Optimal stabilization of a flow past a partially hydrophobic circular cylinder

Μαστρόκαλος, Μάριος; Papadopoulos, Christos I.; Kaiktsis, Lambros

doi:10.1016/j.compfluid.2014.11.010

Cited by 15 publications

(14 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These drag reduction percentages for this geometry are similar to previously published results 24 where drag reductions of 28% were achieved on cylinders in the same Reynolds number range as tested here. CFD simulations have also been conducted on cylinders 42 43 and have shown the effect of slip on cylinders. Other superhydrophobic geometries have led to drag reductions of 40% in microchannels 12 44 and 66% in a rheometer set-up 25 .…”

Section: Resultsmentioning

confidence: 99%

Flexible conformable hydrophobized surfaces for turbulent flow drag reduction

Brennan

Geraldi

Morris

et al. 2015

Sci Rep

View full text Add to dashboard Cite

In recent years extensive work has been focused onto using superhydrophobic surfaces for drag reduction applications. Superhydrophobic surfaces retain a gas layer, called a plastron, when submerged underwater in the Cassie-Baxter state with water in contact with the tops of surface roughness features. In this state the plastron allows slip to occur across the surface which results in a drag reduction. In this work we report flexible and relatively large area superhydrophobic surfaces produced using two different methods: Large roughness features were created by electrodeposition on copper meshes; Small roughness features were created by embedding carbon nanoparticles (soot) into Polydimethylsiloxane (PDMS). Both samples were made into cylinders with a diameter under 12 mm. To characterize the samples, scanning electron microscope (SEM) images and confocal microscope images were taken. The confocal microscope images were taken with each sample submerged in water to show the extent of the plastron. The hydrophobized electrodeposited copper mesh cylinders showed drag reductions of up to 32% when comparing the superhydrophobic state with a wetted out state. The soot covered cylinders achieved a 30% drag reduction when comparing the superhydrophobic state to a plain cylinder. These results were obtained for turbulent flows with Reynolds numbers 10,000 to 32,500.

show abstract

Section: Resultsmentioning

confidence: 99%

Flexible conformable hydrophobized surfaces for turbulent flow drag reduction

Brennan

Geraldi

Morris

et al. 2015

Sci Rep

View full text Add to dashboard Cite

show abstract

“…Helical strakes are often wrapped around long flexible pipelines that bring oil from the sea bottom so as to suppress unwanted flow-induced vibrations [7][8][9]. As an alternative to passively control the flow around a cylindrical structure, its surface can be fully or partially covered with hydrophobic or hairy-like microfiber coatings [10][11][12], or the geometry of the cylinder exterior be modified to have mild disturbances along its span [13,14].…”

Section: Flow Control Definitions and Preliminary Remarksmentioning

confidence: 99%

Active Control of Bluff-Body Flows Using Plasma Actuators

Konstantinidis

2019

Actuators

View full text Add to dashboard Cite

Actuators play an important role in modern active flow control technology. Dielectric barrier discharge plasma can be used to induce localized velocity perturbations in air, so as to accomplish modifications to the global flow field. This paper presents a selective review of applications from the published literature with emphasis on interactions between plasma-induced perturbations and original unsteady fields of bluff-body flows. First, dielectric barrier discharge (DBD)-plasma actuator characteristics, and the local disturbance fields these actuators induce into the exterior flow, are described. Then, instabilities found in separated flows around bluff bodies that controlled actuation should target at are briefly presented. Key parameters for effective control are introduced using the nominally two-dimensional flow around a circular cylinder as a paradigm. The effects of the actuator configuration and location, amplitude and frequency of excitation, input waveform, as well as the phase difference between individual actuators are illustrated through examples classified based on symmetry properties. In general, symmetric excitation at frequencies higher than approximately five times the uncontrolled frequency of vortex shedding acts destructively on regular vortex shedding and can be safely employed for reducing the mean drag and lift fluctuations. Antisymmetric and symmetric excitation at low frequencies of the order of the natural frequency can amplify the wake instability and increase the mean and fluctuating aerodynamic forces, respectively, due to vortex locking-on to the excitation frequency or its subharmonics. Results from several studies show that the geometry and arrangement of the electrodes is of utmost significance. Power consumption is typically very low, but the electromechanical efficiency can be optimized by input waveform modulation.

show abstract

“…The work was advanced subsequently to further consider the effects of particle-fluid viscosity ratio [35], finite Reynolds number [36], the presence of slip or no-slip walls [37] and even other particles [38]. Recently, the slip effect has been used to optimally control the wake of cylinder by carefully designing the distribution of slip region on the surface [39,40]. Daniello et al [41] further investigated the vortex-induced vibration (VIV) of a super-hydrophobic cylinder, while Van et al [42] considered the VIV of a three dimensional cylinder with one end fixed at the wall in a slip flow.…”

Section: Introductionmentioning

confidence: 99%

Numerical study on the sedimentation of single and multiple slippery particles in a Newtonian fluid

2017

View full text Add to dashboard Cite

The dynamics of a single or a group of slippery spheres settling under gravity in a Newtonian fluid is studied numerically. We focus particularly on the effect of particle surface slip on the sedimentation behavior. The flows containing moving slippery spheres are solved by a three-dimensional lattice Boltzmann model where a kinetic boundary condition is used to handle the slip phenomenon at the curved particle surface. The method is first validated by simulating the slip flow in a cylindrical tube, and the no-slip flows around one and two spheres settling in a container. The hydrodynamic behaviors of one, two and multiple slippery spheres settling under gravity are then investigated. The results for a single sphere show that the surface slip makes the sphere fall faster than a no-slip particle and the wall correction factor decreases as the level of particle-surface slip is increased, indicating a drag reduction caused by the slip condition. For two settling spheres, when the no-slip particle is placed below the slip one, the two spheres will enter into the kissing phase earlier; on the contrary, deploying the no-slip particle above the slip one, the DKT process does not occur beyond a critical slip level and initial gap distance. If the two spheres are both slippery, the settling dynamics are similar to the no-slip case, but the time duration of the kissing phase decreases. As for the sedimentation of multiple spheres, it is found that the initial geometric arrangement has a significant impact on the sedimentation behavior. In general, slippery spheres in a cluster will experience larger fluctuations in the vertical velocity and position in the accelerated-falling stage, and smaller fluctuations in the decelerated-falling stage.

show abstract

Optimal stabilization of a flow past a partially hydrophobic circular cylinder

Cited by 15 publications

References 40 publications

Flexible conformable hydrophobized surfaces for turbulent flow drag reduction

Flexible conformable hydrophobized surfaces for turbulent flow drag reduction

Active Control of Bluff-Body Flows Using Plasma Actuators

Numerical study on the sedimentation of single and multiple slippery particles in a Newtonian fluid

Contact Info

Product

Resources

About