bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling of Turbulent Swirl Stabilized Flame With Flamelet Generated Manifold and Hybrid LES-RANS Turbulence Model
Authors: Verma Ishan , Yadav Rakesh , Sharkey Patrick , Li Shaoping , Meeks Ellen 
Published: November 2019

Abstract
Hybrid turbulence modeling is a practical approach to efficiently model the wall-bounded turbulent flows. In this paper, a stress-blended eddy simulation (SBES) model is used with the flamelet generated manifold model (FGM) for modeling turbulent combustion. In the current SBES, the near-wall region is modeled using a two-equation k-ω Reynolds-averaged Navier-Strokes (RANS) formulation, and switches to a large eddy simulation (LES) model in the core region using a blending function. Similarly, the turbulence-related combustion modeling parameters, such as the variances in scalar transport equations and scalar dissipation, are also blended using the same blending function. This combined hybrid FGM-SBES approach is implemented into ANSYS Fluent software and then used to model a swirl-stabilized flame. The flame used is a methane-fueled burner, developed at DLR Stuttgart as the PRECCINSTA combustor. The experimental data for this combustor are available for multiple operating conditions. A stable operating point (φ = 0.83, P = 30 kW) is chosen. The current FGM-SBES results are compared with experimental data as well as with FGM-LES computations. Differences in predictions of mean and variance of reaction progress and mixture fraction in the core versus the near wall region are analyzed and quantified. The impact of the differences in these parameters is then evaluated by comparing temperature and species mass fractions. The findings from the current work, in terms of accuracy, validity and best practices when modeling wall-bounded flows with FGM-SBES are discussed and summarized.
Effects of Fuel Staging on the Hydrodynamic Stability of Multi Nozzle Swirl Flows
Authors: Gupta Saarthak , Manoharan Kiran , Hemchandra Santosh 
Published: November 2019

Abstract
Hydrodynamic instability in lean premixed gas turbine combustors can cause coherent flow velocity oscillations. These can in turn drive heat release oscillations that when favourably coupled with combustor acoustic modes can result in combustion instability. The aim of this paper is to understand the impact of fuel staging on the characteristics of hydrodynamic modes in multi-nozzle combustors. We extend our recent numerical study on the hydrodynamic stability characteristics of a multi-nozzle combustor having three nozzles in a straight line with uniform fuel-air ratio in each nozzle, to the non-uniform fuel-air ratio case. As before we construct the base flow model for this study by super-posing contributions from individual nozzles, determined using a base flow model for a nominally axi-symmetric single nozzle, at every point in the computational domain. The impact of fuel staging is captured by changing the burnt to unburnt gas density ratio parameter in the individual contribution from each nozzle. We investigate the characteristics of the most locally absolutely unstable mode for two cases. The first one is when the middle nozzle is made fuel rich when compared to the side nozzles and the second is when the side nozzles are made fuel rich relative to the middle nozzle. The impact of non-uniform fuel/air ratio on the local absolutely unstable temporal eigenvalues is seen to be small. However, significant changes in the spatial structure of the flow oscillations associated with the hydrodynamic eigen-modes are observed. In the first case, the flow oscillations with a different locally azimuthal nature on the middle nozzle when compared to the side nozzles emerge as the middle nozzle is made richer. In the second case, the oscillations on the two side nozzles are suppressed leaving the middle nozzle in a state that closely matches that of a single unconfined nozzle with the same nominal base flow velocity field. These types of inter-nozzle variations in flow oscillation characteristics can explain the emergence of non-uniformity in heat release oscillation characteristics between individual nozzles in multi-nozzle combustors.
Introduction and Commissioning of the New Darmstadt Transonic Compressor Test Facility
Authors: Kunkel Christian , Werner Jan , Franke Daniel , Schiffer Heinz-Peter , Wartzek Fabian , Biela Christoph , Starke Christoph 
Published: November 2019

Abstract
With the well-known Transonic Compressor Darmstadt (TCD) in operation since 1994, profound knowledge in designing and operating a sophisticated test-rig is available at the Institute of Gas Turbines and Aerospace Propulsion of TU Darmstadt. During this period, TCD has been subject to a vast number of redesigns within different measurement campaigns (see [1], [2], [3], [4], [5], [6], [7], [8]). To expand the capabilities and ensure a sustainable process of compressor research, a new test facility was designed and built by the institute. The new test rig Transonic Compressor Darmstadt 2 (TCD2) features increased power for higher pressure ratios and higher mass-flow, a state of the art control system, increased flexibility towards different compressor geometries and modern data acquisition hardware and software.
Following the successful commissioning of the test-rig in March 2018, a first measurement campaign has been conducted. Early test results regarding aerodynamic performance and aeroelastic effects of the test compressor are presented together with a detailed overview of test-rig infrastructure and control systems as well as the test compressor and the measurement hardware.
High Momentum Jet Flames at Elevated Pressure: Part D — Simultaneous Measurements of OH/PAH PLIF and Mie Scattering on Liquid Fuels
Authors: Schäfer Dominik , Gounder James D. , Lammel Oliver , Ax Holger , Lückerath Rainer , Aigner Manfred 
Published: November 2019

Abstract
A promising alternative to modern swirl combustors for gas turbines are high momentum jet stabilized combustors. This gas turbine burner concept consists of circular arranged jet nozzles through which partially premixed high momentum jets enter the combustion chamber in axial direction. Furthermore, it features fuel flexibility, load flexibility and low pollutant emissions. The investigated generic combustor consists of an eccentric single nozzle in a square chamber. This nozzle represents a full-scale segment of a concentrically arranged multi-nozzle configuration. All measurements were carried out at the high pressure combustion test rig (HBK-S) at the German Aerospace Center (DLR) in Stuttgart.
The generic single nozzle model combustor has been operated in a high-pressure test rig with large optical access in order to gain a detailed understanding of fuel distribution, droplet distribution, fuel air mixing and high temperature regions through various sections of the combustion chamber. For this purpose, different laser based measurement techniques have been applied simultaneously under gas turbine relevant conditions on liquid fuels (oil and oil/water). Other measurements in this combustor on gaseous fuels were presented in preceding (parts A and B) and current publications (part C).
Mie scattering was used to visualize the liquid phase of oil and water downstream of the nozzle. In order to gain knowledge about the droplet velocity, a Nd:YAG double pulse laser at 532 nm was used for Particle Image Velocimetry (PIV). Additionally the gaseous and liquid phases of oil have been visualized through Planar Laser Induced Fluorescence (PLIF) by excitation of poly-cyclic aromatic hydrocarbons (PAHs) with a laser wavelength of 266 nm. To observe high temperature regions, OH and PAH PLIF was also performed with a low bandwidth at 283 nm from a Nd:YAG pumped dye laser.
It was possible to separate the low-intensity OH signal of the hot gas regions from the PAH signal by collecting the different LIF signals simultaneously through a dual camera setup. Instantaneous PAH LIF images of the liquid and gaseous phase were compared with Mie scattering images for a qualitative impression of the evaporation. For this a structural comparison between the liquid phases of both images has been carried out. Results indicate, that the evaporation of most of the liquid fuel takes place near the hot gas region, as a large proportion of droplets are carried far downstream of the nozzle by the high momentum jet.
Influence of Tip Shroud Modeling on the Flutter Stability of a Low Pressure Turbine Rotor
Authors: Pinelli Lorenzo , Vanti Federico , Arnone Andrea , Beßling Benjamin , Vogt Damian M. 
Published: November 2019

Abstract
Since the modern design trend of low pressure turbine blades for aeronautical propulsion leads to lighter and more loaded blades, thus prone to flutter induced vibrations; flutter assessment is now a standard verification within the design loop of these components. Flutter stability assessment requires FEM and CFD tools able to predict the pressure response of fluid flow due to blade oscillation in order to compute the aerodynamic damping. Such tools are mature and validated, yet some geometrical aspects of the blade-row as contact interfaces at the blade tip shroud have to be carefully simulated to obtain accurate flutter results. The aim of this paper is to demonstrate the capability of the Open Source FEM tool (CalculiX) to deal with complex interlocked rotor geometries when performing modal analysis and to show the influence of different contact interface modeling on flutter stability. The solid mesh of a single-pitch row sector has been generated by using the Open Source suite Salome and the modal analysis has been carried out with CalculiX with cyclic symmetry conditions. The following uncoupled flutter simulations have been performed with the CFD TRAF code, an in-house solver developed at the University of Florence, which implements a non-linear method for flutter evaluation. An in-depth comparison among the FEM models with different boundary conditions in terms of mode shape frequency and aerodynamic damping curves are reported. These results show the effect of different contact interface models, especially on the first bending mode family, and confirm the overall row stability detected during a dedicated experimental flutter campaign.
Thermal Optimization of Air Foil Thrust Bearings Using Different Foil Materials
Authors: Rieken Markus , Mahner Marcel , Schweizer Bernhard 
Published: November 2019

Abstract
Air foil bearings are used in turbomachinery applications with high speeds and in oil-free environments. Their numerical analysis has to account for the multiphysicality of the problem. This work features a detailed thermo-elasto-hydrodynamic model of an air foil thrust bearing with bump-type foil-structure. The bearing geometry is designed to produce a high load capacity while maintaining thermally stable conditions. The presented model considers foil deformations using a Reissner-Mindlin-type shell theory. Dry friction (stick-slip approach) between the top foil, the bump foil and the base plate is taken into account in the model. Reynolds equation from lubrication theory is used to study the hydrodynamic behavior of the air film. A thermal model of the lubricating gap, the foil sandwich and the rotor disk including heat fluxes into the rotor and the periphery as well as a cooling flow on the backside of the rotor disk are presented. Elastic deformations of the rotor disk due to centrifugal effects are calculated; deformations caused by temperature gradients are investigated as well. In air foil thrust bearings, very high temperatures are often observed and a forced cooling flow through the foil sandwich has to be applied. Using a cooling flow by applying a pressure difference between the inner and outer radius of the thrust bearing has several drawbacks: the additional cooling flow reduces the overall efficiency of the machine and requires additional constructive measures. In this work, a passive cooling concept is analyzed, where the typical steel foils are replaced with other materials, which have a significantly higher thermal conductivity. The simulation results show that the bearing temperatures can be reduced markedly (up to 70°C in the considered test case) by this approach.
Nonlinear Harmonic Analysis of a Blade Model Subjected to Large Geometrical Deflection and Internal Resonance
Authors: Di Palma Nicolas , Martin Adrien , Thouverez Fabrice , Courtier Vivien 
Published: November 2019

Abstract
This paper is devoted to the study of the nonlinear harmonic response of an industrial blade model subjected to large geometrical deflection. A reduction procedure is performed on the blade model using the linear normal modes of the structure. Geometrical nonlinear effects are taken into account by considering cubic and quadratic stiffnesses in the dynamical reduced model. Reduced nonlinear stiffness coefficients are computed with the STiffness Evaluation Procedure (STEP) and periodic solutions are sought using the Harmonic Balance Method (HBM) coupled to a pseudo-arclength continuation. Along with the harmonic response, a bifurcation analysis is performed to compute both turning and branching points. Specific attention is paid to the internal resonance phenomenon. 2 to 1 internal resonance occurred during the frequency response analysis close to the first and second modes of the reduced model. Mode coupling phenomena occurred during the harmonic analysis and secondary branches of solutions were obtained from branching point bifurcations.
Probabilistic FE-Analysis of Cooled High Pressure Turbine Blades: Part B — Probabilistic Analysis
Authors: Högner Lars , Voigt Matthias , Mailach Ronald , Meyer Marcus , Gerstberger Ulf 
Published: November 2019

Abstract
Modern high pressure turbine (HPT) blade design stands out due to high complexity comprising three-dimensional blade features, multi-passage cooling system (MPCS) and film cooling to allow for progressive thermodynamic process parameters. During the last decade, probabilistic design approaches have become increasingly important in turbomachinery to incorporate uncertainties such as geometric variations caused by manufacturing scatter.
In part B of this two-part paper, real geometry effects are considered within a probabilistic finite element (FE) analysis that aims at sensitivity evaluation. The knowledge about the geometric variability is derived based on a blade population of more than 400 individuals by means of parametric models that are introduced in part A (cf. Högner et al. [1]). The HPT blade population is statistically assessed which allows for reliable sensitivity analysis and robustness evaluation taking the variability of the airfoil, profiled endwalls (PEW) at hub and shroud, wedge surfaces (WSF) and the MPCS into account.
The probabilistic method — Monte-Carlo simulation (MCS) using an extended Latin Hypercube Sampling (eLHS) technique — is presented subsequently. Afterwards, the FE model that involves thermal, linear-elastic stress and creep analysis is described briefly. Based on this, the fully automated process chain involving CAD model creation, FE mesh morphing, FE analysis and post-processing is executed. Here, the mesh morphing process is presented involving a discussion of the mesh quality. The process robustness is assessed and quantified referring to the impact on input parameter correlation.
Finally, the result quantities of the probabilistic FE simulation are evaluated in terms of sensitivities. For this purpose, regions of interest are determined, wherein the statistical analysis is conducted to achieve the sensitivity ranking. A significant influence of the considered geometric uncertainties onto mechanical output quantities is observed which motivates to incorporate these in modern design strategies or robust optimization.
Recognition of Structures Leading to Transition in a Low Pressure Turbine Cascade: Effect of Reduced Frequency
Authors: Lengani D. , Simoni D. , Ubaldi M. , Zunino P. , Bertini F. 
Published: November 2019

Abstract
The boundary layer developing over the suction side of a low pressure turbine cascade operating under unsteady inflow conditions has been experimentally investigated. Time-resolved Particle Image Velocimetry (PIV) measurements have been performed in two orthogonal planes, the blade to blade and a wall parallel plane embedded within the boundary layer, for two different wake reduced frequencies. Proper Orthogonal Decomposition (POD) has been used to analyze the data and to provide an interpretation of the most significant flow structures for each phase of the wake passing cycle. To this purpose, a POD based procedure that sorts the data synchronizing the measurements of the two planes has been developed. Phase averaged data are then obtained for both cases. Moreover, once properly sorted, POD has been applied to sub-ensembles of data at the same relative phase within the wake passing cycle. Detailed information on the most energetic turbulent structures at a particular phase are obtained with this procedure (called phased POD), overcoming the limit of classical phase average that just provides a statistical representation of the turbulence field. Furthermore, the synchronization of the measurements in the two planes allows the computation of the characteristic dimension of boundary layer structures that are responsible for transition. These structures are often identified as vortical filaments parallel to the wall, typically referred to as boundary layer streaks.
The largest and most energetic structures are observed when the wake centerline passes over the rear part of the suction side, and they appear practically the same for both reduced frequencies. The passing wake forces transition leading to the breakdown of the boundary layer streaks. Otherwise, the largest differences between the low and high reduced frequency are observed in the calmed region. The post-processing of these two planes further allowed us to compute the spacing of the streaks and make it non-dimensional by the boundary layer displacement thickness observed for each phase. The non-dimensional value of the streaks spacing is about constant, irrespective of the reduced frequency.
A Steady State Thermal Prediction Method for Ship Board Turbocharger and its Validation With Experiments
Authors: Ohuchida Satoshi , Seo Satoshi , Okita Yoji 
Published: November 2019

Abstract
The present study aims to develop prediction method of turbocharger’s turbine wheel temperature at working conditions. To take fluid-solid heat transfer physics into account, CHT (Conjugate Heat Transfer) based approach is introduced. The model mesh comprises turbine wheel, rotor shaft, and stationary parts of the turbine side together with internal fluid region. Remaining parts, compressor or surrounding atmosphere are not included in the calculation mesh yet boundary conditions at contact surface of the outer mesh region were carefully considered and coupled into CHT.
An actual ship board turbocharger was selected to investigate presented calculation method. Multiple point thermal measurement was conducted both for the turbine wheel and the stationary parts to obtain verification data. CHT calculation for this model case was demonstrated and results were compared. The results, especially at the rotor wheel surface shows fairly good agreement with the measured temperatures within the range of ± 5degC. Stationary part temperatures showed larger discrepancy yet high/low relationship of temperatures from parts to parts was agreed with the experiment. The reason for temperature discrepancy was considered to come from too simplified modeling of heat transfer path and this can be improved in future work.
Inlet Turbulence and Off-Design Incidence Response of High Efficiency, Turbine OGV Profiles
Authors: Lazaro Benigno J. , Gonzalez Ezequiel , Parra Jorge , Robles David Cadrecha 
Published: November 2019

Abstract
In spite of advances in CFD prediction tools, the current design of outlet guide vane (OGV) stages for flow recovery downstream from low pressure turbines (LPT) still has to face significant flow entrance uncertainties. To ensure proper response of modern, high efficiency OGV’s, the sensitivity in the aerodynamic response of the vanes to both different levels of inlet turbulence and off-design incidence must be analyzed. To that end, a systematic experimental investigation of a current design LPT OGV airfoil has been undertaken in a low-speed linear cascade. Wall pressure distributions as well as high-resolution total pressure drop and LDV measurements have been used to determine the flow response. The experimental facility includes different boundary suction strategies for proper control of flow periodicity and endwall effects at significant off-design incidences. In addition, different inlet grids to promote an entrance flow having controlled isotropic background turbulence are included. The experimental flow response of the OGV airfoil is presented for a wide range of Reynolds numbers and different values of the inlet flow incidence and turbulence properties. Both at design and off-design incidences, different flow regimes and performance degradation mechanisms are discussed. In addition, the effect of inlet turbulence at close to design incidence is discussed, with the experimental evidence suggesting that its effect can be described by defining a properly scaled Reynolds number. The ability of CFD simulations based on currently available RANS transition models to describe the flow in high efficiency turbine OGV airfoils is finally explored.
Improving Emission and Blow-Out Characteristics of Novel Natural Gas Low NOx Burners for Heavy Duty Gas Turbine
Authors: Cerutti Matteo , Roma Michele , Picchi Alessio , Becchi Riccardo , Facchini Bruno 
Published: November 2019

Abstract
The development and the optimization of a novel dry low NOx burner may require several steps of improvement.
The first step of the overall development process has been documented by authors in a previous paper and included an exhaustive experimental characterization of a set of novel geometries. The in-depth results analysis allowed to correlate the investigated design parameters to burner performances, discovering possible two-fold optimization paths.
Recurrent verifications of the assumptions made to define prototypes design are considered a mandatory step to avoid significant deviation from the correct optimization path, which strongly depends on both objective function definition and selection of design variables.
Concerning the objective function, a proper mathematical formulation was proposed in the previous work, which represented a balance between two apparently conflicting aspect like flame stability and low emissions.
Concerning design variables, outcomes of the first test campaign have been used in the present work to define new burner geometries. Starting from a new baseline who has showed the widest low NOx operating window, additional geometrical features have been considered in this survey as potentially affecting flame stabilization. Thanks to the degree of freedom offered by DMLM technology, rapid prototyping of alternative geometries allowed to easily setup a new experimental plan for the second optimization step.
Exploiting the same approach used in the first test campaign, new geometries have been tested in a single-cup test rig at gas turbine relevant operating conditions, showing
Stable low-NOx operating windows have been evaluated throughout dedicated objective functions for all geometries and results showed lower NOx and CO emissions as a consequence of the newly introduced geometrical modifications.
Moreover, the comparison with the estimates of the previous campaign proved the existence of the identified optimization path. Indeed, it furnished valid elements for further using of the proposed methodology for the improvement of emission and blow-out characteristics of novel burners and, more in general, for the development of a novel dry low NOx technology.