Control of a laminar separating boundary layer by induced stationary perturbations

Бойко, А. В.; Dovgal, A. V.; Hein, Stefan

doi:10.1016/j.euromechflu.2007.09.005

Cited by 11 publications

(3 citation statements)

References 27 publications

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“…Transitional and turbulent boundary layers have long attracted the attention of the flow control community (see e.g. Joslin 1998;Kim 2003;Saric, Reed & White 2003;Archambaud et al 2008;Boiko, Dovgal & Hein 2008), mainly as a result of their ubiquity in vehicle aerodynamics and their central role as the source of skin friction. For all three examples, flow control techniques that effectively eliminate instabilities, efficiently reduce noise amplification or successfully diminish drag are essential in maintaining the desired flow conditions.…”

Section: Introductionmentioning

confidence: 99%

Closed-loop control of unsteadiness over a rounded backward-facing step

et al. 2012

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International audienceThe two-dimensional, incompressible flow over a rounded backward-facing step at Reynolds number Re = 600 is characterized by a detachment of the flow close to the step followed by a recirculation zone. Even though the flow is globally stable, perturbations are amplified as they are convected along the shear layer, and the presence of upstream random noise renders the flow unsteady, leading to a broadband spectrum of excited frequencies. This paper is aimed at suppressing this unsteadiness using a controller that converts a shear-stress measurement taken from a wall-mounted sensor into a control law that is supplied to an actuator. A comprehensive study of various components of closed-loop control design - covering sensor placement, choice and influence of the cost functional, accuracy of the reduced-order model, compensator stability and performance - shows that successful control of this flow requires a judicious balance between estimation speed and estimation accuracy, and between stability limits and performance requirements. The inherent amplification behaviour of the flow can be reduced by an order of magnitude if the above-mentioned constraints are observed. In particular, to achieve superior controller performance, the estimation sensor should be placed upstream near the actuator to ensure sufficient estimation speed. Also, if high-performance compensators are sought, a very accurate reduced-order model is required, especially for the dynamics between the actuator and the estimation sensor; otherwise, very minute errors even at low energies and high frequencies may render the large-scale compensated linearized simulation unstable. Finally, coupling the linear compensator to nonlinear simulations shows a gradual deterioration in control performance as the amplitude of the noise increases

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Section: Introductionmentioning

confidence: 99%

Closed-loop control of unsteadiness over a rounded backward-facing step

et al. 2012

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“…The effect of mean flow deformation is inherently a nonlinear effect: considering the Navier-Stokes equations for the mean flow, it can be seen that MFD is caused through the action of the Reynolds stress terms. Boiko, Dovgal & Hein (2008) investigated the effect of steady spanwise perturbations in the separated flow behind a backward-facing step. They found a spanwise-modulated modification of mean velocity gradients of the separated flow.…”

Section: Introductionmentioning

confidence: 99%

Mean flow deformation in a laminar separation bubble: separation and stability characteristics

Marxen

Rist

2010

J. Fluid Mech.

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The mutual interaction of laminar–turbulent transition and mean flow evolution is studied in a pressure-induced laminar separation bubble on a flat plate. The flat-plate boundary layer is subjected to a sufficiently strong adverse pressure gradient that a separation bubble develops. Upstream of the bubble a small-amplitude disturbance is introduced which causes transition. Downstream of transition, the mean flow strongly changes and, due to viscous–inviscid interaction, the overall pressure distribution is changed as well. As a consequence, the mean flow also changes upstream of the transition location. The difference in the mean flow between the forced and the unforced flows is denoted the mean flow deformation. Two different effects are caused by the mean flow deformation in the upstream, laminar part: a reduction of the size of the separation region and a stabilization of the flow with respect to small, linear perturbations. By carrying out numerical simulations based on the original base flow and the time-averaged deformed base flow, we are able to distinguish between direct and indirect nonlinear effects. Direct effects are caused by the quadratic nonlinearity of the Navier–Stokes equations, are associated with the generation of higher harmonics and are predominantly local. In contrast, the stabilization of the flow is an indirect effect, because it is independent of the Reynolds stress terms in the laminar region and is solely governed by the non-local alteration of the mean flow via the pressure.

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“…Various studies in the field of active and passive control mechanisms over backward-facing step have been conducted by different authors. Passive control mechanisms include the use of permeable re-attachment surface [ 7 , 8 ], surface hump [ 9 ], step height [ 10 ], cavities [ 11 ], and porous surfaces [ 12 ]. In the field of active flow control through an area of the boundary, Ravindran [ 4 ] explored the possibility of developing POD-based reduced order models for the control of laminar separation flow over a forward-facing step with a Reynolds number of 1000.…”

Section: Introductionmentioning

confidence: 99%

Feedback control of laminar flow behind backward-facing step by POD analysis and using perturbed Navier–Stokes equations

Zare

Emdad

Rad

2011

Proceedings of the Institution of Mechanical Engineers, Part C:

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The purpose of this article is to design a reduced order model based on the proper orthogonal decomposition/Galerkin projection and perturbation method to develop a non-autonomous model. The resulting model can be used in optimal control of flow over backward-facing step. The main disadvantage of the proper orthogonal decomposition approach for control purposes is that, controlling parameters or inputs do not show up explicitly in the resulting reduced order system. The perturbation method can solve this problem and insert control inputs in the resulting system. The resulting system captures the time-varying influence of the controlling parameters and precisely predicts the Navier–Stokes response to external excitations. At last, optimal control theory is introduced to design a control law for a non-linear forced reduced model, which attempts to minimize the vorticity content in the fluid domain. The test bed is laminar flow behind backward-facing step [Formula: see text] actuated by a pair of blowing/suction jets. Results show that the wall jet can significantly influence the flow field and delay separation, while the perturbation method can predict the flow field in an accurate manner. The method is also found to be fast and efficient in computational time.

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Control of a laminar separating boundary layer by induced stationary perturbations

Cited by 11 publications

References 27 publications

Closed-loop control of unsteadiness over a rounded backward-facing step

Closed-loop control of unsteadiness over a rounded backward-facing step

Mean flow deformation in a laminar separation bubble: separation and stability characteristics

Feedback control of laminar flow behind backward-facing step by POD analysis and using perturbed Navier–Stokes equations

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