bluuebunny/crossref_metadata_2025 huggingface dataset:
Instability Amplitude Suppression in a Double Orifice Flow Through External Periodic Forcing
Authors: Singh Ashutosh , Mukherjee Isha , Nair Vineeth
Published: August 2024

Various afterburners, ramjets, and combustors exhibit vortex shedding lock-in with an acoustic mode of the duct. In the present study, we experimentally analyse the effect of external forcing on the flow through a square duct containing two circular orifices (double-orifice cavity). As the mean flow is altered, the system transitions from a noisy state to periodic oscillations (lock-in) through a quasiperiodic regime. Periodic forcing of the system close to its instability frequency leads to amplitude suppression via synchronous quenching and 1:1 lock-in. The phase lock-in happens via phase drifting and phase slipping. We also observe asynchronous quenching on forcing the system far from the instability frequency. However, the phase lock-in asynchronous quenching happens via phase drifting and phase trapping. These approaches serve as effective active control strategies for instability control. Synchronisation maps are presented and the dynamics of transition is explored using return maps. In this study, we introduce phenomenological oscillatory models of these phenomena that effectively depict the transition between different lock-in regimes, including the occurrence of a saddle-node bifurcation near the natural frequency and torus death for forcing at a frequency far from the natural frequency. We also study a model that transforms the continuous domain into a discrete map. Synchronisation maps obtained from both models are compared and validated with the experimental results.
Experimental Investigation on the Effect of Nozzle Bluntness Thickness on the Combustion Characteristics of a High-Speed Parallel Jet Mild Combustor
Authors: Yang Ningjing , Xiong Yan , Liu Zhigang , Xu Xiang
Published: August 2024

The safe, stable, and low-emission combustion of high-content hydrogen and pure hydrogen fuels is a crucial aspect of the gas turbine combustion system for achieving carbon-neutral and ultimately carbon-free combustion. However, employing high hydrogen content and even hydrogen as a fuel in combustors presents unique challenges due to distinct fuel characteristics compared to natural gas. This study parametrically investigates the impact of three different nozzle bluntness thicknesses on the reaction zone morphology, combustion stability, and NOx emission characteristics of the high-speed parallel jet MILD combustor. The findings demonstrate that the effect of bluntness thickness variation on the reaction zone morphology can be classified into two distinctive stages: the reaction zone morphology is dominated by the flow field at relatively low hydrogen content and equivalence ratios and by the chemical reactivity of the reactants at higher hydrogen content and equivalence ratios. Meanwhile, the change in lip thickness affects combustion stabilization. The trend of the dynamic pressure main frequency with hydrogen contents and equivalence ratios for the combustor with different lip thicknesses varies in the same way that the trend of the liftoff height of the reaction zone does. Despite significant differences in thermoacoustic characteristics among different bluntness thicknesses, total nitrogen oxide emissions remain relatively unchanged. Total NOx emissions were all less than 10 ppm@15%O2 when the combustion chamber adiabatic flame temperature was less than 2000 K.
Exploiting Active Subspace for Modeling Uncertainty and Optimization in Fan-Shaped Film Cooling Simulation
Authors: Cai Feixue , Zhou Hua , Yao Min , Ren Zhuyin
Published: August 2024

The numerical studies for film cooling performance have gained considerable interest for the development of advanced gas turbines and aero-engines. However, the accuracy of Reynolds-Averaged Navier-Stokes simulations is significantly influenced by the uncertainties associated with turbulence modeling closure coefficients. The traditional Monte Carlo methods for uncertainty quantification are computationally prohibitive as the cost of constructing an accurate response surface increases exponentially with the number of input parameters. The active subspace method, developed recently as a means of dimension reduction, incurs a moderate cost when dealing with high-dimensional uncertain inputs. In this study, the active subspace (AS) method is applied to quantify the modeling uncertainties related to SST turbulence modeling parameters in a fan-shaped film cooling simulation. The results reveal that the quantified modeling uncertainties exhibit distinct characteristics across different blowing ratios, and the response functions are constructed based on the primary control parameters. Subsequently, the turbulence model parameters are optimized to minimize the computational error based on the response functions. In the optimized test point, the average relative errors decrease to 1.3% and 0.3%, respectively, under blowing ratios of 0.5 and 2.5 after optimization. Furthermore, a set of unified model parameters is optimized and applied across different blowing ratios (0.5, 1.5, 2.5), resulting in average relative error of 4.3%, 3.7%, and 3.1%, respectively, demonstrating the advantages of the AS method for modeling uncertainty quantification and optimization in film cooling simulation.
Flow and Heat Transfer in a Rotating Disc Cavity With Axial Throughflow at High Speed Conditions
Authors: Wang Ruonan , Chew John W. , Gao Feng , Marxen Olaf
Published: August 2024

Flow and heat transfer in a compressor rotating disc cavity with axial throughflow is investigated using wall-modelled large-eddy simulations (WMLES). These are compared to measurements from recently published experiments and used to investigate high Reynolds number effects. The simulations use an open-source CFD solver with high parallel efficiency and employ the Boussinesq approximation for centrifugal buoyancy. Kinetic energy effects (characterised by Eckert number) are accounted for by scaling the thermal boundary conditions from static temperature to rotary stagnation temperature. The WMLES shows very encouraging agreement with experiments up to the highest Reynolds number tested, Reϕ = 3.0 × 106. A further simulation at Reϕ = 107 extends the investigation to an operating condition more representative of aero engine high pressure compressors. The results support the scaling of shroud heat transfer found at lower Reϕ, but disc heat transfer is higher than expected from a simple extrapolation of lower Reϕ results. This is associated with transition to turbulence in the disc Ekman layers and is consistent with the boundary layer Reynolds numbers at this condition. The introduction of swirl in the axial throughflow, as may occur at engine conditions, could reduce the boundary layer Reynolds numbers and delay the transition.
Computational Study of Flow Characteristics of an Inducer Dropleg Configuration for Pulp Pumping Applications
Authors: Dhanasegaran Radheesh , Tiitinen Kalle , Vahteri Timo
Published: August 2024

The present work numerically investigates the flow characteristics and performance of a dropleg-inducer configuration for medium consistency (MC) pulp pumping applications. The study employed a commercial CFD solver package to carry out the steady-state single-phase Newtonian fluid (water) simulations using RANS-based k-ε turbulence model. Three different normalized axial spacing of the inducer from the dropleg exit (L/D = 0.75, 1.15 & 1.5) were studied for three normalized rotational speeds (Ṅ = 0.6, 1 & 1.2) considering both design and off-design operating conditions. The results are discussed in the context of velocity streamlines at different planes, contours of velocity and turbulence intensity, and plots of performance parameters such as power consumed, and power number thereby allowing for an assessment of the inducer’s performance with changing distances from the dropleg and different rotational speeds considering the operational range of the MC pump. The findings reveal that change in the axial spacing and rotational speeds significantly impacts the flow pattern within the dropleg and the inducer passage. Consequently, these changes affect the turbulence characteristics and the power consumption by the inducer, which will in turn affect the overall performance of the MC pump.
Assessment of Measurement Techniques for Adiabatic Cooling Effectiveness in Transonic Flow Over a Flat Plate
Authors: Zeng Wei , Dai Siming , Liu Yisu , Ma Haiteng
Published: August 2024

Adiabatic cooling effectiveness, as a primary indicator of film cooling performance, still suffers from the disputable measurement principle in transonic flow. The two measuring techniques in the state of the art, linear regression method and dual linear regression technique, produce different results, due to their distinct treatment of local recovery temperature. To resolve this controversy, this paper first established a criterion for judging the two methods, based on similarity/dimensional analysis. It is concluded that adiabatic cooling effectiveness is uniquely determined by six dimensionless numbers: Mach number, Reynolds number, Prandtl number of the mainstream, blowing ratio, momentum ratio and temperature ratio between coolant and mainstream. Then, the two methods were gauged against the judging criterion through transient thermal measurements by infrared thermography, for transonic flow over a flat plate with film cooling. All the six dimensionless numbers were fixed during experiments. Only the value of mainstream temperature and coolant temperature varied by 8K and 14K respectively. It is shown that adiabatic cooling effectiveness obtained by linear regression method is roughly unaltered at different mainstream and coolant temperatures, when the coolant-to-mainstream temperature ratio is fixed. However, results measured by dual linear regression technique display noticeable variation (by a maximum of 0.3) under the same circumstance. This is because the assumption of this technique conflicts with the similarity principle. Therefore, linear regression method aligns much better with the judging criterion based on dimensional analysis, than dual linear regression technique, and is hence recommended to measure adiabatic cooling effectiveness in transonic flow.
Experiment on Tuned Open-Test-Case Fan ECL5/CATANA: Structural Characterization Under Vacuum Conditions
Authors: Billon Kevin , Sanchez Lionel , Bouvard Gaëtan , Gibert Claude , Blanc Laurent , Thouverez Fabrice
Published: August 2024

The CATANA project aims to promote the development of the next generation of Ultra-High-Bypass-Ratio Turbofan engines by closing the knowledge gaps concerning multi-physical interactions which affect performance and limit the stability range. It involves a composite-material fan stage, called ECL5, representative of near future UHBR architectures. It has been designed at Ecole Centrale de Lyon to provide an open for the community benchmark configuration. This fan had been extensively tested previously at the aerodynamic Phare-2 test facility (rotating machinery platform for environmental risk control) in different running conditions at the LMFA laboratory (Ecole Centrale de Lyon fluid mechanics and acoustics laboratory) concerning synchronous and asynchronous responses (NSV).

It is tested here under vacuum, in rotating conditions in the Phare-1 facility in order to identify structural modal parameters, ie mainly the whole fan blade assembly structural damping. Each blade is equipped with piezoelectric actuators to excite structural modes. Blades’ vibratory responses are measured via embedded strain gauges. The instrumented fan blades are firstly individually tested on a specific test hub mounting. Piezoelectric actuators efficiency is demonstrated by reaching representative amplitudes. Also, individual blades frequencies dispersion is quantified and shows in particular that the added exciters have negligible influence on mistuning and dynamics. The fan response is measured using the same instrumentation as for aerodynamic experiments and at the same rotational speed. Influence of rotating speed and vibration level on modal damping is shown and quantified.
Machine Learning Regression Models for Turbofan Engines: A Comparative Study on Remaining Useful Life Prediction
Authors: Omer Zahi M. , Al Seiari Abdulla , Cen Zhaohui , Bilendo Francisco
Published: August 2024

This study conducts a systematic comparison of data-driven regression models for predicting the Remaining Useful Life (RUL) of turbofan engines in aviation Prognostics Health Management (PHM) field, utilizing the C-MAPSS dataset with advanced feature engineering, the paper evaluates models from simple linear to complex high-dimensional ensemble structures. Notably, the CatBoost model and other ensemble techniques demonstrated superior performance, with CatBoost achieving an R2 value of 99% and other ensembles averaging 92%, significantly outperforming other models with 65% to 77% values. This indicates the robustness of ensemble machine learning methods in precise RUL estimation.
Conventional Design to Design for Additive Manufacturing for Frame 5/1 Stage 1 Nozzle
Authors: Avaiya NIkunj , Cocchi Lorenzo , Soman Abhimanyu , Tripoli Girolamo , Colantoni Simone , Santhana Gopalakrishnan Babu , Del Turco Paolo
Published: August 2024

Baker Hughes has been providing industrial gas turbines globally since the 1950s. Baker Hughes’s Frame 5/1 machine is well-known for its long-running performance in the field. After service life of parts are over, these parts are replaced with new parts. New technologies like Additive Manufacturing (AM) can reduce lead time and provide freedom to design engineers to explore designs that were not possible with conventional manufacturing in the past. This paper discusses the journey from conventional design to design for additive manufacturing for stage 1 nozzle (S1N) of the Frame 5/1 Machine. Direct Metal Laser Melting (DMLM), an AM technology, is considered for manufacturing of this nozzle. Furthermore, the extensive experience accumulated over the years from numerous 5/1 machines operating in the field is leveraged to enhance the optimization of nozzle design. Considering an in-house developed equivalent material in DMLM, the nozzle is redesigned to be compatible with the operating conditions of the current machine and its supporting structure without affecting performance. The structural integrity of the newly developed AM design of the S1N is validated by part life assessment, using the thermo-mechanical finite element Analysis (FEA), and compared against the product requirements. Based on the results of the part life assessment, further improvements were made through multiple design changes and iterations, resulting in the final design. The redesign leads to a significant improvement in the temperature gradient and lowers the metal temperature in S1N in comparison with conventional design. The analysis results demonstrate a significant improvement in overall stresses, plastic strains, creep strains and crack initiation life when compared to the conventional nozzle. Moreover, the predicted amount of oxidation for the new design is much lower than that for the conventional design.
Development of Heat Exchanger Modelling Capability for a Finite Volume Aeroelasticity Solver
Authors: Mitchell Sam , Tartaruga Irene , Stapelfeldt Sina
Published: August 2024

Heat exchangers are frequently used in aero engines and are known to significantly affect the surrounding steady and unsteady flow. In certain applications, they may thereby also influence the aeroelastic stability of upstream or downstream components but there is limited research on this in the public domain. This paper aims to demonstrate the influence of heat exchangers on unsteady flows relevant to aeroelastic problems. This is achieved by developing heat exchanger modelling capability for an in-house finite volume aeroelasticity solver, for which heat exchanger is represented as a porous medium, as this is the established approach in existing aerodynamic studies using commercial CFD software. The governing equations for a Darcy-Forchheimer porous media model suitable for unsteady and compressible flows are presented, which are derived by the application of volume averaging theory to the Navier-Stokes equations. The implementation of this model within the time integration method used for the solver is then described and verified by comparison of results for steady flows against an established commercial CFD solver, where close agreement between both in-house and commercial solvers has been observed. Lastly a preliminary demonstration of the capability to model unsteady heat exchanger flows is presented by application to an aeroacoustic problem, where the interaction of the pressure waves and the heat exchanger is investigated.
The Role of the Working Fluid and Non-Ideal Thermodynamic Effects on Performance of Gas Lubricated Bearings
Authors: de Waart Wessel , Pini Matteo
Published: August 2024

Small-scale turbomachinery operating at high rotational speed is a key technology for increasing the power density of energy and propulsion systems. A notable example is the turbine of an organic Rankine cycle turbogenerator for thermal recuperation from prime engines and industrial processes. Such systems typically operate with organic compounds characterized by complex molecular structures, to allow the design of efficient fluid machinery and flexibility in matching the heat source and sink temperature profiles. Gas lubricated bearings are considered advantageous compared to traditional oil-lubricated rolling element bearings for supporting the turbine rotor, enabling greater machine compactness and reduced complexity, and to avoid contamination of the working fluid. In certain operating conditions, however, the lubricant of the gas bearing is in thermodynamic states near the saturated vapor line or in the vicinity of the fluid critical point whereby non-ideal effects are relevant and may affect bearing performance. This work investigates the physics of thin film flows in gas bearings operating with fluids made by complex molecules. The influence of non-ideal thermodynamic effects on gas bearing performance is discussed by analysis of the fluid bulk modulus. Reduced values of the non-dimensional bulk modulus near the critical point or saturated vapor line decrease bearing performance. The main parameter characterizing the influence of molecular complexity on bearing performance is shown to be the acentric factor. For complex fluids with large acentric factors, the impact of non-ideal thermodynamic effects on non-dimensional bearing load capacity and rotor-dynamic characteristics is less pronounced.
Experimental and Numerical Investigations of Flow Patterns at Low Volume Flow Rate Conditions in Low Pressure Steam Turbine
Authors: Tabata Soichiro , Segawa Kiyoshi , Takahashi Tadashi , Aoyagi Jin
Published: August 2024

This study investigates the flow patterns at the last stage exit of a low-pressure steam turbine under low volume flow conditions. The 0.33 scale 5-stage model steam turbine was used to measure turbine performance and flow patterns at the last stage exit. Numerical simulations were performed to verify the accuracy of flow pattern prediction under low volumetric flow conditions by using a mixing plane (MP), a multiple mixing plane (MMP), and a frozen rotor (Frozen). Equilibrium and nonequilibrium condensation analyses were also performed to investigate the effects of subcooling under low volume flow conditions. Numerical simulations showed good agreement with measured turbine efficiencies over a wide range of volume flow rates. A comparison of MP, MMP, and Frozen results under low volumetric flow conditions showed that the results were generally similar, but Frozen was the closest to the experimental results. Comparison of measured and equilibrium condensation analysis results for the flow pattern at the last stage exit under the low, middle, and high volumetric flow rates showed that the numerical results basically represent the experimental results well. However, the equilibrium condensation analysis results for the absolute swirl angle at middle and high volumetric flow conditions showed a discrepancy with the experimental results. The non-equilibrium condensation analysis confirmed that secondary nucleation occurred in the last stage rotating blade under middle and high volumetric flow conditions. On the other hand, no secondary nucleation was observed in the last stage rotating blade in the non-equilibrium condensation analysis for the low volume flow condition. The results show good agreement between the numerical predictions and the experimental data, highlighting the importance of considering non-equilibrium condensation effects under design conditions, but also emphasizing that such effects do not need to be considered under low volume flow conditions because of the presence of backflow at the last stage outlet.
High-Fidelity Predictions of Aerodynamic Losses Through a Supersonic Stator Vane
Authors: Matar Camille , Gloerfelt Xavier , Cinnella Paola
Published: August 2024

This study aims at providing evidence of the importance of using high-fidelity methods for accurate loss estimation during initial ORC turbine design. The case of a supersonic stator vane in both linear and annular cascades is used to exemplify the divergences in loss between flows where crucial features including the boundary layers, the wake and secondary flow are disparately modeled. Specifically, well known strategies, namely Reynolds-Averaged Navier-Stokes (RANS) modeling, Delayed Detached Eddy Simulation (DDES) and Large Eddy Simulation (LES), are used. In the linear cascade, the misprediction of the boundary layer properties leads to large deviations in trailing edge loss attributed to momentum deficit. On the other hand, resolving the unsteady wake dynamics provides substantial improvement of the base pressure estimation, which is the strongest contributor to overall trailing edge loss. In the annular cascade, fair agreement is found with experimental pressure measurements and numerical data from the literature. Stagnation pressure deficit through the wake is well reproduced by the DDES, while the RANS solution features a wider and slightly displaced wake. Overall, the present study shows that, although the computational cost varies over orders of magnitude, accurately resolving the complex flow phenomena that exist in a turbine vane is a crucial step for improved ORC turbine design.
Analysis of Liquid Fuel Effect on Swirl-Assisted Jet-Stabilized Combustor Performance
Authors: Izadi Saeed , Seliger-Ost Hannah , Zanger Jan , Kutne Peter , Aigner Manfred
Published: August 2024

Growing interest in reducing pollutant emissions from gas turbines is driving efforts to develop combustor system solutions with low NOx, CO and UHC emissions while maintaining a wide range of performance and fuel flexibility. The paper describes an investigation of the spray produced by flash boiling mechanism (superheated injection) and mechanical liquid bulk breakup (pressure-swirl atomization) in a lean premixed swirl-assisted jet-stabilized combustion system. Fuel vaporization prior to combustor inlet is greatly enhanced by the combustor design and elevated liquid fuel temperature. A comprehensive analysis of combustion behavior for a range of fuels in both liquid and superheated regimes has been performed. The fuel atomization is based on the mechanical and thermal breakup of the liquid fuel in a temperature range of 150–300°C. Variable thermophysical properties of four different liquid fuels from various origins are investigated under atmospheric conditions. OH* chemiluminescence and Mie scattering have been used as optical and laser diagnostic methods. These measurement techniques were used to analyze the combustion behavior and spray breakup mechanism. A mixing condensation particle counter (MCPC) was used to determine the particulate emissions of the various liquid fuels and spray generation techniques. Measurement of exhaust gas emission levels of NOx, CO and UHC are conducted simultaneously for each operating point. The underlying factor effects are presented and discussed. The results indicate that while NOx and CO emissions are not majorly affected by the fuel atomization technique, the thermophysical properties of the fuel, such as the saturation temperature, play an important role in the fuel atomization process and to a minor degree on the emitted NOx and CO emissions. Furthermore, it is shown that, except for differences in spray penetration length and evaporation quality, the combustion performance was similar in terms of flame operating range for all tested liquid fuels. The effect of different fuel atomization techniques on particulate emissions was minimal. However, due to their origins, the different fuels had large variations in the particulate matter measurements.
Assessment of the Wilshire-Cano-Stewart (WCS) Model Using Strain Energy Density Dissipation (SEDD)
Authors: Pellicotte Jacob , Hossain Md Abir , Cano Jaime , Stewart Calvin M.
Published: August 2024

In this study, Strain Energy Density Dissipation (SEDD) is employed as a creep damage parameter to calibrate the Wilshire-Cano-Stewart (WCS) Model. The WCS model is an adaptation of the Wilshire equations combined with continuum damage mechanics to enable predictions of creep deformation and damage. In WCS, the analytical calibration methods for the Wilshire equations remain unchanged and the additional damage parameters are found using numerical optimization. Though the WCS model can accurately predict progressive creep deformation, the damage remains phenomenological. Herein, damage is represented as SEDD. In SEDD, it is assumed that a material system has a finite amount of energy it can dissipate until reaching failure. Assuming that SEDD is caused by the accumulation of microstructural defects, the damage process is represented as a scalar value from zero (undamaged) to unity (rupture). By combining the WCS model with SEDD, damage evolution is pinned physically and can be measured experimentally. Stress-rupture, minimum-creep-strain-rate, and creep deformation data is gathered for alloy P91 at 600 °C and stresses from 100 to 200 MPa. The Wilshire constants are analytically determined and compared with the literature. The damage-trajectory constant is calibrated using SEDD measurements. The new calibration accurately predicts the material response across the range of stresses and temperatures. A comparison between numerical optimization and measured damage-trajectory constants is performed. Parametric simulations verify the interpolation and extrapolation capabilities of this new approach.
Generic Framework for an Accurate, and Efficient Flutter Analysis
Authors: Zori Laith , Patel Purvic , Patil Sunil , Orlando Stephen , Campregher Rubens
Published: August 2024

Accurate and efficient prediction of blade aerodynamic damping is critical for the design and durability of turbomachines such as gas and steam turbines. Several empirical and linearized methods have been developed and used with varied degrees of success over the past decade, especially for bladed components. This paper presents a generic framework to carry out flutter analysis which is equally applicable for bladed turbomachinery components as well as other complex components in the engines such as seals, and valves.

A streamlined workflow to carry modal analysis and then perform efficient CFD analysis using one or multiple modes to obtain accurate aerodamping is outlined. A recent implementation of phase-lag approach with traveling wave method in Ansys Fluent is described. This approach enables calculation of flutter for any nodal diameter with just a single sector of the turbomachinery. Furthermore, the implementation of Aerodynamic Influence Coefficient method for a very fast turnaround time to get aerodamping for a range of nodal diameters is discussed.

The framework presented is validated and presented for two cases. The first testcase is Rotor 1 from the 4.5 stage high-speed Hannover compressor, which represents standard bladed turbomachinery. A range of nodal diameters are investigated using both the travelling wave method and influence coefficient method. The accuracy of phase lag approach is compared with the reference full-wheel solution. The speedup provided by the phase lag approach and influence coefficient method is discussed in detail. The second testcase is a generic gas turbine seal representing a complex feature in modern turbomachinery. It is shown that the framework presented and validated for bladed geometry can be used without any further modifications for such a complex case.
Using Pseudotime Marching for the Solution of Harmonic Balance Problems
Authors: Frey Christian , Backhaus Jan , Ashcroft Graham , Geiser Georg , Winhart Benjamin , Stüer Heinrich
Published: August 2024

The aim of this paper is to study approaches to implement implicit pseudotime marching for the harmonic balance system in the frequency domain. We first give a motivation for using pseudotime marching as a solution technique. It turns out that, when the discretization errors of the pseudospectral time derivative and the pseudotime derivative are neglected, the harmonic balance solution converges to a stable periodic flow, provided that the initial solution is sufficiently close to a stable periodic solution. This motivates the choice of a robust pseudotime marching approach, e.g., an implicit solver based on backward Euler integration. This approach requires the Jacobian of the harmonic balance residual. As for the steady problem, the Jacobian can be approximated without changing the final solution as long as the solver converges. Therefore, a central question is which simplifications are appropriate in terms of the overall efficiency and robustness of the solver.

As has been shown in the literature, the spectral timederivative operator should be taken into account in the implicit system. On the other hand, the linearization of the flow residual can be simplified to a certain extent, especially if the system is solved in the frequency domain. In this paper, we show that, up to terms which scale with the amplitude of the disturbances, the linear system matrix is the sum of a scalar diagonal and a block diagonal matrix with identical blocks for each harmonic. The deviation from this structure is due to to the nonlinearity of the unsteady flow problem. We show that when the unsteadiness is small, the nonlinear coupling terms can be neglected in the implicit solver and the resulting special matrix structure can be exploited to massively speed up the solver. In contrast, when a strong disturbance is simulated, this simplification can lead to significant losses in robustness. To illustrate our findings we apply the implemented methods to predict the flow response to a disturbance prescribed at the inlet of a transonic compressor. When the disturbance amplitude is increased, a strong oscillation is induced, and the harmonic balance solver converges only when the nonlinear coupling between the harmonics is taken into account.
Combining Machine Learning, Embedded Sensor Networks and Additive Burner Design for Combustor Structural Health Monitoring
Authors: Giuliani Fabrice , Paulitsch Nina , Hofer Andrea , Petrovic-Filipovic Vojislav , Maier Benjamin , Bailer Werner , Winter Martin , Unterberger Roland , Schricker Alexander
Published: August 2024

The crystAIr project is a method of sensitising a burner for flame monitoring based on a discrete number of dynamic pressure sensors and a machine learning approach. The context is the development of better aircraft engines, and in particular the development of solutions for hydrogen-fuelled gas turbines. The combination of sensors and appropriate signal processing is designed to mimic a ‘feel’ for the state of the flame. The idea is to monitor the correct operation of the gas turbine in real-time and to anticipate impending problems such as flame blowout, combustion instability or flashback. Compared to conventional flame monitoring based on signal sampling, thresholding, bandpass analysis and time-lag measurement, this method should be less computationally intensive, more sensitive and more robust to artefacts. Not only should it be more responsive, but it should also anticipate problems based on a lessons-learned approach and outperform the conventional precursors. An unassisted machine learning method is used to achieve this. Acustom-built AM burner designed for this experiment provides multiple instrumentation options. A powerful data acquisition system is set up to collect data on multiple channels, over a long time duration and at high speed to collect the learning signal chunks. The focus is on the detection of flames and, more specifically, the moment of their ignition and extinction, the operating conditions that are prone to flashback and the stability of the combustion. Additional measurement techniques are used to refine the learning method. The paper covers all these points and presents the first results.
The Parameter Augmentation Pretraining Neural Network Model of Aero-Engine Thrust Prediction
Authors: You Rui , Xiao Hong , Chen Guo , Liang Yufeng
Published: August 2024

Accurately predicting the thrust of aero-engine is important for engine health management and engine performance control. Thrust prediction neural network models have been widely applied in recent years. This paper proposes a parameter augmentation pretraining method and designs an aero-engine neural network model with physical significance. It is known that ground test system measures more engine parameters compared to onboard system. Due to the limitations of using onboard models, typically only the parameters measured by both systems are used as training parameters, which may lead to incomplete training. In this study, a 0-1 encoded vector is utilized to distinguish ground test system data and onboard system data. The model is first pretrained using the measurable parameters from the ground test system, following by retraining using parameters measured by both the ground test system and the onboard system. The parameter augmentation pretrain method allows the model to learn more mapping relationships of aero-engine and resolves the issue of parameter dimension matching. Furthermore, this study investigates the impact of the weight loss function on the prediction accuracy of the model. This research provides guidance for engine performance evaluation and further studies.
Evaluation of a Commercial 65 kW Recuperated Gas Turbine Engine Operated on Up to 30% Hydrogen Added to Natural Gas
Authors: Villatoro Walther , Navarro Aris , McDonell Vincent , Hu Ray
Published: August 2024

A commercial natural gas 65 kW microturbine generator produced by Capstone Green Energy Corporation is used to study the impact of hydrogen addition to natural gas. Hydrogen addition in natural gas turbines can reduce carbon dioxide and carbon monoxide emission as a step towards carbon neutrality. Exhaust emissions and power output are evaluated for increasing levels of hydrogen in the fuel mixture. Additionally, a chemical reactor network (CRN) is used in conjunction with injector mixing characterization to support the development. The CRN analysis predicts NOx using perfectly stirred reactors (PSR) therefore, a strategy to account for the measured fuel concentration at the injector exit was implemented to estimate NOx emissions for the actual fuel/air mixing. At full load, experimental NOx emissions remain almost unchanged as the %vol of hydrogen increases from 0 to 30%. CO and CO2 decrease with increasing vol% of hydrogen in the fuel as expected. The CRN captures the general emissions trends with hydrogen addition and illustrates sensitivity to the mechanism utilized. Visual inspection of the injectors following hydrogen addition tests indicated that flashback or combustion inside the injectors did not occur. Measured engine system efficiency was not impacted by the addition of hydrogen. Mixing performance tests for the injectors showed that the fuel and air were well mixed prior to combustion, consistent with the single digit NOx ppm levels measured. The study indicates that addition of hydrogen, up to 30% by volume, is possible without any modification to this gas turbine engine.
Benchmarking Gas Turbine Outages: Creating an Expectation Model of Performance Recovery
Authors: Perullo Christopher , Gerlings Andrew , Tomlinson Rick , Koskey Steven , Noble David
Published: August 2024

Gas turbines are the lynchpin of a stable and prospering U.S. power grid and economy. As more forward growth emphasizes renewables, maintaining the existing gas turbine fleet will become even more critical. Gas turbines undergo regular maintenance cycles that inspect, repair, and replace life limited parts. The complexity and invasiveness of maintenance often leads to variability in the resulting performance recovery. For example, parts may not be installed correctly or controls may not be adjusted after the outage as needed. While engineers have a personal ‘expectation model’, this often is incorrect and few organizations rigorously benchmark outage recovery to identify lost performance and incorrect repairs. This paper applies the EPRI Gas Turbine Digital Twin to a historical set of outages for B class gas turbines. A methodology is presented to track outage recovery by comparing model performance to site data pre and post outage and accounting for model and measurement uncertainty through the use of machine learning. This provides a probabilistic estimate of outage recovery which is used to create a fleet outage recovery expectation model. The intent is to use this model to benchmark and score future outages’ effectiveness. The resulting expectation model is also presented here for others to use in their own benchmarking efforts.
Transient Analysis of Flow Unsteadiness and Machine Instabilities in a Centrifugal Compressor at Surge and Second Quadrant Operation
Authors: Serena Alberto , Bakken Lars Eirik
Published: August 2024

Instabilities in turbomachinery operation originate from intrinsic flow unsteadiness, sudden variations of operating conditions, and interactions with the surrounding system, affecting both system stability and machine reliability. The flow unsteadiness, presenting a characteristic behaviour, requires a deep understanding of the underlying flow fundamentals, a careful analysis using advanced experimental methods and a clear distinction on how the system might lead to instabilities.

The identified approach addresses deep surge and second quadrant characterization. A non adequate test procedure might strongly affect the overall behaviour and transient evolution. The analysis presented here benefits from the responsiveness and flexibility of the experimental test rig, fine tuning of the system layout, the instrumentation installation, and the transient tests procedure. The main focus area is the time-frequency analysis of flow and pressure signals at transients, thus providing a proper reconstruction of flow mechanisms and instability evolution. Valuable techniques include: short-time fast Fourier transform, wavelet analysis, and Wigner-Ville distribution; coherence between flow and pressure, to trace waves propagation, is considered too. These, presented outlining their strengths and weaknesses, are evaluated considering real time field applicability with regards to computational resources too.

The experimental campaigns and data processing are presented, with a test matrix covering a wide range of parameters, including system layout and surge volume size, rotational speeds, flow rates ranging from nominal point to full second quadrant operation. These data are vital for system modeling validation for a full compressor-system digital twin.

Results indicate the importance of ensuring reliable data acquisition and analysis, with adequate instrumentation range, accuracy, synchronization, responsiveness and positioning.
Investigation of the Effects of Geometry Variations on the Performance of an Adjoint Optimized Film Cooling Hole
Authors: Ellinger Molly E. , Flachs Elise M. , Bogard David G.
Published: August 2024

In recent studies, a turbine film cooling shaped hole designed by adjoint optimization techniques (X-AOpt) was found to substantially increase film cooling performance with 90% greater adiabatic effectiveness than a reference 7-7-7 shaped hole. Two aspects of the geometry contribute to the high adiabatic effectiveness levels achieved by the X-AOpt holes: the shape of the internal geometry which improves the diffuser performance, and the external protrusions that generate counter-rotating vortices that push the core of the coolant jets towards the wall and spread the coolant laterally. In this study, insight into the relative importance of these two factors was obtained by testing the performance of a row of X-AOpt holes with the protrusions removed from the external surface. Experiments were also performed with varying pitch between X-AOpt holes to determine how the hole spacing affects film cooling effectiveness. Results from the tests of X-AOpt holes without external protrusions showed a 9% increase in adiabatic effectiveness compared to the baseline 15-15-1 holes, while the X-AOpt holes had a 45% higher adiabatic effectiveness than this standard. Experiments were also conducted using X-AOpt holes with varying pitch between holes of P/D = 4.0, 5.45, and 7.0. Results from these experiments showed that a decrease in pitch to P/D = 4.0 provided only a slightly increased adiabatic effectiveness compared to standard P/D = 5.45. However, increasing the pitch to P/D = 7.0 caused a 33% decrease in adiabatic effectiveness compared to the standard spacing. Superposition was found to significantly under predict adiabatic effectiveness for P/D = 4.0 and 7.0, indicating there is a dependence on lateral spacing for the X-AOpt geometry due to vortex interaction.
Validation of a Numerical Model Based on an Optical Surface Scan and Experimental Modal Analyses Under Vacuum Conditions
Authors: Langheinrich Denny , Beirow Bernd , Elmasry Seif
Published: August 2024

A safe operation of compressors requires a profound understanding of the vibrational behaviour of their components. The focus of this work is on the identification of the modal quantities of an impeller of a radial compressor. The prediction of the mistuned mode shapes and eigenfrequencies is carried out by a finite element model which is adapted to surface scan data via mesh morphing to capture geometrical deviations from CAD. A validation of this model is given by an experimental modal analysis, which is conducted under vacuum conditions to eliminate the damping and coupling influence of the surrounding medium. In consequence, the better separation of peaks in the frequency response function (FRF) enables the identification of all modes. The modal parameters as eigenfrequencies, damping ratios and modal constants are extracted from the measurement data by an improved multi-degree-of-freedom-fit algorithm which is capable to process the entire frequency band of a measured FRF. This is necessary due to a high density of modes preventing the separate assessment of certain frequency ranges without errors at the edges of the frequency band. In addition, a laser scan is carried out to support the assignment of measurement data to results from the numerical model based on vibration modes. It can be shown that a majority of the roughly 600 modes in the range of interest can be assigned to measurement data in terms of eigenfrequencies, modified cyclic symmetry mode shapes and blade mode shapes.
Multi-Aeroelastic Phenomena Modelling Part II: Application for the Evaluation of Fan OGV Cyclic Pattern Designs
Authors: Kulkarni Davendu Y. , di Mare Luca
Published: August 2024

The cyclic pattern design of fan outlet guide vanes (OGVs) is key to achieving the fan stage performance and to set the aeromechanical behaviour of low-pressure compressor (LPC). Current trend of compact engine architectures leads to the stronger interaction between LPC components, which in turn results in larger modifications in OGV pattern geometry. A thorough verification of OGV patterns is necessary to avoid the risks associated to LPC performance.

This paper describes the application of high-fidelity aeroelastic model for evaluating OGV cyclic patterns that are commonly designed using low-fidelity design-optimisation methods. The whole fan system model, described in the first part of this paper, is used to conduct time-accurate unsteady CFD simulations to perform various low-harmonic aeroelastic phenomena investigations simultaneously. The simulation results are post-processed to extract 1EO fan forced response, a measure of OGV buffet and the fan efficiency at multiple flight conditions. Multiple OGV patterns are assessed using this approach to explore the OGV pattern design space.

Further, these simulation results are used to produce a Pareto front, which effectively demonstrates the OGV pattern design robustness. This methodology allows comparing various OGV pattern designs against a common set of criteria, to perform design trade-off studies and to identify a right-first-time OGV cyclic pattern design within design timescales.
In-Situ Species Concentration Measurements in Ammonia-Mix Flames Using FTIR Spectroscopy
Authors: Bedick Clinton , Tulgestke Andrew , Boyette Wesley
Published: August 2024

Hydrogen and ammonia represent two carbon-free fuel sources that could be used in place of current fossil energy sources in combustion systems. To develop optimized ammonia combustion systems, validated modeling tools are needed. In the open literature, it has been shown that the complex chemistry associated with fuel-bound nitrogen contained in ammonia differs greatly from natural gas or hydrogen combustion. As a result, several new chemical kinetic mechanisms have been developed. Many of these mechanisms have been validated experimentally, however this has primarily focused on bulk parameters such as laminar flame speed and ignition delay time. Critically, high quality measurements of species concentrations are needed under controlled conditions which are easily represented by simple models. In this paper, direct, in-situ measurements of species concentrations and gas temperature are performed in a laminar flat-flame burner. This arrangement enables comparison with 1D model predictions, better isolating chemical kinetics from the fluid dynamics. Quantitative species concentrations are determined by absorption spectroscopy using an FTIR spectrometer. Fuel compositions representative of cracked ammonia (NH3/H2) and ammonia-natural gas (NH3/CH4) are considered for rich and lean equivalence ratios. A major focus of the paper is on the selection of spectral features for nitric oxide and ammonia and correcting for large amounts of baseline H2O absorption.
Experimental Study of High-Diodicity Inlet Effects on Rotating Detonation Combustor Performance and Operability
Authors: Barnouin Provence , Bach Eric , Paschereit Christian Oliver , Bohon Myles D.
Published: August 2024

Implementing high-diodicity inlets is critical to reduce back-flow and mitigate the pressure loss across the injector in RDCs. Experiments on air injection diodicity were conducted in a non-premixed RDC for both cold-flow and reacting conditions. The introduction of a Tesla-like diode impacted operating modes and injector dynamics, but the extent of that effect depended on the throat-to-combustor area ratio. A smaller ratio mitigated the impact of the diode on detonation characteristics, while a larger ratio extended the operating range of stronger wave modes. The diode stabilized RDC operation through an increased static pressure drop, but limited performance most likely due to poor reactant mixing and local equivalence ratio distribution. Cold-flow tests showed a higher diodicity for the diode, which may contribute to higher pressure gain in reacting experiments. A modified diodicity formulation based on reacting flow measurements was introduced, suggesting that a multi-metric approach can be useful to assess injector performance. High-diodicity air inlets could be useful tools for reducing total pressure loss and controlling operating modes, but careful consideration is required to limit adverse effects on processes like reactant mixing.