bluuebunny/crossref_metadata_2025_split huggingface dataset:
RANS and LES Modeling of a Linear-Array Swirl Burner Using a Flamelet-Progress Variable Approach
Authors: Jella Sandeep , Bourque Gilles , Bergthorson Jeffrey , Kwong Wing Yin , Steinberg Adam 
Published: August 2018

Multiple, interacting flames in DLE systems can increase flame surface area and promote mixing of hot-products into the reactants — leading to an efficient usage of combustion volume and improved injector performance. An optically-accessible, confined, linear array of five swirl nozzles was recently built [1] to investigate flame dynamics and validate computational strategies. The present work focuses on modeling a dataset representative of lean gas turbine conditions, using a flamelet approach. A preheated (500K), premixed fuel-air mixture (ϕ = 0.55, Tflame = 1732K) at atmospheric pressure was injected through the swirlers at 40 m/s into a rectangular chamber. High-speed laser measurements of the flow (3 component velocity field from 10 kHz stereoscopic particle image velocimetry (S-PIV)) and flame (planar laser induced fluorescence of the hydroxyl radical (OH-PLIF)) were used for model validation.
The objectives of this work: (1) Evaluate a flamelet-progress variable method based on flamelet-generated manifolds (FGM) and examine its sensitivity to models for micro (scalar dissipation) and large scale mixing (anisotropic RANS vs LES) and (2) Obtain insight into the velocity field and flame stabilization in an interacting system.
Computations indicate that high-swirl nozzles produce bluff-body flames anchored to shear-layer vortices due to an arrested flow expansion. The anisotropic RANS turbulence model under-predicts the recirculation zone strength but predicts flow development and Reynolds stress profiles fairly well. While LES is more accurate overall, both models over-predict flow fluctuations in the transitional flow at the end of the recirculation bubble where flow becomes axially positive. The flamelet approach predicts the flame-shape and length correctly but over-predicts the reaction rate in-between swirlers. The effect of including a reactive SDR model is to significantly increase flame-flow interaction (higher scalar variance) but does not appear to influence the overall shape or location of the flame.
Benchmark of a Novel Aero-Elastic Simulation Code for Small Scale VAWT Analysis
Authors: Marten David , Lennie Matthew , Pechlivanoglou George , Paschereit Christian Oliver , Bianchini Alessandro , Ferrara Giovanni , Ferrari Lorenzo 
Published: August 2018

After almost 20 years of absence from research agendas, interest in the vertical axis wind turbine (VAWT) technology is presently increasing again, after the research stalled in the mid 90’s in favour of horizontal axis turbines (HAWTs). However, due to the lack of research in past years, there are a significantly lower number of design and certification tools available, many of which are underdeveloped if compared to the corresponding tools for HAWTs. To partially fulfil this gap, a structural FEA model, based on the Open Source multi-physics library PROJECT::CHRONO, was recently integrated with the Lifting Line Free Vortex Wake method inside the Open Source wind turbine simulation code QBlade and validated against numerical and experimental data of the SANDIA 34m rotor. In this work some details about the newly implemented nonlinear structural model and its coupling to the aerodynamic solver are first given. Then, in a continuous effort to assess its accuracy, the code capabilities were here tested on a small scale, fast-spinning (up to 450 rpm) VAWT. The study turbine is a helix shaped, 1kW Darrieus turbine, for which other numerical analyses were available from a previous study, including the results coming from both a 1D beam element model and a more sophisticated shell element model. The resulting data represented an excellent basis for comparison and validation of the new aero-elastic coupling in QBlade.
Based on the structural and aerodynamic data of the study turbine, an aero-elastic model was then constructed. A purely aerodynamic comparison to experimental data and a BEM simulation represented the benchmark for QBlade aerodynamic performance. Then, a purely structural analysis was carried out and compared to the numerical results from the former. After the code validation, an aero-elastically coupled simulation of a rotor self-start has been performed to demonstrate the capabilities of the newly developed model to predict the highly nonlinear transient aerodynamic and structural rotor response.
Nonsmooth Thermoelastic Simulations of Blade-Casing Contact Interactions
Authors: Thorin Anders , Guérin Nicolas , Legrand Mathias , Thouverez Fabrice , Almeida Patricio 
Published: August 2018

In turbomachinery, it is well known that tighter operating clearances improve the efficiency. However, this leads to unwanted potential unilateral and frictional contact occurrences between the rotating (blades) and stationary components (casings) together with attendant thermal excitations. Unilateral contact induces discontinuities in the velocity at impact times, hence the terminology nonsmooth dynamics. Current modeling strategies of rotor-stator interactions are either based on regularizing penalty methods or on explicit time-marching methods derived from Carpenter’s forward Lagrange multiplier method. Regularization introduces an artificial time scale in the formulation corresponding to numerical stiffness which is not desirable. Carpenter’s scheme has been successfully applied to turbomachinery industrial models in the sole mechanical framework, but faces serious stability issues when dealing with the additional heat equation.
This work overcomes the above issues by using the Moreau–Jean nonsmooth integration scheme within an implicit θ-method. This numerical scheme is based on a mathematically sound description of the contact dynamics by means of measure differential inclusions and enjoys attractive features. The procedure is unconditionally stable opening doors to quick preliminary simulations with time-steps one hundred times larger than with previous algorithms. It can also deal with strongly coupled thermomechanical problems.
Investigation of Spectral Vanishing Viscosity for Stabilizing and Accelerating Solution of Time Spectral Equation System
Authors: Wu Hangkong , Wang Dingxi , Huang Xiuquan , Yan Hong , Li Jianling 
Published: August 2018

Time spectral method (TSM), as a very effective frequency domain method for analyzing temporal periodic flow field, is more popular than other frequency domain methods such as the nonlinear harmonic method (NLHM), the linear harmonic method (LHM) and the classic harmonic balance method. This is due to the fact that it is much easier to be implemented in an existing steady flow solver. But the aliasing errors caused by the nonlinear terms in the Euler/Navier-Stokes equations can have an adverse effect on the convergence rate. On the worse side, it can even lead to solution instability. This paper will present investigation of the application of the time spectral vanishing viscosity (SVV) method to stabilizing the solution of time spectral method. The spectral vanishing viscosity method has long been investigated for stabilizing spectral solution of conservation laws in space. Its application to time spectral solution of unsteady flow equations is very limited. In this investigation, the accuracy and time cost of the time spectral method with the SVV will be compared with that without the SVV and the traditional time domain dual time stepping method (DT). The stiffness of the SVV and the time spectral source terms is relieved by implicitly integrating the source terms in time using the block Jacobi method (BJ). To accelerate the convergence rate, the Lower Upper Symmetric Gauss Seidel (LU-SGS) method is used as the residual smoother for a multi-stage Runge-Kutta time integration.
The following points can be drawn from this investigation:
1. Time spectral vanishing viscosity method can accelerate convergence rate and reduce time cost.
2. Time spectral vanishing viscosity method can improve the solution accuracy and fewer harmonics can be used to analyze the flow field with the SVV than without the SVV.
Evaluation of Friction Models for Rotor-Rubbing Predictions
Authors: Jauregui Juan C. , Saenz Jorge A. , Gonzalez Claudia A. 
Published: August 2018

Rubbing, in turbomachinery, is a phenomenon difficult to identify and predict. Rubbing is a sudden event that can cause catastrophic damage, therefore, it is necessary to have good prediction models. In order to predict this phenomenon, several models have been proposed which are based on representing rubbing as an external friction force acting on the rotor.
The work presented here includes the results of two experiments. In the first one, the accelerations of a rotor rubbing a fixed spot were recorded. In the second experiment, the accelerations and the friction force were measured. All the data were analyzed using the Continuous Wavelet Transform and the data from the second experiment were used for estimating the friction force.
It was found that modelling the stiffness of the system as a Fourier Series gives better results than other models.
Computationally Efficient Modelling of Oil Jet-Breakup and Film Formation for Bearing Chamber Applications
Authors: Hee Jee Loong , Simmons Kathy , Kakimpa Bruce , Hann David 
Published: August 2018

In previously published experimental work completed at the Gas Turbine and Transmissions Research Centre (G2TRC), oil fed to an aeroengine location bearing via underrace feed was seen to shed from the cage, forming a film on static surfaces near the bearing and subsequently shedding into the bearing chamber. A high-fidelity computational model of the two-phase flow in an aeroengine bearing chamber must adequately reproduce such behaviour but there are significant challenges in modelling both the oil breakup after shedding and the subsequent film formation. It is very computationally costly to resolve an oil film interface using the Volume of Fluid (VOF) approach at regions of thin film and it is unacceptably inaccurate to resolve thick film using an explicit thin film modelling technique such as the Eulerian Thin Film Model (ETFM). A proposed solution is to couple together VOF, ETFM and discrete phase modelling (DPM). Previously published G2TRC work shows how VOF and ETFM can be successfully coupled. This paper investigates the coupling of ETFM and DPM. The evaluation of film momentum transport and air-particle momentum transfer/Lagrangian particle tracking are studied using a low Reynolds number turbulence model.
Validation is required to ensure that these models work together as intended. To this end a preliminary CFD study was carried out on a published case investigated experimentally and computationally in which a jet is injected into a duct via a nozzle, breaking up into droplets before forming a wall film. The droplets are produced by primary atomization due to liquid instabilities at the injection point. Secondary breakup occurs due to surface instabilities prompted by the high-velocity cross-flow. Small droplets are transported downstream whereas larger droplets deflect minimally hitting the wall and forming a thin film. In the work presented here quantitative film thickness data from experiments and prior simulations are compared to current data.
The success of the simulation is found to depend on shear-transportation, turbulent dispersion of the particles, particle grouping, mass transportation as well as accurate prediction of interfacial shear-stresses. With suitable modelling parameters it was possible to predict film thickness to within 28.9% of those seen experimentally. The present ETFM-DPM modelling showed improvements over previously published models in prediction of shear-stresses and film transportation as the ω-equation could be integrated through the viscous sublayer. The developed approach is now mature enough to be applied to the bearing chamber geometry investigated experimentally at G2TRC and this is proposed for future work.
Start-Up Optimization of a CCGT Power Station Using Model Based Gas Turbine Control
Authors: Nannarone Alessandro , Klein Sikke A. 
Published: August 2018

The rapid growth of renewable generation and its intermittent nature has modified the role of combined cycle power stations in the energy industry, and the key feature for the operational excellence is now flexibility. Especially, the capability to start an installation quickly and efficiently after a shutdown period leads to lower operational cost and a higher capacity factor. However, most of existing thermal power stations worldwide are designed for continuous operation, with no special focus on an efficient start-up process. In most current start-up procedures, the gas turbine controls ensure maximum heat flow to the heat recovery steam generator, without feedback from the steam cycle. The steam cycle start-up controls work independently with as main control parameter the limitation of the thermal stresses in the steam turbine rotor. In this paper, a novel start-up procedure of an existing combined cycle power station is presented, and it uses a feedback loop between the steam turbine, the boiler and the gas turbine start-up controls. This feedback loop ensures that the steam turbine can be started up with a significant reduction in stresses.
To devise and assess this start-up methodology, a flexible and accurate dynamic model was implemented in the Simulink™ environment. It contains more than 100 component blocks (heat exchangers, valves, meters and sensors, turbines, controls, etc.), and the mathematical component sub-models are based on physical models and experimental correlations. This makes the model generally applicable to other power plant installations. The model was validated against process data related to the three start-up types (cold start, warm start, hot start). On this basis, the optimization model is implemented with feedback loops that control for example the exit temperature of the gas turbine based on the actual steam turbine housing temperature, resulting in a smoother heating up of the steam turbine.
The optimization model was used to define the optimal inlet guide vanes position and gas turbine power output curves for the three types of start-up. These curves were used during real power station start-ups, leading to, for cold and warm starts, reductions in the start-up time of respectively 32.5% and 31.8%, and reductions in the fuel consumption of respectively 47.0% and 32.4%. A reduction of the thermal stress in the steam turbines is also achieved, thanks to the new start-up strategy.
Design of an Air-Cooled Radial Turbine: Part 2 — Experimental Measurements of Heat Transfer
Authors: Zhang Yang , Duda Tomasz , Scobie James A. , Sangan Carl M. , Copeland Colin D. , Redwood Alex 
Published: August 2018

The paper focuses on manufacture and testing of an additively manufactured, cooled radial turbine. To the authors knowledge, this is the first published work that provides experimental temperature data for a small, internally cooled radial wheel constructed using Selective Laser Melting. This work is highly relevant observing the close correlation between turbine inlet temperature and system efficiency.
An internally cooled radial turbine was tested on the hot gas turbocharger rig at the University of Bath and compared with a baseline uncooled rotor. Thermal history paint was applied to the turbine rotor surfaces to determine the distribution of maximum exposed metal temperature. Both the uncooled and internally cooled turbine rotors were manufactured using Selective Laser Melting (SLM) technology. The resolution and strength of the printed prototype was tested prior to the high speed and high temperature experiment. The highest temperature at turbine leading edge and overall average thermal loading were compared quantitatively between the baseline uncooled rotor and the cooled rotor with internal secondary air plenums. The coolant was supplied from the compressor to the turbine through the centerline of the rotor shaft. The aerodynamic performance and component efficiency were also measured during the experiments. The test results indicate that the internally cooled turbine has a pronounced temperature drop at the blade leading edge and, indeed, throughout the blade passage. This increases the potential for increased turbine inlet temperature in order to achieve improved cycle efficiency. This experimental work has established a foundation for radial turbine internal cooling technology in the turbocharger and micro gas turbine industry.
Influence of Top Coat and Bond Coat Pre-Oxidation on the Corrosion Resistance of Thermal Barrier Coatings in the Presence of SO2
Authors: Jonnalagadda Krishna Praveen , Yuan Kang , Li Xin-Hai , Ji Xiaojuan , Yu Yueguang , Peng Ru Lin 
Published: August 2018

Thermal barrier coatings (TBCs) degradation due to corrosion is one of the commonly observed failure types in land-based gas turbines due to the usage of low grade fuels. Sulfur in its gaseous form, as SO2, can attack the TBC system and result in the degradation of both the coating and the turbine component. The present study aims to understand the difference in the corrosion induced damage caused by SO2 gas mixture in different coating architectures. Corrosion tests were conducted at 780 °C in a tube furnace for a period of 168h. The inlet test gas had a composition of 1SO2-0.1CO-20CO2-N2 (bal.) in vol. %. The coating architectures consisted of 1) an overlay coating, 2) a single-side bond coat TBC, 3) an all-side bond coat TBC, 4) an all-side bond coat TBC subjected to pre-oxidation prior to the corrosion tests.
The results from the corrosion tests showed that the damage was the most severe for the overlay followed by single-side bond coat TBC. Between the other two systems, the TBC subjected to pre-oxidation had relatively lower corrosion damage. The corrosion damage started from the edges for the overlay and single-side bond coat TBC and as well as through the penetration of the gas through the coating. For the coatings with bond coat on all sides, the edge damage appeared to be considerably reduced and the damage is predominantly through the gas infiltration.
High-Fidelity Sensitivity Analysis of Modal Properties of Mistuned Bladed Disks Regarding Material Anisotropy
Authors: Koscso Adam , Dhondt Guido , Petrov E. P. 
Published: August 2018

A new method has been developed for sensitivity calculations of modal characteristics of bladed disks made of anisotropic materials. The method allows the determination of the sensitivity of the natural frequencies and mode shapes of mistuned bladed disks with respect to anisotropy angles that define the crystal orientation of the monocrystalline blades using full-scale finite element models. An enhanced method is proposed to provide high accuracy for the sensitivity analysis of mode shapes. An approach has also been developed for transforming the modal sensitivities to coordinate systems used in industry for description of the blade anisotropy orientations.
The capabilities of the developed methods are demonstrated on examples of a single blade and a mistuned realistic bladed disk finite element models. The modal sensitivity of mistuned bladed disks to anisotropic material orientation is thoroughly studied.
Prediction of Aerodynamically Induced Blade Vibrations in a Radial Turbine Rotor Using the Nonlinear Harmonic Approach
Authors: Kovachev Nikola , Waldherr Christian U. , Mayer Jürgen F. , Vogt Damian M. 
Published: August 2018

Resonant response of turbomachinery blades can lead to high cycle fatigue (HCF) if the vibration amplitudes are excessive. Accurate and reliable simulations of the forced response phenomenon require detailed CFD and FE models that may consume immense computational costs.
In the present study, an alternative approach is applied, which incorporates nonlinear harmonic (NLH) CFD simulations in a one-way fluid-structure interaction (FSI) workflow for the prediction of the forced response phenomenon at reduced computational costs. Five resonance crossings excited by the stator in a radial inflow turbocharger turbine are investigated and the aerodynamic excitation and damping are predicted using this approach. Blade vibration amplitudes are obtained from a subsequent forced response analysis combining the aerodynamic excitation with aerodynamic damping and a detailed structural model of the investigated turbine rotor. A comparison with tip timing measurement data shows that all predicted values lay within the range of the mistuned blade response underlining the high quality of the utilized workflow.
Gas Turbine Fouling Tests: Review, Critical Analysis and Particle Impact Behavior Map
Authors: Suman Alessio , Casari Nicola , Fabbri Elettra , Pinelli Michele , di Mare Luca , Montomoli Francesco 
Published: August 2018

Fouling affects gas turbine operation and airborne or fuel contaminants, under certain conditions, become very likely to adhere to surfaces if impact takes place. Particle sticking implies the change in shape in terms of roughness of the impinged surface. The consequences of these deposits could be dramatic: these effects can shut an aircraft engine down or derate a land-based power unit. This occurrence may happen due to the reduction of the compressor flow rate and the turbine capacity, caused by a variation in the HPT nozzle throat area (geometric blockage due to the thickness of the deposited layer and the aerodynamic blockage due to the increased roughness, and in turn boundary layer).
Several methods to quantify particle sticking have been proposed in literature so far, and the experimental data used for their validation vary in a wide range of materials and conditions. The experimental analyses have been supported by (and have given inspiration to) increasingly realistic mathematical models. Experimental tests have been carried out on (i) a full scale gas turbine unit, (ii) wind tunnel testing or hot gas facilities using stationary cascades, able to reproduce the same conditions of gas turbine nozzle operation and finally, (iii) wind tunnel testing or hot gas facilities using a coupon as the target.
In this review, the whole variety of experimental tests performed is gathered and classified according to composition, size, temperature and particle impact velocity. Using particle viscosity and sticking prediction models, over seventy (70) tests are compared with each other and with the model previsions providing a useful starting point for a comprehensive critical analysis. Due to the variety of test conditions, the related results are difficult to be pieced together due to differences in particle material and properties.
The historical data of particle deposition obtained over thirty (30) years are classified using particle kinetic energy and the ratio between particle temperature and its softening temperature. Qualitative thresholds for the distinction between particle deposition, surface erosion and particle break-up, based on particle properties and impact conditions, are identified. The outcome of this paper can be used for further development of sticking models or as a starting point for new insight into the problem.