the overall design space. This paper shows that machine learning can be used to augment a designer in the process of developing loss models for complex flows. It is shown that it helps both in understanding how to put together the underlying physical models in a more accurate way, and also in discovering new, and more general, underlying physical models. The paper illustrates the new method using the problem of compressor and turbine profile loss. This problem was chosen because it is well understood and therefore is a good way of validating the new method. However, surprisingly the new method is shown to be able to develop a new profile loss model which is more accurate than previous models. This is shown to have been achieved by the machine learning finding a new, more general, underlying model for trailing edge mixing loss.