Closed-loop separation control: An analytic approach

Alam, Mohammad-Reza; Liu, W.; Haller, George

doi:10.1063/1.2188267

Cited by 23 publications

(25 citation statements)

References 16 publications

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“…The wake dynamics depends strongly on whether the boundary layer at separation is laminar, transitional or turbulent and whether the flow disturbances are 2-D or 3-D. For a 2-D laminar separating boundary layer, the flow is said to be an "amplifier" flow and exhibits only convective instability. Numerical simulations of such flows have been used as a test-bed in several active control studies, in which simplification of the Navier-Stokes equations was either used as a basis for feedback controller design [9,10], or input-output models were used as a basis for feedforward controller design [11,12]. For a BFS whose separating boundary layer has 3-D flow fluctuations at sufficiently high Reynolds number, the wake flow exhibits global instability and is an "oscillator" flow; most previous studies agree on the existence of a shedding/step mode and a lower frequency flapping or bubble pumping mode [13][14][15].…”

mentioning

confidence: 99%

Reducing the pressure drag of a D-shaped bluff body using linear feedback control

Longa

Morgans

Dahan

2017

Theor. Comput. Fluid Dyn.

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The pressure drag of blunt bluff bodies is highly relevant in many practical applications, including to the aerodynamic drag of road vehicles. This paper presents theory revealing that a mean drag reduction can be achieved by manipulating wake flow fluctuations. A linear feedback control strategy then exploits this idea, targeting attenuation of the spatially integrated base (back face) pressure fluctuations. Large-eddy simulations of the flow over a D-shaped blunt bluff body are used as a test-bed for this control strategy. The flow response to synthetic jet actuation is characterised using system identification, and controller design is via shaping of the frequency response to achieve fluctuation attenuation. The designed controller successfully attenuates integrated base pressure fluctuations, increasing the time-averaged pressure on the body base by 38%. The effect on the flow field is to push the roll-up of vortices further downstream and increase the extent of the recirculation bubble. This control approach uses only body-mounted sensing/actuation and input-output model identification, meaning that it could be applied experimentally.

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mentioning

confidence: 99%

Reducing the pressure drag of a D-shaped bluff body using linear feedback control

Longa

Morgans

Dahan

2017

Theor. Comput. Fluid Dyn.

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“…Our results are directly applicable in unsteady separation control when combined with the analytic approach of Alam, Liu and Haller [1]. In that approach, the solution of the skin-friction equation (7) was controlled via two-point boundary actuation to satisfy the kinematic separation conditions of Haller [6].…”

Section: Discussionmentioning

confidence: 98%

“…The velocity derivative σ, however, was obtained from observations rather than from a model. We expect an improvement in the controller derived in [1] once the present RNS equations are used to obtain predictions for σ. This is explored in ongoing work.…”

Section: Discussionmentioning

confidence: 99%

Reduced Navier-Stokes Equations Near a Flow Boundary

Kılıç¹,

Jacobs²,

Haller³

2005

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We derive a hierarchy of PDEs for the leading-order evolution of wall-based quantities, such as the skin-friction and the wall-pressure gradient, in two-dimensional fluid flows. The resulting Reduced Navier-Stokes (RNS ) equations are defined on the boundary of the flow, and hence have reduced spatial dimensionality compared to the Navier-Stokes equations. This spatial reduction speeds up numerical computations and makes the equations attractive candidates for flow-control design. We prove that members of the RNS hierarchy are well-posed if appended with boundary-conditions obtained from wall-based sensors. We also derive the lowest-order RNS equations for three-dimensional flows. For several benchmark problems, our numerical simulations show close finite-time agreement between the solutions of RNS and those of the full Navier-Stokes equations.

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“…Our kinematic theory of two-dimensional separation (develop under prior AFOSR support) enables the design of controllers that reduce separation or reattachment zones to a required size [5]. We demonstrated this in direct numerical simulations of channel-and step flows.…”

Section: Two-dimensional Separation Controlmentioning

confidence: 94%

Control of Unsteady Separation: A Dynamical Systems Approach

Haller¹

2005

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Closed-loop separation control: An analytic approach

Cited by 23 publications

References 16 publications

Reducing the pressure drag of a D-shaped bluff body using linear feedback control

Reducing the pressure drag of a D-shaped bluff body using linear feedback control

Reduced Navier-Stokes Equations Near a Flow Boundary

Control of Unsteady Separation: A Dynamical Systems Approach

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