bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Analysis of a Shrouded Centrifugal Compressor for Use in Supercritical Carbon Dioxide (s-CO2) Brayton Cycle
Authors: Fenil Arockia , Seshadri Lakshminarayanan , Kumar Pramod , Nassar Abdul , Giri Gaurav
Published: September 2023

This paper presents the work that entails the design and analysis of a sub megawatt s-CO2 centrifugal compressor. The compressor is intended to be part of a 20 kWe sCO2 Brayton cycle test facility at Indian Institute of Science (IISc) which presently uses a reciprocating compressor. The cycle operates at a maximum temperature of 773K with a flow rate of 45 kg/min and the compressor that feeds the loop must operate between pressures of 21 MPa and 9 MPa whilst rotating at 40000 RPM. The compressor comprising of rotor, vaned diffuser and volute is designed using the AxSTREAM® software suite and is verified numerically using the commercial CFD software ANSYS CFX. Since, initial testing of the compressor will be performed with air, simulations are performed with air as well. A comparison of the flow field revealed that the flow structure in the rotor remains similar at design condition while significant deviation is observed with the vaned diffuser.
Analytical and Numerical Study for the Reduction of Shock Waves in Supersonic Stators Through Trailing Edge Modifications
Authors: Martínez-Alvarado Luis Enrique
Published: September 2023

This paper introduces a method to reduce total pressure losses due to shock wave generation across a supersonic stator by modifying its trailing edge shape. Indeed, it aims at controlling the shape and strength of the generated shock waves to reduce their impact on a full stage supersonic turbine performance. Several approaches were proposed and evaluated using 2D CFD periodic inviscid computations with SU2 solver focusing on the shape, thickness, and deflection of the stator’s trailing edge. The chosen approach is based on a horizontal plate that represents the trailing edge of the stator blade. Shock wave generation was then analyzed following different cases of trailing edge geometries. This analysis has led to the identification of the best-case trailing edge geometry which reduces the number of shock waves generated, their intensity and their interaction between each other. An analytical analysis of the shock wave generation exiting the blade trailing edge was also performed. This analysis introduces the limitations of the maximum blade deflection angle from where reflected shock waves interaction from adjacent blades start to develop. These limitations are presented as a function of Mach number and cutting angle at the trailing edge. The analysis has contributed to the understanding of the shock wave generation in a supersonic stator cascade. Additionally, a simplified method for the predesign of supersonic blades with reduction shock wave generation was completed.
Exploring Physics of Acoustic Flow Control Over Airfoils Towards Potential Application to High Work and Lift Turbines
Authors: Celik Acar , Mitra Abhijit , Agarwal Tapish , Clark John , Jacobi Ian , Cukurel Beni
Published: September 2023

In this study, acoustic actuation was applied experimentally to massively separated flows on simplified hump geometries which mimic the pressure distribution over high-work-and-lift low Reynolds airfoils. The acoustic excitation demonstrated significant control over flow separation, resulting in higher relative lift enhancement than standard, localized actuation techniques with similar momentum coefficients. Full field velocity measurements were used to examine the transient behavior of the actuated flow in order to explain the physical mechanism of separation control. The velocity measurements revealed the presence of a viscous wall-mode that organized the vorticity upstream of the separation point. A spatio-temporal correlation analysis found that the generation of these wall modes in the attached flow was the dominant cause of the subsequent reorganization of the separating shear layer and the change in separation dynamics. The importance of wall-modes to acoustic flow control mechanism has important implications for the design of new acoustic control strategies for high-speed turbomachinery. Along these lines, the ramifications of this phenomena are explored over geometries which are designed to approximate flow fields in high-speed turbomachinery. At the conducive Strouhal number, which scale linearly with the square root of Reynolds numbers, up to 22% lift enhancement is observed for excitation amplitudes in the range of ∼128dB, typical to the engine environment. Of the many diverse flow-control techniques, acoustics can be effectively employed in low Reynolds turbine blades, which are prone to flow separation in the off-design conditions with the ever-increasing demand for higher flow turning.
Pump-Turbine Development for Geomechanical Pumped Storage Facility
Authors: Patil Abhay , Wilkes Jason , Nielson Jordan , Hill Bunker
Published: September 2023

A significant effort is focused on developing cost-effective long-duration energy storage for integrating and expanding the use of renewable energy resources. Geo-mechanical pumped Storage (GPS) leverages the natural energy storage capability of subsurface formations to store water under pressure. The approach is in a way similar to oil and gas production with the potential to leverage an already established supply chain for drilling, reservoir formation, and production. However, with the proposed approach, the head and flow requirement to charge and discharge the subsurface reservoir changes, needing the pumps and turbines with high head flow conditions. The current study explores the design space for the development of turbines and pumps for GPS systems with a focus on expanding the pump as a Turbine option in line with the overall vision of achieving the lowest possible Levelized Cost of Storage Energy (LCOSE). Initial installations focus on two 1 MW systems (522.4 m3/hr and 1044 m3/hr). Design space includes single and multi-stage options at different rotational speeds to optimize the roundtrip efficiency and Net Positive Suction Head-requirements (NPSHr) for surface-installed equipment. Design iterations investigate the rotor-stator interactions, flow slip in reversible direction, and means to optimize the outlet performance to minimize the cavitation occurrence. The analysis lays out different configurations and concludes with the discussion about proposed design that outputs a round trip efficiency of 74% with a path to minimize manufacturing and assembly cost for different installations using modular configurations.
Reducing the Energy Penalty of Retrofit Decarbonization in Combined Cycle Power Plants
Authors: Ravelli Silvia
Published: September 2023

This study is a continuation of previous work aimed at elucidating the effect of hydrogen-cofiring and exhaust gas recirculation (EGR) on combined cycle (CC) performance. The thermodynamic analysis was expanded to include post-combustion capture (PCC) by means of mono-ethanolamine (MEA). Attention was paid to net power output and thermal efficiency.

Part-load operation of the CC without carbon capture was taken as reference. Decarbonization solutions, in ascending order of complexity, included the following: 1) adding a PCC unit; 2) combining EGR with PCC, so as to exploit the increase in the flue gas CO2 concentration while reducing the exhaust gas flow delivered to the absorber; 3) including hydrogen co-firing at the largest capability dictated by the gas turbine (GT) combustion system, with the opportunity to explore a wider range of EGR rates, while still relying on PCC of the residual CO2 in flue gas, before discharge into the environment.

Scenarios were firstly discussed under the same GT load for consistency with the published literature, thus enabling the validation of the modelling procedure. Then, CC net power production was assumed as the basis of comparison. The third solution was found to be the most promising thus minimizing both the energy penalty due to carbon capture and CO2 emission intensity (EI).
Performance Assessment of an Innovative Turbocharged Proton-Exchange Membrane Fuel Cell System
Authors: Iester Federico , Mantelli Luca , Bozzolo Michele , Magistri Loredana , Massardo Aristide Fausto
Published: September 2023

This paper presents an innovative turbocharged proton-exchange membrane fuel cell system (TC-PEMFC) fuelled by hydrogen. Their high efficiency and absence of pollutant emissions allowed interest in hydrogen-powered PEMFCs to grow constantly over the past few decades. Nowadays, both industry and academia consider PEMFCs as one of the most promising solutions to replace conventional fossil fuel plants and achieve decarbonization of the energy and transportation sectors.

The system proposed in this study further improves the performance of standalone PEMFCs (generally within the 60–40% range), using the pressurization of the fuel cells. Two separate stacks are operated in parallel and integrated with a turbocharger, which pressurizes the cathode air flows. Before being discharged into the ambient, the PEMFC outlet flow expands in the turbine, providing part of the mechanical power absorbed by the compressor and increasing the net power output of the plant. The remaining part is supplied by an electrical motor connected to the shaft of the turbocharger.

To guarantee the proper operation of the PEMFCs in terms of mass flows, pressures, temperatures, chemical compositions and humidity, the layout incorporates many auxiliary components. They include a polymeric membrane cross-flow humidifier on the cathode side, a gas-to-gas heat exchanger on the air loop, a side channel blower on the anode recirculation and a liquid cooling system for the stacks.

A dedicated control system was designed to keep all the operative parameters of the plant on the proper values. A proportional-integral-derivative controller and a set of look-up tables regulate the opening of fuel and bypass valves, as well as the rotational speed of turbocharger, cooling fluid pump and blower.

To fully understand the potential of this innovative solution, Rolls-Royce Solutions and Thermochemical Power Group (University of Genoa) developed a simulation model using GT-Power, a commercial software by Gamma Technologies Inc. The complete layout of the system was recreated within GT-Power relying on its extensive library of components. This is the first time a turbocharged PEMFC system was modelized including all the main balance of plant components and implementing the full control logics.

The model was used to simulate the TC-PEMFC system under different conditions, to monitor its operative parameters, and to compare its performance with a standalone PEMFC. The promising results obtained during this analysis confirm the potential of the turbocharged layout and open the way for even more sophisticated simulation studies and experimental activities.
Systematic Approach for Modelling Modern Turbofan Engines
Authors: Ramdin Shivan , Visser Wilfried , Regueiro Juan , Rootliep Tim
Published: September 2023

Turbofan engine technology has evolved over several decades resulting in highly efficient and reliable propulsion systems for commercial airliners. Maintenance costs have decreased, but still represent a major part of the overall aircraft operating costs. To further minimize these, engine maintenance needs to be planned timely and strategically. Advanced diagnostics and health monitoring methods are being developed at KLM Engine Services (ES) to improve engine maintenance. For health monitoring, gas path analysis is used which requires accurate engine performance models. The modelling task is complicated further by the reduced number of measured gas path parameters with modern turbofan engines. This paper presents a systematic approach to overcome these complications. An engine model usually comprises of a cycle reference point, representing a design point such as maximum take-off thrust. As a first step, a genetic algorithm is used to determine the set of unknown cycle reference point parameters and component efficiencies best matching a set of known engine measurement data. Additionally, physical relations were used as constraints to compensate for the missing data. Off-design performance is calculated by solving a set of non-linear algebraic equations which depend on the unknown component performance maps. The customary method of deriving the performance maps by scaling similar maps at the cycle reference point only, often suffers from large deviations at off-design conditions. Consequently, these ‘baseline’ maps require corrections across the entire operating envelope. In the second step of the method, genetic algorithms determine the best off-design performance estimations at multiple measured operating points by finding the optimal coefficients of polynomial scaling functions for map parameters such as efficiency, corrected pressure ratio and mass flow. The modelling method has been verified by developing CF6-80C2 and GEnx-1B turbofan engine models using test cell data. The GEnx-1B engine model has subsequently been validated using on-wing operating data. The largest validation error was attained at cruise flight conditions and was found to be equal to 3.9%. The resulting method provides a systematic way to deal with missing data and can be used for developing accurate engine models for better gas path analysis reliability, resulting in more effective engine maintenance.
Determination of Cetane Numbers via Chemical Kinetic Mechanism
Authors: Schmidt Marleen , Schlichting Samuel , Melder Jens , Methling Torsten , Köhler Markus , Huber Andreas
Published: September 2023

Minimizing global warming is a major task of todays’ society. For air transport, sustainable aviation fuels (SAF) produced from renewable sources are a promising key solution. While electric flight is intriguing for short distances, SAF are required for mid and long distance flights and in addition, enable fuel design strategies to minimise environmental effects. The qualification and approval for SAF is standardised in the ASTM D4054, which include fuel properties as an essential part. Among others, lean blow-out (LBO) limits are a key performance parameter. The experimental determination of LBO is very time and cost consuming. The LBO of a specified engine is highly dependent on the fuel properties affecting evaporation, mixing, and ignitability. Therefore, prediction tools are desired to identify early promising SAF for decreasing the certification cost. Due to the correlation between LBO and derived cetane numbers (DCN), a tool for the prediction of the DCN is presented in this study. The DCN-model uses chemical kinetic ignition delay time, simulated in a constant volume combustion chamber based on the ASTM D6890 standard, and seven representative physical properties of a fuel. A high agreement of the predicted DCN to the literature DCN with root mean square errors of 3.3 and correlation coefficients of 0.974 was found.
SGT5-4000F Hydrogen Capability – High Pressure Combustion Rig Tests
Authors: Blaette Lutz , Schmitz Udo , Streb Holger , Vogtmann Daniel
Published: September 2023

Gas turbines will play an important role in the future energy mix with a growing but volatile share of renewable energy sources, because of both their unique grid stabilization capabilities and the ability to burn hydrogen or other green fuels. The hydrogen capability of the Siemens Energy heavy duty gas turbine SGT5-4000F is currently investigated and extended. The first engine was introduced in 1997, the fleet consists of more than 360 units in operation today with ∼23Mio accumulated operating hours. The desired reduction of the fleets CO2-footprint cannot be achieved solely by efficiency enhancements, but also requires the ability to operate on fuel gas mixtures of natural gas and hydrogen. Likely scenarios foresee hydrogen contents in the fuel gas of up to 30%vol in the near future and mid-term operation in the range of 30%vol to > 50%vol H2. This appears to be feasible with the existing SGT5-4000F combustion architecture.

Combustion tests with hydrogen mixtures with varying H2 content have been performed at the Siemens Energy Clean Energy center (CEC) under realistic thermodynamic boundary conditions in a single burner high pressure test rig. The relevant burner variants operating in the fleet as well as burner upgrades have been tested on their maximum H2 capability with regards to combustion dynamics, overheating/ flashback and NOx emissions.

This paper provides an overview of the test results, gives an outlook on the resulting anticipated hydrogen capabilities of the SGT5-4000F fleet and outlines the next steps in the SGT5-4000F hydrogen program.
Physics-Driven Priors for Improved Spatial Models and Averages
Authors: Seshadri Pranay , Duncan Andrew B. , Thorne George , Vazquez Raul
Published: September 2023

This paper proposes a new physics-driven prior structure for engine spatial models. It is designed to be used on engine measurements, with the objective of obtaining more accurate spatial models and subsequent averages, even in the absence of extensive measurements. We demonstrate our methods on a fan bypass measurement plane using data from experiments and simulations.
Analysis and Optimisation of Polymer Electrolyte Membrane Fuel Cell (PEMFC)
Authors: Singh Neha , Shahpar Shahrokh , Indi Tristanto
Published: September 2023

Increased focus on net-zero carbon emission in various industries has called for diversification of sustainable energy sources to limit the dependency on fossil fuels. Hydrogen fuel cells have thus become a promising technology offering zero emission and high efficiency. It has a myriad of applications in the power generation, stationary and automotive industries. For short and medium haul flights, fuel cells offer a promising solution to combat climate change. It is light and efficient, utilising hydrogen as a readily available energy source. In this paper, extensive multi-physics CFD modelling is used in the development of fuel cell technology to build more efficient PEMFC with lower cost and weight for aviation application. The purpose of this paper is first to conduct a multi-physics simulation and analyse in detail the distribution of reactant species along the channels, water content, and pressure distribution. A multiphase simulation over a 22-channel serpentine PEMFC is carried out. The simulation results are validated by comparing the resultant polarization curve to the available experimental data. The analysis is then extended to the optimisation of fuel cells by parameterising the PEMFC fuel and air channels, and then conducting a Design of Experiment (DOE) which can be used to produce an optimal combination of parameters influencing the performance of the unit fuel cell.
Experimental and Numerical Investigations of Steam Expansion Rate in Low Pressure Steam Turbine
Authors: Tabata Soichiro , Segawa Kiyoshi , Takahashi Tadashi , Aoyagi Jin
Published: September 2023

This study focused on the expansion rate of steam; the effect on efficiency was investigated experimentally and numerically by varying the expansion rate of steam in the stage where condensation occurs by varying the flow rate and inlet temperature using a five-stage model steam turbine. The steam expansion rate of the stator blades in each stage was evaluated from the measured wall pressure and total pressure. In addition, the turbine efficiency was evaluated from the measured torque and mass flow rate, and the effect of flow rate and condensing stage can be taken into account for losses caused by condensation. In addition, numerical calculations to account for the effects of non-equilibrium condensation were performed using ANSYS CFX. The numerical calculations were able to show the details of the nucleation situation and the resulting changes in flow patterns.

Numerical evaluation of the subcooling loss showed that there was no difference in subcooling loss between different mass flow rates. The steam expansion rate was evaluated from the measurement results, and it was found that there was no difference in the steam expansion rate due to differences in mass flow rate. This corresponds to the numerical result that the subcooling loss does not vary with flow rate.
An Educated Guess - Predicting Turbomachinery Efficiencies of Aero Engines During Conceptual Design
Authors: Häßy Jannik , Bolemant Martin , Becker Richard-Gregor
Published: September 2023

Evolutionary advancements and disruptive concepts for future gas turbine-based propulsion systems are researched to reduce the environmental impact of aviation. In the initial design phase, only few data on component efficiencies is available and assumptions have to be introduced. However, comparability and consistency between assumed efficiencies is crucial to benchmark different designs or concepts in a feasible way and to avoid misleading findings. The assumptions made have to reflect the impact of design parameters on efficiency considering underlying physical phenomena. A simple model is developed to predict the design efficiencies of axial flow turbo components of aero engines with the aim to generate traceable, consistent and comparable assumptions for conceptual engine design. The efficiency prediction model combines existing approaches from published sources using a superposition principle and is calibrated by means of available data on engines with an entry into service later than 2010. For a stage-wise evaluation approach, the calibrated model predicts the component efficiencies of database engines with a maximum absolute deviation of 0.1 % for fans, 2.2 % for compressors, 1.4 % for cooled turbines and 0.6 % for low-pressure turbines. The deviations between predictions and database values create a sense for the uncertainty that has to be expected using the calibrated model. The future application of the predictive capability contributes to feasible comparisons between different engine configurations during the conceptual design phase.
Soot Formation and Flame Characterization in a Swirl Kerosene Spray Rich Burn-Quench-Lean Burner at Elevated Pressure
Authors: Perrier Aurélien , Milea Andrei-Silviu , Caceres Marcos , Vandel Alexis , Godard Gilles , Cayre Alain , Collin-Bastiani Félix , Cabot Gilles , Grisch Frédéric
Published: September 2023

Swirl-stabilized, turbulent, non-premixed kerosene-air flames were studied experimentally in an RQL (Rich burn/Quick-quench/Lean-burn) model combustor equipped with large optical accesses. The goal of these studies was to characterize the flame topology as well as soot and NO formation processes in the rich primary zone of the RQL combustor, and to establish a large database for future validation of numerical simulations. The experiments were performed under relevant operating conditions up to 4.5 bar. The aerodynamic flow field was measured by Particle Image Velocimetry, the flame structure, fuel and NO distributions by Planar Laser-induced Fluorescence and soot volume fractions by Planar Laser-induced Incandescence. Additional measurements were performed by a scanning mobility particle sizer technique to record the number of soot particles per unit volume as well as the particles size. Two equivalence ratio conditions were used to study the impact of relevant scalar parameters on NO and soot production. For each condition, instantaneous and average distributions of the measured parameters are presented and discussed. The coupling of the optical and intrusive measurement techniques has finally enabled to highlight the impact of the liquid and gas phases fuel distribution on the flame structure, but also on NO and soot formation.
Investigation of Radial Preswirl Nozzle – Coverplate System Using CFD
Authors: Erdem Erinc , Yalcinkaya Abdulkadir , Sertcakan Mustafa Cem , Sal Sinan , Dogu Yahya
Published: September 2023

This article focuses on a radial preswirler system using CFD, and the effect of different parameters such as the number and the angle of the holes at the preswirl nozzle exit, and the diameter of the preswirl nozzles have been investigated. Three-dimensional steady CFD simulations on a 22.5deg sector model showed a non-monotonic trend of swirl velocity at the inlet of the receiver holes and associated flow angles when different preswirl nozzle configurations are tested. Sudden rise in swirl ratio can be attributed to interactions of adjacent nozzle jets. Due to this flow feature swirl velocities are enhanced up to a certain angle where the interaction starts to diminish. Free vortex assumption in between nozzle exit and receiver inlet holds, as angular momentum of the nozzle jet is much more dominant compared to torques exerted by stator surfaces.
Tacholess Instantaneous Speed Estimation of a Wind Turbine Gearbox Using Vibration Signals
Authors: Sankarankutty Rahul , Rathna Prasad Sagi , Shakya Piyush , Sekhar A. S.
Published: September 2023

Early turbine component failures continue to be a problem in the wind energy sector with the gearbox being the costliest subcomponent to maintain. In this study, an in-house wind turbine experimental test rig has been designed to simulate the on-site transient wind speed and load conditions on a scaled-down 3-stage planetary gearbox. A total of 19 different wind profiles from commercial wind farms are validated from the measured vibration data using statistical performance criteria. Tracking the rotational speed, especially in a wind turbine gearbox operating in highly non-stationary environments, is extremely essential. Conventional speed measurement by tachometers or encoders is sensitive to random disturbances, and hence Instantaneous Angular Speed measurement from vibration signals is an alternate approach to estimating the instantaneous frequency of the system from accelerometer data. The present study compares different speed estimation methods based on phase demodulation and time-frequency approaches for their accuracy on various wind speed datasets. A new method is proposed, combining both the time-frequency and demodulation techniques. A performance comparison of the methods is done, and their results are compared with the data collected from an angular encoder.
Virginia Tech Optical Inlet Sensor for Particle Detection: Rolls Royce M250 Turboshaft Demonstration
Authors: Antous Brittney , Byun Gwibo , Lowe K. Todd , Smith C. Fred
Published: September 2023

Propulsion systems are exposed to environmental ingestion hazards that can cause significant damage and decrease performance. Particles are ingested in a wide range of flight environments that can cause immediate engine failure or long-term damage. An accurate measurement technique has been developed to quantify particle ingestion and aid engine health monitoring. This sensor utilizes scattering and extinction techniques along with machine learning models to measure particle characteristics based on a robust and versatile library. The capabilities of this sensor have been demonstrated using solid quartz particles on the Rolls-Royce M250-C20B particle ingestion turboshaft test engine. To the authors’ knowledge, this work presents the first demonstration and validation of optical solid particle sensing in a turbine engine. CSPEC sand (Mil-E-5007C) was ingested for the validation test at two different feed rates using a sand feeder. The sand concentrations were 45mg/m3 and 22mg/m3. The sensor outputs the particle characteristics of aspect ratio (AR), size distribution (σ), Sauter mean diameter (D32), and the particle mass flow rate. The Sauter mean diameter and mass flow rate of ingested sand were calculated using the machine learning model outputs and validated by independent measurements. The sensor produced a 0.1 g/min RMS error compared to the validation measurement.
Elastic and Damping Characterization of Open-Pore Metal Foams Filled or Not With an Elastomer for Vibration Control in Turbomachinery
Authors: Laçaj Endri , Jolly Pascal , Bouyer Jean , Doumalin Pascal
Published: September 2023

In this work, an experimental investigation into vibration damping of elastomer filled open-pore metal foams and their effectiveness as a bearing support in turbomachinery is presented. The polyurethane fillers known for their high-energy absorption capacity were chosen to enhance the damping performance of the metal skeleton. Aluminum (Al), copper (Cu) and nickel-chromium foams (NiCr), with different relative density and pore size were tested dynamically using a dedicated device based on a single degree-of-freedom model. The results indicate that the storage modulus and the loss factor for foam-polymer composites were greater than the combined contribution of both phases taken separately. Foam morphology plays an important role in this effect and it is shown that the increase in performance was more significant for higher specific surface area. Fillers with different properties were also considered. The optimal combination of foam and polymer was selected and tested on a rotor kit test bench. Annular shaped samples were placed between the external race of the ball bearing and the housing. The tests were carried out using a flexible rotor configuration where the vibration amplitudes of the rotor were monitored for foam and foam-polyurethane composites for rotational speeds up to 100 Hz while hammer impact tests were performed using a semi-rigid shaft configuration due to higher resonance frequencies. In the first case, no significant difference was observed between the foam, foam composite and the bearings-only set-up. In the second case, the foam composite resulted with the highest energy dissipation capacity.
Measurements of Turbulence in Compressible Low-Density Flows at the Inlet of a Transonic Linear Cascade With and Without Unsteady Wakes
Authors: Pastorino Giacomo , Simonassi Loris , Lopes Gustavo , Boufidi Elissavet , Fontaneto Fabrizio , Lavagnoli Sergio
Published: September 2023

In the present work, hot-wire anemometry was employed for the characterization of the turbulent field at the inlet of a high-speed low-pressure turbine cascade, in terms of turbulence intensity and integral length scales. This work addresses two major topics relevant to the turbomachinery field: the application of hot-wire anemometry in transonic and rarefied flow regimes and the decoupling of the deterministic and the stochastic fluctuations when measuring unsteady phenomena. In compressible and rarefied flows, a hot-wire is strongly sensitive to both density and velocity fluctuations, and the commonly used Nusselt-Reynolds correlations are not valid. In this paper, a non-dimensional calibration methodology, based on Nusselt, Reynolds and Knudsen numbers, was coupled with a sensitivity analysis and employed to post-process the experimental dataset, allowing to decouple the fluctuations of density and velocity and compute the turbulence parameters. In the presence of unsteady wakes generated upstream of the cascade, two different phase-locked averaging techniques were employed to distinguish the wake deterministic fluctuations from the background turbulence intensity.
Investigation of Rotor Stator Cavity Flowfield at Downstream of a High Pressure Turbine Disk
Authors: Yazan A. , Karasu Z. T. , Yilmaz S. , Erdem E. , Sal S.
Published: September 2023

The present study aims to investigate the flow field of the cavity, that is bordered by HPT rotor disk and LPT stator disk, via CFD and 1D flow solver for a symbolic engine geometry. The cavity has two outlet regions, namely disk rim side and labyrinth seal side, and one inlet that is located at the middle of the stator surface. The test rig data, that is used for validating CFD method in the study, from Kilic and Owen [5] is performed at various disk speeds. It is intended to demonstrate unorthodox rotor-stator flow physics, in which rotor pumping is hindered by an impinged air on to the rotor surface. In order to expand the scope, analyses are conducted by varying turbulent flow parameters. The explanations, which are constructed on stream lines, temperatures, swirl ratios and pressures, on the results are carried out based on physicals concepts such as free & force vortex behaviour and windage effect. The outcomes of the unfamiliar rotor-stator behavior in the study is expected to be a guide for the ones who have an interest in rotor-stator designing in terms of thermal /flow discipline.
Spray Combustion and Emissions of a Hydrothermal Liquefaction Biofuel for Gas Turbine Applications
Authors: Broumand Mohsen , Shahzeb Khan Muhammad , Thomson Murray J. , Singh Devinder , Yun Sean , Hong Zekai
Published: September 2023

Biomass liquefaction oil (BLO), obtained from biomass resources through thermochemical processes like fast pyrolysis (FP) or hydrothermal liquefaction (HTL), is widely regarded as one of the most economically feasible energy solutions in our future sustainable energy mix. However, the utilization of BLO as a drop-in fuel in the current in-line gas turbines has encountered several challenges due mainly to the difficulties in atomization and ignition, originating from the fuel’s chemical composition and physicochemical properties. The present study compares the combustion performance and gas- and solid-phase emissions of a HTL oil (also called biocrude), as well as its diesel blends, with those of a conventional FP oil (also called bio-oil). Considering diesel as a baseline fuel, the properties and combustion performance of the HTL oil compare favorably with those of the FP oil. An anchored spray flame using the 100% HTL oil is achieved in the experiments with much smaller degrees of fuel coking and nozzle clogging problems and a lower amount of particulate matter (PM) emissions. However, its CO and NO emissions are measured higher by more than two times. The insights drawn from the present study indicates the potentials of high quality HTL oils as sustainable fuels to replace fossil fuels in gas turbines and other energy conversion systems.
Investigation of Rear Blisk Drum Dynamics Under Consideration of Multi-Stage Coupling
Authors: Gambitta Marco , Beirow Bernd , Klauke Thomas
Published: September 2023

The analysis of the structural dynamics of multistage cyclic structures as linked components is required to model the interstage coupling. In turbomachinery, this can result in a collaboration between different compressor or turbine stages. This paper investigates the coupling between two rear drum blade integrated disk stages of an axial compressor to support the mechanical design process.

Considering the vibration modeshapes of a multistage system, different components may co-participate in the dynamics. For this reason, a criteria to identify the modes affected by the coupling and to quantify this coupling is defined. This allows to distinguish between modes with inter-stage coupling, requiring the multistage system for their description, and uncoupled modes, involving a single stage. In addition, it is of interest to research methods to reduce the impact of the coupling on the vibrating system without drastically altering the geometry of the components.

The vibration analyses of a two-stage compressor generalized geometry, representative of a compressor rear drum blisk, is presented as a study case. The use of a reducing method allows to describe the behavior of the nominal multistage system with a computationally efficient technique, enabling a parametric analysis of the stages’ coupling. The investigation considers the effect of a set of geometrical and mechanical parameters on the dynamics, identifying the driving parameters of the coupled vibration characteristics.
Development of a Novel Steam Turbine Low Pressure Section for Variable Speed Application
Authors: Auciello Jury , Maceli Nicola , Arcangeli Lorenzo , Cosi Lorenzo
Published: September 2023

Low Pressure (LP) stage design characteristics play a key role in Steam Turbine (ST) product line as they typically set limits to the maximum turbine flow and rotating speed and have a strong influence on the overall turbine efficiency.

LP stages design presents a combination of structural and aerodynamics challenges that obliges the manufacturers to develop and test the design well in advance with respect to the turbine design schedule.

For the same reason (development complexity) an LP stages design is usually scaled to cover a wide range of rotating speed and annulus area. The set of scaled LP stage is referred to as LP stage family.

The author’s company has started the design of a new family of LP stages for power generation and mechanical drive application. The initial phase of the development has focused on the design of the master size, development of the entire family and manufacturing process qualification.

This paper will present a comprehensive review of all the phases of development with the intent to share an OEM perspective of the key technical aspects involved in the development of these components.
Analysis of Infiltration and Solidification of Brazing Materials Into Porous Hastelloy X Feltmetal Using Differential Scanning Calorimetry
Authors: Motyka Elaine , Kweder Jonathan , Noyes Tyler , Roeseler Stefan , Schricker Robert
Published: September 2023

The diffusional solidification of high-temperature brazing compound interacting with open-pore metallic Feltmetal materials were investigated using simultaneous differential scanning calorimetry analysis with thermogravimetric analysis (DSC-TGA). Feltmetal is an abradable seal material primarily used to sustain pressure differentials between stages gas turbines. It is a sintered particle material with an open-pore structure and high total pore volume, typically 80%. Because Feltmetal is commonly brazed into the turbine stage directly to the outer shroud, the effect of the braze layer on the pore structure and on the properties of the seal material is important to the seal function. The characteristics of non-vacuum brazed Feltmetal is of particular interest in this work, as we explore processes for overhaul and repair of Feltmetal abradable seals while in-field and away from a particular service center. The ability to repair these seals in-situ, could provide a faster and less expensive route for an engine back into service. The DSC-TGA responses of a Ni-based Feltmetal material and a Fe-based Feltmetal material with one braze material AMS 4777 were examined. The DSC-TGA data to 1200°C were used to identify elemental diffusion, eutectic melting, and high temperature oxidation reactions. The target microstructure consists of a porous matrix of Feltmetal fibers where fibers and pores adjacent to the braze have reacted with the braze alloy to make a metallurgical bond. This research demonstrates that thermal analysis methods can indicate key process reactions, such as onset of oxidation and eutectic phase transformation, during atmospheric brazing process development. The results of this work are used to aid in the development of in-field seal installation where full system disassembly, and vacuum brazing, is not practical.
On the Feasibility of Helicity-Based Corrections of Turbulence Models for Improving RANS Predictions of Centrifugal Compressor Stages
Authors: Pela Alessandro , Marconcini Michele , Arnone Andrea , Toni Lorenzo , Valente Roberto , Agnolucci Andrea , Grimaldi Angelo , Pacciani Roberto
Published: September 2023

In order to face the challenges of energy transition, turbomachinery designers claim for appropriate numerical tools able to keep up with robust, and fast design iterations.

High fidelity analyses are becoming feasible for assessing the performance of selected geometries, however RANS-based CFD codes are still the workhorse exploited for daily design and optimization iterations when a large number of geometrical configurations are needed to scrutinize a wide and complex design space. The proper selection of the numerical framework, and in particular of the turbulence model, is always critical in order to guarantee a sufficient confidence level in the predicted results, and, at the same time, robustness and numerical stability with quick simulations. Major sources of inaccuracy are often associated with 3D flow features, secondary flows, flow separations, and shock wave boundary layer interaction.

The present work proposes helicity-based corrections for the production terms of two-equation turbulence models as a mean of improving predictions of the aforementioned flow features. A discussion on the treatment of helicity-based terms when changing frame of reference represents one novelty aspect of the paper.

The numerical framework is first validated on a transonic axial fan test case (NASA Rotor 67) and then applied to the analysis of two centrifugal compressor stages for in the high peripheral Mach number regime.

The feasibility of the helicity-based approach is proven via a comparison with the available experimental data in terms of spanwise distributions of flow quantities and performance characteristics of work input and polytropic efficiency. The impact of turbulence modeling on the prediction of the flow field details is investigated, to assess the capability of a steady state numerical approach to identify the physical mechanisms that limit the operating range at low mass flows.
Part II: Validation and Verification of CFD Analysis for NASA SDT Transonic Fan Stage Coupled With Nacelle
Authors: Lee Daryl Y. , Robles Vega Gregorio , Ni Michael , Ni Ron-Ho
Published: September 2023

The airframe and engine are a tightly coupled system but are generally designed in isolation. It is only during final installation testing that the interaction effects of the airframe and the engine are quantified. There are many reasons for the separation of effort, but one blocker is the availability of a validated modeling approach that incorporates best practice methodologies for both components while providing an estimate of the coupling effects within a time reasonable for the design cycle.

In Part I, a CFD code validation was completed on the NASA SDT (Source Diagnostic Test) with the focus on the turbomachinery components. The turbomachinery model was compared against two experimental data sets that consisted of seven speedlines, an operating line and 2D radial profiles each. The outcome of Part I showed good agreement with the experimental data. In this paper, the turbomachinery model is integrated with the SDT nacelle geometry with baseline nozzle area from Part I. By not changing the modeling approach for the turbomachinery components and simply connecting the model from Part I to the nacelle, nacelle installation effects can be isolated. These simulations predict lower adiabatic efficiency due to the inclusion of the nacelle and the CFD model illustrates the reasons for the loss.

In addition, four freestream operating conditions from Mach 0.05 to Mach 0.2 are analyzed, and fan stage distortion sensitivity is evaluated across an entire operating line to understand the effects on the nacelle behavior from different flight operating conditions. The coupled nacelle analysis shows that the effects of higher boundary layer buildup and changes in the stagnation point of flow entering the nacelle can cause efficiency losses between 1% to 3% or more and increases as the Mach number is decreased.

The methodologies developed in this paper, could be applied within the design cycle to understand inlet and engine coupling effects prior to test for future aircraft designs. The rapid evaluation of different design choices offered by this methodology provides designers with another tool to optimize the coupling effects caused by the various design parameters.
CO Laser Absorption Measurements During Syngas Combustion at High Pressure
Authors: Cooper Sean P. , Nativel Damien , Mathieu Olivier , Fikri Mustapha , Petersen Eric L. , Schulz Christof
Published: September 2023

Syngas is a desirable fuel for combustion in the Allam-Fetvedt cycle which involves combustion under supercritical-CO2 (sCO2) conditions. While some work has been conducted in collecting ignition delay times at the extreme pressures required by these systems, significant model deficiencies remain. Additionally, considerable barriers in terms of non-ideal gas dynamic effects have been shown for these experiments in shock tubes. Further investigation into the fundamental combustion kinetics of H2/CO/CO2 mixtures is required. Time-resolved speciation measurements for target species have been shown to better aid in improving the understanding of underlying chemical kinetics than global ignition delay time measurements. Therefore, laser absorption measurements of CO were collected behind reflected shock waves during combustion of syngas at 5 and 10 bar and temperatures between 1080 and 2100 K. The mixtures investigated utilized H2-to-CO ratios of 1:1 and 1:4, respectively, each at stoichiometric conditions, allowing for discussions of the effect of initial fuel composition. A ratio of fuel to CO2 of 1:2 was also utilized to represent commercially available syngas. The mixtures were highly diluted in helium and argon (20% He, 76.5% Ar) to minimize thermal effects and to expedite CO thermal relaxation during the experiment. The resulting CO time histories were then compared to modern chemical kinetics mechanisms, and disagreement is seen for this system which is assumed to be fairly well known. This study elucidates particular chemistry that needs improvement in moving toward a better understanding of syngas combustion at elevated pressures.
Forced Response Analysis of a Highly-Loaded Low-Pressure Compressor Stage With Inlet Distortions
Authors: Toracchio Riccardo , Stapelfeldt Sina , Hillewaert Koen , Fontaneto Fabrizio
Published: September 2023

Due to modern evolutions in propulsion, in view of obtaining higher propulsive efficiency, turbofan engines are subjected to ever higher inlet flow distortions. In these systems, structural damage can be induced by distortion patterns with excitation close to the blade natural frequency. To fill the gap currently present in literature about the impact of inlet distortions on the aeroelastic behaviour of engine components, this paper presents an aerodynamic damping and forced-response analysis on a highly-loaded axial compressor subjected to intake total pressure distortions. First, a stability analysis for the vibrational mode with natural frequency close to the resonance condition at the nominal speed of the machine is performed. Blade deformations are then computed through a distortion induced forced-response analysis at different distortion amplitudes. This work aims at studying the aeromechanical behaviour of a modern compressor, highlighting that the amplitude of the blade vibration does not increase linearly with the distortion amplitude.
The Effect of Upstream Unsteadiness on the Unstarting of a Supersonic Inlet Turbine
Authors: Mushtaq Noraiz , Gaetani Paolo
Published: September 2023

A 15% increase in thermal efficiency at medium pressure ratios is promised by rotating detonation engine technology over conventional Joule-Bryton cycles. A supersonic inlet turbine is a viable option to extract substantial work from the highly fluctuating and supersonic flow delivered by the detonating combustor. However, an additional unstarting mechanism based on the generation of a collective shock from the coalescence of leading-edge bow-shock waves further restricts the available design space. Firstly, the effect of unsteady inlet conditions with variable frequency, amplitude, and mean value on collective shock generation is investigated. Then, a fast and cost-effective tool was developed and verified to predict bow shock wave motion from a prescribed inlet Mach trend; the parameters of the transfer function were estimated with a classical identification method based on a step-response CFD simulation. The model was employed to rapidly calculate the maximum amplitude of fluctuations accepted by the supersonic blade row for each frequency and average inlet Mach number. Finally, the influence of the inlet geometric angle, pitch to leading-edge thickness ratio, and static temperature on the model parameters is studied. The preliminary observations of the parametric analysis were confirmed by the rigorous quantitative approach of a global sensitivity analysis based on Sobol sensitivity indices.