Model-based Coherent-structure Control of Turbulent Shear Flows Using Low-dimensional Vortex Models

Pastoor, Mark; King, Rudibert; Noack, Bernd R.; Dillmann, Andreas; Tadmor, Gilead

doi:10.2514/6.2003-4261

Cited by 26 publications

(13 citation statements)

References 12 publications

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“…A study of the authors based on a three-dimensional direct numerical simulation and refined vortex models of the backward-facing step confirm similar flow and particle behavior. 29 Hence, several conclusions from the present control study can be expected to qualitatively hold in real flows, e.g., that an increase of the frequency gives rise to a increase of the average residence time.…”

Section: Discussionmentioning

confidence: 88%

Optimal mixing in recirculation zones

et al. 2004

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Coarse-scale mixing in a recirculation zone is described with a simple vortex model. Time-dependent forcing is employed to change the vortex motion and mixing properties. An optimal mixing problem is defined in which the flux across the recirculation region shall be maximized under the side-constraints of bounded vortex motion and bounded actuation. Concepts of control theory and chaotic advection are used to achieve this goal. In particular, controllability is proven with a transformation into flat coordinates. Thus, a feedforward law for the optimal trajectory and a feedback law for its stabilization are derived. Observability of the vortex motion is indicated by a dynamic observer. Mixing in the optimized flow is studied using Poincaré maps. The low-frequency modulations to vortex motion are shown to substantially increase mixing in the average. Generalizations of the mathematical framework for mixing optimization are suggested for a larger class of models and flows.

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Section: Discussionmentioning

confidence: 88%

Optimal mixing in recirculation zones

et al. 2004

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“…Some recent control strategies are based on confined vortex models of actuated flow and on efficient methods of nonlinear control theory (Noack et al 2004a;Tadmor & Banaszuk 2002). However, the hybrid nature of open vortex models with continuous production, merging and elimination of vortices complicates the application of control theory methods (Pastoor et al 2003).…”

Section: Introductionmentioning

confidence: 99%

The need for a pressure-term representation in empirical Galerkin models of incompressible shear flows

2005

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Low-dimensional empirical Galerkin models are developed for spatially evolving laminar and transitional shear layers, based on a Karhunen-Loève decomposition of incompressible two-and three-dimensional Navier-Stokes simulations. It is shown that the key to an accurate Galerkin model is a novel analytical pressure-term representation. The effect of the pressure term is elucidated by a modal energy-flow analysis in a mixing layer, which generalizes the framework developed by Rempfer (1991). In convectively unstable shear layers, it is shown in particular that neglecting small energy terms leads to large amplitude errors in the Galerkin model. The effect of the pressure term and small neglected energy flows is very important for a twodimensional mixing layer, is less pronounced for the three-dimensional analogue, and can be considered as small in an absolutely unstable wake flow.

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“…These methods that are very robust and low-cost to simulate high Reynolds number recirculating flows (see for example [11], [26]), are more recently used to implement control techniques in fluid mechanics [24]. In this kind of approach, the VTE equation (4) is solved using a two-fractional step (or viscous splitting) method.…”

Section: Methodsmentioning

confidence: 99%

“…The main target of this control technique is to influence directly the vortex shedding and the main recirculation zone: the upper jet changes the shedding dynamics and the lower one perturbates and pushes away the recirculation zone. The flow around the step is characterized by the vortex shedding process and the roll-up of the separating boundary layer into Kelvin-Helmholtz type shear layer vortices [24]. Implementing actuators on two upper and lower levels of the step modifies both of the above characteristics and then is a useful control tool to study.…”

Section: Control With Active Jets On the Step Wallmentioning

confidence: 99%

Vortex simulation of active control strategies for transitional backward-facing step flows

Creusé

Giovannini²,

Mortazavi

2009

Computers & Fluids

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In this work a vortex method is used to simulate an incompressible two-dimensional transitional flow over a backward-facing step. The simulations are validated for two different Reynolds numbers comparing to previous studies. Then, two different control strategies are implemented to modify the shedding, the recirculation zone behind the step and the transport in the channel. The first technique consists in using a pulsing inlet velocity and the second one is based on local oscillating jets implemented on the step vertical wall. The influence of these controls on several characteristic functionals related to the flow is carefuly investigated. Both, openloop and closed-loop active control approaches are performed in order to choose the most efficient control methods.

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Model-based Coherent-structure Control of Turbulent Shear Flows Using Low-dimensional Vortex Models

Cited by 26 publications

References 12 publications

Optimal mixing in recirculation zones

Optimal mixing in recirculation zones

The need for a pressure-term representation in empirical Galerkin models of incompressible shear flows

Vortex simulation of active control strategies for transitional backward-facing step flows

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