bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Leading Edge Shape on Effusion Film Cooling
Authors: Chang Yu-Chuan , Huang Szu-Chi , Huang Chih-Yung , Liu Yao-Hsien
Published: September 2023

This study investigated effusion film cooling on turbine leading edge model using pressure sensitive paint (PSP) technique. Three leading edge profiles were tested, including a semi-cylinder and two elliptical leading edge models. Effusion cooling was implemented using a large number of holes with small hole-to-hole spacing, and Stereolithography was used to produce the perforated region. Effects of blowing ratio (0.4, 0.8, and 1.2) were tested and the density ratio was maintained at unity. Three rows of film cooling holes were employed on these leading edge models as a traditional film cooling scenario for benchmark testing. These film cooling rows exhibited 15 holes, located at the stagnation line (0°) and at ±30° away from the stagnation line. These test models were installed in a low-speed wind tunnel for testing. The Reynolds number was 100,000, which was estimated using the mainstream velocity and semi-cylinder diameter. Two streamwise spacings of the effusion holes were studied. The effusion cooling showed higher cooling effectiveness compared to the traditional film cooling. Increasing the streamwise spacing lowered the cooling effectiveness regardless of the leading edge profile. The variation of the blowing ratio had smaller effect on the effusion cooling effectiveness and coolant blow-off was not substantial.
Recursive Sequential Combustion Using Multiple Discrete Sectors
Authors: Giuliani Fabrice , Hofer Andrea , Paulitsch Nina , Akin Bugra
Published: September 2023

Recursive Sequential Combustion (RSC, introduced in paper GT2021-59592) is a new concept that maximises the interaction between burned gases and fresh reactants. The novelty compared to other concepts of flue gas recirculation in gas turbines is that this interaction is solely driven by the flow dynamics in the combustor. It consists of a novel inlet/outlet arrangement and an advanced flow design, which avoids complex extraction, reconditioning and re-injection of flue gases. The key feature is the burner arrangement which places the flames one after the other in a closed loop, maintaining a trapped circulation of constantly renewed hot gases flowing along annulus of the chamber. The aim is to achieve robust lean combustion supported by the high temperature of the flue gases, combined with the reburning effect of sequential combustion. The expected benefit of this technology is a steady lean operation with significantly lower NOx and soot formation than in conventional GT combustors.

This paper focuses on the flow design using a multiple discrete sector approach. A discrete sector has an inlet and an outlet accompanying the recursive hot gas flow, which is supplemented by fresh mixture injection, a flow mixer/conditioner, a flame tube and a flue gas separator. The N sectors are then arranged in a closed loop. Side feeds and outlets, as well as periodic boundaries along the annulus, allow circulation to occur.

An advanced discrete-sector concept designed for demonstration purposes is presented. The flow design is studied by CFD and supported by basic experiments. It is shown that the burnt gas circulation and interaction are effective, and that the closed loop recursive sequential combustion is within reach, demonstrating the plausibility of the concept.
A Data-Driven Approach for Generalizing the Laminar Kinetic Energy Model for Separation and Bypass Transition in Low- and High-Pressure Turbines
Authors: Fang Yuan , Zhao Yaomin , Akolekar Harshal D. , Ooi Andrew S. H. , Sandberg Richard D. , Pacciani Roberto , Marconcini Michele
Published: September 2023

The laminar kinetic energy (LKE) transition model recently has shown good predictions on separation-induced transition that frequently experienced by low pressure turbines (LPT). In contrast to LPTs, high-pressure turbines (HPT) often are subject to bypass transition which currently is not captured well with the LKE model. Because these two types are common transition modes for turbines, the current effort is focused on generalizing and improving the LKE model to be able to predict the different types of transition. In addition to modify the transition model to achieve better on-blade predictions, the turbulence model in the wake region is also revised for more accurately capturing the wake mixing. Hence, the main purpose of this study is to use a data-driven approach to simultaneously develop spatially separate transition and turbulence closures suitable for a range of different turbine configurations. To achieve this, two strategies are adopted. The first is to employ a multi-case multi-objective computational fluid dynamics (CFD) -driven model training framework. The training is performed on several LPT and HPT configurations, specifically the T108, T106A, and LS89 sections, that feature both separation-induced and bypass transition to ensure better generalizability of the models. The second strategy employed is the use of a newly derived set of local non-dimensionalized variables, that serves as the inputs for the LKE model corrections. Among the training cases, steady calculations are conducted for LPTs. The LS89 case is an HPT characterized by shocks, acoustic waves, and unsteady trailing edge vortex shedding. To capture these, for the first time an unsteady solver is utilized during the CFD-driven training, and the time-averaged results are used to calculate the cost function as part of the model development process. The model obtained from the new training process are tested on the a steady case - T108 with a higher Reynolds number and an unsteady case - PakB profile. Their performance are assessed in terms of pressure coefficient, wall shear stress and wake losses.
Mistuning Strategy on Long Blades to Mitigate Flutter
Authors: Pinelli Lorenzo , Arnone Andrea , Peruzzi Lorenzo , Bettini Claudio , Finzel Conrad , Kellerer Rudolf
Published: September 2023

Nowadays, the current favoured form for energy production is combined cycle, which allows efficient solutions through reduction of fuel consumption and hence a lower impact in terms of pollutant emissions. At the same time, the continuous request of more efficient solutions translates into large, higher flowing machines with slender and loaded blades.

The design of such blades now needs to include aeromechanical interactions, such as transonic conditions at the tip, leading to shock wave systems that impinge on and interact with the blade surfaces and high load conditions increasing the occurrence of flow induced vibrations as flutter.

Nowadays reliable CFD prediction models are used to estimate flutter stability based on the minimum of the logarithmic decrement curve to design robust configurations for the long rotor blades.

Currently, mistuning is one of the most used flutter mitigation techniques as it can be implemented in the field via, for instance, blade mass removal (e.g. Trailing Edge cutback), that also leads to a performance degradation. Methods are available for the application of mistuning to free standing blades. This paper provides an introduction to the physics of and methodology for determining mistuning solutions on mechanically coupled blade systems.
Preliminary Numerical Study of Methane-Hydrogen Co-Combustion Effects on Heavy-Duty Gas Turbines
Authors: Ancona Maria Alessandra , Bianchi Michele , Branchini Lisa , Catena Francesco , De Pascale Andrea , Ferrari Federico , Melino Francesco , Peretto Antonio
Published: September 2023

The use of hydrogen as a fuel for gas turbines is certainly an opportunity to limit greenhouse gas emissions, despite the still not-negligible limitations related to materials and the management of combustion processes.

This work aims at proposing a numerical model, developed by the Authors by means of the link between Matlab™ environment and Aspen HYSYS™ environment, able to evaluate the performance of commercial gas turbines with a set geometry in response to the co-combustion of CH4 and H2 for different fuel mixture compositions.

The purpose of this study is therefore to propose a modelling approach to assess the use of hydrogen injection in the combustion chamber of commercial gas turbines, already in operation, as a short-term strategy for reducing carbon emissions.

The preliminary results obtained by the simulation process show that the increase in the hydrogen content in the fuel mixture, up to a maximum of 62% by volume, corresponds to a slight decrease in the performance of the machine, in particular net electrical power and efficiency, of about 3%, but also to a reduction in CO2 emissions of more than 30%.
Automated Analysis of Stall Inception in Multistage Compressors Using 1D Methods
Authors: Conser Benjamin , Goldenberg Vlad
Published: September 2023

A compressor operating in stall can lead to large aerodynamic losses and potentially compressor surge. Understanding the operating point where stall first occurs is of importance to turbomachinery design engineers as they iterate between designs during the design process. A methodology has been developed which predicts the onset of stall using a 1D-solver approach. This methodology shows reasonable agreement in the stall inception point compared to both 3D CFD and experimental approaches. Utilizing this 1D approach allows for the prediction of the stall point, as well as the identification of the compressor stage where stall inception occurs, all in a matter of minutes. This allows for more rapid and targeted design changes earlier on in the engineering design process.
A New Empirical Correlation for Transition in Both Short and Long Separation Bubbles
Authors: Petronio Daniele , Dellacasagrande Matteo , Simoni Daniele , Lengani Davide
Published: September 2023

With the aim of improving the predicting capability of current correlation-based transition models, a new correlation for transition in separated flows is presented, which is based only on local quantities. The peak value of the vorticity-based Reynolds number at the detachment position has been chosen as a local indicator of the boundary layer state. As largely discussed in the literature [1], this facilitates the implementation of transition models into modern numerical schemes, characterized by parallel execution and unstructured grids.

The current experimental database consists of a total amount of almost 90 flow conditions concerning a flat plate boundary layer developing under variable Reynolds number, free-stream turbulence intensity and adverse pressure gradient. The typical operating conditions of low-pressure turbine profiles have been reproduced. Due to the wide range of Reynolds numbers tested, the bursting process of the laminar separation bubble has been observed. Using the present database, a proportionality coefficient between the momentum-thickness and the vorticity-based Reynolds numbers at the separation position has been computed, which is found to be the same for both short and long bubbles. This provides the link between local and integral quantities of the boundary layer. Then, the vorticity-based Reynolds number is adopted as main ingredient of a correlation for the prediction of the transition onset in separated boundary layers. The influence of other factors such as the free-stream turbulence and the streamwise pressure gradient has been also considered. The present work is thought to improve the code ability in predicting the profile losses and the blade loading distribution in case of separated flows, for both short and long bubble states.
On the Demonstration of a Humid Combustion System Performing Flexible Fuel-Switch From Pure Hydrogen to Natural Gas With Ultra-Low NOx Emissions
Authors: Dybe Simeon , Yasir Muhammad , Güthe Felix , Alemela Reddy , Bartlett Michael , Schuermans Bruno , Paschereit Christian Oliver
Published: September 2023

To fight global warming the European Union formulated the objective of completely decarbonising the energy sector, stimulating the advent of unconventional fuels and the adaption of the corresponding energy infrastructure. The decarbonisation strategy identified hydrogen to play a key role as an energy storage medium, making systems capable of pure hydrogen operation essential.

This requirement can be fulfilled with humid power cycles which offer additional advantages such as highly efficient and fuel-flexible operation with low emissions. As an integral part of such a cycle, a humid combustion system was presented previously showing promising results with respect to complete combustion with low emissions for a variety of fuels.

The current work introduces an upgraded version of that combustion system. The new Double Swirler system is capable of stable and safe combustion of low calorific value bio-syngas surrogate, hydrogen, and natural gas, from dry to steam-rich conditions within the required pressure drops. The inclusion of dry operation of the system can benefit the start-up procedure of the humid cycle.

The combustor’s fuel switching performance is demonstrated by a fast fuel switch at full load from pure hydrogen to pure natural gas and vice versa, while maintaining a stable performance with low NOx-emissions at otherwise constant operation parameters.
Role of the Inducer in Flow Instability of a High-Speed Centrifugal Compressor Impeller
Authors: Zhang Meijie , Wu Wangxia
Published: September 2023

The performance of a high-speed centrifugal compressor has been numerically studied in this paper. The flow instability of the centrifugal compressor impeller, in the inlet blade tip Mach number range of 0.57 to 0.92, is reviewed from the different perspectives of the inducer and centrifuge. The results show that the roles of the inducer and the centrifuge in the evolution of impeller flow instability are fickle. At the large mass flow rate far away from the onset of impeller flow instability, the inducer has been unstable, and the flow field analysis indicates that the leading-edge flow spillage can be used as the criterion for the onset of inducer flow instability. As the mass flow decreases further, the flow stability of the inducer worsens first and then becomes neutral. However, the flow stability of the centrifuge worsens continually and finally results in impeller flow instability. The back flow relates closely to the flow instability of the inducer and the centrifuge, and the detailed blade-to-blade flow field and the back flow loss are investigated. The results imply that the design of a new device to control the back flow in the centrifuge may obtain a wider stable flow range than the traditional recirculation casing treatment on the inducer casing.
Design of a Swirl-Stabilized Burner With Fluidically Variable Swirl Number
Authors: Eck Mattias Ettore Giulio , zur Nedden Philipp Maximilian , von Saldern Jakob Georg Raimund , Orchini Alessandro , Paschereit Christian Oliver
Published: September 2023

For flame stabilization, burner systems are usually equipped with swirlers which incite a defined air rotation, quantified by the swirl number. In consequence, the swirl number, which significantly influences the flame dynamics, is fixed. Applications exist in which the swirl number can be varied through mechanically adjustable swirler geometries. Such systems, however, comprise moving parts and actuators, the operation of which might be disadvantageous in a combustor environment. Hence, a swirler is developed that allows for continuous swirl number changes by means of fluidic flow control. The direction of a primary air flow is changed through the injection of an adjacent wall jet which follows a curved surface. This causes a directional change of the primary flow due to entrainment effects. The swirler consists of a cylindrical plenum into which a primary air flow is led through azimuthally distributed channels. Each channel comprises a slotted wall. A secondary air mass flow can be induced passing through the slots, hence creating an adjacent wall jet, which subsequently follows a curved surface. The resulting azimuthal direction change of the primary flow depends on the induced secondary air mass flow. The angular flow momentum and thus the swirl number can be therefore continuously changed. The development process of the proposed swirler is presented and the efficiency of swirl variation of different geometries is qualitatively assessed through computational flow simulations. The effects of stationary operation and unsteady swirl number variations are herein investigated and, moreover, the variation performance is assessed for a range of different air mass flows. The simulation results show the potential of a linear swirl number variation with respect to the induced secondary air mass flow. Moreover, the simulation results show that the achieved swirl numbers are comparable to those of state-of-the-art swirlers.
Quantifying Part-to-Part Flow Variations and Cooling Effectiveness in Engine-Run Blades
Authors: McCormack Kelsey E. , Gailey Nicholas L. , Berdanier Reid A. , Barringer Michael D. , Thole Karen A.
Published: September 2023

As turbine inlet temperatures continue to increase for modern gas turbine engines, the lifing of hot section components operating in a range of environments is becoming increasingly challenging. Engine operations in harsh environments can cause a reduction in cooling capability leading to reduced blade life relative to existing experience. This study analyzes the effects of harsh environments on the deterioration of blade flow and cooling effectiveness in turbine blades by comparing three commercially-operated engines with varied operational times referenced against a baseline blade. Spatially-resolved surface temperatures measured using infrared thermography at high-speed rotating conditions were evaluated to determine variations in cooling effectiveness as a function of engine operation and blade-to-blade variability from the different commercial applications. Engine-run blades were found to have reduced flow as well as greater part-to-part variation when compared to baseline blades. Blade surface temperature measurements on the deteriorated operational blades indicated film cooling traces dissipated closer to the hole exit relative to baseline blades. Furthermore, the cooling effectiveness varied significantly even between blades from the same engines. The reduction in cooling effectiveness in the engine-run blades led to higher blade temperatures and significantly shorter component life, with some exhibiting as much as an 18% reduction in life compared to baseline blades. This knowledge allows lifing models to be developed toward predicting blade operational effects in harsh environments.
An Optimized Chemical Kinetic Mechanism for the Accurate Modelling of Low Temperature Combustion of Syngas and Methane
Authors: Methling Torsten , Schmidt Marleen , Naumann Clemens , Köhler Markus
Published: September 2023

In the present study, the chemical kinetic mechanism DLR SynNG for the combustion of syngas and natural gas is optimized with various experimental data points with a focus on low temperature chemistry. For the optimization approach, the framework of the linear transformation model (linTM) is applied. The linTM was designed to optimize chemical kinetic model parameters with target quantities from a broad range of experimental facilities, like shock tubes, flow reactors, jet stirred reactors or various burner configurations. In this work, the optimization capabilities were extended for data from rapid compression machines (RCM), which are commonly used to investigate the ignition behavior under low temperature combustion conditions. RCM are typically simulated with homogeneous reactors with constrained pressure or volume profiles derived from the experiments. With the implementation of the RCM into the linTM framework, a novel parameterization approach for the simulation with constrained volume profiles is proposed. This new approach results in significantly reduced computational costs of RCM simulations and increased numerical stability for solving the underlying ordinary differential equation systems. Since several thousand RCM simulations throughout the optimization process are needed, this is highly beneficial for the applied optimization of the chemical kinetic mechanism.

In detail, the rate coefficients of sensitive reactions were optimized within their uncertainty boundaries. The optimized chemical kinetic model is capable of reproducing a broad range of experimental data for a large field of boundary conditions and fuel mixtures of hydrogen, carbon monoxide, methanol and methane. The experimental data include ignition delay times, laminar burning velocities as well as species profiles from flow reactors, jet stirred reactors and different laminar flame configurations.
Application of Compressed Sensing Method With ℓ1/2-Norm in Fan/Compressor Mode Detection
Authors: Li Zhaoyin , Yang Zeyuan , Chai Pengfei , Sun Zonghan , Tian Jie , Ouyang Hua
Published: September 2023

In this paper, ℓ1/2-norm method is used to replace the traditional ℓ1-norm to improve the compressed sensing technique. Numerical experiments and fan/compressor tests were performed to validate the applicability and robustness of the CS method based on ℓ1/2-norm. Numerical experiments show that ℓ1/2-norm method can effectually eliminate the spurious mode peaks generated by failed recovery of ℓ1-norm method. Further study with random sensor failure shows the stronger robustness and applicability of ℓ1/2-norm method. In the low-order acoustic mode detection experiment on cooling fan, 24 sensors were used to conduct a mode decomposition at blade passing frequency (BPF). The recovered signal using ℓ1/2-norm method was sparser than that using ℓ1-norm method. In the case two sensors were randomly selected and removed as failed sensors, the deviation between results of ℓ1/2-norm method and original signal was also found smaller. In the condition that more sensors failed and ℓ1-norm method did not work properly, ℓ1/2-norm method could still detect the main mode. For further validation, the data from a high-order aerodynamic pressure mode detection experiment on axial compressor with two sensors damaged was processed through ℓ1/2-norm method. The mode decomposition results at both BPF and the rotating instability frequency (RIF) agreed with the conclusion of the first experiment. Numerical experiments and fan/compressor tests show that using ℓ1/2-norm instead of ℓ1-norm can significantly improve the application and robustness of compressed sensing in mode detection.
Numerical Investigation Into the Impact of Operating Boundary Conditions on NOx Formation in Hydrogen Micromix Combustion System
Authors: Singh Gaurav , Zghal Malika , Sun Xiaoxiao , Gauthier Pierre , Sethi Vishal
Published: September 2023

Hydrogen micromix combustion is a promising technology for achieving zero mission-level carbon emissions with ultra-low NOx potential. A reduced-order NOx emissions prediction model is essential for preliminary hydrogen engine cycle design space exploration and optimization studies.

Hence, this paper investigates the influence of key operating conditions, including equivalence ratio (ϕ), combustor inlet temperature (T3) and pressure (P3) on NOx emissions in a hydrogen micromix combustion. The assessments were performed using steady Reynolds-Averaged Navier-Stokes (RANS) simulations with thermal NOx model at various power conditions representative of the aircraft mission. The RANS model constants were calibrated against Large Eddy Simulations (LES) conducted previously by the group. The comprehensive numerical database was developed from these assessments to derive a NOx emissions correlation as a function of the operating conditions defined above.

The study demonstrates that the LES-calibrated RANS models can predict NOx emissions trends, which agrees with the known physics of NOx formation. When experimental data is not yet available, the resulting correlation can be used at the preliminary stage of the design process to identify low NOx engine cycles that merit (more resource-intensive) higher fidelity numerical simulations or experiments. The methodology is flexible and extensible and may be applied to future low-emissions hydrogen combustion technologies.
Numerical Investigation of a Hydrogen-Air Flame for NOx Prediction
Authors: Leparoux Julien , Mercier Renaud , Puggelli Stefano , Cailler Mélody , Moureau Vincent
Published: September 2023

Sustainable Aviation Fuels (SAF) are a major candidate to reduce pollutant emissions in future aeronautical engines. Recently, the use of hydrogen as a fuel has gained a high interest partly because its combustion is free from carbon dioxide, a greenhouse gas, and produces few pollutants, mainly nitrogen oxides (NOx). Over the last decades, efforts on numerical methods for combustion simulation in aero-engines have largely been focused on kerosene-air combustion. However, the current transition may have a significant impact on the computational methodologies for combustor design. Hydrogen defines novel modeling issues and challenges the current state of art on numerical methodologies. The current study presents a numerical investigation of a hydrogen-air burner using Large-Eddy Simulations (LES) with a focus on NOx prediction. The considered configuration is a two-staged combustor, similar to the well-known RQL (Rich-Quench-Lean) technology, supplied by a single coaxial injector characterized experimentally. Two combustion models are investigated: i) tabulated chemistry based on premixed flamelets ii) transported chemistry description by using a 21-species chemical scheme. Numerical results are compared with experimental data (NOx concentrations, temperature distributions, pressure losses). A focus on models predictions is carried out.

Results show a good agreement to predict the main flow characteristics and the premixed flame position over different operating points and geometries for both frameworks. In contrast, NOx emissions are more sensitive: while the overall trend is well captured, the quantification is more scattered. Finally, an in-depth analysis is proposed to link NOx production with the non-premixed flame size.
Integrated Hybrid Engine Cycle Design and Power Management Optimization
Authors: Ghelani Raj , Roumeliotis Ioannis , Saias Chana Anna , Mourouzidis Christos , Pachidis Vassilios , Bacic Marko , Norman Justin
Published: September 2023

A novel integrated gas turbine cycle design and power management optimization methodology for parallel hybrid electric propulsion architectures is presented in this paper. The gas turbine multi-point cycle design method is extended to turboprop and turbofan architectures, and several trade studies are performed initially at the cycle level. It is shown that the maximum degree of electrification is limited by the surge margin levels of the booster in the turbofan configuration.

An aircraft mission-level assessment is then performed using the integrated optimization method initially for an A320 Neo style aircraft case. The results indicate that the optimal cycle redesigned hybrid electric propulsion system (HEPS) favors take-off and climb power on-takes while optimal retrofit HEPS favor cruise power on-takes. It is shown that for current battery energy density (250 Wh/Kg), there is no fuel burn benefit. Furthermore, even for optimistic energy density values (750 Wh/kg) the maximum fuel burn benefit for a 500 nm mission is 5.5% and 4% for redesigned and retrofit HEPS, respectively. The power management strategies for HEPS configurations also differ based on gas turbine technology with improvement in gas turbine technology showing greater scope for electrification.

The method is then extended to ATR 72 style aircraft case, showing greater fuel burn benefits across the flight mission envelope. The power management strategies also change depending on the objective function, and optimum strategies are reported for direct operating cost or fuel burn. The retrofit case studies show a benefit in direct operating cost compared to redesigned case studies for ATR 72. Finally, a novel multimission approach is shown to highlight the overall fuel burn and direct operating cost benefit across the aircraft mission cluster.
Mitigation of Start-Up Coupled Lateral-Torsional Vibration of a Synchronous Motor Driven Integrally Geared Centrifugal Compressor
Authors: Luo Zhusan , Schwarz Carl L.
Published: September 2023

This paper presents a study on the enhancement of the coupled lateral-torsional rotordynamic performance of a synchronous motor driven main air compressor. This is a four-stage integrally geared centrifugal compressor with two pinions. In compressor commissioning, the low speed pinion experienced excessive lateral vibration during start. This pinion was intensely excited when the motor speed passed through the first torsional natural frequency of the compressor drive train. A coupled lateral-torsional vibration analysis is performed to predict the oscillating torques in different shafts, gear mesh forces and lateral vibrations of the pinions. To understand the mechanisms for the high pinion start-up vibration, main design variables and operating conditions that may affect the pinion vibration are examined. The results show that the pinion start-up vibration is sensitive to the coupling torsional stiffness, the pinion bearing design, the impeller mass properties, and the gear mesh direction (upmesh or downmesh). It has been found from the frequency response functions that the vibration is strongly associated with the first backward mode frequency and logarithmic decrement, whose importance has not been realized in this sense. To effectively mitigate the excessive lateral vibration, rotordynamic design considerations are briefly discussed in this paper.
On the Development of High Lift, High Work Low-Pressure Turbines
Authors: Clark John P. , Paniagua Guillermo , Cukurel Beni
Published: September 2023

Here we describe a combined design, numerical, and experimental program intended substantially to increase the lift and work of low-pressure turbine stages. This exercise is critically dependent upon the appropriate modeling of boundary-layer transition over airfoil surfaces. The effort proceeds through the design of turbine stages consistent with future unmanned air vehicle engine cycles. Then, a series of experiments are described that increase in complexity while driving the technology to more realistic embodiments. Representative experimental data are compared to pre-test predictions of the flow field, and it is shown that acceptable Reynolds lapse behavior is achievable even for turbines with significantly increased lift and work over state-of-the-art systems. Additionally, it is shown that through the judicious use of appropriate flow control technologies, it is possible to improve further the lapse characteristics of very high-lift airfoils. Finally, the benefits of applying such high lift, high work low-pressure turbine components are outlined with respect to a notional aircraft system, and future experiments are proposed.
Non-Destructive Inspection of Hot Corrosion Damage on Internal Surfaces of Turbine Blades
Authors: Kuipers Justin , Wiens Kevin
Published: September 2023

Two non-destructive techniques for the identification of hot corrosion damage on internal surfaces were investigated: magnetic permeability measurements and x-ray computed tomography (CT). A group of sixty-one Solar Titan 130 stage 1 blades which were known to have hot corrosion damage on the internal surfaces at a specific location were used for the investigation. X-ray CT was able to accurately identify the presence of hot corrosion as well as the extent to which it had progressed through the wall at the location of interest. The magnetic permeability technique was found to accurately identify whether hot corrosion damage had occurred at the location of interest, but could not as accurately determine the extent to which the damage had progressed through the wall. The results of the non-destructive testing were validated by destructive examination of some blades. The non-destructive testing methods evaluated through the study were able to determine the presence and extent of localized hot corrosion damage on internal surfaces, allowing for higher repair yields.
One Dimensional Model to Predict the Total Pressure Loss of Volute for Inward Flow Radial Supercritical CO2 Turbines
Authors: Hoque Syed Jiaul , Kumar Pramod , Gopi Pramod Chandra
Published: September 2023

Inward flow radial sCO2 turbines operate at considerably higher speeds than conventional gas or steam turbines making only the low specific speed designs practically realizable. Low specific speed designs suffer from significantly high viscous losses in the volute due to long and narrow flow passages. The volute loss in low specific speed designs causes an 8–12% efficiency drop, approximately 50% of the total loss. The paper proposes a quasi-one-dimensional model to estimate the total pressure loss of a volute with acceptable accuracy while consuming negligible computational power compared to a three-dimensional CFD simulation. The model converts the three-dimensional flow of a volute into an equivalent quasi-1D flow. Boundary layer-based momentum integral method is used on the quasi-1D flow path to calculate the total pressure loss. A computer program is developed to implement the proposed model. The accuracy of the model is tested with three-dimensional CFD results in the kW to MW power scale for different boundary conditions. The validation study is conducted for two volute cross-sections – circular and trapezoidal, to check the universality of the model. The model estimates the total pressure loss with less than 10% error for all test conditions. For the same conditions, a fully developed pipe flow model shows a considerably high error (∼50%) in total pressure loss prediction. The model can also accurately calculate losses under off-design operations and volute with surface roughness.
Mistuning Sensitivity of a Fan Bladed-Disk With Geometrical Nonlinearities
Authors: Quaegebeur Samuel , Thouverez Fabrice
Published: September 2023

In order to decrease their environmental impact, turboengine manufacturers tend to increase the span of fan blades while maintaining a slender profile. This design leads to more pronounced geometrical nonlinear effects. Computing the frequency response function of such structures is complicated due to the size of their associated finite element model. Classical substructuring approaches are no longer efficient to reduce the size of the problem as all the nodes of the system must be kept since they experience nonlinear behaviors. Different reduction methodologies have been defined in the past decades to tackle such nonlinear systems. Among these strategies, the Direct Normal Form extends the theory of normal form to finite element models. This methodology is here applied to a single blade model. Based on the assumption of a fairly rigid disk and of the cyclic symmetric properties, a full cyclic symmetric reduced-order model is computed. In this work, this methodology is extended to account for random mistuning. Such a strategy allows to perform, for instance, fast parametric studies. This paper studies the sensitivity of the random mistuning on a nonlinear Open Rotor system in order to help turboengineers in their design phase. Three ranges of the excitation level are studied. At low level of excitation, the system is close to the linear case. For higher forcing amplitude, a high amplification factor due to the merge of an isolated branch is observed, which is detrimental for the structure. For the last range (contains the highest forcing amplitudes), the nonlinearities are highly activated and low values of the amplification factor are obtained due to the spread of the vibrational energy over the frequency range.
Data-Driven Surrogate Modeling of Microturbine Combustors Burning Hydrogen Blends
Authors: Bhattacharya Chandrachur , Christopher Joshua , Thierry David , Biruduganti Munidhar , Supekar Sarang , Dasgupta Debolina
Published: September 2023

Hydrogen is a good candidate as an alternative fuel for power generation, due to the absence of carbon. Retrofitting available combustion systems to run hydrogen or its blends with natural gas is an effective option to decarbonize this sector. This demands a reassessment of the system response for the entire range of operation. Experimentation can be expensive and prohibitive from safety standpoints, and though computational models can provide data to fill the gaps, they come with their own sets of challenges. Data-driven surrogates use machine learning methods to learn from the sparse available data and can fill this knowledge gap by learning statistical correlations that describe the system. In this paper, a data-driven surrogate model is developed for a Capstone C65 microturbine combustor that is modified to burn pure natural gas and blends with up to 60% hydrogen for various power demands. Gaussian process (GP) regression modeling is used to learn from this dataset to emulate the system characteristics. Active learning is also invoked to learn a good model using as few data points as possible. Additional data is, then, generated using Reynolds-averaged Navier-Stokes (RANS) simulations of the same combustor geometry across a wider range of operating conditions i.e., 0–100% hydrogen for 0–65kW power loads. This provides low-fidelity information that can be included in a multi-fidelity learning setting which shows distinct improvements over the single-fidelity model. The novel multi-input-multi-output multi-fidelity GP surrogate modeling framework used in this work, is developed in-house using GPyTorch, which runs on a PyTorch backend, and is capable of superior scaling compared to traditional GP approaches.
Effect of Reduced Oil Flow Rate on the Performance of a Load on Pad Journal Bearing: Flooded vs. Evacuated Conditions
Authors: San Andrés Luis , Ouyang Zihan , Qin Yudi
Published: September 2023

Means to decrease the energy consumption of tilting pad journal bearings (TPJBs) without affecting their performance and structural integrity are mandatory in a cost efficient operation. Reducing the lubricant flow supplied to a bearing is a distinct method to diminish drag power losses along with savings in oil storage and pump equipment. However, a too low flow remains questionable in industrial practice. Starved flow conditions produce hot pad surfaces that could lead to Babbitt failure; and under certain loads, generate subsynchronous vibrations (SSV). This paper aims to resolve some of the issues above via measurements of the load performance conducted with a four-pad TPJB configured as load-on-pad (LOP) and having its ends sealed or open to make flooded and evacuated conditions. Prior measurements were conducted with the same bearing under load-between-pads (LBP); see Refs. [1,2]. The nominal supplied flow (Q) of ISO VG 46 oil at 60 °C is proportional to shaft speed (max. 12 krpm: 62.8 m/s surface speed). In the tests, the flow Qs ranges from 1.5 Q to just ¼ Q, and the applied units load reaches 2.07 MPa. Compared to the flooded bearing, the evacuated bearing produces a slightly larger eccentricity across the range of flow rates. For a unit load = 2.07 MPa and shaft speed of 6 or 12 krpm, the highest pad subsurface temperature reaches ∼ 130° C for Qs below 50% nominal. For both bearings, flooded or evacuated, drag power losses decrease ∼30% as the oil flow drops from 100% to 50% Q. As the oil flow increases to 1.5 Q, the drag power increases ∼10% for both bearing types at 6 krpm and for the flooded one at 12 krpm, while the evacuated bearing shows a reduction of ∼7%. The drag power grows as the static load increases; the evacuated bearing producing up to ∼ 40% lesser power loss than the flooded bearing. Both bearings produce similar size direct stiffnesses though largely orthotropic, Kyy >> Kxx. Direct damping coefficients Cxx ∼ Cyy increase with shaft speed and unit load but dramatically decrease as Qs drops, in particular for the evacuated bearing. The current measurements and those in Refs. [1,2] demonstrate that LOP and LBP bearings can safely operate with 50% of nominal flow thus saving drag power and without too large pad temperature rises. Alas, too low Qs produce a significant reduction in the damping coefficient orthogonal to the applied load direction. The effect is most evident in the LOP evacuated bearing which is most prone to show SSV Hash.
Impact of Fuel Type on Aircraft Range: An Initial Optimization Study
Authors: de Nercy - Maingard Hugo , Palies Paul
Published: September 2023

Aviation decarbonization is an essential step to contribute to reduce the CO2 footprint and the impact on climate. Among the various possible avenues to fulfill this requirement, thermal-powered aircraft fueled with liquid hydrogen is considered in this paper. Considering the several challenges at stake, one central question that subsists in deploying such aircraft is the impact of the fuel on the Breguet range. For example, for hydrogen, the density either as a gas or as a liquid is very low compared to other in-use or being considered fuels, yet its specific energy (MJ/kg) is the highest. These two major differences, fluid density and energy density, need to be coupled to the aircraft range to assess accurately what type of flights mission can be covered with hydrogen or other fuel. In this paper, a model is developed and applied to three different fuels to determine the corresponding aircraft range, volume of tank, and engine fuel mass flow rate for two mission profiles and two aircraft class. The mission profiles considered are both short and long haul. The aircraft studied are narrow-body and wide-body aircraft class. The two main fuels considered in this paper are SAF and hydrogen. The model development is presented as well as the iterative procedure to calculate key quantities. It is shown that for a narrow-body aircraft and a range of 1322 km, it would require nearly one ton of liquid hydrogen, which represents an estimated corresponding tank volume of 15 m3. This result is of major importance because as of today narrow-body aircraft are responsible for nearly 50% of the aviation CO2 footprint worldwide and are used on average over distances of 1322 km.
Rotordynamics of a Rotor Supported by Foil Bearings Under Various Housing Excitation
Authors: Lee Woongeon , Kim Daejong
Published: September 2023

Proton Exchange Membrane (PEM) Fuel cell Systems (FCS) are rapidly growing technology in the field of electric cars, buses, and trucks. In such applications, a motor-driven oil-free air compressor is one of the most critical auxiliary subsystems for the FCSs. Foil bearings are the perfect choice as oil-free bearings for FCS compressors due to high rotordynamics stability and shock-resistance. The platform of a motor-driven oil-free compressor can also be used as an electric turbocharger for traditional internal combustion engines. All electromechanical subsystems for electric vehicles must satisfy vibration endurance requirements following ISO 16750-3:2012, characterized by certain g-loading at specific frequencies. FCS air compressors also follow the same ISO 16750 standard. For the compressor to satisfy ISO 16750 requirement, detailed rotordynamics simulations with externally excited compressor housing under certain g-loading are essential to design the foil bearings considering the static and dynamic loads to the bearing and rotordynamics stability. The main objectives of the current research are 1) to develop a six degree of freedom (6-DOF) dynamic model of the rotor supported by foil bearings under external excitation to the compressor housing, 2) to simulate linear and non-linear rotordynamics of the compressor rotor supported by two radial foil bearings, and 3) to provide appropriate design guideline such as bump stiffness and axial length of the foil bearings. The simulations show that the rotor is stable for both under single frequency excitation and simultaneous excitations of all the frequencies in ISO 17650 standard. 4-DOF modal analyses were applied to identify natural mode of the system under the housing excitation.
Dynamic Evaluation of Integrated Thermal Energy Storage Concept for the Recuperated Gas Turbine Application
Authors: Flores Garcia Juan Diego , Harun Nor Farida , Traverso Luis M. , Zhou Nana , Tucker David
Published: September 2023

Increasing thermal energy storage (TES) installation across countries is anticipated to enable greater adoption of distributed energy systems to meet the Net Zero Emission goals by 2050. Emerging TES technologies have been widely considered as a key component to support transition towards carbon neutrality as well as to secure grid stability for more flexible, reliable, and efficient energy systems. Integrating a sensible thermal energy storage in an existing energy cycle can be a feasible solution to enhance system flexibility for following fluctuations in power demand and supply. This research investigates the ability of a recuperated gas turbine cycle to reduce carbon emissions and optimize the system efficiency during load following with a thermal energy storage. This cycle was selected due to its reconfigurability for integration of renewable energy resources for thermal sources and sinks. To first demonstrate the concept and identify the key performance requirements, dynamic performance tests were conducted using hardware-based facility at the U.S Department of Energy, National Energy Technology Laboratory. A new control strategy using a hot air bypass valve to control the discharging and charging states was proposed. The sensible heat medium (i.e., air mass flow) entering the thermal energy storage was modulated through opening and closing hot air bypass simulating the cycle has excess energy or requires energy. It was observed that the thermal energy storage has a maximum heat dissipation of 103 kW. This latent heat represents 57% of the electric load capacity of the turbomachinery, assuming a 33% efficiency heat to electricity. The thermal energy storage was able to maintain heat dissipation for 4 minutes. Load following is possible since the change in dissipation rates over one second are double of what is achievable with a fuel valve. Some optimizations to the surface area to mass ratio are needed to maximize the integrated cycle.
Design of an Innovative Experimental Rig for the Study of Deposition Phenomena in Axial Compressors
Authors: Suman Alessio , Zanini Nicola , Pinelli Michele
Published: September 2023

Compressor fouling is one of the main causes of gas turbine performance degradation. Fouling is promoted by micrometric particles of industrial pollutants in the air and unfavorable environmental conditions (fog, rain, humidity). Airborne particles ingested in heavy-duty gas turbines deposit on the compressor blades and sidewalls, increasing the surface roughness and changing the shape of the profile. This work aims to design a subsonic wind tunnel to study the gas turbine fouling phenomenon. Lump-parameter analysis and two- and three-dimensional fluid dynamics simulations support the design. Simulations were needed to optimize the blade cascade and identify particular fluid dynamic phenomena, such as separation, stagnation point, and vortex. In addition, great attention was devoted to the thermo-hygrometric conditions responsible for the capillarity forces. All these factors strongly influence the compressor cascade performance and the contamination rate. Particle concentration, number, and size are specified to perform a quantitative analysis of the particle impact on the blade surface and a qualitative analysis of the impact zones. As a result, realistic impact conditions of industrial relevance are reproduced in the wind tunnel in order to forecast the adhesion rate, the areas of the compressor airfoils impacted by particles, and thus the performance losses over the operation.