Introduction to Flow Control

Gad‐el‐Hak, Mohamed

doi:10.1007/3-540-69672-5_1

Cited by 21 publications

(11 citation statements)

References 295 publications

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“…While the origin of opposition control is somewhat uncertain [11], the first simulations demonstrating this method are those of [5] who used DNS at Re τ = 180 reporting about 20% drag reduction when the sensing plane is located at y + s = 10. The more recent DNS by [14] shows that, again for Re τ = 180, the optimal sensing plane location is y + s = 15 which gives about 25% drag reduction.…”

Section: Review Of Opposition Controlmentioning

confidence: 99%

Variational Multiscale Modeling for Turbulence Control

Ramakrishnan

Collis

2002

1st Flow Control Conference

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We explore the capabilities of the variational multiscale (VMS) method in the context of turbulence control by applying VMS to the simulation of a simple opposition control strategy for turbulent channel flow with the results compared to prior direct numerical simulations and large-eddy simulations (LES). In all cases, the VMS method is found to be more efficient and more accurate than traditional LES with the dynamic subgrid-scale model. The simplicity, accuracy, and generality of VMS makes it particularly attractive for turbulence control investigations.

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Section: Review Of Opposition Controlmentioning

confidence: 99%

Variational Multiscale Modeling for Turbulence Control

Ramakrishnan

Collis

2002

1st Flow Control Conference

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“…To make the discussion concrete, we focus on one popular control strategy, opposition control, that has been extensively (and almost exclusively) studied using low Reynolds number DNS (Choi et al, 1994;Hammond et al, 1998). As such, the results presented here are not general in that they do not necessarily extend to other control strategies [see the review articles by (Gad-el-hak, 1998;Moin and Bewley, 1994;Lumley and Blossey, 1998) for discussions of other control strategies.] However, opposition control has been used both as a foundation upon which other (potentially more practical) control strategies are developed and as a reference against which other strategies are compared.…”

Section: Introductionmentioning

confidence: 99%

Viscous effects in control of near-wall turbulence

2002

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Prior studies of wall bounded turbulence control have utilized Direct Numerical Simulation (DNS) which has limited investigations to low Reynolds numbers where viscous effects may play an important role. The current paper utilizes Large Eddy Simulation (LES) with the dynamic subgrid-scale model to explore the influence of viscosity on one popular turbulence control strategy, opposition control, that has been extensively studied using low Reynolds number DNS. Exploiting the efficiency of LES, opposition control is applied to fully developed turbulent flow in a planar channel for turbulent Reynolds numbers in the range Re τ = 100 to 720. As Reynolds number increases, the predicted drag reduction drops from 30% at Re τ = 100 to 19% at Re τ = 720. Furthermore, the ratio of power saved to power input drops by more than a factor of four when Reynolds number increases over this range, indicating that the drag reduction mechanism in opposition control is indeed less effective at higher Reynolds numbers. However, for sufficiently high Reynolds numbers, Re τ > 400, the ratio of power saved to power input becomes constant at a value near 40 indicating that opposition control is a viable turbulence control strategy at high Reynolds numbers.

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“…Before reviewing the three classes of materials above, it is useful to examine the physical requirements that pressure sensors must meet to solve modern technological challenges. To our knowledge, the most stringent conditions are set by the need to image turbulent flow . Currently, the best pressure and shear stress sensors are micromachined in‐silico.…”

Section: Flexible Electronicsmentioning

confidence: 99%

“…They have dimensions of 100 microns and sensitivity of 50–500 kPa, which is inadequate . Imaging turbulence in the air boundary layer of an aircraft is an outstanding challenge, which calls for sensor arrays sampling pressure changes at a rate of 1 kHz, with sensitivity of at least 1 kPa, and spatial resolution better than 26 μm.…”

Section: Flexible Electronicsmentioning

confidence: 99%

Negative differential conductance materials for flexible electronics

Nogaret

2013

J of Applied Polymer Sci

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The need for electronics that is compatible with life is driving the search for electronically active materials that may be used for transferring integrated circuits onto flexible substrates. One route is to build transistors, which modulate the conductivity of organic thin films with a lateral gate. However, as is well known in the case of graphene, the in‐plane conductivity cannot easily be switched off. Another route is to use negative differential resistance (NDR) phenomena. Until recently, NDR was only obtained from band engineered semiconductors. This article reviews the recent development of flexible materials that specifically make use of transport perpendicular to graphite planes to obtain NDR. These materials include h‐boron‐nitride/graphene multilayers and graphite‐silicone composites. We report on the dependence of their current‐voltage curves on deformation, changes in structural and experimental parameters. We also describe device implementations in the form of flexible oscillators, amplifiers and memories. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40169.

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Introduction to Flow Control

Cited by 21 publications

References 295 publications

Variational Multiscale Modeling for Turbulence Control

Variational Multiscale Modeling for Turbulence Control

Viscous effects in control of near-wall turbulence

Negative differential conductance materials for flexible electronics

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