This file was created by the Typo3 extension sevenpack version 0.7.16 --- Timezone: CET Creation date: 2023-02-04 Creation time: 00-19-36 --- Number of references 68 article Lommel2021 Indoor Air 2021 31 6 1860--1873 The SARS-CoV-2 pandemic has created a great demand for a better understanding of the spread of viruses in indoor environments. A novel measurement system consisting of one portable aerosol-emitting mannequin (emitter) and a number of portable aerosol-absorbing mannequins (recipients) was developed that can measure thespread of aerosols and droplets that potentially contain infectious viruses. The emissionof the virus from a human is simulated by using tracer particles solved in water. The recipients inhale the aerosols and droplets and quantify the level of solved tracer particles in their artificial lungs simultaneously over time. The mobile system can be arranged in a large variety of spreading scenarios in indoor environments and allows for quantification of the infection probability due to airborne virus spreading. This study shows the accuracy of the new measurement system and its ability to compare aerosol reduction measures such as regular ventilation or the use of a room air purifier. aerosol, infection transmission, measurement system, respiratory droplets, virus spread https://www.researchgate.net/publication/352223190_Novel_measurement_system_for_respiratory_aerosols_and_droplets_in_indoor_environments 10.1111/ina.12860 M.Lommel V.Froese M.Sieber M.Jentzsch T.Bierewirtz Ü.Hasirci T.Rese J.Seefeldt S.Schimek U.Kertzscher C. O.Paschereit article Noack02072020 Physical Review Fluids 2020 5 7 We compute, model, and predict drag reduction of an actuated turbulent boundary layer at a momentum-thickness-based Reynolds number of Reθ=1000. The actuation is performed using spanwise traveling transversal surface waves parametrized by wavelength, amplitude, and period. The drag reduction for the set of actuation parameters is modeled using 71 large-eddy simulations (LESs). This drag model allows us to extrapolate outside the actuation domain for larger wavelengths and amplitudes. The modeling novelty is based on combining support vector regression for interpolation, a parametrized ridgeline leading out of the data domain, a scaling for the drag reduction, and a discovered self-similar structure of the actuation effect. The model yields high prediction accuracy outside the training data range. 073901 https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.5.073901 :10.1103/PhysRevFluids.5.073901 D.Fernex R.Semaan M.Albers W.Schröder B. R.Noack article Alber2020 Wind Energy Science 2020 5 4 1645--1662 https://wes.copernicus.org/articles/5/1645/2020/ 10.5194/wes-5-1645-2020 J.Alber R.Soto-Valle M.Manolesos S.Bartholomay C. N.Nayeri M.Schönlau C.Menzel C. O.Paschereit J.Twele J.Fortmann article Noack_25082020 Journal of Fluid Mechanics 2020 897 27 46 An artificial intelligence (AI) control system is developed to maximize the mixingrate of a turbulent jet. This system comprises of six independently operated unsteadyminijet actuators, two hot-wire sensors placed in the jet and genetic programmingfor the unsupervised learning of a near-optimal control law. The ansatz of thislaw includes multi-frequency open-loop forcing, sensor feedback and nonlinearcombinations thereof. Mixing performance is quantified by the decay rate of thecentreline mean velocity of the jet. Intriguingly, the learning process of AI controldiscovers the classical forcings, i.e. axisymmetric, helical and flapping achievable fromconventional control techniques, one by one in the order of increased performance,and finally converges to a hitherto unexplored forcing. Careful examination of thecontrol landscape unveils typical control laws, generated in the learning process, andtheir evolutions. The best AI forcing produces a complex turbulent flow structurethat is characterized by periodically generated mushroom structures, helical motionand an oscillating jet column, all enhancing the mixing rate and vastly outperformingothers. Being never reported before, this flow structure is examined in variousaspects, including the velocity spectra, mean and fluctuating velocity fields and theirdownstream evolution, and flow visualization images in three orthogonal planes, allcompared with other classical flow structures. Along with the knowledge of theminijet-produced flow and its effect on the initial condition of the main jet, theseaspects cast valuable insight into the physics behind the highly effective mixing ofthis newly found flow structure. The results point to the great potential of AI inconquering the vast opportunity space of control laws for many actuators and sensorsand in optimizing turbulence.� mixing enhancement, jets, turbulence control https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/artificial-intelligence-control-of-a-turbulent-jet/FD1BA8BD9F20C797DC6FFBAE0173187B 0022-1120 https://doi.org/10.1017/jfm.2020.392 Y.Zhou D.Fan B.Zhang R.Li B. R.Noack article Noack_14092020 Journal of Fluid Mechanics 2020 906 21 1-41 We propose an automatable data-driven methodology for robust nonlinear reduced-ordermodelling from time-resolved snapshot data. In the kinematical coarse-graining, thesnapshots are clustered into a few centroids representing the whole ensemble. Thedynamics is conceptualized as a directed network, where the centroids represent nodesand the directed edges denote possible finite-time transitions. The transition probabilitiesand times are inferred from the snapshot data. The resulting cluster-based network modelconstitutes a deterministic–stochastic grey-box model resolving the coherent-structureevolution. This model is motivated by limit-cycle dynamics, illustrated for the chaoticLorenz attractor and successfully demonstrated for the laminar two-dimensional mixinglayer featuring Kelvin–Helmholtz vortices and vortex pairing, and for an actuatedturbulent boundary layer with complex dynamics. Cluster-based network modelling opensa promising new avenue with unique advantages over other model-order reductions basedon clustering or proper orthogonal decomposition. low-dimensional models, shear layers, turbulent boundary layers https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/clusterbased-network-model/8252D04A5438ED01E624A7C41CCF81BB https://doi.org/10.1017/jfm.2020.785 H.Li D.Fernex J.Tan MorzynskiM. B. R.Noack article Balduzzi2020 ASME Digital Collection 2020 Power augmentation devices in wind energy applications have been receiving increasing interest from both the scientific and the industrial community. In particular, Gurney Flaps (GFs) showed a great potential thanks to the passive functioning, the simple construction and the possibility to add them as a retrofit to existing rotors. Within this context, the authors have performed an extended investigation on the lift increase capabilities of GFs for the well-known NACA 0021 airfoil, which has been used in several wind energy applications up to now. The present paper shows the results of a combined experimental and numerical analysis considering different geometrical configurations of the flaps under both static and dynamic conditions. Experimental data were first obtained for the AoA range of 180 degrees at a Reynolds number of 180 k to analyze the impact of three different geometrical configurations of the GF on the aerodynamic behavior. The geometrical configurations were defined by varying the length of the flap (1.4 % and 2.5 % of the chord) and its inclination angle with respect to the blade chord (90 degrees and 45 degrees). The experimental investigation involved also dynamic sinusoidal pitching movements at multiple reduced frequencies to evaluate the stall hysteresis cycle. An unsteady CFD numerical model was calibrated against wind tunnel data and then exploited to extend the investigation to a wider range of Reynolds numbers for dynamic AoA rates of change typical of vertical-axis wind turbines, i.e. characterized by higher reduced frequencies with a non-sinusoidal motion law. https://doi.org/10.1115/1.4048908 F.Balduzzi D.Holst P. F.Melani F.Wegner C. N.Nayeri G.Ferrara C. O.Paschereit A.Bianchini article Noack07022020 Flow Turbulence Combustion 2020 105 125 - 157 Wall-resolved large-eddy simulations are performed to study the impact of spanwisetraveling transversal surface waves in zero-pressure gradient turbulent boundary layer flow.Eighty variations of wavelength, period, and amplitude of the space- and time-dependentsinusoidal wall motion are considered for a boundary layer at a momentum thickness basedReynolds number of Re= 1000 . The results show a strong decrease of friction drag of upto 26% and considerable net power saving of up to 10% . However, the highest net powersaving does not occur at the maximum drag reduction. The drag reduction is modeled asa function of the actuation parameters by support vector regression using the LES data.A dependence of the spanwise pressure drag on the wavelength is found. A substantialattenuation of the near-wall turbulence intensity and especially a weakening of the nearwallvelocity streaks are observed. Similarities between the current actuation techniqueand the method of a spanwise oscillating wall without any normal surface deflection arereported. In particular, the generation of a directional spanwise oscillating Stokes layer isfound to be related to skin-friction reduction. Turbulent boundary layer Drag reduction Transversal traveling surface wave Large-eddy simulation ·Active flow control https://link.springer.com/article/10.1007/s10494-020-00110-8 15731987,13866184 https://doi.org/10.1007/s10494-020-00110-8 M.Albers P. S.Meysonnat D.Fernex R.Semaan B. R.Noack W.Schröder article Noack12062020 Experiments in Fluids 2020 61 152 13 A fast triple-parameter extremum seeking method is applied for jet control based on the pioneering work of Gelbert et al.(J Process Control 22(4):700, 2012). The simultaneous adaptation of three input parameters takes less time than the singleinputadaptation of each parameter combined. The key enablers are phase-shifted sinusoids for the input each of which isevaluated by an extended Kalman filter (EKF). An acceleration of the adaption is obtained by a combined EKF couplingthe output to all inputs. The method is illustrated for an analytical optimization problem and experimentally demonstratedfor a turbulent jet mixing control. The considered Reynolds numbers ReD based on the jet exit diameter and velocity are5700, 8000 and 13,300. The main jet is manipulated by a pulsed radially injected minijet which is varied by a mass flowcontroller and an electromagnetic valve up to high frequencies. The mixing performance is characterized by the centerlinejet decay rate and monitored by a hot-wire sensor five diameters downstream at the end of the potential core. The proposedtriple-parameter extremum seeking method optimizes the actuation mass flow ratio, frequency and duty cycle. The decayrate increases 11-fold from the unforced reference value of 0.05 to the optimal actuation level of 0.56. The reproducibilityis demonstrated with various initial actuation parameters. Moreover, the adaptive control robustly tracks the optimal openloopactuation for varying ReD ; the optimal decay rate remains unchanged given the mass flow rate, frequency and dutycycle are optimized. The unforced and actuated flow are investigated with hot wires and visualizations. The three-input ESsignificantly outperforms a two-parameter optimization for the same configuration in multiple respects (Wu et al. in AIAAJ 56(4):1463, 2018): First, the jet decay rate is 8% faster. Second, the convergence time for three parameters is only 25% ofthe adaptation period of two parameters when ReD is varied. Finally, the current steady-state error is 45% less than that ofthe two-parameter optimization. We expect the proposed triple-parameter extremum seeking to be applicable for a largerange of flow control experiments.� https://link.springer.com/article/10.1007/s00348-020-02953-3 14321114,07234864 https://doi.org/10.1007/s00348-020-02953-3 D.Fan Y.Zhou B. R.Noack article Noack21122020 Physics of Fluids 2020 32 125117 1-18 A machine learning control (MLC) is proposed based on the explorative gradient method (EGM) for the optimization and sensitivity analysis of actuation parameters. This technique is applied to reduce the drag of a square-back Ahmed body at a Reynolds number Re = 1.7 × 105. The MLC system consists of pulsed blowing along the periphery of the base, 25 pressure taps distributed on the vertical base of the body, and an EGM controller for unsupervised searching for the best control law. The parameter search space contains the excitation frequency fe, duty cycle α, and flow rate blowing coefficient Cm. It is demonstrated that the MLC may cut short the searching process significantly, requiring only about 100 test runs and achieving 13% base pressure recovery with a drag reduction of 11%. Extensive flow measurements are performed with and without control to understand the underlying flow physics. The converged control law achieves fluidic boat tailing and, meanwhile, eliminates the wake bistability. Such simultaneous achievements have never been reported before. A machine-learned response model is proposed to link the control parameters with the cost function. A sensitivity analysis based on this model unveils that the control performance is sensitive to fe and α but less so to Cm. The result suggests that a small sacrifice on performance will give a huge return on actuation power saving, which may provide important guidance on future drag reduction studies as well as engineering applications. https://aip.scitation.org/doi/full/10.1063/5.0033156 1070-6631 https://doi.org/10.1063/5.0033156 B.Zhang Y.Zhou Y.Fan B. R.Noack book Noack_072020 2020 1 https://publikationsserver.tu-braunschweig.de/servlets/MCRFileNodeServlet/dbbs_derivate_00047503/2020_xROM-Book_Semaan.pdf zRom Machine Learning Tools for Fluid Mechanics 10.4355/dbbs.084-202007011404-0 R.Semaan D.Fernex A.Weimer B. R.Noack article Marten2019 ASME 2019 141 4 13 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 favor of horizontal axis wind 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 fulfill this gap, a structural finite element analysis (FEA) model, based on the Open Source multiphysics library PROJECT::CHRONO, was recently integrated with the lifting line free vortex wake (LLFVW) method inside the Open Source wind turbine simulation code QBlade and validated against numerical and experimental data of the SANDIA 34 m 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, 1 kW Darrieus turbine, for which other numerical analyses were available from a previous study, including the results coming from both a one-dimensional 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 blade element momentum (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. GTP-18-1489 Blades, Rotors, Simulation, Turbines, Vertical axis wind turbines, Modal analysis, Flow (Dynamics), Vortices https://asmedigitalcollection.asme.org/gasturbinespower/article/141/4/041014/367187/Benchmark-of-a-Novel-Aero-Elastic-Simulation-Code English doi.org/10.1115/1.4041519 D.Marten M.Lenni G.Pechlivanoglu C. O.Paschereit A.Bianchini A.Ferrara L.Ferrari article Tschepe'2019 Chalmers Research Publications 2019 102 417 - 434 In order to assess the accuracy of drag prediction methods for high-speed trains, experimental and numerical investigations were performed. Besides the drag coefficient, skin friction and pressure distributions on and near the model have been measured for a 1:22 model of the ICE/V. For the experiments, a moving model rig called DIWA (Drag measurement in water) was realised in a 120 m long towing tank to allow for a realistic simulation of the flow around the train, even in the underbelly region. Numerical investigations were performed using Partially-averaged Navier-Stokes (PANS) simulations based on the k-ω-SST turbulence model. Both experimental and numerical methods can be considered as a novelty in the field of train aerodynamics. The results are compared with data from full-scale tests. It is shown, that the moving model rig DIWA allows for the measurement of drag coefficients of trains with high accuracy. Furthermore, the data acquired using the PANS approach compares well with the experimental data. Towing tank, Train aerodynamics, Drag measurement, PANS, Moving model https://research.chalmers.se/en/publication/510116 1386-6184 10.1007/s10494-018-9962-y J.Tschepe D.Fischer C. N.Nayeri C. O.Paschereit S.Krajnovic article Pampaloni2019 Journal of Propulsion and Power 2019 35 994 - 1004 The prediction of thermo-acoustic instabilities is of paramount importance for gas-turbine combustion systems to meet the emission and efficiency targets. To predict the frequencies and amplitudes of pressure oscillations, and as a consequence, their impact on engine reliability, the nonlinear behavior of the system should be studied. An atmospheric lean-premixed combustor has been numerically investigated for validation purposes. A decoupled approach, separating the acoustic behavior and the nonlinear flame response, which is represented in this work by the flame describing function, has been used. As the first step, the flame describing function calculation from large-eddy simulations has been validated, including the effects of flame stretch and heat loss into the turbulence combustion model. Then, frequency-domain calculations using a three-dimensional Helmholtz solver have been carried out, and results have been validated against experimental measurements and a self-excited large-eddy simulation. https://apps.webofknowledge.com/full_record.do?product=WOS&search_mode=GeneralSearch&qid=10&SID=C4u2D5PtIHZKOxMnzhi&page=1&doc=2&cacheurlFromRightClick=no English 0748-4658 10.2514/1.B37490 D.Pampaloni A.Andreini B.Faccini C. O.Paschereit article Holst_2019 Journal of Engineering for Gas Turbines and Power 2019 141 10 The wind industry needs airfoil data for ranges of angle of attack (AoA) much wider than those of aviation applications, since large portions of the blades may operate in stalled conditions for a significant part of their lives. Vertical axis wind turbines (VARTs) are even more affected by this need, since data sets across the full incidence range of 180 deg are necessary for a correct performance prediction at different tip-speed ratios. However, the relevant technical literature lacks data in deep and poststall regions for nearly every airfoil. Within this context, the present study shows experimental and numerical results for the well-known NACA 0021 airfoil, which is often used for Darrieus VAWT design. Experimental data were obtained through dedicated wind tunnel measurements of a NACA 0021 airfoil with surface pressure taps, which provided further insight into the pressure coefficient distribution across a wide range of AoAs. The measurements were conducted at two different Reynolds numbers (Re = 140 k and Re = 180 k): each experiment was performed multiple times to ensure repeatability. Dynamic AoA changes were also investigated at multiple reduced frequencies. Moreover, dedicated unsteady numerical simulations were carried out on the same airfoil shape to reproduce both the static polars of the airfoil and some relevant dynamic AoA variation cycles tested in the experiments. The solved flow field was their exploited both to get further insight into the flow mechanisms highlighted by the wind tunnel tests and to provide correction factors to discard the influence of the experimental apparatus, making experiments representative of open-field behavior. The present study is then thought to provide the scientific community with high quality, low-Reynolds airfoil data, which may enable in the near future a more effective design of Darrieus VAWTs. GTP-18-1435 Airfoils, Computational fluid dynamics, Flow (Dynamics), Pressure, Reynolds number, Simulation, Wind tunnels, Blades, Cycles, Engineering simulation https://doi.org/10.1115/1.4041150 0742-4795 10.11115/1.4041150 D.Holst F.Balduzzi A.Bianchini B.Church F.Wegner G.Pechlivanoglou L.Ferrari G.Ferrara C. N.Nayeri C. O.Paschereit article Eulalie2018 International Journal of Numerical Methods for Heat & Fluid Flow 2018 Purpose This research paper presents an experimental investigation of an active flow control solution mounted at rear of a Sport Utility vehicle (SUV) with the objective of drag reduction, thanks to a selection of flow control parameters leading to a pressure increase on the tailgate. Design/methodology/approach A flow control design of experiments was conducted with a pulsed jet system mounted on the top and sides of the rear window of the vehicle. The wall pressure, instantaneous velocity and drag were measured with this prototype in a wind tunnel. A Dynamic Modal Decomposition (DMD) analysis of the pressure enables to describe the pressure fluctuations. Fluid Dynamic Computations show relation between pressure and velocity fields. Findings Measurements with this prototype in the wind tunnel revealed small improvements in drag for the best flow control configurations. This small benefit is due to the core of the upper span wise vortex further away from the rear window than the lower span wise vortex. These small improvements in drag were confirmed with pressure measurements on the rear window and tailgate. The DMD analysis of the surface pressure showed a low frequency pendulum oscillation on the lower area of the tailgate, linked with low velocity frequencies in the shear layers near the tailgate. Originality/value Experimental and numerical results show interest to increase pressure at bottom of the rear end of this SUV prototype. The dynamic description of the wall pressure shows importance of flow control solutions reducing pressure fluctuations at low frequencies in the lower area of the tailgate. https://www.emeraldinsight.com/doi/abs/10.1108/HFF-06-2017-0230# 0961-5539 10.1108/hff-06-2017-0230 Y.Eulalie E.Fournier Ph.Gilotte D.Holst S.Johnson C. N.Nayeri Th.Schütz D.Wieser article Marten2018 Aerospace Research Central 2018 A model to assess the performance of active trailing edge flaps on wind turbine blades has recently been integrated with a Liftigng Line Free Vortex Wake code. Successively the codes ability, to accurately predict the effect of trailing edge flaps on the rotor performance and loads in a steady inflow setting was validated with results from tools of ranging fidelity performance in a more complicated setting including yawed inflow was then carried out. For the second benchmark, results between the vortex code, a CFD code and experimental measurements obtained from a model wind turbine were compared. This comparison also highlights the influence of the wind tunnel walls on the experimental results and shows how the free vortex code can predict the experimental results without explicitly including a model o the wind tunnel. AIAA SciTech Forum 2018 Wind Energy Symposium, Kissimmee, Florida https://arc.aiaa.org/doi/10.2514/6.2018-1246 10.2514/6.2018-1246 D.Marten S.Bartholomay G.Pechlivanoglou C. N.Nayeri C. O.Paschereit A.Fischer Th.Lutz inproceedings Holst2018a 2018 6 12 The wind industry needs airfoil data for ranges of Angle of Attack (AoA) much wider than those of aviation applications, since large portions of the blades may operate in stalled conditions for a significant part of their lives. Vertical axis wind turbines (VAWTs) are even more affected by this need, since data sets across the full incidence range of 180 degree are necessary for a correct performance prediction at different tip-speed ratios. However, the relevant technical literature lacks data in deep and post stall regions for nearly every airfoil. Within this context, the present study shows experimental and numerical results for the well-known NACA 0021 airfoil, which is often used for Darrieus VAWT design. Experimental data were obtained through dedicated wind tunnel measurements of a NACA 0021 airfoil with surface pressure taps, which provided further insight into the pressure coefficient distribution across a wide range of AoAs. The measurements were conducted at two different Reynolds umbers (Re=140k and Re=180k): each experiment was performed multiple times to ensure repeatability. Dynamic AoA changes were also investigated at multiple reduced frequencies. Moreover, dedicated unsteady numerical simulations were carried out on the same airfoil shape to reproduce both the static polars of the airfoil and some relevant dynamic AoA variation cycles tested in the experiments. The solved flow fieldwas then exploited both to get further insight into the flow mechanisms highlighted by the wind tunnel tests and to provide correction factors to discard the influence of the experimental apparatus, making experiments representative of open-field behaviour. The present study is then thought to provide the scientific community with high quality, low-Reynolds airfoil data, which may enable in the near future a more effective design of Darrieus VAWTs. GT2018-75426 https://www.asme.org/events/turbo-expo2018 ASME Proceedings of ASME Turbo Expo 2018 Turbomachinery Technical Conference and Exposition Proceedings of the ASME Turbo Expo 2018 ASME D.Holst F.Balduzzi A.Bianchini B.Church F.Wegner G.Pechlivanoglou L.Ferrari G.Ferrara C. N.Nayeri C. O.Paschereit inbook Menzel2017 2017 430 - 434 http://www.etz.de/files/10_02_menzel-holst-fischer.pdf Rahman J., Heinze R. VDE Verlag Forschung und Lehre in Virtuelle Instrumente in der Praxis 2017 978-3-800-4441-1 C.Menzel D.Holst J.Fischer C. N.Nayeri C. O.Paschereit article Marten2016 ASME 2016 139 2 9 Interest in vertical-axis wind turbines (VAWTs) is experiencing a renaissance after most major research projects came to a standstill in the mid 1990s, in favor of conventional horizontal-axis turbines (HAWTs). Nowadays, the inherent advantages of the VAWT concept, especially in the Darrieus configuration, may outweigh their disadvantages in specific applications, like the urban context or floating platforms. To enable these concepts further, efficient, accurate, and robust aerodynamic prediction tools and design guidelines are needed for VAWTs, for which low-order simulation methods have not reached yet a maturity comparable to that of the blade element momentum theory for HAWTs' applications. The two computationally efficient methods that are presently capable of capturing the unsteady aerodynamics of Darrieus turbines are the double multiple streamtubes (DMS) theory, based on momentum balances, and the lifting line theory (LLT) coupled to a free vortex wake model. Both methods make use of tabulated lift and drag coefficients to compute the blade forces. Since the incidence angles range experienced by a VAWT blade is much wider than that of a HAWT blade, the accuracy of polars in describing the stall region and the transition toward the “thin plate like” behavior has a large effect on simulation results. This paper will demonstrate the importance of stall and poststall data handling in the performance estimation of Darrieus VAWTs. Using validated CFD simulations as a baseline, comparisons are provided for a blade in VAWT-like motion based on a DMS and a LLT code employing three sets of poststall data obtained from a wind tunnel campaign, XFoil predictions extrapolated with the Viterna–Corrigan model and a combination of them. The polar extrapolation influence on quasi-steady operating conditions is shown and azimuthal variations of thrust and torque are compared for exemplary tip-speed ratios (TSRs). In addition, the major relevance of a proper dynamic stall model into both the simulation methods is highlighted and discussed. Paper No: GTP-16-1286 http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=2541658&resultClick=3 10.1115/1.4034326 D.Marten S.Bianchini G.Pechlivanoglou F.Balduzzi C. N.Nayeri G.Ferrara C. O.Paschereit L.Ferrari inproceedings Marten2016b 2016 9 11 Interest in vertical-axis wind turbines (VAWTs) is experiencing a renaissance after most major research projects came to a standstill in the mid 90’s, in favour of conventional horizontal-axis turbines (HAWTs). Nowadays, the inherent advantages of the VAWT concept, especially in the Darrieus configuration, may outweigh their disadvantages in specific applications, like the urban context or floating platforms. To enable these concepts further, efficient, accurate, and robust aerodynamic prediction tools and design guidelines are needed for VAWTs, for which low-order simulation methods have not reached yet a maturity comparable to that of the Blade Element Momentum Theory for HAWTs’ applications. The two computationally efficient methods that are presently capable of capturing the unsteady aerodynamics of Darrieus turbines are the Double Multiple Streamtubes (DMS) Theory, based on momentum balances, and the Lifting Line Theory (LLT) coupled to a free vortex wake model. Both methods make use of tabulated lift and drag coefficients to compute the blade forces. Since the incidence angles range experienced by a VAWT blade is much wider than that of a HAWT blade, the accuracy of polars in describing the stall region and the transition towards the “thin plate like” behaviour has a large effect on simulation results. This paper will demonstrate the importance of stall and post-stall data handling in the performance estimation of Darrieus VAWTs. Using validated CFD simulations as a baseline, comparisons are provided for a blade in VAWT-like motion based on a DMS and a LLT code employing three sets of post-stall data obtained from a wind tunnel campaign, XFoil predictions extrapolated with the Viterna-Corrigan model and a combination of them. The polar extrapolation influence on quasi-steady operating conditions is shown and azimuthal variations of thrust and torque are compared for exemplary tip-speed ratios (TSRs). In addition, the major relevance of a proper dynamic stall model into both simulation methods is highlighted and discussed. Paper No. GT2016-56685, pp. V009T46A007 http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2555663 Seoul, South Korea, June 13–17, 2016 Oil and Gas Applications; Supercritical CO2 Power Cycles; Wind Energy ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition ASMe 10.1115/GT2016-56685 D.Marten A.Bianchini G.Pechlivanoglou F.Balduzzi C. N.Nayeri G.Ferrara C. O.Paschereit L.Ferrari 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 article Darvish2015a Journal of Turbomachinery 2015 137 10 TURBO-15-1063 101500-1 (9 pages) ASME 0889-504X 10.1115/1.4030498 M.Darvish S.Frank C. O.Paschereit article GokeSTRGKFGP2014 Journal of Engineering for Gas Turbines and Power 2014 139 091508 1-8 http://gasturbinespower.asmedigitalcollection.asme.org/article.aspx?articleid=1838118&resultClick=1 0742-4795 10.1115/1.4026942 S.Göke S.Schimek S.Terhaar T. G.Reichel K.Göckeler O.Krüger J.Fleck P.Griebel C. O.Paschereit article Goeke2012b Fuel Processing Technology 2013 107 14-22 http://www.sciencedirect.com/science/article/pii/S0378382012002408 Goeke_FuProc2012.pdf 0378-3820 10.1016/j.fuproc.2012.06.019 S.Göke M.Füri G.Bourque B.Bobusch K.Göckeler O.Krüger S.Schimek S.Terhaar C. O.Paschereit inproceedings Cosic2012d 2013 ASME paper GT2013-94782 V01AT04A056 (11 pages) Proc. ASME Turbo Expo 2013, June 3-7, San Antonio, Texas, USA 978-0-7918-5510-2 10.1115/GT2013-94782 S.Göke S.Schimek S.Terhaar T. G.Reichel K.Göckeler O.Krüger J.Fleck P.Griebel C. O.Paschereit inproceedings Hodzic2013 2013 AIAA paper 2013-3080 1--13 http://arc.aiaa.org/doi/abs/10.2514/6.2013-3080 American Institute of Aeronautics and Astronautics 21th AIAA Computational Fluid Dynamics Conference, June 24-27, 2013, San Diego, California, USA 10.2514/6.2013-3080 E.Hodizc C.Duwig R.Szasz O.Krüger L.Fuchs inproceedings Goeke2012a 2012 The Eleventh International Conference on Combustion and Energy Utilization (11th ICCEU) S.Göke M.Füri G.Bourque K.Göckeler O.Krüger B.Bobusch S.Schimek S.Terhaar C. O.Paschereit book Leutz2011 2011 8 Die vorliegende Gedenkschrift aus Anlass des 100. Geburtstages von Professor Dr.-Ing. Rudolf Wille zeichnet seinen beruflichen Werdegang nach und würdigt seine Verdienste als Hochschullehrer, Forscher, Reformer. Rudolf Wille war letzter Oberingenieur bei Professor Hermann Föttinger, hat dessen Institut nach dem Zusammenbruch 1945 wieder aufgebaut und „sein“ Hermann Föttinger Institut für Strömungsmechanik zu internationalem Ansehen geführt. In der schwierigen Zeit des Neubeginns der Technischen Universität Berlin hat sich Wille verdient gemacht, ebenso wie in den nicht minder schwierigen Zeiten um 1968, als er Prorektor der TU Berlin war. Die Vielzahl seiner Publikationen, Patente und von ihm betreute Promotionen, die im Anhang aufgelistet sind, zeugen von seiner hohen wissenschaftlichen Reputation. http://opus.kobv.de/tuberlin/volltexte/2011/3201/ Universitätsverlag TU Berlin 978-3-7983-2349-0 (online), 978-3-7983-2348-3 (print) H. H.Fernholz A.Leutz inproceedings Kruger2011c 2011 AIAA paper 2011-3549 1--14 The isothermal flow dynamics of a generic swirl burner are studied employing large eddy simulation (LES). A sensitivity analysis was conducted, considering different mesh sizes and subgrid-scale models and the results were compared to experimental data. It was found that the overall influence of the computational grid and the subgrid-scale model was neglectable and the simulations were in line with the experiments. A dominant frequency was found in the turbulent kinetic energy spectrum representing a coherent structure. Moreover, by applying the proper orthogonal decomposition (POD) this structure could be identified as a convective helical instability. This helical instability and can be represented by a pair of modes, and is assumed to be triggered by a precessing vortex core (PVC). 20th AIAA Computational Fluid Dynamics Conference, June 27-30, 2011, Honolulu, Hawaii, USA O.Krüger C.Duwig K.Göckeler S.Terhaar C.Strangfeld C. O.Paschereit L.Fuchs inproceedings Goeke2011b 2011 AIAA paper no. 2011-5535 47th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, San Diego, California, Jul 31 -- Aug 3 S.Göke S.Schimek A.Fateev S.Clausen P.Kuhn S.Terhaar C. O.Paschereit inproceedings Kruger2011b 2011 1--6 The present study employs large eddy simulations (LES) to investigate a generic swirl-stabilized burner operated with methane at ultra-wet conditions. In order to investigate the reactive flow, a customized solver for handling low Mach number flows based on an implicit LES approach was developed. A reduced 4 steps / 7 species global scheme was used as combustion model . To compare the simulations with experiments, OH chemiluminescence pictures served as a reference. Kruger2011b.pdf Proceedings of the European Combustion Meeting 2011, Jun 29 – Jul 1, Cardiff, UK O.Krüger C.Duwig S.Göke C. O.Paschereit L.Fuchs inproceedings Kruger2011a 2011 ASME paper GT2011-45866 The present study focuses on the numerical investigation of a generic swirl-stabilized burner operated with methane at ultra-wet conditions. The burner is fed with a preheated homogeneous mixture formed by steam and air. As a set of operating conditions atmospheric pressure, inlet temperature of 673 K, equivalence ratio of 0: 85 and a steam content of 30% is applied. Large eddy simulations have been performed to investigate the flow features. In a first step the non-reacting flow field was in-vestigated with water as working medium. Comparison with Par-ticle Image Velocimetry (PIV) and Laser-Doppler Velocimetry (LDV) measurements conducted in a water tunnel facility showed that an excellent agreement within the experimental uncertainty is obtained for the flow field. A dominant frequency in the tur-bulent energy spectrum was identified, which corresponds to the motion associated with a precessing vortex core (PVC). In order to investigate the reactive flow in a second step, a customized solver for handling low Mach number reacting flows based on an implicit LES approach was developed. As reaction mechanism a reduced 4 steps / 7 species global scheme was used. To compare the simulations qualitatively with a wet flame, OH chemiluminescence pictures serve as a reference. The simula-tions showed a more compact flame compared to the OH pic-tures. Nevertheless, the prolongation and position of the flame were found to be reasonable. The reduced mechanism captures the main effects, such as the reduction of the peak and mean temperatures. Furthermore, the presence of a PVC in the react- ing flow could be determined and was not suppressed by heat- release. Proc. ASME Turbo Expo 2011: Advancing Clean and Efficient Turbine Technology (GT2011), June 6-10, Vancouver, BC, Canada O.Krüger C.Duwig S.Göke K.Göckeler C. O.Paschereit L.Fuchs inproceedings Pechlivanoglou2010b 2010 ASME paper no. GT2010-23258 845-855 The effects of distributed roughness on wind turbines are extensively investigated in this paper. The sources of roughness are identified and analyzed and their effects on airfoil are estimated from simulations and measured with wind tunnel measurements. In addition to the environmental and manufacturing induced roughness, several forms of roughness-related shape deviations are investigated and their effects on the aerodynamic performance of airfoils is qualitatively predicted through numerical simulations. The actual effects of roughness on wind turbine performance are also presented through power production measurements of wind turbines installed in sandy environments. These measurements are correlated with simulated power predictions, utilizing a steady state BEM code. http://link.aip.org/link/abstract/ASMECP/v2010/i44007/p845/s1 ASME Proc. ASME Turbo Expo 2010: Power for Land, Sea, and Air (GT2010), June 14–18, Glasgow, Scotland 978-0-7918-4400-7 10.1115/GT2010-23258 G.Pechlivanoglou S.Führ C. N.Nayeri C. O.Paschereit article Konle2009 International Journal of Spray and Combustion 2009 1 2 251-281 Thermo-acoustic investigations require reliable measurement techniques in hot environments for pressure, density fluctuations with a high dynamic range and acoustic particle velocity. This paper presents recent developments of optical measurement techniques in combustion diagnostics. A fibre-optic microphone based on the interferometric detection of membrane deflections was designed to measure acoustic pressure oscillations. Due to the heat resistant design, the sensor has an upper temperature limitation of approximately 970 K. Rayleigh-Scattering measurements, using the density dependent intensity of scattered light were performed in an unconfined flame with approximately 1600 K to study amplitude and phase distribution of the flame pulsation. Acoustic particle velocity can be determined applying acoustic PIV (particle image velocimetry) technique. This paper shows a way to measure simultaneously the acoustic particle velocity and the locally resolved mean flow velocity of a turbulent flow. Together these non-invasive techniques are applicable to study thermo-acoustic processes and sound generation in combustion chambers or turbines. http://lambda.qsensei.com/content/164v7m H. J.Konle A.Rausch A.Fischer U.Doll C.Willert C. O.Paschereit I.Röhle article Lacarelle2009b Journal of Engineering for Gas Turbines and Power 2009 131 3 031504-1 (12 pages) http://link.aip.org/link/?GTP/131/031504/1 ASME 0742-4795 0742-4795 (online), 1528-8919 (print) 10.1115/1.2982139 A.Lacarelle T.Faustmann D.Greenblatt C. O.Paschereit O.Lehmann D. M.Luchtenburg B. R.Noack inproceedings Lacarelle2008a 2008 Volume 3: Combustion, Fuels and Emissions, Parts A and B Paper no. GT2008-50970 735-748 Proc. of GT2008, ASME Turbo Expo 2008: Power for Land, Sea and Air, 9-13 June 2008, Berlin, Germany 978-0-7918-4313-0 10.1115/gt2008-50970 A.Lacarelle T.Faustmann D.Greenblatt C. O.Paschereit O.Lehmann D. M.Luchtenburg B. R.Noack inproceedings Gutmark2007 2007 AIAA paper no. 2007-3697 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), May 21-23, 2007, Rome, Italy E. J.Gutmark C. O.Paschereit D.Guyot A.Lacarelle J. P.Moeck S.Schimek T.Faustmann M. R.Bothien inproceedings Guyot2007b 2007 AIAA paper no. 2007-5630 43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, July 8-11, 2007, Cincinnati, OH, USA D.Guyot M. R.Bothien J. P.Moeck A.Lacarelle S.Schimek T.Faustmann C. O.Paschereit E. J.Gutmark article Paschereit2006 Journal of Turbomachinery 2006 128 4 679-688 C. O.Paschereit P.Flohr E. J.Gutmark article Bellucci2005 Journal of Turbomachinery 2005 127 2 372-379 V.Bellucci B.Schuermans D.Nowak P.Flohr C. O.Paschereit inbook Paschereit2005 2005 210 445-479 Lieuwen, T. C. and Yang, V. Published by AIAA Progress in Astronautics and Aeronautics Implementation of instability prediction in design: ALSTOM approaches C. O.Paschereit B.Schuermans V.Bellucci P.Flohr inproceedings Sonnenberger2005 2005 Proc. of the International Conference on Jets, Wakes and Separated Flows, Oct. 5-8, 2005, Mie, Japan R.Sonnenberger C. N.Nayeri H. H.Fernholz C. O.Paschereit article Bellucci2004 AIAA Journal 2004 42 8 1543-1549 V.Bellucci C. O.Paschereit P.Flohr inproceedings Schuermans2004 2004 2004-GT-53831 ASME Turbo Expo, June 14-17, 2004, Vienna, Austria B.Schuermans V.Bellucci F.Güthe P.Flohr C. O.Paschereit inproceedings Sonnenberger2004 2004 X 713-716 Andersson, H. I. and Krogstad, P. A. Advances in Turbulence R.Sonnenberger H. H.Fernholz C. O.Paschereit inproceedings Sonnenberger2004a 2004 10th European Turbulence Conference (ETC10), June 29-July 2, 2004, Norwegian University of Science and Technology, Trondheim, Norway R.Sonnenberger H. H.Fernholz C. O.Paschereit inproceedings Flohr2004 2004 Proc. of CHT-04, International Symposium on Advances in Computational Heat Transfer, CHT-04-233, April 19-24, 2004, Norway P.Flohr C. O.Paschereit inproceedings Schuermans2004a 2004 AIAA paper no. 2004-456 42nd AIAA Aerospace Sciences Meeting and Exhibit, January 5-8, 2004, Reno, Nevada, USA B.Schuermans V.Bellucci C. O.Paschereit P.Flohr inproceedings Flohr2003 2003 41st AIAA Aerospace Sciences Meeting and Exhibit, January 6-9, 2003, Reno, Nevada, USA P.Flohr C. O.Paschereit V.Bellucci inproceedings Paschereit2002 2002 2002-GT-30462 ASME Turbo Expo, June 3-6, 2002, Amsterdam, Netherlands C. O.Paschereit P.Flohr H.Knöpfel W.Geng C.Steinbach P.Stuber K.Bengtsson E. J.Gutmark inproceedings Flohr2002 2002 Proc. of IMECE, New Orleans, LA, USA P.Flohr P.Schmitt C. O.Paschereit inproceedings Flohr2002a 2002 ASME International Mechanical Engineering Congress and Exposition, Symposium on Computational Modeling of Industrial Combustion Systems, November 17-22, 2002, New Orleans, LO P.Flohr C. O.Paschereit inproceedings Bellucci2002 2002 ASME Turbo Expo, June 3-6, 2002, Amsterdam, Netherlands. V.Bellucci C. O.Paschereit D.Tabacco P.Flohr inproceedings Paschereit2001c 2001 39th AIAA Aerospace Science Meeting and Exhibit, January 8-11, 2001, Reno, Nevada, USA C. O.Paschereit P.Flohr B.Schuermans inproceedings Bellucci2001 2001 ASME Turbo Expo, June 4-6, 2001, New Orleans, Louisiana, USA V.Bellucci C. O.Paschereit P.Flohr F.Magni inproceedings Paschereit2001d 2001 AIAA paper no. 2001-484 39th AIAA Aerospace Science Meeting and Exhibit, January 8-11, 2001, Reno, Nevada, USA C. O.Paschereit P.Flohr B.Schuermans inproceedings Bellucci2001a 2001 AIAA paper no. 2001-2794 31st AIAA Fluid Dynamics Conference (Aeroacoustics Section), June 11-14, 2001, Anaheim, California, USA V.Bellucci C. O.Paschereit P.Flohr B.Schuermans inproceedings Flohr2001 2001 ASME Turbo Expo, June 4-6, 2001, New Orleans, Louisiana P.Flohr C. O.Paschereit B.van Roon inproceedings Paschereit2000b 2000 Ziada, Staubli, Flow Induced Vibrations, Balkema C. O.Paschereit P.Flohr W.Polifke M.Bockholts inproceedings Paschereit2000d 2000 6th AIAA/CEAS Aeroacoustics Conference, June 12-14, 2000, Maui, Hawaii C. O.Paschereit P.Flohr E. J.Gutmark L.Haber article Fiedler1998 Experimental Thermal and Fluid Science 1998 16 3-21 10.1016/s0894-1777(97)10003-6 H. E.Fiedler C. N.Nayeri R.Spieweg C. O.Paschereit article Paschereit1995a Journal of Fluid Mechanics 1995 283 365-407 C. O.Paschereit I.Wygnanski H. E.Fiedler inbook Paschereit1993a 1993 21 115-123 Bonnet, J. P. and Glauser, M. N. Kluwer Academics, Dordrecht/ Boston/ London Fluid Mechanics and its Applications On the influence of initial parameters on subharmonic resonance in an axisymmetric jet C. O.Paschereit H. E.Fiedler I.Wygnanski inproceedings Paschereit1993b 1993 Bulletin of the American Physical Society/ Division of Fluid Dynamics, 46th Annual Meeting, Albuquerque, New Mexico, USA C. O.Paschereit H. E.Fiedler article Paschereit1992 Experiments in Fluids 1992 12 3 189-199 Springer-Verlag 0723-4864 (print), 1432-1114 (online) 10.1007/BF00188258 C. O.Paschereit D.Oster T. A.Long H. E.Fiedler I.Wygnanski article Fiedler1990 Progress in Aerospace Sciences 1990 27 4 305-387 Concepts of turbulent flow control have become of growing importance during the last few years, following increased interest in the detailed structural scenario of turbulence—in particular our improved understanding of coherent structures on the one hand (the prerequisite), and a need for improvement of technological processes on the other (the goal). These considerations have mainly been followed by engineers and physicists concerned with problems in aerodynamics. It is our aim to draw the attention of a wider group of engineers to turbulent flow control in order to speed up the transfer of knowledge from aerodynamics to applications in other fields of engineering. In this paper an attempt is made to compile a major body of the available knowledge on flow control in separated and wall bounded turbulent flows. After a brief introduction of the basics of control theory (Section 2) and of the major flow structures and their stability characteristics (Section 3) free and wall bounded turbulent shear flows are discussed (Sections 4 and 5). This discussion summarizes the main relationships between structure and flow behaviour and shows possibilities of influencing properties of these flows such as increasing mixing or avoiding separation. http://www.sciencedirect.com/science/article/pii/0376042190900022 0376-0421 10.1016/0376-0421(90)90002-2 H. E.Fiedler H. H.Fernholz inproceedings Paschereit1989a 1989 2 467-471 Fernholz, H. H. and Fiedler, H. E. Springer Verlag, Berlin Advances in Turbulence C. O.Paschereit M.Schüttpelz H. E.Fiedler article Fiedler1988 Progress in Aerospace Sciences 1988 25 3 231-269 Coherent structures—loosely defined as regions of concentrated vorticity, characteristic and flow-specific organization, recurrence, appreciable lifetime and scale—have been the foremost object of scientific curiosity and dispute in turbulence research for more than ten years past. The concept, based on visual observations, that turbulence, hitherto viewed as a purely random phenomenon, appears to contain a constituent of clearly organized structure promised an alternative to the frustrating verdict that turbulence can only be understood and tackled on statistical grounds. After a first period of enthusiasm, which was then nourished by a few supportive survey papers, the concept was challenged and criticism as to the uniqueness, the ubiquity and finally the importance of those structures was put forward. Although a great number of turbulent flow configurations—essentially all of ‘classical’ flows—have to some extent been investigated and scrutinized for their content of structural organization, many questions remain open and the dispute is by no means settled. In this review we shall restrict ourselves to trying to summarize a few of the more important results and issues without trying to settle this argument. At the same time some open questions will be discussed. Meanwhile an abundance of knowledge has been collected on some free flows, in particular the mixing layer, the wake and—to a lesser extent—the turbulent far jet. All free flows undergo at least one transformation before they become self-similar and unique (do they indeed become unique?). Thus, the mixing layer is the eventual outcome of the transformation of the boundary layer flow from the nozzle. Jets and wakes in their early stages go through intermediate mixing-layer manifestations. Little wonder that also in those cases we often find more than one characteristic structure. Different structural developments appear to be related to different behaviours of the basic flow: The more complex structures, characterized by three-dimensional (Reynolds number and/or lifetime-dependent) agglomerations of hairpin, ring and spiral vortices as in a spot or a puff, are found in those flows which are primarily frictionally unstable (wall flows). Particularly in the boundary layer, we observe a whole zoo of structures, some of which (e.g. the wall streaks) clearly violate the obviously too limiting ‘classical” definition of coherent structures being exclusively ‘large scale’ events. Consequently, as much as these findings undoubtedly add to our understanding of turbulent processes, the concept of coherent structures forfeits some of its original meaning for a more refined picture, the larger the structural multitude becomes. In those flows where inviscid (inflection-point) instability dominates, we find comparatively simpler structures of large scales like single line or ring vortices as in mixing-layer, jet and wake flows, with three-dimensionalities following secondary instabilities. But also there we find the corresponding ‘small scale structures’, longitudinal vortices along the interconnecting braids between the large-scale structures. The common aspect then for all shear flows seems to be the existence of at least two coherent scales, the small one with longitudinal (stretched) vortices being responsible for turbulence-energy production, while the large scale takes care of part of the diffusion. An independent aspect is introduced by the consideration of spiral turbulence as being an intrinsic feature of turbulence eventually leading to the formation of coherent structures in all three-dimensional flows. Formation of coherent structures, as we observe it, touches on a phenomenon of greater generality and significance: spontaneous formation of organized structures from a state of relative disorder is found in organic as well as in inorganic nature. This process is known as Synergetic, and chaos theory is but one of the theoretical tools of this discipline. It is evident that organized structures could not be observed or educed by methods applying any indiscriminate averaging scheme such as Reynolds-averaging. As a consequence, after existence of those structures was evident from visualization, adequate techniques had to be developed to educe repetitive flow events of a certain similarity. The true fraction of coherent energy in the overall turbulent energy can, however, not possibly be assessed with any claim to accuracy. Estimates (their reliability supported by the fact that different methods give similar numbers) show the coherent structures to be responsible for between 10% and 25% of the turbulent energy in most of the flows considered (contrary to Townsend's “big eddies” whose energy content was assumed to be essentially negligible). This figure emphasizes the importance of coherent structures in correctly modelling turbulent flows and, even more so, as a medium to manipulate turbulence (by mechanical, acoustical or chemical means) and thereby influence its most notable technical consequences: noise, mixing, combustion and drag. http://www.sciencedirect.com/science/article/pii/0376042188900012 0376-0421 10.1016/0376-0421(88)90001-2 H. E.Fiedler