This file was created by the Typo3 extension sevenpack version 0.7.16 --- Timezone: CET Creation date: 2023-01-27 Creation time: 08-18-32 --- Number of references 30 article 10.1115/1.4052087 Journal of Engineering for Gas Turbines and Power 2022 2 21 144 5 {Machine learning and automatized routines for parameter optimization have experienced a surge in development in the past years, mostly caused by the increasing availability of computing capacity. Gradient-free optimization can avoid cumbersome theoretical studies as input parameters are purely adapted based on output data. As no knowledge about the objective function is provided to the algorithms, this approach might reveal unconventional solutions to complex problems that were out of scope of classical solution strategies. In this study, the potential of these optimization methods on thermoacoustic problems is examined. The optimization algorithms are applied to a generic low-order thermoacoustic can-combustor model with several fuel injectors at different locations. We use three optimization algorithms – the well established downhill simplex method, the recently proposed explorative gradient method, and an evolutionary algorithm – to find optimal fuel distributions across the fuel lines while maintaining the amount of consumed fuel constant. The objective is to have minimal pulsation amplitudes. We compare the results and efficiency of the gradient-free algorithms. Additionally, we employ model-based linear stability analysis to calculate the growth rates of the dominant thermoacoustic modes. This allows us to highlight general and thermoacoustic-specific features of the optimization methods and results. The findings of this study show the potential of gradient-free optimization methods on combustor design for tackling thermoacoustic problems, and motivate further research in this direction.} 051004 https://doi.org/10.1115/1.4052087 0742-4795 10.1115/1.4052087 M.Reumschüssel J.von Saldern Y.Li C. O.Paschereit A.Orchini proceedings 10.1115/GT2021-59071 2021 Volume 3A: Combustion, Fuels, and Emissions {In gas turbine combustion systems, the reduction of emissions of harmful combustion by-products is a main development goal. This study provides a methodology to model NOX emissions effectively for varying levels of pilot fuel flows at different operational points. It combines one-dimensional flame simulations using detailed chemistry with a stochastic approach for equivalence ratio fluctuations to account for the effect of fuel-air unmixedness. This split allows for computationally fast variations of the gas inlet condition and the consideration of different shares of pilot gas. The generation of emissions is split into a share of prompt formation at the flame front and a slower formation mechanism, occurring within the combustion products in the post flame region. The influence of unmixedness of the fuel-air mixture on both effects is taken into consideration by means of probability density functions (PDFs) of the equivalence ratio. These are modeled on the basis of sampled values from Large Eddy Simulations at the flame front and adapted for different shares of pilot gas. It is shown that with a superposition of Gaussian PDFs the equivalence ratio distribution at the flame front resulting from the main gas supply and the pilot share can be well approximated. Measurement data from experiments in atmospheric conditions as well as emission measurements from high pressure tests are used to evaluate the model. Good agreement is found for atmospheric data, allowing for explanations on the effect of pilot fuel ratio on emissions. For elevated pressure, only qualitative trends could be reproduced. Hypotheses to explain this deviation are made that motivate further research.} V03AT04A035 https://doi.org/10.1115/GT2021-59071 Turbo Expo: Power for Land, Sea, and Air 10.1115/GT2021-59071 M.Reumschüssel J.von Saldern T.Kaiser T.Reichel J.-P.Beuth B.Ćosić F.Genin K.Oberleithner C. O.Paschereit article VonSaldern2020a Journal of Engineering for Gas Turbines and Power 2020 11 19 Heavy-duty gas turbines are commonly designed with can-annular combustors, in which all flames are physically separated. Acoustically, however, the cans communicate via the upstream located compressor plenum, or at the downstream gaps found at the transition to the turbine inlet. In the present study, a coupling condition that is based on a Rayleigh conductivity and acoustic flux conservation is derived. It enables acoustic communication between adjacent cans, in which one-dimensional acoustic waves propagate. In addition, because can-annular systems commonly feature a discrete rotational symmetry, the acoustic field can be expressed as a Bloch-periodic wave in the azimuthal direction. We demonstrate how the coupling conditions resulting in a combustion system with $N$ cans can be expressed as an effective impedance for a single can. By means of this Bloch-type boundary condition, the thermoacoustics of a can-annular system can be analyzed considering only one can, thus reducing the size of the problem by a factor of N. Using this method, we investigate in frequency domain the effect of the coupling strength of a generic can-annular combustor consisting of 12 identical cans, which are connected at the downstream end. We describe generic features of can-annular systems and derive results on the frequency response of the cans at various Bloch numbers in the low-frequency and high-frequency limits. Furthermore, the formation of eigenvalue clusters with eigenvalues of close frequency and growth rate, but very different mode shapes is discussed. Boundary-value problems, combustion chambers, acoustics, eigenvalues, waves, combustion systems, compressors, electrical conductivity, flames, frequency response, gas turbines, ode shapes, hermal conductivity,tThermoacoustics, turbines https://asmedigitalcollection.asme.org/gasturbinespower/article/doi/10.1115/1.4049162/1091623/Analysis-of-Thermoacoustic-Modes-in-CanAnnular 0742-4795 10.1115/1.4049162 J.von Saldern A.Orchini J.Moeck article vonSaldern2020 Proceedings of the Combustion Institute 2020 A can-annular combustor consists of a set of nominally identical cans, in which the flames burn in an essentially isolated manner. However, adjacent cans are able to communicate acoustically, which provides dynamic coupling of the entire can-annular arrangement. Recently, it was shown that the acoustic coupling is not negligible and can cause clustering of eigenfrequencies. In this study, we present a low-order modeling framework for self-excited thermoacoustic oscillations in generic can-annular combustors consisting of N identical cans. The dynamics of the flames are modeled with the nonlinear G-equation; the acoustic model accounts for plane acoustic waves inside the cans and can-to-can communication. The latter is enabled through a coupling boundary condition that is based on conservation of mass and a Rayleigh conductivity. For weak coupling between adjacent cans, the thermoacoustic feedback cycle shows clusters of linearly unstable modes of different azimuthal order, which are close in frequency and growth rate. Their interaction in the nonlinear regime is investigated using time-domain simulations. Two simulations for generic can-annular combustors consisting of 4 and 6 cans with weak acoustic coupling are discussed in this study. We observe a strong interaction between the modes, which can cause long transition times and allows modes that do not dominate the system dynamics in the linear regime to be dominant in the nonlinear regime. While the N=6 case converges to a periodic oscillation pattern with one dominant frequency, the N=4 case converges to a quasi-periodic oscillation involving modes of different azimuthal order. Moreover, we observe a synchronization of these modes. These results raise the questions whether it is possible to predict which mode(s) will dominate the system in the saturated state and under which conditions synchronization of clustered modes can occur. Can-annular combustor, thermoacoustics, nonlinear interaction, weak coupling, kinematic flame model https://www.sciencedirect.com/science/article/pii/S154074892030328X 1540-7489 https://doi.org/10.1016/j.proci.2020.06.236 J.von Saldern J.Moeck A.Bianchini article Vanierschot2020 Journal of Fluid Mechanics 2020 883 A31 https://www.cambridge.org/core/product/identifier/S0022112019008723/type/journal{\_}article Cambridge University Press (CUP) 0022-1120 10.1017/jfm.2019.872 M.Vanierschot J.Müller M.Sieber M.Percin B.van Oudheusden K.Oberleithner inbook Gonzalez2020 2020 1-57 This chapter focuses on the application of passive flow control technologies to wind turbine blades. The motivation of using these technologies is always an enhancement of the wind turbine performance (increase of power production, load reduction, noise reduction, etc.) in comparison to the standard blade. Passive flow control solutions can be limited to static add-ons or involve more significant modifications of the blade for dynamic approaches. Furthermore, these technologies can be included in the initial design of the blade or included later as add-ons to improve the performance of an existing blade design. A large number of passive technologies have been proposed for wind turbine applications, although the level of maturity is not the same for all of them ranging from conceptual studies in some cases to commercial products in others. Some representative examples of specific technologies are included in this chapter: vortex generators, static miniflaps, root spoilers, serrations, winglets, passive flaps, and aeroelastic coupling. For each technology, some aspects related to the state of the art, main concept, impact on the wind turbine performance, application, and design have been described. Finally, passive flow control technologies have to be integrated into the design process of wind turbines. To select and properly apply the most suitable technology for each specific problem, the chapter highlights the importance of modeling tools, design methodologies, objectives and restrictions, design parameters, and scale of impact of each passive flow control solution. In addition, from a general point of view, some design guidelines have been mentioned. Passive flow control Aerodynamic flow control Aerodynamic control devices Smart blade design Vortex generators Serrations Root spoilers Aeroelastic coupling Miniflaps Passive flaps Noise Power production Loads Fatigue loads Extreme loads Cost of energy https://link.springer.com/referenceworkentry/10.1007/978-3-030-05455-7_6-1 Stoevesandt B., Schepers G., Fuglsang P., Yuping S. Springer, Cham eprint Handbook of Wind Energy Aerodynamics 1 eprint 978-3-030-05455-7 https://doi.org/10.1007/978-3-030-05455-7_6-1 A.González-Salcedo A.Crace C.Arce León C. N.Nayeri D.Baldacchino K.Vimalakanthan Th.Barlas proceedings Edwige2018 ASME 2018 5th Joint US-European Fluids Engineering Division Summer Meeting 2018 2 Development and Applications in Computational Fluid Dynamics; Industrial and Environmental Applications of Fluid Mechanics; Fluid Measurement and Instrumentation The research on the external aerodynamics of ground vehicles can nowadays be related to sustainable development strategies, confirmed by the worldwide CO2 regulation target. Automotive manufacturers estimate that a drag reduction of 30% contributes to 10g/km of CO2 reduction. However, this drag reduction should be obtained without constraints on the design, the safety, comfort and habitability of the passengers. Thus, it is interesting to find flow control solutions, which will remove or remote recirculation zones due to separation edges with appropriate control techniques. In automotive sales, the SUV, 4x4 and compact cars represent a large part of the market share and the study of control approaches for this geometry is practically useful. In this work, appropriate control techniques are designed to decrease the drag forces around a reduced scale SUV car benchmark called POSUV. The control techniques are based on the DMD (Dynamic Mode Decomposition) algorithms generating an optimized drag reduction procedure. It involves independent transient inflow boundary conditions for flow control actuation in the vicinity of the separation zones and time resolved pressure sensor output signals on the rear end surface of the mockup. This study, that exploits dominant flow features behind the tailgate and the rear bumper, is performed using Large Eddy Simulations on a sufficient run time scale, in order to minimize a cost function dealing with the time and space average pressure coefficient. The resulting dynamic modal decomposition obtained by these LES simulations and by wind tunnel measurements has been compared for the reference case, in order to select the most appropriate run time scale. Analysis of the numerical results shows a significant pressure increase on the tailgate, for independent flow control frequencies. Similar decomposition performed in the wake with and without numerical flow control help understanding the flow modifications in the detachment zones. Montreal, Quebec, Canada, July 15–20, 2018 http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2710650 ASME Proceedings | 25th Symposium on Industrial and Environmental Applications of Fluid Mechanics ASME 978-0-7918-5156-2 10.1115/FEDSM2018-83444 S.Edwige Ph.Gilotte I.Mortazavi Y.Eulalie D.Holst C. N.Nayeri J.-L.Aider E.Varon article Gray_2016 Proceedings of ASME Turbomachinery Technical Conference & Exposition. Seoul, South Korea, June 13–17, 2016 2016 Volume 4B: Combustion, Fuels and Emissions Paper No. GT2016-57813, pp. V04BT04A044 9 Constant-volume (pressure-gain) combustion cycles show much promise for further increasing the efficiency of modern gas turbines, which in the last decades have begun to reach the boundaries of modern technology in terms of pressure and temperature, as well as the ever more stringent demands on reducing exhaust gas emissions. The thermodynamic model of the gas turbine consists of a compressor with a polytropic efficiency of 90%, a combustor modeled as either a pulse detonation combustor (PDC) or as an isobaric homogeneous reactor, and a turbine, the efficiency of which is calculated using suitable turbine operational maps. A simulation is conducted using the one-dimensional reacting Euler equations to obtain the unsteady PDC outlet parameters for use as turbine inlet conditions. The efficiencies for the Fickett–Jacobs and Joule cycles are then compared. The Fickett–Jacobs cycle shows promise at relatively low compressor pressure ratios, whereas the importance of the harvesting of exhaust gas kinetic energy for the cycle performance is highlighted. Proceedings of ASME Turbomachinery Technical Conference & Exposition. Seoul, South Korea, June 13 – 17, 2016 http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2555111 978-0-7918-4976-7 10.1115/gt2016-57813 J.Gray J.Vinkeloe J. P.Moeck C. O.Paschereit P.Stathopoulos P.Berndt R.Klein article Nayeri2015 DEWEK 2015 2015 Modern turbines control load and power by actively adjusting the angle of attack via pitch variation. However, this technology is not suited for compensating the inflow variations generated by the atmospheric boundary layer or from upstream wind turbines (wind farms) or yaw errors, sudden gusts or turbulence which can occur within seconds or less and can have local impact on a rotor blade. In a collaborative research effort of five German universities, passive and active flow control methods for the alleviation of dynamic loads, load fluctuations and for reduction of wake effects are investigated, both experimentally and numerically. Furthermore, numerical tools suitable for evaluating the overall cost reduction and benefit of flow control methods on wind turbines will be validated and extended such that the results can be transferred to fullscale wind turbines under realistic inflow conditions. http://15.dewek.de/fileadmin/downloads/Book_of_Abstracts_2015.pdf DEWI C. N.Nayeri S.Vey D.Marten G.Pechlivanoglu C. O.Paschereit article Fischer2015 DEWEK 2015 2015 The development of a medium scale research wind turbine is a part of the research project PAK 780 funded by the German Science Foundation (DFG). In this project six universities from all over Germany join forces and pursue fundamental research in the field of wind turbine aerodynamics, inflow turbulence as well as wake and flow control. The Modular Research Wind Turbine (MoReWiT) design and development is an integral part of this research program designed to assist the research tasks of all project partners. The PAK 780 project consists of HFI TU Berlin, RWTH Aachen, Univ. of Oldenburg, Univ. of Stuttgart and TU Darmstadt and it is one of the major DFG funded projects in wind energy. Book of abstracts 2015 http://15.dewek.de/fileadmin/downloads/Book_of_Abstracts_2015.pdf DEWI J.Fischer O.Eisele G.Pichlivanoglou S.Vey C. N.Nayeri C. O.Paschereit conference Stathopoulos2015 2015 11 Toranomon Hills, Tokyo, Japan International Gas Turbine Congress IGTC Nov 15-20, 2015 P.Stathopoulos J.Vinkeloe C. O.Paschereit inproceedings Vey2015a 2015 AIAA paper no. 2015-3392 AIAA Aviation, 33rd AIAA Applied Aerodynamics Conference, June 22-26, 2015, Dallas, Texas, USA 978-1-62410-363-6 10.2514/6.2015-3392 S.Vey D.Marten G.Pechlivanoglou C. N.Nayeri C. O.Paschereit inproceedings VonGosen.2015 2015 AIAA paper no. 2015-0782 AIAA SciTech, 53rd Aerospace Sciences Meeting, 5-9 January, Kissimmee , Florida, USA 10.2514/6.2015-0782 F.Von Gosen F.Ostermann R.Woszidlo C. N.Nayeri C. O.Paschereit inproceedings Huang2015a 2015 AIAA paper no. 2015-2310 AIAA Aviation, 45th AIAA Fluid Dynamics Conference, June 22-25, 2015, Dallas, Texas, USA 978-1-62410-362-9 10.2514/6.2015-2310 X.Huang S.Vey M.Meinke W.Schroeder G.Pechlivanoglou C. N.Nayeri C. O.Paschereit inproceedings Vey2015a 2015 ASME Paper GT2015-43407 V009T46A021 (6 pages) Results from a quantitative tuft flow visualization of a utility scale wind turbine undergoing a yaw movement are presented. Based on the turbine’s SCADA data suitable pre- and post-yaw timeframes were defined and the surface flowfields were analysed. A distinct asymmetry between the surface flow patterns of the 90° and 270° azimutal blade positions was observed in the pre-yaw timeframe. After the turbine yawed back into the wind the symmetry was restored. Yaw-misalignment is a source of dynamic loads which limit a turbine’s life time. The characterization of the involved flow structures and their dynamics is an essential step towards possible future load alleviation techniques. The quantitative tuft flow visualization technique is a measurement tool that can be used to assess the surface flow field. Proceedings of ASME Turbo Expo 2015, June 15-19, 2015, Montreal, Quebec, Canada 978-0-7918-5680-2 10.1115/GT2015-43407 S.Vey H. M.Lang C. N.Nayeri C. O.Paschereit G.Pechlivanoglou G.Weinzierl article Vey2014a Journal of Physics: Conference Series 2014 524 1 http://iopscience.iop.org/1742-6596/524/1/012011/pdf/1742-6596_524_1_012011.pdf The Science of Making Torque from Wind 2014 10.1088/1742-6596/524/1/012011 S.Vey H. M.Lang C. N.Nayeri C. O.Paschereit G.Pechlivanoglou article DuroxMBMVSC2013 Combustion and Flame 2013 160 9 1729--1742 10.1016/j.combustflame.2013.03.004 D.Durox J. P.Moeck J.-F.Bourgouin P.Morenton M.Viallon T. S.Schuller S.Candel inproceedings Vey2012 2012 AIAA paper no. 2012-317 http://arc.aiaa.org/doi/pdfplus/10.2514/6.2012-317 50th AIAA Aerospace Science Meeting, Nashville, Tennessee, USA, Jan. 9-12 10.2514/6.2012-317 S.Vey C. N.Nayeri C. O.Paschereit D.Greenblatt inproceedings vey2011 2011 2 614-625 http://toc.proceedings.com/10945webtoc.pdf Proc. 51st Israel Annual Conference on Aerospace Sciences 2011, Feb 23-24, Tel-Aviv and Haifa, Israel 978-1-61782-401-2 S.Vey C. N.Nayeri D.Greenblatt C. O.Paschereit article TerhaarVAS2010 International Communications in Heat and Mass Transfer 2010 37 5 457-462 07351933 10.1016/j.icheatmasstransfer.2010.01.009 S.Terhaar A.Velazquez J. R.Arias M.Sanchez-Sanz inproceedings Vey2010 2010 AIAA paper no. 2010-4865 http://pdf.aiaa.org/preview/2010/CDReadyMFD10_2120/PV2010_4865.pdf 40th Fluid Dynamics Conference and Exhibit, June 28 - July 1, 2010, Chicago, Illinois S.Vey D.Greenblatt C. N.Nayeri C. O.Paschereit inproceedings Vey2010a 2010 AIAA paper no. 2010-1222 http://pdf.aiaa.org/preview/2010/CDReadyMASM10_1812/PV2010_1222.pdf 48th AIAA Aerospace Science Meeting, January 4 - 7, 2010, Orlando, Florida, USA S.Vey C. N.Nayeri C. O.Paschereit D.Greenblatt inproceedings Kastantin2010 2010 AIAA paper no. 2010-4864 http://pdf.aiaa.org/preview/2010/CDReadyMFD10_2120/PV2010_4864.pdf 40th Fluid Dynamics Conference and Exhibit, 28 June - 1 July 2010, Chicago, Illinois Y.Kastantin S.Vey C. N.Nayeri C. O.Paschereit article Greenblatt2009 AIAA Journal 2009 47 12 2845-2856 10.2514/1.41767 D.Greenblatt S.Vey C. O.Paschereit R.Meyer inproceedings Bachmann2009 2009 1-20 Proc. 49th Israel Annual Conference on Aerospace Sciences, Tel Aviv, Israel 9781605609836 M.Bachmann C. O.Paschereit S.Utehs S.Vey D.Greenblatt inproceedings Greenblatt2008 2008 paper No. AIAA 2008-4186 Online-Ver\"ffentlichung Proc. 4th Flow Control Conference, Invited Paper, 23-26 June 2008, Seattle, Washington, USA 978-1-56347-942-7 D.Greenblatt C. S.Yao S.Vey C. O.Paschereit R.Meyer inproceedings Vey2008 2008 AIAA paper no. 2008-1058 Online-Veröffentlichung Proc. 46th AIAA Aerospace Sciences Meeting and Exhibit, 7-10 January 2008, Reno, Nevada, USA 1-56347-937-0 S.Vey D.Greenblatt C. O.Paschereit R.Meyer inproceedings Lacarelle2007 2007 AIAA paper no. 2007-1417 45th AIAA Aerospace Sciences Meeting and Exhibit, Jan. 8-11, 2007, Reno, Nevada, USA A.Lacarelle J. P.Moeck H. J.Konle S.Vey C. N.Nayeri C. O.Paschereit inproceedings Flohr2001 2001 ASME Turbo Expo, June 4-6, 2001, New Orleans, Louisiana P.Flohr C. O.Paschereit B.van Roon inproceedings Schuermans2000a 2000 ASME Turbo Expo, May 13-16, 2000, Munich, Germany B.Schuermans W.Polifke C. O.Paschereit J.van der Linden