bluuebunny/crossref_metadata_2025 huggingface dataset:
Computational Flow Field Assessment of the Inlet Region of Centrifugal Compressor Under Unsteady Flow Conditions Near Surge
Authors: Parikh Aakeen , Ale-Martos Pablo , Barrera-Medrano Maria Esperanza , Hayashi Yoshihiro , Martinez-Botas Ricardo
Published: October 2022

The centrifugal compressor of a turbocharger is affected by the opening and closing of the engine intake manifold and consequently experiences a pulsating backpressure. The imposed pulsating conditions generate internal losses and reduce the overall compressor performance and efficiency. However, previous studies have shown that these dynamic conditions can also lead to a surge margin improvement, benefiting the lower limit of stability, in certain conditions. The stability of the compressor arises from the flow behaviour in the inlet region and the interaction between the rotating and stationary components at the inlet. In this paper, the computational flow field of the inlet region of a centrifugal compressor under pulsating flow has been studied. A full stage, 3D URANS model of a compressor exposed to pulsating backpressure has been solved using ANSYS-CFX for the near surge operating point. The transient behaviour of this operating point has been studied at six instances in time within one cycle of the pulse. The flow field is assessed using Mach number, static entropy, static pressure and local flow direction in the inlet region. Flow separation regions have been identified. The authors propose that the variation in flow field at the inlet due to the dynamic response to the imposed boundary condition could explain the improvement in surge margin under pulsating flow conditions for this compressor system.
Design and Development of a Fast Response Torque Meter for Unsteady Flows in Turbocharger Applications
Authors: Parikh Aakeen , Singh Gunin , Noon Chris , Flora Harminder , Martinez-Botas Ricardo
Published: October 2022

A high-speed torque meter has been designed and tested for turbocharger applications in order to assess the effect of unsteady boundary conditions. The torque meter is designed using the shaft-twist method by measuring the change in relative angle between the two ends of the drive shaft. Two encoder wheels are mounted on either end of the shaft and a high-speed FPGA measures the variation of time between edges from optical switches. The angular twist in the shaft is calibrated against a reference torque transducer over a range of torque values. The torque meter is installed on an existing compressor rig testing facility at Imperial College London equipped with a pulse generator capable of producing different pulse frequencies and amplitudes. To test the response to unsteady conditions, a centrifugal compressor is driven under a pulsating backpressure while torque is measured at the drive shaft. The torque measurement is compared against static pressure measurements corresponding to the pulsating conditions. Twelve combinations of frequency and pulse amplitudes have been tested. Due to its simple construction and development, the authors believe that where high-speed measurement equipment is already in place, effective torque measurements of this kind can be added with a low cost to help explore unsteady performance in turbomachinery.
Optimization of a Turbomachinery Blade With Regards to Tip-Rub Events
Authors: de Cherisey Marin , Salles Loic , Renson Ludovic , Vizzaccaro Alessandra , Wong Chian
Published: October 2022

Tip-rub events, also called blade-casing interactions, are problematic structural phenomena that can lead to complete engine failure. They mainly occur in compressors when a blade tip touches the casing and starts vibrating. If one of the blade natural modes is excited by an engine order, this can lead to an uncontrolled resonance. Therefore, the understanding and the consideration of these interactions is crucial to the development of safe aircraft engines.

Various numerical models and dynamic simulators have been developed, including the in-house one, jm62. It implements a stick-slip model and considers a potential liner and casing wear. Even if it gives precise results, it is computationally expensive and needs a significant amount of post-processing. It is therefore not really adapted to early design stages or quick automated processes (parametric study or optimization).

An automated workflow using SALOME-MECA and its sub-modules had been developed and permits to perform simple and fast parametric studies and shape optimizations. The proposed tool has been used to study the influence of the twist, lean, sweep and tip thickness-to-chord ratio on a modified version of a NASA Rotor 37 blade. The risk of high-level vibration of a blade due to tip-rub events is assessed using the concept of clearance consumption. The clearance consumption is defined as the component of the linear or nonlinear mode shape that defines the distance between the tip of the blade and the casing. From the reference blade and the parametric study results, an optimized candidate was generated using the clearance consumption as the objective function to minimize This process resulted in a geometry with a lower twist angle and a significant forward sweep. Two scenario of tip rub events have been performed on the optimised blades. The testing relies on the in-house time integration software jm62. The candidate has showed a 85% reduction in the amplitude of the vibratory response for the first scenario, demonstrating that the clearance consumption can be used to perform successful shape optimizations for tip-rubbing.
Validation of New Numerical Analysis Tools for Nonlinear Forced Response in Anisotropy-Mistuned Bladed Disks With Friction Joints
Authors: Koscso Adam , Hartung Andreas , Petrov E. P.
Published: October 2022

New numerical tools ContaDyn and InterDyn have been developed at University of Sussex for the analysis of nonlinear forced response for tuned and anisotropy mistuned bladed disks with friction contact interfaces. The tools offer capabilities for calculating the nonlinear forced response and its sensitivity with respect to the anisotropy orientation variation of single crystal blades in tuned and mistuned bladed disk assemblies. The calculation method is based on the high-accuracy reduction techniques and the multi-harmonic balance method.

A comprehensive validation campaign has been done to validate these numerical capabilities. The calculated nonlinear forced responses are compared with the experimental values obtained for different bladed disk configurations and excitations. The friction contact interfaces at blade roots, blade shrouds and under-platform dampers are considered. For the validation, the measurement data, that were obtained earlier at MTU Aero Engines AG using their rotating test rig, are used. The vibratory measurements were carried out with the contact-less expected time-of-arrival method allowing capturing the vibratory amplitudes for all blades in a mistuned bladed disk assembly.

The nonlinear forced response for tuned and anisotropy mis-tuned bladed disks have been calculated for four different resonances and compared with the minimum, maximum and mean values of the measured amplitudes. Moreover, the individual blade forced response levels obtained from measurements and calculations are compared with the maximum amplitude distributions in the mistuned bladed disks. Parametric studies considering the number of harmonics used in the multiharmonic representation of periodic response, the number of mode shapes, the contact stiffness and friction coefficient values have been performed.
Flow Dynamics of a Subsonic Axial Compressor Rotor With Leaned Tandem Blades
Authors: Kumar Amit , John Jerry T. , Kumar Akshay , Chhugani Hitesh , Pradeep A. M.
Published: October 2022

For higher diffusion, tandem blading has demonstrated performance superiority over a conventional blade. Modern compressor blades are often designed with three-dimensional blade shapes such as sweep, lean, dihedral, end bent etc., to achieve optimum performance. However, the performance benefit reported due to the three-dimensional blade shapes have been design-specific. Since a tandem rotor involves an unconventional design approach, each aspect of the 3D blade design needs to be looked at separately. The present numerical study aims to investigate the performance of a tandem rotor with lean. The performance of the leaned tandem rotor is also compared with the conventional leaned rotor. Positively leaned tandem configurations exhibited a higher total pressure rise than the other configurations, but at the expense of the operating range. On the other hand, a significant improvement in the operating range is observed for the negatively leaned tandem rotor. This, however, comes with a total pressure penalty. For the negatively leaned tandem rotor, a higher mass flow migration towards the tip region is observed. This reduces the effective incidence of the rotor tip. Therefore, a higher stall margin is observed for the negatively leaned tandem rotor. However, a higher tip incidence angle for the +20° leaned tandem rotor results in an early breakdown of the forward rotor tip leakage vortex, resulting in a lower stall margin. Although incorporating lean within the design of conventional rotor has certain performance benefits, it appears to be more beneficial for the tip sensitive tandem rotor design.
An Iterative Neural Operator to Predict the Thermo-Fluid Information in Internal Cooling Channels
Authors: Yang Li , Wang Qi , Rao Yu
Published: October 2022

The design of internal cooling channels played an important role in turbine cooling. Distributions of thermo-fluid information, including surface distributions, cross section distributions and projected distributions are common forms of data for internal cooling research. For over half a century since 2-D thermo-fluid data were obtainable, there were very few universal tools to regress images. While several mathematical methods worked well with regressing zero-dimensional data, they were hardly compatible with 2-D data. Recent progress in the deep learning domain provided capability for image regression by using a convolutional feature encoding-decoding process. However, deep learning models usually had a huge number of trainable parameters, which substantially reduced the generalization accuracy on small datasets. Therefore, the convective heat transfer field has been continuously searching for reduced ordered models to regress images that could generalize on an obtainable small dataset. This study proposed a reduced ordered model to regress thermo-fluid image data by integrating the physics nature of thermo-fluid problems with neural networks. This effort started from a general partial differential equation and utilized a series of derivation to convert the equations into a recurrent convolutional neural networks. By releasing the convolutional kernels to trainable parameters and using data to train the kernels, a single layer convolutional neural networks could accurately replace a spatial advancing step of the thermo-fluid image within an iteration step. The recurrent convolution neural networks were tested on a convective heat transfer dataset obtained from simulating a cooling channel with random surface patterns on one side. The tested data included the temperature distribution on the cooled solid surface, the projected heat flux image on the fluid-solid interfaces, and the pressure distribution in the middle cross section. Results indicated an excellent regressing accuracy of the presented model for the three types of data, which was elevated as compared with a widely used cGAN deep learning model. Most importantly, the proposed model only consumed 1/290 trainable parameters as compared with the cGAN model. The key features that led to the success of proposed reduced ordered model included: the matching between the differential nature of a convention-diffusion phenomenon and the convolution calculation process, the compliance of the time evolution nature of thermo-fluid images with the recurrent structure of the model, the embedding of boundary condition images into the inputs, and the introduction of hidden state images into the networks.
High-Order Spectral/hp Compressible and Incompressible Comparison of Transitional Boundary-Layers Subject to a Realistic Pressure Gradient and High Reynolds Number
Authors: Vivarelli Guglielmo , Isler João Anderson , Montomoli Francesco , Sherwin Spencer J. , Adami Paolo
Published: October 2022

Within the literature, there are limited high-order results concerning large Reynolds number flows under the influence of strong adverse pressure gradients, mainly due to the computational expense involved. The main advantage in employing high-order methodologies over standard second-order finite-volume solvers, relates to their ability to increase accuracy with a significantly lower number of degrees of freedom. In theory, this would permit Direct Numerical Simulation sort of analysis. Yet, there is still a significant computational cost involved. For this reason, an efficient approach to analyse such flows by means of a Nektar++ high-order Implicit Large Eddy Simulation is proposed.

The flow conditions considered in this case cause a separation bubble to form with consequent turbulent transition. In particular, Tollmien-Schlichting instabilities trigger Kelvin-Helmholtz behaviour, which in turn cause the turbulent transition.

The bulk of the study will be carried out with the incompressible flow solver, as it is assumed that compressibility effects are negligible within the boundary layer. An initial 2D analysis will be conducted to determine the necessary spatial resolution and whether it is possible to consider a subset of the overall simulation domain to reduce the computational expense. Once this will have been established, the 3D results will be achieved by Fourier expansion in the cross-flow direction. These results will prove the cost-effectiveness of the methodology, that could be used within an industrial setting with a limited turn-around time. Additionally, a comparison between the results achieved by means of the Nektar++ compressible flow solver in 2D and 3D will be provided, to assess any differences that may be present.
Assessment of Thickened Flame Model Coupled With Flamelet Generated Manifold on a Low-Swirl Partially Premixed Gaseous Lifted Flame
Authors: Langone Leonardo , Amerighi Matteo , Mazzei Lorenzo , Andreini Antonio , Orsino Stefano , Ansari Naseem , Yadav Rakesh
Published: October 2022

The present work focuses on the numerical modeling through Large Eddy Simulations (LES) of a low-swirl partially premixed lean flame operated with gaseous fuel using a hybrid Thickened Flame (TF)-Flamelet Generated Manifolds (FGM) combustion model. This approach aims to overcome the challenges of modeling the flame lift-off in this burner and the stabilization of the reaction zone at a remarkable distance from the nozzle outlet section, for which the reproduction of finite rate effects on combustion physics is crucial. The underlying strategy consists of applying the artificial thickening to the scalar equations required for the query of the look-up table computed a priori. The mentioned combustion model has been implemented in a general-purpose commercial CFD solver and Non-Adiabatic Flamelets have been employed for the look-up table computation. The goal is to include a detailed chemistry description while maintaining a cost-effective approach and improving the reproduction of the turbulence-chemistry interaction. Results are validated with experimental data in terms of temperature and chemical species concentration maps, showing the potential of the coupled TF-FGM approach for describing this type of flame.
Integration of Secondary Airflow Modeling Into Synergetic Cycle Calculation of F Class Industrial Gas Turbine
Authors: Staple Shanel , Vogel Gregory , Torkaman Alex , Khandrymailov Andrii , Yevlakhov Viktor
Published: October 2022

Industrial gas turbines are complex systems, and their proper analysis requires specific knowledge of the different components interacting with each other. One of the challenges is to accurately predict the overall performance of the system. To do so, a performance analysis tool can be used but it needs to rely on representative characteristics from the different elements. One of the key items required for the performance derivation is the understanding of the total cooling and leakage air (TCLA) and its distribution within the machine. A secondary air flow (SAF) tool is used to evaluate TCLA, but it needs to be “connected” with the overall performance model. The source locations of the SAF system are relatively straightforward to handle, but the sink (or dump) locations occurring in the turbine section require a detailed understanding of the pressure distribution within the flowpath. As a matter of fact, a change in SAF distribution to the turbine yields a change in turbine work output and load distribution that needs to be captured in the overall engine performance assessment. Furthermore, a change in turbine inlet boundary conditions also yields a change in pressure values for the SAF system. For these reasons, an accurate performance modeling of a gas turbine requires a so-called Synergy Loop to converge the overall boundary conditions of all its interacting modules and sub-models. This paper will describe the method used to integrate different commercial and in-house software to complete the Synergy Loop. The authors will also describe the different iteration steps possible between the specific components and the recommended iteration loop sequence for fast convergence.
Effect of Location and Rotational Reynolds Number on Film Cooling of Rotating Blade Pressure Side
Authors: Long Meng , Haiwang Li , Gang Xie , Zhiyu Zhou
Published: October 2022

The film cooling performance on the pressure side of turbine blades with single-row film holes is experimentally investigated. Three blades with single-row film holes at three locations (x/S = 10%, 29%, and 48%) of the pressure-side are studied at three rotating Reynolds numbers of 3.6 × 105, 5.4 × 105, and 7.2 × 105 (i.e., the rotational speeds of 400 rpm, 600 rpm, and 800 rpm). The pressure-sensitive paint (PSP) technology is used to measure the film cooling distribution at three blowing ratios (BR = 0.50, 1.00, and 1.50). The results indicate that the film cooling performance varies with the location of pressure side. Upstream of the pressure side, the film cooling performance is poor, with the film trajectories deflecting mainly upward. Downstream of the pressure side, the cooling effectiveness is higher, with the film trajectories deflecting upward and downward. The film trajectories closer to the downstream location are longer than those upstream, and are more prone to detach from the wall at higher blowing ratios. Moreover, the cooling performance slightly improves as the rotating Reynolds number increases.
The Evaluation of Ammonia/Hydrogen Combustion on the H Permeation and Embrittlement of Nickel-Base Superalloys
Authors: Kovaleva Marina , Dziedzic Dominik , Mashruk Syed , Evans Sam , Valera-Medina Agustin , Galindo-Nava Enrique
Published: October 2022

Recent studies exploring ammonia as a green hydrogen energy carrier have established its suitability for a variety of combustion technologies including gas turbines, furnaces, and internal combustion engines. Of significant interest are ammonia/hydrogen blends, which possess combustion benefits over pure ammonia, including an extended stability range and higher laminar burning velocity. Despite extensive research characterising the flame properties of these blends, very few studies explore the suitability of existing materials for the manufacture of ammonia/hydrogen combustors. The present study evaluates the impact of ammonia/hydrogen flame chemistry on the H permeation and possible loss of ductility of nickel-superalloys through exposing the samples to pure methane and ammonia/hydrogen flames at atmospheric pressure for a 5-hour period. The effect of the two flame compositions on the materials are compared through thermal desorption analysis (TDA) and room temperature tensile testing. The results showed that exposure to an ammonia/hydrogen combustion environment led to hydrogen being absorbed by the nickel superalloys but a possible variation in ductility is influenced by the combustion conditions. Furthermore, the formation of an oxide layer was shown to likely impact the hydrogen absorption rate of the materials. This work shows that ammonia/hydrogen flame chemistry on combustor materials should not be ignored and warrants further studies on material’s mechanical and environmental stability controlled by nitrogen and hydrogen species permeating at industrially relevant conditions.
Numerical Investigation on Radial Turbines Aerodynamics Aimed at the Definition of Design Rules for Industrial Applications
Authors: Lottini Fabrizio , Marconcini Michele , Arnone Andrea , Biliotti Davide , Toni Lorenzo
Published: October 2022

The design of turbomachines is a long iterative process, which involves several teams and disciplines. Hence, a lot of efforts are put on making it as smooth and accurate as possible. This paper introduces a procedure aimed at improving the aerodynamic design process of radial turbines for industrial applications. The procedure is based on a Baker Hughes proprietary tool for the generation of the Turbo-Expander stage geometry. An extensive CFD campaign is used both to investigate the design space of the stage and analyze the performance while varying the geometry of the rotor. Three main geometrical parameters of the wheel are identified as the ones having the biggest impact on the stage performance: the stiffness (wheel hub outlet diameter-to-outer diameter ratio), the inlet metal angle and the outlet metal angle. An automatic procedure is developed in order to generate and calculate all the different stages, with the goal to find the values for stiffness, wheel inlet and outlet metal angles which maximize the total-to-static stage efficiency in a wide range of flow coefficients. More than 700 different geometries are ultimately generated and simulated with the TRAF code, a 3D flow solver developed at the University of Florence. The results of all these simulations describe response surfaces, which not only allow to define the optimum geometry, but also to understand the influence of the main input parameters on the stage performance. Finally, the procedure was tested on a few case studies, which confirm the validity of the rules even under different conditions from the ones studied in the activity. The main outcome of the activity is the release of a tool (property of Baker Hughes) able to generate an efficient turbo-expander in a short time. Furthermore, general considerations can be outlined about the effect of the stiffness, wheel inlet and outlet metal angles on the performance of the machine.
Advanced Combustion System for High Efficiency (ACE) of the New SGT5/6- 9000HL Gas Turbine
Authors: Krebs Werner , Schulz Anatol , Witzel Benjamin , Johnson Clifford , Laster Walter , Pent Jared , Schilp Reinhard , Wasif Samer , Weaver Adam
Published: October 2022

Under the international climate pact (Paris Agreement), participants agreed upon a framework to reduce greenhouse gas emissions and cap the rise in global temperatures at “well below” 2°C above pre-industrial levels by 2100, with 1.5°C being the ideal scenario. To meet this goal, the development of highly efficient power plants fired with natural gas or blends of natural gas and increased share of H2 is a central cornerstone to provide controllable electrical power generation.

The new HL class addresses these needs by raising the combined cycle efficiency above 64% while offering high fuel flexibility with H2 blends up to 50% and significant turndown capability.

The new HL class is equipped with the new ACE combustion system which was developed over the last decade, and which has been successfully tested in the SGT6-9000HL at Lincoln County (North Carolina, USA). The ACE combustion system is a can annular design which is equipped with a jet stabilized main burner piloted by a central swirl burner and an axial stage which is turned on at higher loads. The paper describes the combustion technologies applied to offer stability and low emissions over a large engine operation envelope and the associated development steps. Finally, test results from rig and engine testing are presented.
Unpacking Inter-Mineral Synergies and Reactions During Dust Deposition in an Impingement Coolant Jet
Authors: Nied Eric P. , Bons Jeffrey P. , Lundgreen Ryan K.
Published: October 2022

This paper seeks to unpack the synergies that exist between minerals during deposition of the heterogeneous AFRL02 mixture in gas turbine engines and demonstrate that the contributions of each mineral cannot be considered independently of others. In each experiment, one gram of a mineral dust (0–10μm particle diameter distribution) was injected into an 894K, 57m/s coolant flow impinging normally on a Hastelloy X plate with a surface temperature of 1033K, 1144K, or 1255K. Capture efficiency measurements, deposit morphology analyses, and X-ray diffraction results are reported. Besides AFRL02, single mineral dusts, dual mineral dusts, and AFRL02-like dust blends lacking in one mineral were tested. The results of the experiments elucidate that the deposition behavior of single minerals indeed cannot explain the composite deposition of heterogeneous mixtures of minerals. For example, gypsum had the highest capture efficiency of any single mineral in ARFL02, and yet removing gypsum from AFRL02 counterintuitively raised the capture efficiency of that blend when compared to AFRL02. Quartz was found to erode albite deposits but stick to and build upon dolomite and halite deposits, even though quartz did not deposit significantly as a single mineral. Quartz also chemically reacted with gypsum and dolomite to form wollastonite and diopside, respectively. Finally, we found that the capture efficiency of each blend increased with plate temperature, but not according to the same trend. Results are interpreted through the lens of CaO-MgO-Al2O3-SiO2 eutectic chemistry, but the chemical pathways by which these eutectics come into existence is found to be of equal importance.
A Methodology for a Coupled Structural - CFD Analysis of Compressor Rotor Blades Subjected to Ice Impact With Uncertain Impactor Parameters
Authors: Böhm Holger , Hornig Andreas , Gude Maik , Högner Lars , Meyer Marcus
Published: October 2022

A method for a coupled structural – Computational Fluid Dynamics (CFD) analysis of a compressor rotor blade subjected to an ice impact scenario is investigated to assess the impact related blade deformations from a structural and fluid-dynamics perspective. On the basis of a probabilistic approach, in total 50 impact scenarios are derived for this study. In a first step the numerical structural model based on Finite Elements (FE) is discussed, including several parameter variations like impact location, ice diameter, ice density and rotor speed. Different analysis steps are subsequently carried out using LS-DYNA implicit / explicit on a high performance computing (HPC) cluster. Resulting blade deformations are evaluated in terms of local plastic deformation, cup size and modal parameters in comparison to the undamaged reference structure. The resultant post-impact blade geometry is extracted from the result data and passed to the CFD simulation setup in a fully automated manner. Based on this deformed structural mesh data, the fluid mesh is morphed via a radial basis function (RBF) approach and analysed with CFD. Finally, an uncertainty quantification study is performed to assess the variability of results with regard to the definition of the ice impactor.
Calibration of a CFD Methodology for the Simulation of Additively Manufactured Components Accounting for the Effects of Diameter and Printing Direction on Friction and Heat Transfer
Authors: Mazzei Lorenzo , Da Soghe Riccardo , Bianchini Cosimo
Published: October 2022

Additive manufacturing (AM) enables designs that are not manufacturable with conventional techniques and that offer reduced weight and better thermal performance. This is of particular relevance for gas turbine cooling as well, as proved by the first applications of combustors and turbine blades made entirely by AM.

Despite that, the effects of the increased surface roughness on friction and heat transfer are not fully understood yet and this hinders the design process demanding further characterization by means of experimental tests. Also the exploitation of CFD simulations is complicated by the current modelling approaches, still based on the equivalent sand-grain roughness (ks) that results in a velocity shift in the boundary layer. The estimation of such parameter is not straightforward and the approach leads to an unphysical overestimation of the heat transfer even using ks values calibrated with experiments.

This work represents the continuation of the benchmarking and calibration of a CFD methodology based on friction and thermal corrections proposed by Aupoix from ONERA. The results presented in the previous two papers focused on three literature test cases representative of straight and wavy additively-manufactured minichannels with circular and rectangular cross-section. In this paper a new dataset published by Penn State University is considered, investigating the effect of diameter and printing direction on the fluid-dynamical performance of circular straight minichannels. This work confirms the validity as a first approximation of a linear relation between ks/Dh and the relative arithmetic roughness Ra/D, provided that the build orientation is sufficient to avoid excessive channel deformation (i.e. greater or equal to 45°). On the contrary, a similar calibration for the heat transfer was unsatisfactory, suggesting a role of channel shape or other parameters not understood at the moment.
The Role of Endwall Shape Optimization in the Design of Supersonic Turbines for Rotating Detonation Engines
Authors: Mushtaq Noraiz , Persico Giacomo , Gaetani Paolo
Published: October 2022

Rotating detonation engines (RDE) are characterized by a thermodynamic cycle with an efficiency gain up to 15% at medium pressure ratios with respect to systems based on the conventional Joule-Bryton cycle. Multiple turbine designs can be considered and this paper deals with the supersonic inlet configuration. After having reviewed the main design steps of an exemplary RDE supersonic turbine, the paper focuses on the considerable effects that endwall losses have on the performance of supersonic-inlet turbines and on the reasons why endwall contouring is strongly recommended for an efficient design. Parametric analyses, carried out by a novel in-house mean-line code validated against CFD, reveal that endwall friction losses contribute significantly to the overall stage loss. Endwall boundary layers also reduce the effective area, which can be critical for the self-starting capability of the supersonic channel. Therefore, a variable blade height geometry is necessary to extend the design space and guarantee a higher efficiency with respect to a constant-span configuration. The in-house CFD-based evolutionary shape optimization code was adapted to search for the optimal endwall shape for these unconventional machines. The optimal shape reduces shock losses and deviation angles and provides a significant gain in efficiency and work extraction. Finally, a novel technique is proposed to design the three-dimensional shape of the rotor based on the method of characteristics and tailored on the flow delivered by the stator.
A New Interpretation of Hot Gas Ingress Through Turbine Rim Seals Influenced by Mainstream Annulus Swirl
Authors: Graikos Dimitrios , Tang Hui , Sangan Carl M. , Lock Gary D. , Scobie James A.
Published: October 2022

Rim seals are fitted at the periphery of the stator and rotor discs to reduce the adverse effects of hot gas ingress on highly stressed turbine components limited by temperature. Ingress is induced by rotational effects such as disc pumping, as well as by asymmetric pressure-driven unsteady phenomena. These influences superpose to form a complex flow-physics problem that is a challenge for computational fluid dynamics. Engine designers typically use practical low-order models that require empirical validation and correlating parameters. This paper identifies the swirl ratio in the mainstream annulus as a dominant characterising parameter to predict ingress. This is a new interpretation that is supported by extending a low-order model based on turbulent transport using an effective eddy mixing length based on the difference in swirl between the annulus and seal clearance.

Experimental measurements were made using a 1.5-stage turbine rig at low Reynolds number. The influence of annulus swirl ratio was investigated over a range of flow conditions and two rim-seal geometries, with the ingress quantified using CO2 tracer concentration in the sealing flow. The concentration data were complemented by measurements in the annulus using a five-hole aerodynamic probe.
Highly Resolved Large-Eddy Simulations of a Transonic Compressor Stage Midspan Section - Part II: Effect of Rotor-Stator Gap
Authors: Przytarski Pawel J. , Leggett John , Sandberg Richard , Bode Christoph
Published: October 2022

The need for increased power density and reduced weight in modern gas turbines often leads to shorter inter-row distances. This translates into stronger blade-to-blade and row-to-row interactions. These interactions are particularly difficult to predict for low-order methods such as URANS due to the overlap between deterministic unsteadiness frequencies and stochastic unsteadiness frequencies. This lack of a spectral gap results in complex broadband energy spectra that necessitate the use of high-fidelity scale resolving simulations to predict such flows and understand how they affect the flow behavior of subsequent bladerows. In this study, wall-resolved large eddy simulations have been conducted of a transonic compressor stage at a realistic rotor Reynolds number of 1 × 106, varying the axial gap between rotor and stator. The analysis of the data focuses on the impact of the rotor-stator gap on the downstream stator boundary layer behavior and employs phase averaging to describe the flow in a detailed manner. We then report on how the rotor-stator gap affects loss generation and loss mechanisms. Overall, a 2.5% overall stage loss decrease was found when the gap size was reduced by 25%. This reduction nearly entirely stems from the stator bladerow, despite the stator contributing only 15% to the total stage loss. The high-fidelity simulations are complemented by unsteady RANS calculations of the same configuration, to assess how accurately current design tools capture the complex row-to-row interactions. Although the overall loss magnitudes were captured reasonably well, no significant variation with gap size were found with URANS.
Low Cycle Fatigue Characterization of Additive Manufactured Specimen With as Printed Surface Roughness Made From Multiple Nickel Based Super Alloys
Authors: Torkaman Alex , Keshava Bhattu Ramesh
Published: October 2022

Additive manufacturing is a transformative technology that can enable advanced designs for gas turbines that are not otherwise possible. While the expansion of design envelope can greatly contribute to improvement in efficiency and fuel flexibility of gas turbines, limitations in material properties can adversely affect durability of additively manufactured components if not properly characterized and accounted for in the design phase. An important consideration for durability of turbine components is the LCF (Low Cycle Fatigue) life, and it is influenced by the surface effects that are characteristic of the layer by layer build process of additive manufacturing. The influence of as printed surface texture on LCF properties of multiple additive manufactured alloys is evaluated in this work as part of a broader incorporation of additive alloys in gas turbines. Hastelloy-X is a commonly produced alloy that is utilized in combustion components, enabling state of the art fuel flexibility and hydrogen combustion. An Inconel-939 derivative alloy has been recently utilized in static turbine components due to its high temperature creep capability and oxidation resistance, resulting in improved cooling efficiency and increased turbine performance. In this paper, specimens with as printed and machined gauge (machined from additive manufactured bars) are produced with both Hastelloy-X and IN939 derivative alloys. Specimens are tested for LCF at multiple temperature and strain range conditions and comparisons between as printed (or rough gauge) versus machined gauge specimen are made to determine influence of as printed surface conditions. Results of the experiments for both alloys are presented in normalized form to evaluate performance of as printed versus machined surfaces at various test conditions. Fractographic analysis is conducted on IN939 derivative failed specimens and the influence of surface roughness on crack initiation at the microstructural level is discussed.
The Influence of Boundary Layer State and Trailing Edge Wedge Angle on the Aerodynamic Performance of Transonic Turbine Blades
Authors: Rossiter A. D. , Pullan G. , Melzer A. P.
Published: October 2022

Trailing edge loss typically accounts for a third of the profile loss of a transonic turbine blade. In this paper, two dominant influencing factors — boundary layer state and trailing edge wedge angle — are quantified using a combined experimental (single airfoil transonic tests) and computational (wall resolved LES) approach. Three key findings are reported. First, the switch between two flow regimes — detached vortex shedding and transonic vortex shedding — as the Reynolds number is increased, is identified and explained. It is shown that the transition of the pressure surface boundary layer drives the switch from the former to the latter; this change is associated with a jump in loss of close to 100%. The switch is also shown to affect the base pressure distribution around the trailing edge, changing it from uniform, with an isobaric dead-air region, to non-uniform. Second, the influence of the trailing edge wedge angle is explored. It is found that higher wedge angles can offer performance benefits in both loss and base pressure — with a change from an 8° to 14° geometry providing up to a 29% reduction in overall loss for the geometry tested. Finally, as these findings are the result of changes to the unsteady flow phenomena around the trailing edge, they would not be picked up by current low-fidelity, steady design tools. A method is proposed to use data, such as that presented in this paper, to improve low fidelity modelling.
Computational Modeling of the Effects of Rain on Wind Turbine Performance
Authors: Gahlot Aishwerya , Sankar Lakshmi , Pichitkul Auraluck
Published: October 2022

Wind turbines often operate under misty or rainy conditions. There is a considerable body of experimental evidence on the adverse effects of rain on wind turbine power production. Physical understanding of these effects, guided by quantitative modeling, is necessary to fully understand the effects of rain power production. This work presents an application of a two-way coupled computational fluid dynamics approach to the modeling of the effects of rain on airfoil and rotor performance. The aerodynamics is modeled by solving the Reynolds averaged Navier-Stokes equations with a suitable turbulence model. The droplet transport is modeled using an Eulerian approach that allows droplets of different diameters to be treated as individual/independent species, although all the studies presented here were for specified droplet sizes. The external flow exerts a drag force on the water droplets, and a reaction force is exerted by the droplets on the airflow.

2-D viscous flow simulations are presented for a representative wind turbine airfoil for several angles of attack under wet and dry conditions. Regression fits of these drag polars have been used in a combined blade element-momentum analysis for the NREL Phase VI rotor. The calculations indicate a loss of 30% to 40% in power production, attributable to rain, over a range of wind speeds.
Accurate Prediction of Confined Turbulent Boundary Layer Flashback Through a Critically Strained Flame Model
Authors: Novoselov Alex G. , Ebi Dominik , Noiray Nicolas
Published: October 2022

A promising path forward for power converting gas turbines that must produce low-to-no carbon emissions is the transition from burning pure natural gas to a mixture that includes cleanly produced hydrogen. However, such a transition also modifies the flame dynamics within the burner and so must therefore be studied. One important change that occurs with increased hydrogen content is the heightened propensity of boundary layer flashback, wherein the flame propagates upstream through the low velocity region near the wall. Propagation of the flame into the poorly shielded mixing section can have disastrous results, and therefore must be avoided. In this work, a newly developed model to predict the boundary layer flashback limits based on a balance between the extinction limit flame speed and the near-wall velocity is presented. The model is capable of accurately predicting flashback limits in non-swirling burners and can be extended to swirling burners using information about a single flashback event. In addition, inclusion of a mean non-reacting velocity field computed via Large Eddy Simulation allows for a significant increase in the accuracy of the model when applied to swirling flows. Ultimately, this model provides a new pathway for the design of flashback resistant gas turbines, even with the addition of new fuels like hydrogen.
Uncertainty Quantification on the Cooling Performance of a Transonic Turbine Vane With Upstream Endwall Misalignment
Authors: Hao Mingyang , Li Yuanyuan , Li Zhigang , Li Jun
Published: October 2022

With increasing aerodynamic and thermal loads, film cooling has been a popular technology integrated into the design of the modern gas turbine vane endwall, especially for the first-stage vane endwall. A staggering amount of research has been completed to quantify the effect of operating conditions and cooling hole geometrical properties. However, most of these investigations did not address the influence of the manufacturing tolerances, assembly errors and operation degradations on the endwall misalignment. In this paper, therefore, uncertainty quantification (UQ) analysis was performed to quantify the impacts of upstream endwall misalignment uncertainties on the film cooling performance of endwalls as well as the phantom cooling performance of the vane pressure side surface.

The upstream endwall misalignment represents the step geometry between the combustor exit and the first-stage vane endwall. Based on the non-intrusive polynomial chaos expansion (NIPC) and the Uniform probability distribution assumption, the deviation (step height) uncertainties of the upstream endwall misalignment were quantified. To predict the endwall secondary flow and film cooling effectiveness in the transonic linear vane passage, the commercial CFD solver ANSYS FLUENT is used to numerically solve the three dimensional steady-state Reynolds-Averaged Navier-Stokes (RANS) equations. The robustness analysis of endwall film cooling performance and phantom cooling to the upstream endwall misalignment was conducted for three design upstream step heights (ΔH): a baseline configuration (ΔH = 0 mm), two misaligned configurations with forward step (ΔH = −5 mm) and backward step (ΔH = 5 mm) respectively.

Results show that the actual cooling performance has a high probability of deviating from the nominal value for the baseline configuration. The critical regions that are most sensitive to the upstream step misalignment are also identified by variances. The UQ results also show that the design geometry with a forward step has a more robust film cooling performance on endwall and phantom cooling performance on the vane pressure side surface which means a smaller variance and a better expectation than the no step configuration. In contrast, the design geometry with a backward step induces the reductions of the expectation of the film cooling effectiveness and coolant coverage and the amplification of performance fluctuations. This work provides a certain guiding direction for the optimization design for the upstream step geometry.
Calculating Windage Losses: A Review
Authors: Karg Bulnes Fernando , Kerr Thomas , Rimpel Aaron
Published: October 2022

Windage is the effect of aerodynamic drag on the surfaces of a rotating system due to fluid shear effects. The fluid-friction losses that occur on the rotor of rotating machines often constitute a non-negligible drag on the system that must be estimated for proper sizing of the driving or driven element. This is especially true in high-pressure environments, such as hermetic compressors and turbines. Fluid-friction loss modeling is based on the size and rotation speed of the shaft, the density of the fluid, and an empirically-determined drag coefficient. The drag coefficient is generally a function of the Reynolds number but may also be dependent on the Taylor number. Several papers have provided empirical predictions for drag coefficients based on the Reynolds and Taylor numbers of the fluid, but other factors such as rotor shapes, assemblies, and surrounding fluid conditions can also affect the drag coefficient. There are two main geometries for a rotor: a face parallel to the axis of rotation, and a face that is perpendicular. The gap between the rotating component and the stationary housing also plays an important role in the drag coefficient. This review summarizes and compares these findings in a way that makes it easy for the reader to predict the total windage losses on a system for any rotor shape, speed, or operating condition. A quick reference table is presented in the conclusions section.
CFD Based Investigation of Effects of Liquid Contamination on Dry Gas Seal Performance
Authors: Patil Abhay , Rimpel Aaron , Kurz Rainer
Published: October 2022

Previous studies identified liquid contamination as a major root cause of dry gas seal (DGS) failures and highlighted the need for model development to simulate the liquid-gas interaction and its effect on DGS operation. The current study presents Computational Fluid Dynamics (CFD) based performance prediction of a DGS under single-phase (gas) and two-phase (gas-liquid) flow conditions. The presented numerical model includes the conjugate heat transfer (CHT) analysis for the three pressure conditions at a constant rotational speed. Initial modeling involved the qualification of different turbulent models by analyzing and comparing leakage flow, torque, and temperature distribution. The two-phase CFD model employs the Eulerian approach to predict the oil distribution and modified pressure and temperature predictions. Two-phase flow simulations focused on improving the understanding of oil distribution as a function of droplet size at the imposed inlet volume fraction and the consequential effect on the seal performance parameters. The presence of liquid causes localized pressure and temperature change while flow transitions from the cavity to the seal area. Also, two-phase interaction due to oil presence increases heat generation and consequential temperature rise in the pressure dam region. Overall, the systematic variation in performance parameters with liquid fraction provides greater insight into DGS performance, also laying out a path for establishing an incipient failure mechanism that will be validated in future testing.