TY - JOUR A1 - Kaiser, Eurika A1 - Noack, Bernd R. A1 - Cordier, Laurent A1 - Spohn, Andreas A1 - Segond, Marc A1 - Abel, Markus A1 - Daviller, Guillaume A1 - Osth, Jan A1 - Krajnovic, Sinisa A1 - Niven, Robert K. T1 - Cluster-based reduced-order modelling of a mixing layer JF - Journal of fluid mechanics KW - low-dimensional models KW - nonlinear dynamical systems KW - shear layers Y1 - 2014 U6 - https://doi.org/10.1017/jfm.2014.355 SN - 0022-1120 SN - 1469-7645 VL - 754 SP - 365 EP - 414 PB - Cambridge Univ. Press CY - New York ER - TY - JOUR A1 - Parezanovic, Vladimir A1 - Cordier, Laurent A1 - Spohn, Andreas A1 - Duriez, Thomas A1 - Noack, Bernd R. A1 - Bonnet, Jean-Paul A1 - Segond, Marc A1 - Abel, Markus A1 - Brunton, Steven L. T1 - Frequency selection by feedback control in a turbulent shear flow JF - Journal of fluid mechanics N2 - Many previous studies have shown that the turbulent mixing layer under periodic forcing tends to adopt a lock-on state, where the major portion of the fluctuations in the flow are synchronized at the forcing frequency. The goal of this experimental study is to apply closed-loop control in order to provoke the lock-on state, using information from the flow itself. We aim to determine the range of frequencies for which the closed-loop control can establish the lock-on, and what mechanisms are contributing to the selection of a feedback frequency. In order to expand the solution space for optimal closed-loop control laws, we use the genetic programming control (CPC) framework. The best closed-loop control laws obtained by CPC are analysed along with the associated physical mechanisms in the mixing layer flow. The resulting closed-loop control significantly outperforms open-loop forcing in terms of robustness to changes in the free-stream velocities. In addition, the selection of feedback frequencies is not locked to the most amplified local mode, but rather a range of frequencies around it. KW - free shear layers KW - instability control KW - turbulence control Y1 - 2016 U6 - https://doi.org/10.1017/jfm.2016.261 SN - 0022-1120 SN - 1469-7645 VL - 797 SP - 247 EP - 283 PB - Cambridge Univ. Press CY - New York ER - TY - JOUR A1 - Parezanovic, Vladimir A1 - Laurentie, Jean-Charles A1 - Fourment, Carine A1 - Delville, Joel A1 - Bonnet, Jean-Paul A1 - Spohn, Andreas A1 - Duriez, Thomas A1 - Cordier, Laurent A1 - Noack, Bernd R. A1 - Abel, Markus A1 - Segond, Marc A1 - Shaqarin, Tamir A1 - Brunton, Steven L. T1 - Mixing layer manipulation experiment from open-loop forcing to closed-loop machine learning control JF - Flow, turbulence and combustion : an international journal published in association with ERCOFTAC KW - Shear flow KW - Turbulence KW - Active flow control KW - Extremum seeking KW - POD KW - Machine learning KW - Genetic programming Y1 - 2015 U6 - https://doi.org/10.1007/s10494-014-9581-1 SN - 1386-6184 SN - 1573-1987 VL - 94 IS - 1 SP - 155 EP - 173 PB - Springer CY - Dordrecht ER - TY - GEN A1 - Parezanović, Vladimir A1 - Cordier, Laurent A1 - Spohn, Andreas A1 - Duriez, Thomas A1 - Noack, Bernd R. A1 - Bonnet, Jean-Paul A1 - Segond, Marc A1 - Abel, Markus A1 - Brunton, Steven L. T1 - Frequency selection by feedback control in a turbulent shear flow T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Many previous studies have shown that the turbulent mixing layer under periodic forcing tends to adopt a lock-on state, where the major portion of the fluctuations in the flow are synchronized at the forcing frequency. The goal of this experimental study is to apply closed-loop control in order to provoke the lock-on state, using information from the flow itself. We aim to determine the range of frequencies for which the closed-loop control can establish the lock-on, and what mechanisms are contributing to the selection of a feedback frequency. In order to expand the solution space for optimal closed-loop control laws, we use the genetic programming control (CPC) framework. The best closed-loop control laws obtained by CPC are analysed along with the associated physical mechanisms in the mixing layer flow. The resulting closed-loop control significantly outperforms open-loop forcing in terms of robustness to changes in the free-stream velocities. In addition, the selection of feedback frequencies is not locked to the most amplified local mode, but rather a range of frequencies around it. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 572 KW - free shear layers KW - instability control KW - turbulence control Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-413693 SN - 1866-8372 IS - 572 ER - TY - GEN A1 - Kaiser, Eurika A1 - Noack, Bernd R. A1 - Cordier, Laurent A1 - Spohn, Andreas A1 - Segond, Marc A1 - Abel, Markus A1 - Daviller, Guillaume A1 - Osth, Jan A1 - Krajnovic, Sinisa A1 - Niven, Robert K. T1 - Cluster-based reduced-order modelling of a mixing layer T2 - Postprints der Universität Potsdam : Mathematisch Naturwissenschaftliche Reihe N2 - We propose a novel cluster-based reduced-order modelling (CROM) strategy for unsteady flows. CROM combines the cluster analysis pioneered in Gunzburger's group (Burkardt, Gunzburger & Lee, Comput. Meth. Appl. Mech. Engng, vol. 196, 2006a, pp. 337-355) and transition matrix models introduced in fluid dynamics in Eckhardt's group (Schneider, Eckhardt & Vollmer, Phys. Rev. E, vol. 75, 2007, art. 066313). CROM constitutes a potential alternative to POD models and generalises the Ulam-Galerkin method classically used in dynamical systems to determine a finite-rank approximation of the Perron-Frobenius operator. The proposed strategy processes a time-resolved sequence of flow snapshots in two steps. First, the snapshot data are clustered into a small number of representative states, called centroids, in the state space. These centroids partition the state space in complementary non-overlapping regions (centroidal Voronoi cells). Departing from the standard algorithm, the probabilities of the clusters are determined, and the states are sorted by analysis of the transition matrix. Second, the transitions between the states are dynamically modelled using a Markov process. Physical mechanisms are then distilled by a refined analysis of the Markov process, e. g. using finite-time Lyapunov exponent (FTLE) and entropic methods. This CROM framework is applied to the Lorenz attractor (as illustrative example), to velocity fields of the spatially evolving incompressible mixing layer and the three-dimensional turbulent wake of a bluff body. For these examples, CROM is shown to identify non-trivial quasi-attractors and transition processes in an unsupervised manner. CROM has numerous potential applications for the systematic identification of physical mechanisms of complex dynamics, for comparison of flow evolution models, for the identification of precursors to desirable and undesirable events, and for flow control applications exploiting nonlinear actuation dynamics. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 605 KW - low-dimensional models KW - nonlinear dynamical systems KW - shear layers Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-416113 SN - 1866-8372 IS - 605 SP - 365 EP - 414 ER -