bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Study on the Influence of Geometrical Parameters on the Performance of a Turbine Exhaust Hood
Authors: Fomina Anastasia , Fuhrer Christopher , Vogt Damian M. , Willeke Tobias 
Published: September 2023

Abstract
Complying with the current environmental requirements, modern turbine designs must be robust, highly efficient and able to operate at flexible operating conditions simultaneously. An improvement of the pressure recovery in the turbine exhaust hood and especially in its diffuser can increase the overall turbine performance at multiple operating conditions.
In a current study, an axial-radial diffuser is investigated, which represents a typical compact design for industrial turbine exhaust hoods. Since this diffuser-exhaust hood system turns the flow direction from axial to radial direction over a short distance, a characteristic complex three-dimensional asymmetric and unsteady flow field results. Due to this flow topology, local flow separations occur in regions with stronger adverse pressure gradients limiting the maximum overall pressure recovery of the exhaust hood. This paper presents the influence of geometrical diffuser parameters on the diffuser-exhaust hood system performance in terms of pressure recovery, pressure loss, and flow-field asymmetry based on numerical flow simulations. For this purpose, a Design of Experiment (DoE) analysis is performed on a parametrized model of a diffuser-exhaust hood system for a newly developed diffuser test rig, whereby the diffuser geometry is modified asymmetrically. A sensitivity study of the geometrical parameters is performed for two operating conditions.
The simulation results indicate that the overall pressure recovery as well as the pressure loss of the diffuser-exhaust hood system can be influenced through asymmetric diffuser-shape modifications. Besides, it is demonstrated, that the aerodynamic origins of these sensitivities emerge from the local diffuser-loading and flow distribution.
Flashback of Hydrogen-Methane Mixtures in a Fixed-Vane, Low-Swirl Burner at Atmospheric Pressure
Authors: Searle Matthew , Strakey Peter 
Published: September 2023

Abstract
Equivalence ratio at flashback, ϕFB, of low swirl injectors for 60%–95% (H2, by mole) hydrogen-methane mixtures was determined experimentally in a &lt; 100 kW atmospheric pressure burner. Pre-mixer velocities equaled 5, 7.5, and 10 m/s, with the reactants entering the burner at 294 K. The swirler design was selected following a literature review, and the test articles were additively manufactured. The test articles had two turning angles, 26° and 33°, with center-body hole diameters equaling 1.08 and 1.16 mm. A test article was built with each parameter combination, which yielded four test articles with measured swirl numbers varying from 0.43 to 0.49. The results showed agreement with prior work. ϕFB increased with increasing pre-mixer velocity and decreasing percent hydrogen. ϕFB was also observed to increase with swirl angle and decrease with increasing center-body hole diameter. The data was correlated using a semi-empirical quenching approach, with Cquench* = 0.01, where the chemical time scale was calculated using a perfectly stirred reactor (PSR) model. Two different chemical kinetics mechanisms independently yielded the same results. The correlation makes the present small-scale laboratory results relevant to large, high-pressure gas turbines. The flashback data set is available for computational fluid dynamics (CFD) validation.
A Toolbox for the Preliminary Aerodynamic Design of Highly Loaded Annular S-Shaped Transition Ducts
Authors: Veyrat A. , Carrotte J. F. , Walker A. D. , Simpson H. G. 
Published: September 2023

Abstract
The drive towards net-zero carbon emissions is favoring lighter, more compact compressors. For the connecting S-shaped ducts, a larger radial offset must be accommodated within the shortest length ensuring no boundary layer separation and minimum losses. The duct aerodynamic design is however significantly affected by highly complex flow field interactions requiring relatively advanced and time-consuming Computational Fluid Dynamics (CFD) simulations. To limit their use at a preliminary design stage, the Agile TooL for Aerodynamic ductS (ATLAS) is currently being developed for the industrial partner. After shaping a baseline annulus, affine transformations can be carried out to change its bulk dimensions and, for example, enforce a desirable dimensionless curvature distribution. The design space can thus be mapped with ducts sharing similar geometric properties. Candidate designs can next be identified by fast exploration via Ordinary Kriging interpolations of minimum axial length and stagnation pressure loss in a CFD database. An even sample mapping by Delaunay triangulations is used to promote a high-quality semivariance model. In the vast area ratio vs hub radius ratio space investigated here, cross-validation showed that the minimum axial length is predicted with an averaged error of 2.2% at separation and 2.1% at the recommended margin from detachment while stagnation pressure loss is approximated with a mean discrepancy of 4.8% and 2.6% respectively. These capabilities are sufficiently accurate to inform a compressor toolbox about the duct performance and therefore enable a holistic preliminary design.
Analytical Modelling of Flame-Dynamics Within Auto-Ignition Hydrogen and Methane Flames in Mach Stabilized Combustion
Authors: Biagioli Fernando , Freitag Ewald , Syed Khawar J. 
Published: September 2023

Abstract
The sequential combustion concept is characterized by two combustor stages. In the first stage a fraction of the fuel is premixed into the air flow before burning in a standard lean premixed flame. In the second stage, which is the focus of the present contribution, the remaining part of the fuel is injected into the hot products arriving from the first stage and combustion takes place in an autoignition-dominated flame. We analyse here a situation where auto-ignition in the second stage takes place in a flow subject to a positive static temperature gradient. This concept allows very short combustor residence times ans is well suited for incorporation into an integrated combustor-nozzle guide vane. In order to set up the static temperature gradient, the mixture of reactants flows through a converging-diverging channel, first accelerated to a relatively high Mach number, ca. M = 0.6, and then decelerated in the diffusing section where the flame is located. A fully analytical model describing the thermo-acoustics behaviour of the converging-diverging combustor is developed. The critical part of this exercise is given by modelling the frequency response of the heat release rate concentrated at the position of the auto-igniting flame. It is shown here how this is closely related to the response of the displacement of the flame for which a novel analytical model, free from empirical assumptions, is provided. The model is finally applied to compare hydrogen and methane flames in terms of their thermo-acoustic behaviour.
Analysis of Flutter Mechanisms and Unsteady Aerodynamics of a Transonic Fan Blade Near Stall
Authors: Zoepke-Sonntag Roger , Hill George , Stapelfeldt Sina 
Published: September 2023

Abstract
This paper investigates the onset of aeroelastic instability of a modern low-pressure ratio transonic fan using numerical simulations, validated against experimental measurements. Different domain configurations are compared in terms of fan characteristic and radial profiles. It is shown that flutter can be predicted over the investigated speed range using a reduced computational domain. The benefit in computational speed justifies simplifications made and allows a more detailed unsteady analysis. During the unsteady analysis, it is shown that the transition from stable to aeroelastic unstable along a constant speed characteristic results from increased negative aerodynamic damping on the pressure side of the blade, accompanied by a drop of damping on the suction side near the tip. The shock and the radial migration have a stabilizing effect on the blade, while the region downstream of the shock tends to destabilize the blade. The drop in stability occurs in multiple low nodal diameters, independent of acoustic propagation conditions. While previous work tried to identify unique mechanisms that drive flutter, this research concludes that the change from stable to unstable is subtle and that it is a combination of many drivers. In addition, the tip region, especially the region downstream of the shock, tends to have a more significant impact than assumed, while the shock shows only small variations near the tip.
The Impact of Thermal Load and Turbulent Flow on Minimum Film Thickness of a Large Tilting-Pad Journal Bearing
Authors: Vetter Daniel , Hagemann Thomas , Schwarze Hubert 
Published: September 2023

Abstract
Thermal loads induced by internal fluid friction significantly influence the operating behavior of high-speed journal bearings. These loads increase on average if critical Reynolds numbers are exceeded. This paper presents a detailed thermo-elasto-hydrodynamic (TEHD) analysis of a large five-pad tilting-pad journal bearing operating up to surface speeds of 94 m/s. The structure mechanical analysis is conducted by a FE-Code that is implemented as a sub-module of the bearing code to improve computational efficiency. The non-linear structure model includes the pads, their aligning ring and the housing while the journal’s thermal expansion is approximated analytically. The contact of pads and ring is modeled with a contact algorithm. Validation with test data from literature indicates the relevance of structure model’s complexity. Besides the pad deflection, in particular, the consideration of the ring and housing thermal expansion is decisive to predict the effective clearance properly. Furthermore, comparisons between measurement and simulation show that the experimentally identified non-linear speed dependent characteristic of minimum film thickness that features an increase due to turbulent flow is well predicted by the theoretical model. Generally, results provide an insight on the impact of the different effects dominating the behavior of the bearing in the respective speed ranges, and therefore, improve the understanding of complex bearing systems. Finally, the quality of results of approximation formulas that are easier to implement and more time efficient than the complex FE-code is investigated.
A Model of Mass and Heat Transfer for Disc Temperature Prediction in Open Compressor Cavities
Authors: Nicholas Thomas E. W. , Scobie James A. , Lock Gary D. , Tang Hui 
Published: September 2023

Abstract
Accurate prediction of heat transfer in compressor cavities is crucial to the design of efficient and reliable aircraft engines. The heat transfer affects the thermal expansion of the compressor rotor and, in turn, the tip clearance of the compressor blades. This paper presents a novel, physically-based predictive theoretical model of heat transfer and flow structure in an open compressor cavity, which can be used to accurately calculate disc temperatures. The radially higher region of the cavity is dominated by buoyancy effects created by the temperature difference between the hot mainstream flow and the axial throughflow used to cool the turbine. Strong interaction between the air in the cavity and this throughflow creates a mixing region at low radius. For a given geometry, the heat transfer and flow physics are governed by four parameters: the rotational Reynolds number Reϕ, the buoyancy parameter βΔT, the compressibility parameter χ, and the Rossby number Ro. The model quantifies both the buoyancy- and throughflow-induced mass and heat transfer, producing a reliable prediction of the disc and air temperatures. The model takes into account a two-fold effect of the throughflow: being entrained into the cold radial plumes directly and creating a toroidal vortex in the radially lower region of the cavity. The exchange of mass between the cavity and throughflow is related to the mass flow rate in the radial plumes in the buoyancy-induced region, considering the effect of flow reversal at low Ro. The model is validated using data collected in the Bath Compressor Cavity Rig and can be incorporated in engine design codes to robustly compute the thermal stress and expansion of the compressor rotor, contributing to more efficient engine designs.
Towards Best Practice for Predicting a Lifted Hydrogen Diffusion Flame Using a Flamelet Generated Manifold Approach
Authors: van Bruygom Ashley , Garmory Andrew , Walker A. Duncan 
Published: September 2023

Abstract
This paper examines a lifted turbulent H2/N2 diffusion flame in a vitiated co-flow, using a Flamelet Generated Manifold (FGM) combustion model. FGM is commonly used in combusting simulations in the gas turbine industry as it is cheaper than solving detailed chemistry as part of the simulation. The aim of this paper is to examine the ability of the FGM model to reproduce experimental results, and its sensitivity to modelling choices, using an implementation within the commercial code, Simcenter STAR-CCM+. Hence, the current study systematically examines the impact of turbulence modelling, inlet conditions, the flamelet model used to generate the FGM table and the chemical mechanisms. Both Reynold Averaged Navier Stokes (RANS) and Large Eddy Simulations (LES) are presented with focus on the effect of inlet conditions, three different flamelet generation methods and two chemical mechanisms. The flame lift-off height is shown to be highly sensitive to chemical mechanism and flamelet table generation method, with the 0D flamelet giving a higher lift-off than the 1D flamelets. The inlet velocity profile was found to have less of an impact on LES results. This work shows that care should be taken when attempting to identify an accurate simulation methodology and that modelling choices are not considered in isolation as the apparent superiority of a modelling choice may be an artefact of other modelling choices.
A Two-Step Approach for Centrifugal Compressor Performance Mapping Based on a Reduced-Order Model and an Evolutionary Algorithm
Authors: Bicchi Marco , Biliotti Davide , Toni Lorenzo , Marconcini Michele , Grimaldi Angelo , Arnone Andrea 
Published: September 2023

Abstract
Due to their good efficiency, robustness, and wide operating range, centrifugal compressors are pivotal in several industrial and civil applications. In this context, predicting the performance of a centrifugal compressor stage is essential for its aerodynamic design and selection during customer orders. Therefore, the present research focuses on performance mapping once the aerodynamic design is complete. Indeed, once the final stage geometry is achieved, experiments and computational fluid dynamics (CFD) analyses are reliable methods for performance map predictions. However, these methods are expensive and time-consuming, in contrast to typical limitations of the industrial scenario. To limit their cost, a two-step approach based on a reduced-order model leveraging CFD analyses and an evolutionary algorithm is proposed. The main goal is to decrease performance mapping efforts while maintaining a high level of accuracy. Specifically, the theoretical contribution of this research is to investigate the joint use of CFDs with reduced-order models to generate accurate performance maps with low computational effort. While on a practical level, a business-friendly tool for performance mapping is provided. As an example case study, the approach is applied on centrifugal compressor stages for high-head low-Mach number applications. Results show good agreement with CFD and experimental data. The present research lays the foundations for future studies aiming to further reduce efforts in performance mapping and time-to-market of centrifugal compressor stages.
Effect of Incoming Wakes on the Passage Flow of an Axial Compressor Rotor
Authors: Koppe Björn , Lange Martin , Mailach Ronald 
Published: September 2023

Abstract
A multistage setup has become indispensable in current turbomachinery rendering the rotor-stator interaction (RSI) to one of the interested fields of modern research. Its inherent complexity originating in its highly unsteady, three-dimensional and turbulent characteristic aggravates the thorough understanding of the underlying phenomena. In an attempt to simplify this interaction an experimental study has been carried out on a single axial rotor of a low speed research compressor (LSRC) utilizing two different wake generators (WG) to simulate incoming disturbances in the flow. Here, cylindrical bars and radially extracted symmetrical profiles generated to some extent isolated wakes without the complexity of secondary flows typically found downstream of a stator row. The rotor was examined at two different tip clearances (tip gap height/channel height = 1.25 %|4.17 %) for its design operating point. Various measuring techniques were conducted to capture steady and unsteady flow features in planes up- and downstream of the rotor. The influence of the wakes on the losses produced by the rotor are discussed including the unsteady effects on the underlying secondary flow phenomena. Here, in particular the tip leakage vortex (TLV) and the suction side separation of the flow near the hub endwall are examined.
Experimental Characterization of Surge Cycles in a Centrifugal Compressor Under Wet Gas Operation
Authors: Serena Alberto , Hundseid Øyvind , Bakken Lars Eirik 
Published: September 2023

Abstract
This investigation focuses on instabilities in turbomachinery operation due to variations in fluid properties and composition, as with the injection of water droplets. The main objective of this study is to experimentally document compressor behaviour and characteristics under off-design condition in the unstable area between surge inception point to zero flow; flow visualization is used at this scope.
The test rig is a single stage compressor operating with air and water. The compressor is full-sized, and the design is based on a traditional dry gas design optimized for wet gas compression. It is equipped with visualization slots enabling detection of unsteady and reversible flow.
A suitable description of the positive slope area requires unsteady mass flow measurement: gas fractions accurate measuring and control still play a key role in a proper description of the flow phenomena involved, with reverse flow detection being the major challenge to be properly identified.
The results quantify the liquid impact on performance and instability of system characteristics and flow composition, and show the development of unsteady flow regimes. This proves valuable for future system modeling tuning and validation and further understanding of the phenomenon, the development of reliable surge onset prediction models and control strategies. In addition, useful guidelines focused on compressor system design and its behaviour, rather than machine design.
Measurement of Surface Pressure Field of Turbocharger Impeller Using Pressure and Temperature Sensitive Paints
Authors: Furuya Takenori , Nakai Takumi , Imai Masato , Kakimoto Tomihiro , Kameda Masaharu , Matsuoka Yuya , Machida Kazuya , Matsuda Masaaki , Taneda Yoshio 
Published: September 2023

Abstract
A pressure-sensitive paint (PSP) technique is developed for measuring the pressure profile of an automotive compressor impeller at various rotational speeds. Short-exposure images from a digital high-speed camera were used for pressure measurements to prevent image blurring due to high rotational speeds. The pressure was calculated by the two-gate lifetime method using the intensity ratio of two images during PSP dye excitation. Temperature correction of the PSP signal was performed using a temperature-sensitive paint (TSP). Polyurethane resin was used as a binder to improve the heat resistance of the PSP and TSP. Pressure and temperature distributions at the impeller surface were obtained at four speeds when the efficiency was maximum at each speed. Characterization of the paint confirms that this PSP technique provides sufficiently high sensitivity and large emission intensity in the turbocharger impeller test range. Temperatures measured by TSP agree quantitatively well with thermography. The impeller surface temperature increases with increasing RPM and exceeds 100 °C at 182,000 rpm. Temperature-corrected PSP signals provide reliable surface pressure distributions consistent with CFD analysis for the same geometry and operating conditions as in the experiment.
Investigation of Power Turbine Casing Thermal Environment Using One Dimensional Thermal-Fluid Network Solver
Authors: Uyav Omer , Bedir Hasan 
Published: September 2023

Abstract
The gas turbine engine operates in high-temperature, instantly changing power demand and various atmospheric conditions. Therefore, turbine inlet temperature and material selection are the most critical parameters to maintain its integrity and satisfy power output, and cooling the engine components is crucial regarding the durability and reliability of both rotating and structural parts. In addition, thermal and secondary air systems design collectively play a crucial role in the successful case cooling, as they determine the heat load and cooling flow distribution. This paper aims to present a 1D network modeling methodology for any turbine geometry at the preliminary design stage. In this sense, a test campaign is carried out to obtain the temperature distribution of a power turbine casing using thermocouples and pressure sensors. In addition, a 1D thermo-fluid steady-state model is established. The results of the model are validated against test data. Furthermore, a sensitivity analysis is performed, which helps to determine critical parameters for the base model and to determine how the model is affected. Additionally, another casing geometry with a different cooling system is designed to examine temperature distribution on the casing by changing the conduction path. Finally, comprehensive comparisons of all the results are evaluated.
Hydrogen Combustor Integration Study for a Medium Range Aircraft Engine Using the Dry-Low NOx “Micromix” Combustion Principle
Authors: Funke Harald H.-W. , Beckmann Nils , Stefan Lukas , Keinz Jan 
Published: September 2023

Abstract
The feasibility study presents results of a hydrogen combustor integration for a Medium-Range aircraft engine using the Dry-Low-NOx Micromix combustion principle. Based on a simplified Airbus A320-type flight mission, a thermodynamic performance model of a kerosene and a hydrogen-powered V2530-A5 engine is used to derive the thermodynamic combustor boundary conditions. A new combustor design using the Dry-Low NOx Micromix principle is investigated by slice model CFD simulations of a single Micromix injector for design and off-design operation of the engine. Combustion characteristics show typical Micromix flame shapes and good combustion efficiencies for all flight mission operating points. Nitric oxide emissions are significant below ICAO CAEP/8 limits. For comparison of the Emission Index (EI) for NOx emissions between kerosene and hydrogen operation, an energy (kerosene) equivalent Emission Index is used.
A full 15° sector model CFD simulation of the combustion chamber with multiple Micromix injectors including inflow homogenization and dilution and cooling air flows investigates the combustor integration effects, resulting NOx emission and radial temperature distributions at the combustor outlet. The results show that the integration of a Micromix hydrogen combustor in actual aircraft engines is feasible and offers, besides CO2 free combustion, a significant reduction of NOx emissions compared to kerosene operation.