bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Evaluation of Phi-Scaling Validity for Local Temperature Predictions of Turbine Components Under Real Engine Conditions
Authors: Wimmer Thomas , Mick York
Published: September 2023

A Siemens Energy Large Gas Turbine was fully instrumented to quantify operation point parameters and to validate turbine components temperature predictions using thermocouples measurements. The engine was operated under real-grid conditions and has also undergone specific testing operation modes over a several months long period. An automated approach was used to detect steady-state operation from the collected data and the average for each sensor signal was calculated for these periods for data reduction. The acquired metal temperature readings have been non-dimensionalized using the ϕ-approach. The non-dimensional temperature data was then categorized by several engine conditions. The standard deviation of the non-dimensional temperatures for the different categories was calculated. The constant ϕ-scaling approach was assessed for its accuracy and validity range. Additionally, a more elaborate ϕ-scaling approach was used to predict metal temperatures using the experimental data which are compared to the measured metal temperatures. A comparison of the different ϕ-scaling approaches in terms of accuracy is presented as well as the uncertainty posed by the approaches for different engine conditions. The conducted analysis shows the range of operating conditions and locations for which the ϕ-scaling approach delivers sufficient accuracy to avoid full detailed component analysis and allows the quantification of the underlying uncertainty.
Influence of Tantalum and Cobalt on the Weldability of New High Gamma Prime Nickel Based Superalloys for Repair and 3D AM of Turbine Engine Components
Authors: Gontcharov Alexandre , Louden Paul , Brochu Mathieu
Published: September 2023

The propensity of high gamma prime Ni-based superalloys to weld cracking is examined with emphasis on the influence of Ta and Co on weldability. This study focuses on the behavior of LW4280 and LW4280W superalloys containing 16 wt.% Co and 32 wt.% Co respectively. The weldability of experimental compositions of LW4280 with Ta ranging between 0.6 and 6.5 wt.% were also studied. LW4280W alloy, with significantly higher Co fraction, showed a reduced propensity to liquation and stress-strain cracking, improving weldability. However, tensile strength of welds above 982°C (1800°F) was reduced relative to LW4280. The optimal level of Ta in LW4280 was found to be in the middle of the range examined, allowing sound laser DED and GTAW welds to be produced at ambient temperature. Higher or lower levels of Ta resulted in weld cracking produced by GTAW-MA. Possible mechanisms by which Ta and Co levels impact weldability are discussed.
Hydrogen and Gas Turbines – A Rational Approach
Authors: Gülen S. Can , Singh Raj , Banerjee Pritam
Published: September 2023

Hydrogen, as an energy vector, has been receiving significant attention as a prime actor in decarbonization of a wide variety of industry sectors including electricity, chemicals, steel, and cement. In order to be a true decarbonizing agent, H2 must be produced without concomitant generation of carbon dioxide (CO2). Presently, this is only possible via energy-intensive water electrolysis (green H2) using zero-carbon resources such as wind, solar PV, and nuclear power (pink H2). Worldwide, the bulk of H2 production for industrial use is via steam-methane reforming (SMR) with natural gas feedstock, which generates significant amount of CO2 (gray H2). This can be alleviated by combining SMR with carbon capture utilization and sequestration (CCUS), which is labeled as blue H2.

In this paper, utilization of H2 in gas turbine power plants will be investigated for identification of the most promising combination of production, storage, transportation, and power generation. Gasification of coal and/or other “dirty” fuels is shown to be a more sensible way of producing blue H2. Detailed process simulation and performance models will be used to identify the technology challenges as realistically as possible. The objective is to provide a concise and comparative assessment of decarbonization opportunities free of over-optimistic assumptions to help facilitate a realistic understanding of the impact of hydrogen economy on the electricity sector.
Finite Element Analysis of APU Mounting (3-2-1) in Aircraft/Helicopter Application Using Lumped Mass Modal Analysis
Authors: Savela Gregory , Mathuria Parag H. , Taubler James , Belotto Daniel , Masloski James
Published: September 2023

The mounting of the auxiliary power unit (APU) and gear box in Aircraft/Helicopter is discussed in the paper. The APU is usually connected to a Gear box to drive other components. The APU is exposed to shock and vibration environments. The shock and vibration concerns dealing with the design of a stiff support system to achieve target frequency. A frequency margin criterion is selected to ensure fundamental system frequencies are at least 15% away from dominant vibration inputs such as harmonics of helicopter blade passing frequency. A lumped parameter dynamic model is formulated to perform the modal analysis and 1g load static analysis. Modal analysis will help to identify the mounting frequencies, while static analysis will help to identify distribution of the load at each mount, driving the design of supports and identifying design equivalent loads for shock and vibration input. A detailed finite element analysis was performed to validate the lumped mass finite element model. The lumped mass model approach helps in quick turnaround in the preliminary phase of the design, to optimize the mount locations and identify required stiffnesses. The connection stiffness between the APU and Gear box was found to be the controlling stiffness for the mounted frequencies. Hence a short-term (compromise) solution and long-term (lower risk) approach were provided to achieve the target frequency.
Effect of Inert Species on the Static and Dynamic Stability of a Piloted, Swirl-Stabilized Flame
Authors: Rodriguez Camacho Javier , Akiki Michel , Blust James , O’Connor Jacqueline
Published: September 2023

Carbon sequestration and utilization has been proposed as a method for decarbonizing high-efficiency industrial gas turbines operating on natural gas fuels for power-generation and industrial markets. To increase the efficiency of the carbon removal process from the exhaust stream of the turbine, exhaust gas recirculation (EGR) can be used. EGR recycles a portion of the engine exhaust into the inlet, increasing the concentration of inert species in the exhaust stream to improve the performance and cost effectiveness of CO2 separation systems. This strategy can, however, reduce the oxygen concentration in the air, leading to changes in flame stabilization in the combustor. In this study, we investigate the effect of air diluted with inert gases of different compositions and the impact that these mixtures have on flame static and dynamic stability. A swirl-stabilized flame in a single-nozzle, variable-length combustor is used to measure the flame behavior for oxygen concentrations of 15% to 21% by volume. A constant adiabatic flame temperature test matrix is conducted to mimic operation in an industrial gas turbine. High-speed chemiluminescence imaging is used to determine the change in flame shape and dynamics for each gas composition. As the oxygen concentration decreases, the flame lifts from the centerbody, resulting in an aerodynamically-stabilized flame at the lowest O2 concentrations. Different compositions of gases result in different flame shapes, where higher levels of N2 in the diluents result in more flame stabilization in the outer recirculation zone as compared to those with higher levels of CO2. The flame oscillation mechanisms also change with oxygen concentration, where the lifted flames at low O2 levels exhibit an ignition/extinction oscillation mode as compared to a vortex-shedding-coupled oscillation mode at high O2 levels where the flame is stabilized on the centerbody. Companion chemical kinetics simulations are used to explain changes in the flame’s shape and behavior.
Evaluation of Torque Transmission Capacity for Centrifugal Compressor Impellers With Pre-Generated Data From Finite Element Analysis
Authors: Jin Hanxiang , Pettinato Brian , Shoup Frank
Published: September 2023

The evaluation of torque transmission capacity for centrifugal compressor impellers can be complicated due to the unique geometric characteristics of the impeller wheels. The existing analytical method for keyless interference fit only works for simple geometries like cylinders. In general, finite element analysis (FEA) simulations are needed to obtain the torque capacity of centrifugal compressor impellers for a specific setup (rotational speed/geometric scale/interference fit rate). However, when the torque capacity needs to be evaluated in multiple working conditions, the time cost of FEA simulations can be an issue if each case is evaluated individually. In this study, a methodology is provided to obtain the torque capacity of centrifugal compressor impellers instantly for any given working conditions with pre-generated data from FEA simulations, especially with scaling of the interference fit rate. If the interference fit rate (ratio of interference fit to diameter) is kept the same as the pre-generated FEA data, the results can be directly scaled by rotational speed and geometric scale factor which is covered by the existing method and not the focus of this study. If the given interference fit rate is different than the setup in pre-generated FEA simulations, then an engineering approximation is used to calculate the contact pressure and torque capacity based on impeller bore deformation. In this methodology, the FEA simulations are performed before knowing the working conditions which can be very useful in many time-sensitive industrial applications.
Windage Loss and Flow Characteristics in Back Gap of Radial Inflow Impellers With Steam Medium
Authors: Zhao Zhuobin , Deng Qinghua , Hu Lehao , Li Jun , Feng Zhenping
Published: September 2023

The impeller back gap of radial inflow turbines generates disk-type windage loss, and it is necessary to accurately predict and minimize the loss. In this paper, a steady-state numerical analysis for a two-stage radial inflow turbine with steam as working medium is carried out, and a modified model for predicting the windage loss is proposed and validated. Under the design condition, the windage loss affects obviously the turbine power output, the power of the Stage 1st and Stage 2nd reduced by 6% and 5%, respectively. The back gap makes the vortex structure of the impeller leading edge enhanced, and pressure distribution turns different at the blade inlet section. With the increase of rotational speed and mass flow rate, the vortex structure near the outlet expand and moves radially to the center of the gap. Finally, models from Daily and Coren indicate that Reynolds number and throughflow Reynolds number are important influencing parameters for windage loss in disk-type gap with throughflow. And the results show that the Daily model is more accurate. Therefore, based on the simulation results, a model is proposed to improve the accuracy of windage loss model. And the model containing these two parameters can accurately predict the windage loss with a maximum deviation of 10.6 %. Despite its preliminary character, the model has an important reference value for the design of radial inflow turbomachinery.
Influence of Elevated Temperature Solid Particle Erosion on Strength Degradation of Oxide/Oxide Ceramic Matrix Composites
Authors: Mirza Farhan , Panakarajupally Ragav P. , Rassi J. E. , Morscher Gregory N. , Abdi Frank , Choi Sung
Published: September 2023

The erosion behavior of an oxide/oxide ceramic matrix composite was characterized at 800 °C and 1200 °C. The effect of erodent particle velocity and temperature were investigated. Microscopic analysis was performed to understand the intensity of damage through depth profiling. The room temperature tensile strengths with digital image correlation were performed to evaluate retained mechanical properties of oxide composites. The results indicate that erosion rate increases with increase in particle velocity and temperature, the former being more consequential. Residual strength tests indicate that specimens impacted at higher velocity and temperature showed lower strengths due to increasing crater depth. The erosion behavior was similar to previous results on oxide/oxide composites.
CFD Analysis and Experimental Validation of a sCO2 Pocket Damper Seal
Authors: Ganiger Manjush , Vannini Giuseppe , Bigi Manuele , Vidyasagar R. , Cangioli Filippo
Published: September 2023

Supercritical CO2 (sCO2) used as a closed loop fluid for power cycles in waste heat recovery or small energy production services significantly reduces the size of turbomachinery due to high operating pressure and density of sCO2 fluid above its critical point. For this reason, this OEM is working to develop the relevant centrifugal compressor technology.

A damper seal like a Pocket Damper Seal (PDS) is a very effective choice for a sCO2 compressor balance piston both in design conditions and in a potential transient scenario operating in multiphase regime. The leakage and rotordynamic coefficients predictions for such a seal are very critical when this is operating close to CO2 critical point due to the large variation in gas properties.

In this paper, a PDS with upstream shunt-holes is the subject of the study. A Bulk Flow Model (BFM) approach was originally used to design the PDS for both leakage and rotordynamic coefficients. To verify the design of such a seal, a Computational Fluid Dynamics (CFD) based approach was employed at a later stage. The CFD approach outlines the use of various Equations of States (EOS) like Peng-Robinson, Redlich-Kwong, and Span-Wagner (NIST-Refprop) for the computation of leakage flow. Sensitivity study on the range of NIST-Refprop look-up table was also carried out to have a trade-off between leakage accuracy and computational time. The CFD based rotordynamic coefficients were also computed using the Integral Perturbation method (IPM) by leveraging NIST-Refprop EOS.

The experimental data are relevant to the sCO2 compressor prototype tested at the Authors’ internal test bench. Various parameters related to compressor performance along with balance piston leakages were measured. The leakage flows predicted by the CFD and BFM approaches were validated against the experimental results.

Leakage comparison results show that BFM approach predictions are underestimating the experimental results. The CFD approach, on the other hand, overpredicts the leakage flow especially for the high-pressure operating points. The CFD approach was also validated for 6 different operating points of the compressor. Rotordynamic coefficients prediction from the CFD approach shows very good agreement with the BFM results at the design point and both agree with the test results which always showed a very stable compressor behavior.
CFD Analysis of The Effect of a Cylindrical Probe Rod in the Axial Gap of the Last Stage on Rotating Instabilities in a Low-Pressure Model Steam Turbine Operating at Low Load
Authors: Ercan Ilgit , Vogt Damian M.
Published: September 2023

Steam turbines are sometimes operated at extreme part-load conditions, specifically when the energy balance in power grids featuring a high share of fluctuating energy sources necessitates such operation. At these extreme operating conditions, the last stage rotating blades of the low-pressure turbine are subject to highly unsteady flow. As the flow is heavily separated, Rotating Instabilities (RI) may develop, among other turbulent effects. These highly unsteady flow structures result in fluctuations of the flow field over a wide range of low frequencies.

This study is based on the findings of a previous study in which Improved Delayed Detached Eddy Simulation (iDDES) has been applied to low-volume flow operating conditions to simulate RI [1]. The analyzed domain consists of a three-stage low-pressure model steam turbine. To capture the resulting rotationally asymmetric effects of the RI in the flow field, the computational model spans the full annulus and comprises the non-axisymmetric inlet section, all three stages, the axial-radial diffuser as well as the exhaust hood.

In a second study, it was shown that rotating instabilities in this analyzed model turbine are formed when the vortices created during perpetual separation mechanisms interconnect due to the increased ratio of the circumferential velocity in relation to the decreasing axial flow velocity during low volume flow [2]. Furthermore, it was found that the frequency spectra of the pressure signals at various radial heights obtained during experimental probe traverse differed from the numerical results recorded from the CFD domain. The present study aims to understand the differences in the flow field caused by the probe rod used for the experimental traverse. The experimental results with and without the probe traverse rod were compared, showing a decrease in pressure amplitudes at the casing when the rod is present in the axial gap of the last stage. In order analyze the difference in unsteady pressure signals, the continuous wavelet transform method was applied to evaluate the changes in frequency content in the signals with time.

Additionally, a cylindrical probe rod spanning the full span from hub to casing was implemented into the CFD domain and this decrease in amplitudes was also replicated numerically. To examine the detailed mechanisms behind this change in the flow field, advanced visualization and quantitative methods were employed.
Development of an Hydrogen Fueled Gas Turbine Combustion System From Conceptual Through Full Scale Verification Test
Authors: Cerutti M. , Pucci E. , Romano C. , Dabiru V. R.
Published: September 2023

The development phases of an hydrogen fueled combustor for industrial gas turbine are presented in this paper, from the conceptual burner design definition to the verification phase in realistic environment.

The development strategy has been conceived to properly balance the market needs and the effort required to achieve them. The hydrogen combustion technology is mainly focused on flashback free burners and gas fuel injectors development, representing a significant fuel flexibility enhancement of the NovaLT gas turbines family.

The readiness of the currently available technology in dealing with hydrogen was verified in a dedicated testing session, in a full scale annular combustor rig. Stable flame windows were identified for different operating conditions, and characterized in terms of pollutant emissions, pressure pulsations and system component temperatures.

As matter of this work, a bunch of alternative burner solutions have been designed with the aim of reducing the NOx emissions while maintaining adequate limits to either blowout, flashback or thermoacoustic instabilities. To further mitigate the risk of high NOx emissions, the abatement though water injection has been investigated as well. An atmospheric reduced scale rig has been used to characterize the different viable burner solutions, ensuring fast and somehow iterative design changes, and arranged to mimic the main features of a industrial sized gas turbine combustor, namely the combustion air inlet temperature, the hot gases residence times and the equivalence ratio.

The results clearly indicate a viable candidate to be assessed in the more realistic environment represented by the full-annular rig. The main outcomes of such a test campaign are also reported in this paper, with focus on both the NOx emissions and the operability related aspects. Flashback and flame holding resistance tests have been thus performed, demonstrating that such a solution is technologically ready for the next verification step in a real engine.

The results, while indicating a design development paths for the investigated solutions, provide an exhaustive data set, useful to either the models validation or the identification of the developments needed for future detailed investigations.
Experimental and Computational Heat Transfer Study of sCO2 Single-Jet Impingement
Authors: Richardson John , Wardell Ryan , Fernandez Erik , Kapat Jayanta S.
Published: September 2023

The present study experimentally and computationally investigates the heat transfer capability of supercritical carbon dioxide (sCO2) single jet impingement. The evaluated jet Reynolds number range is between 80,000 and 600,000, with a non-dimensional jet-to-target surface spacing of 2.8. CO2 impinging jet stagnation conditions were maintained at approximately 200 bar and a temperature of ∼400 °C for most experiments. The goal is to understand how changes in the aforementioned parameters influence heat transfer between the working fluid and the heated surface. Additionally, due to the elevated Reynolds numbers and difference in thermodynamic properties between air and CO2, air derived impingement correlations may not be appropriate for CO2 impingement; these correlations will be evaluated against experimental sCO2 impingement data. At the time of this study, no sCO2 impingement data was available relevant to sCO2 power cycles. The target surface is a 1.5-inch diameter copper block centered on the 3 mm jet orifice. A mica heating element bolted to the bottom of the copper block provides a uniform heat flux. Thermocouples embedded in the copper block are used to determine the surface temperature. Nusselt numbers obtained from experimental sCO2 test data are compared to area averaged Nusselt numbers from air derived correlations. The comparisons showed that air correlations drastically underpredict the heat transfer when sCO2 is used as the working fluid. A modified sCO2 correlation using experimental data at discussed conditions, is derived based on an existing air correlation. A CFD study is also performed to further investigate sCO2 heat transfer characteristics, and asses the numerical model applicability to this problem type.
Pollutant Emissions Reporting and Performance Considerations for Ammonia-Blended Fuels in Gas Turbines
Authors: Douglas Christopher M. , Martz Thomas D. , Steele Robert C. , Noble David R. , Emerson Benjamin L. , Lieuwen Timothy C.
Published: September 2023

To limit climate change and promote energy security, there is widespread interest towards transitioning existing fossil fueled combustion systems to sustainable, alternative fuels such as hydrogen (H2) and ammonia (NH3) without negatively impacting air quality. However, quantifying the emission rate of air pollutants such as nitrogen oxides (NOx) is a nuanced process when comparing pollutant emissions across different fuels, as discussed in our paper GT2022-80971 presented last year. That study indicated that the standardized approach for measuring combustion emissions in terms of dry, oxygen-referenced volumetric concentrations (i.e. ppmvdr) inflates reported pollutant emissions by up to 40% for hydrogen combustion relative to natural gas. In this paper, we extend our prior analysis of these so-called “indirect effects” on emissions values to ammonia (NH3) and cracked ammonia (i.e., molecular hydrogen and nitrogen, 3H2 per N2) fuel blends. The results reveal that ppmvdr-based pollutant reporting approaches have a less prominent influence on emissions interpretations for molecular ammonia-methane blends than for hydrogen-methane blends. Nonetheless, we still find that ppmvdr reporting induces up to a 10% relative increase in apparent emissions when comparing 100% NH3 and 100% methane (CH4) fuels at an equal mass-per-work emission rate. Cracking the ammonia is shown to increase this relative bias up to 21% in comparison to a methane system. Further analysis shows how drying, dilution, thermodynamic, and performance effects each influence the relationship between ppmvdr and mass-per-work emissions across the spectrum of fuels and fuel blends. Following discussion of these findings, we conclude that quantifying combustion emissions using ppmvdr is generally inappropriate for emissions comparisons and advise the combustion community to shift towards robust mass-per-energy metrics when quantifying pollutant emissions.
A Novel Testing Methodology to Predict the Endurance of Ball Joints in Absence of Lubrication at High Temperature
Authors: Bucciarelli Federico , Macoretta Giuseppe , Monelli Bernardo Disma , Beghini Marco , Conforti Federico , Bellacci Michelangelo , Giusti Enrico
Published: September 2023

The enhancement of the operational flexibility of axial expanders can be obtained through the implementation of Nozzle Guide Vane (NGV). This design architecture includes moving parts typically sustained by ball joints, whose wear behavior might be important to define the maintenance interval of the expander and define its operational availability. This is especially true when considering challenging loading and temperature conditions. Usually, tribological tests are performed by pin-on disk or similar test methods. However, these techniques neglect important factors as actual sliding zone and contact morphology, which can be fundamental for ball joints.

This work deals with the design of an innovative experimental test procedure for the characterization of the tribological behavior of ball joints considering the actual operating conditions of a NGV at 500°C. The core of the methodology is a customized test bench specifically designed to investigate actual commercial ball joint in field conditions. Details on the design phase and on the commissioning of the experimental set-up are given. The results of the experimental campaign performed on this novel test bench are presented: the chosen test matrix explores a wide spectrum of load and sliding speed. Specimen pre-load and working velocity have been scaled-up to achieve viable testing duration. The test bench was employed on three different kinds of commercial ball joints for high-temperature applications in absence of lubrication. Measurement of diametral clearance and friction in worn conditions were also performed. The results discussion allowed to choose the most suitable solution for a specific design targeting 50000 working hours.
Design of a New Bench for High Temperature Static and Endurance Testing of Nozzle Guide Vane Bushing
Authors: Bucciarelli Federico , Giusti Enrico , Bellacci Michelangelo , Checcacci Damaso , Maestrale Francesco , Manconi Salvatore
Published: September 2023

Variable Guide Vanes such as Inlet Guide Vanes (IGVs) and Nozzle Guide Vanes (NGVs) are a typical design feature included in gas turbines and axial expanders to achieve improved performance in off-design conditions and, consequently, operational flexibility. In the last years the evolution of the energy market has challenged these components, which were already characterized by an intrinsic complexity, to achieve higher availability performances. For this reason, a deeper experimental characterization of the mechanical behavior of these assemblies has become of interest, especially when considering highly loaded nozzles. In particular, the investigation of the kinematic pairs of NGV is becoming very important in some design configuration. This paper describes the design and the commissioning of a novel advanced bench designed to test full-scale NGVs geometries constituted by stems supported by bushing couples. The bench is designed to perform the measurement of the friction coefficient of the kinematic chain and then to accomplish continuous endurance testing of the bushing/stem pair at high temperature. Details are given regarding the design of the bench components which allow testing of bushing different by size and manufacturing technology. The design verifications needed for the proper bench operation are presented. In addition, the testing procedure is also included which will provide in the upcoming months useful data regarding clearance evolution and, more in general, component lifing.
Mechanical Characterization of Bi-Layer EBC Coatings Under Tension and Bending Using Acoustic Emission and Digital Image Correlation
Authors: P. Panakarajupally Ragav , Morscher Gregory N. , Shi Jun
Published: September 2023

Fracture characteristics of bi-layer environmental barrier coatings (EBC) deposited on a woven ceramic matrix composite (CMC) substrate using air plasma spray (APS) processes were investigated under uniaxial tension and bend tests at room temperature. Health monitoring techniques such as acoustic emission (AE) and digital image correlation (DIC) were employed to better understand the cracking behavior of the coating and its progression. Post-test microscopy was performed to correlate the coating cracks with DIC and AE location. The results indicate that multiple transverse cracks first occurred in the coating, followed by substrate transverse cracks and additional coating cracks. DIC analysis was able to highlight the formation and location of these cracks. The fracture strength of the coating was estimated assuming the composite beam theory.
Experimental Characterization of Flow Structure and Reynolds Stresses Covering an Entire Rotor Passage of an Axial Compressor
Authors: Saraswat Ayush , Koley Subhra Shankha , Evans Simon , Joly Michael , Katz Joseph
Published: September 2023

This experimental study characterizes the mean flow structure, distribution of Reynolds stresses, and the mechanisms affecting turbulence production in the entire rotor passage of an axial compressor. The stereo-PIV (Particle Image Velocimetry) measurements are performed in the JHU refractive index matched facility and cover an entire rotor passage of a 1.5 stage axial compressor. The rotor blades have an aspect ratio of 0.73 and a measured tip gap of 2.8% of the blade span. The primary focus is on pre-stall flow rate, but trends and distributions are compared to those obtained at a higher flow rate. While many flow features exist at both flow rates, they differ in size, magnitude, and location. The tip leakage vortex (TLV) roll up, breakdown, migration, and double leakage occur earlier, and the associated blockage covers a larger area and has a lower axial and higher circumferential velocity at pre-stall. Furthermore, instantaneous velocity samples and cavitation images at pre-stall showcase transient extreme events involving a backward leakage flow extending upstream of the rotor, spillage of the leakage flow and backflow vortices from one passage to the next around the leading edge (LE), and intermittent boundary layer separation on the blade suction side near the trailing edge. All of these intermittent phenomena affect the distribution of turbulence, including an extension of elevated turbulent kinetic energy (TKE) upstream of the rotor LE plane. The turbulence is particularly high around the TLV, at the interface between the backward leakage flow and the forward passage flow upstream of the TLV, and along the boundary of the blockage area radially inward of the TLV. Vortex breakdown expands the elevated turbulence area substantially. As a general observation, the turbulence is highly anisotropic and inhomogeneous. The spatial distribution and the evolution of the normal Reynolds stresses vary greatly with operating condition and among components. In most regions, the associated trends can be explained by examining the corresponding production rate terms. Finally, a comparison of the TKE and normal Reynolds stress distributions downstream of the rotor as well as the production rates across two compressors show striking similarities, demonstrating that the same flow features play dominant roles in both machines.
Effect of the Blowing Ratio on the Interaction Between a Flame and an Air-Cooled Combustor Wall
Authors: Blaise Antoine , Petit Sylvain , Grisch Frédéric , Xavier Pradip
Published: September 2023

Innovative low-carbon aero-engines rely on ultra-compact and high energy density combustors, increasing the thermal loads of the walls. This study aims at experimentally enhancing the understanding of the interrelated physical processes between a flame, a wall and a cooling technology. The test rig operates at atmospheric pressure and generates a methane/air turbulent flame interacting with a wall that is air-cooled by means of a splash cooling plate device. Optical diagnostics are simultaneously implemented, including reactive particle image velocimetry (PIV) to assess the flow field, planar laser induced fluorescence on the OH radical (OH-PLIF) to study the flame structure, and laser induced phosphorescence to measure the wall temperature in contact with the reactive flow. Results show that the mean flame location is shifted away from the wall as the blowing ratio is increased. The wall temperature reveals that to enhance cooling efficiency, blowing ratio and flame location must not be considered without each other. Eventually, a classical flame-wall interaction process is retrieved when the blowing ratio is small, whereas flame strain, originating from the aerodynamic shear layer, pilots the flame dynamics for large blowing ratios.
Rapid Algorithmic Blade Design Applying Machine Learning From Shape Optimization to Satisfy Multidisciplinary Constraints
Authors: Dasadhikari Kingshuk , Kuwamura Yoshihiro
Published: September 2023

This paper presents a new, rapid, flexible approach for turbine blade section design combining algorithmic and inverse techniques to enable automatic generation of blade sections guaranteed to conform to multidisciplinary requirements, with the aim of accelerating turbomachinery design iterations.

The approach links a base algorithm to parametrize and generate blade section geometry conforming to structural and manufacturability constraints such as section area, trailing edge radius, and exit wedge angle with a 2D CFD solver to calculate surface isentropic Mach number profile for aerodynamic performance evaluation. To achieve blade sections with smooth surface and lenticular Mach number profile concave up on the pressure-side and concave down on the suction-side, the base algorithm is tuned by a surrogate inverse model trained by machine learning from pre-generated tuning data obtained by case-by-case shape optimization for a range of design conditions. A weighted objective function is applied to quantify both geometric and aerodynamic quality of blade sections for the optimization.

Shape optimization improves output section quality by 54–87% compared to the untuned algorithm. Aerodynamically, suction-side flow separation is eliminated in the optimized sections, giving 70% less pressure loss compared to the untuned algorithm for the best cases. Across all conditions spanning the examined design space, the surrogate model successfully captures most of this improvement, yielding blade sections of similar quality to explicit optimization sufficient to meet the geometric and aerodynamic requirements for design. Furthermore, section quality is preserved even if imposed structural and manufacturability constraints are perturbed within typical margins, guaranteeing blade sections that are always viable for practical use. Blade sections from the surrogate-tuned algorithm are output within minutes, eliminating time-intensiveness of existing manual or case-by-case design approaches.
The Role of Turbulence Transport in Mechanical Energy Budgets
Authors: Przytarski Pawel J. , Lengani Davide , Simoni Daniele , Wheeler Andrew P. S.
Published: September 2023

In this paper we study the role of turbulence transport on loss prediction using high fidelity scale-resolving simulations. For this purpose we use eight high-fidelity simulation datasets and compute flux of entropy and stagnation pressure transport equation budgets for all the cases. We find that under certain unsteady inflow conditions the stagnation pressure coefficient is not a reliable loss metric even at low Mach number conditions. This is due to the turbulence transport terms. The impact of these terms, typically assumed to be negligible, made stagnation pressure loss coefficient under-predict loss from 0% to over 40% when compared to entropy loss coefficient for cases considered here. This effect was most pronounced for the cases with highly unsteady inflow conditions and at low Reynolds numbers.
Experimental Study on Total Pressure Distortion Characteristics of a High Bypass Ratio Turbofan Engine
Authors: Li Huihui , Teng Jinfang , Luo Guangqi , Zheng Shangnan , Lv Chongyang , Qiu Chao
Published: September 2023

Relative to the surge and stall compliance governed by civil aviation airworthiness regulation of FAR/CCAR33.65, the engine needs to have adequate stability margin throughout its operating envelope. That requires engine compression components to have sufficient surge margin. Inlet distortion is one of the main factors affecting compression components’ surge margin and engine operability. According to the civil aero engine operation scenario, the most likely cause for total pressure distortion formed by the uneven flow field at the exit of the inlet is crosswind condition. In order to quantify the inlet distortion characteristics and understand the distortion attenuation for each compression component of a high bypass ratio turbofan engine, whole engine inlet distortion test was conducted. Three distortion conditions were simulated by different grids, and the distortion characteristics in terms of distortion index was measured by total pressure rake in the test. The test results showed that for high bypass ratio turbofan engine, the inlet distortion is mainly distributed in the area of outer 60% height of fan blade and does not enter the engine inner flowpath. However initial distortion exists in the clean inlet condition at the outlet of both the outer and inner flowpath since the engine structure is not completely circumferentially symmetric. After passing through the flowpath, the degree of distortion will be reduced. At a maximum IDCmax = 6.5% in the inlet, it is reduced to no more than 1% at both outlets of outer flowpath and booster (excluding the initial distortion due to the initial inhomogeneity). The smaller inlet distortion will produce smaller instability effect to the downstream components. At the higher speed/mass flow condition, the amount of distortion attenuation through the flowpath is larger.
Analysis of Different Emission Metrics for Power Generation Machinery in Flexible Co-Generation Energy Systems
Authors: Goßrau Christian , Petersen Nils Hendrik , Wirsum Manfred
Published: September 2023

There are many different metrics used for characterizing the emission behavior of power generation units, making it difficult to compare different technologies, fuels, and cycle layouts comprehensively. The present study analyses and evaluates different metrics for emission quantification (e.g., relative, absolute, or performance-based values). Mixtures of conventional fuels (natural gas, represented by methane) and alternative, carbonneutral fuels (hydrogen and ammonia) are compared. Different cycle adaptations of power generation systems (exhaust gas re-circulation, water and steam injection) are addressed. Both NOx and CO2 emissions are investigated using a gas turbine model and a chemical reactor network for a state-of-the-art industrial gas turbine. The results show that by using common metrics (i.e., ppmvdr) the emission behavior is significantly and moderately exaggerated for H2 and NH3, respectively. Performance-based metrics, however, are found to be most suitable for emission quantification across different fuels and cycle layouts: for example, if a standard gas turbine NOx emission limit of 15 ppmvdr is applied, lower NOx are found for fuel substitution with H2 than with NH3. Additionally, introducing the equivalent NOx emission limit of 150 mg/kWhel for gas turbines (considering full load efficiency of 39 %) as a regulative limit enlarges the suitable hydrogen addition rate from 47 vol.% up to 60 vol.% H2 from an emission perspective.
Computational Analysis of a Savonius Wind Rotor Using Bio-Inspired Corrugated Blades
Authors: Rathod Umang H. , Kulkarni Vinayak , Saha Ujjwal K.
Published: September 2023

For harvesting wind energy, especially at low-velocity regions, Savonius vertical-axis wind rotors are usually preferred. Among other variants of the vertical-axis wind rotors, the Savonius rotor has become an attractive candidate as a small-scale stand-alone system due to its direction independency, ease of fabrication and the absence of yaw-mechanism. The present paper attempts to study the effect of corrugated blades on the performance of a conventional Savonius rotor. The corrugation is a bio-inspired concept derived from the dragonfly wings. As reported in literature, the corrugation applied in the chord-wise direction of the airfoil improves the lift characteristics. This lift improvement is caused by the trapped vortices inside the corrugation that promotes a low-pressure region over the leading edge and suction surface of the airfoil. This concept of corrugation and its effect has been applied to the blades of a conventional Savonius wind rotor to improve its torque characteristics. In this paper, a rotor with corrugated semicircular blade profiles is studied by two-dimensional (2D) transient numerical simulation in ANSYS FLUENT using shear stress transport (SST) k-ω turbulence model. The simulations are conducted in the range of 5 m/s to 7 m/s to suit the lower wind velocities of the Savonius rotor. The torque and power coefficients of the corrugated semicircular-bladed rotor are calculated at the rotating conditions. Further, the pressure and local torque distributions over the corrugated blade surfaces are obtained and analyzed to understand the torque mechanism of the rotor with corrugated blade profiles. In order to have a direct comparison, the study has also been carried out for semicircular-bladed rotor without corrugation.
A Full Three-Dimensional Transient Fluid-Structure Interaction Model for the Dynamic Characteristics Predictions of Bump-Type Gas Foil Journal Bearings
Authors: Li Zhuocong , Li Zhigang , Li Jun
Published: September 2023

Oil-lubricated bearings are used in most present-day rotating machinery due to their high load capacity. This bearing, however, requires a complicated lubrication system which significantly increases the operating cost of the equipment. Moreover, the problem of the heat generation of lubricated oil after a long time of operation cannot be ignored, especially in high-speed turbomachinery. As for oil-free turbomachinery, the gas-lubricated bearing is regarded as a revolutionary technology to support the rotor. Bump-type gas foil bearing (bump-type GFB) is one of the most widely used gas-lubricated bearings, due to its high speed, low wear, no pollution, high temperature and pressure resistance and other excellent properties. As one of the critical components in the rotor system of a rotating machinery, bump-type GFBs can provide not only the static load capacity but also the dynamic gas film response forces, significantly affecting the dynamic stability performance of the rotor system. Therefore, an accurate and efficient dynamic characteristics prediction method for bump-type GFBs is crucial for the industrial safe operation of the rotating machinery system. This paper focuses on the assessment and validation of a novel numerical method for the dynamic coefficients prediction of bump-type gas foil journal bearings (bump-type GFJBs).

To predict the dynamic characteristics of bump-type GFJBs, in this paper, a novel full three-dimensional (3D) transient fluid-structure coupled numerical method was proposed, based on the finite element analysis (FEA) and the computational fluid dynamics (CFD). In order to improve computational efficiency and conform more to the bearing actual situations, a multiple-frequency elliptical-orbit rotor whirling model for arbitrary eccentric positions was proposed to define the rotor whirling motion, based on the mesh deformation techniques. The present full 3D transient CFD/FEA method was validated by the published experimental data of the dynamic stiffness and damping coefficients of a bump-type GFJB. The influences of the disturbance frequency and foil deformation on the dynamic characteristics of bump-type GFJBs were also presented and discussed.

The results indicate that the dynamic characteristics predicted by the present method has reasonable accuracy compared to the experimental results. The dynamic performance of the bearing is influenced by both the gas film and the foil structure. The foil structure adjusts the thickness and pressure distribution of the gas film through the foil deformation to change the dynamic performance of the bump-type GFJBs. The bump-type GFJB has a positive energy dissipation factor so that the rotor-bearing system supported by bump-type GFJBs has the ability to comeback and remain stable.
Dynamic Response and Suppression Method of High-Speed Rotors Under the Rotary Inertial Moment
Authors: Liu Cong , Wang Dong , Wang Yongfeng , Chen Xueqi , Yang Zhefu , Hong Jie
Published: September 2023

Current studies on rotor dynamic response mainly focus on the unbalance forces caused by mass eccentricity, while little attention is paid to the rotary inertial moments caused by the skew angle of the principal axis of inertia. Especially for the rotors operating at high rotational speeds, the influence of rotary inertial moments on rotor response could not be ignored. Therefore, it is necessary to study the influence of rotary inertial moments on the rotor response and provide corresponding response suppression methods. This paper established a dynamic model based on the key structural characteristics of aero-engine high-pressure rotors. The excitations from mass eccentricity and skew of the principal axis of inertia are both considered. Numerical analysis was performed, which shows that the dynamic response excited by the unbalance force remains at a low level after passing the critical speed, however, the response excited by the rotary inertial moment increases continuously with the rotational speed, because of the self-centering of the principal axis of inertia at the high speed. Experiments are conducted on a test rig, results show that the decrease of local angular stiffness around the disk could reduce the influence of rotary inertial moments, eventually suppressing the dynamic response at high rotational speed.
Extension of the MULTALL Open Source Throughflow Code for the Improved Endwall Loss Simulation
Authors: Bilgiç Mustafa , Baran Özgür Uğraş , Aksel Mehmet Halûk
Published: September 2023

Accurate loss modeling is critical for throughflow calculations to capture correct streamtube geometry and the accurate spanwise distribution of flow properties during quasi three-dimensional design of a turbomachinery blade. In this study, the modification of Cf (friction factor)-based loss computation in MULTALL throughflow code and its difference from classical empirical loss-based throughflow solvers are studied. The original form of the MULTALL applies a constant friction factor on all wetted surfaces to account for the losses in the throughflow analysis. However, in a typical turbomachinery blade passage regardless of being compressor or turbine passage, the entropy generation near the endwall regions cannot be handled by imposing constant Cf on the wetted surface due to the complex endwall flow structure. To improve the loss prediction capability of MULTALL, the friction factor near the endwall regions is modified. Therefore, all these complex flow structures can be resolved. In other words, the Cf distributions are recalculated near the endwall regions such that the secondary and tip clearance losses can be represented accurately. Furthermore, an empirical-based loss prediction capability is also brought to the MULTALL via distributed loss model approach. The entropy gradient required for the calculating of friction force on blade surfaces is calculated from empirical loss models. Then, the calculated friction force is included in the solution via the source term. Both methods are validated with the experimental results of a single stage transonic compressor. The modified Cf model shows better agreement with the experimental data near endwalls as compared to results of empirical based model and the original form of MULTALL solver.