Thermal boundary layer near roughnesses in turbulent Rayleigh-Bénard convection: Flow structure and multistability

Salort, Julien; Liot, Olivier; Rusaouen, Eleonore; Seychelles, Fanny; Tisserand, Jean-Christophe; Creyssels, Mathieu; Castaing, B.; Chillà, Francesca

doi:10.1063/1.4862487

Cited by 53 publications

(71 citation statements)

References 52 publications

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“…The velocity fields are then computed using a cross-correlation PIV algorithm 282 O. Liot, J. Salort, R. Kaiser, R. du Puits and F. Chillà implemented in the CIVx software suite (Fincham & Delerce 2000), above and below the critical Nusselt number Nu c , and near several positions on the rough plate: on top of an obstacle, in a groove and inside a notch (see figure 4). The fluid inside the notch is almost at rest, as indirectly assumed by Salort et al (2014). Due to the limitations of our acquisition system, it is not possible to resolve the details of both the slow recirculation inside the notch and the much faster flow away from the plate.…”

Section: Velocity Measurementsmentioning

confidence: 99%

“…Indeed, the critical shear Reynolds number can be lowered in the presence of roughness (Schlichting & Gersten 2000).…”

mentioning

confidence: 99%

“…These observations led us to propose a simple model, which accounted for the observed global heat-transfer enhancements (Salort et al 2014). …”

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confidence: 99%

“…Our own previous experiment, carried out in Lyon, involved a 40 cm × 40 cm rectangular cell with a rough bottom plate and water as the working fluid (Salort et al 2014). The controlled roughness consisted in an array of obstacles 2 mm high and 5 mm × 5 mm square, evenly spaced every 1 cm.…”

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Boundary layer structure in a rough Rayleigh–Bénard cell filled with air

et al. 2015

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In this experimental work, the aim is to understand how turbulent thermal flows are enhanced by the destabilization of the boundary layers. Square-stud roughness elements have been added on the bottom plate of a rectangular Rayleigh-Bénard cell in air, to trigger instabilities in the boundary layers. The top plate is kept smooth. The cell proportions are identical to those of the water cell previously operated and described by Salort et al. (Phys. Fluids, vol. 26, 2014, 015112), but six times larger. The very large size of the Barrel of Ilmenau allows detailed velocity fields to be obtained using particle image velocimetry very close to the roughness elements. We found that the flow is quite different at low Rayleigh numbers, where there is no heat-transfer enhancement, and at high Rayleigh numbers where there is a heat-transfer enhancement due to the roughness. Below the transition, the fluid inside the notch, i.e. between the studs, is essentially at rest, though it is slowly recirculating. The velocity profiles on the top of obstacles and in grooves are fairly compatible with those obtained in the smooth case. Above the transition, on the other hand, we observe large incursions of the bulk inside the notch, and the velocity profiles on the top of obstacles are closer to the logarithmic profiles expected in the case of turbulent boundary layers.

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Section: Velocity Measurementsmentioning

confidence: 99%

“…Indeed, the critical shear Reynolds number can be lowered in the presence of roughness (Schlichting & Gersten 2000).…”

mentioning

confidence: 99%

“…These observations led us to propose a simple model, which accounted for the observed global heat-transfer enhancements (Salort et al 2014). …”

mentioning

confidence: 99%

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confidence: 99%

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Boundary layer structure in a rough Rayleigh–Bénard cell filled with air

et al. 2015

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“…some recent work [1][2][3][4][5][6][7][8], the reviews [9,10], and the textbooks [11,12]). Similarly, several studies have been conducted on turbulent thermal convection over rough plates [13][14][15][16][17][18][19][20]. The vast majority of these studies with rough walls adopt some ordered and symmetrical structures, such as pyramids, squares, rectangles etc.…”

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Controlling Heat Transport and Flow Structures in Thermal Turbulence Using Ratchet Surfaces

et al. 2018

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In this combined experimental and numerical study on thermally driven turbulence in a rectangular cell, the global heat transport and the coherent flow structures are controlled with an asymmetric ratchet-like roughness on the top and bottom plates. We show that, by means of symmetry breaking due to the presence of the ratchet structures on the conducting plates, the orientation of the Large Scale Circulation Roll (LSCR) can be locked to a preferred direction even when the cell is perfectly leveled out. By introducing a small tilt to the system, we show that the LSCR orientation can be tuned and controlled. The two different orientations of LSCR give two quite different heat transport efficiencies, indicating that heat transport is sensitive to the LSCR direction over the asymmetric roughness structure. Through a quantitative analysis of the dynamics of thermal plume emissions and the orientation of the LSCR over the asymmetric structure, we provide a physical explanation for these findings. The current work has important implications for passive and active flow control in engineering, bio-fluid dynamics, and geophysical flows.Turbulent convective flows over rough surfaces are ubiquitous in engineering and geophysical flows. Examples include convective flows in the atmosphere and in oceans, where the ground, sea-bed and ocean floor are generally not smooth. As the ability to enhance convective heat transfer is crucial in many industrial applications, numerous strategies have been proposed to efficiently enhance it. Among several approaches, introducing wall roughness is an effective way to do so. Indeed, the study of surface roughness effects in wall-bounded turbulent flows has been an area of intense research (see e.g. some recent work [1][2][3][4][5][6][7][8], the reviews [9,10], and the textbooks [11,12]). Similarly, several studies have been conducted on turbulent thermal convection over rough plates [13][14][15][16][17][18][19][20]. The vast majority of these studies with rough walls adopt some ordered and symmetrical structures, such as pyramids, squares, rectangles etc. However, the rough surfaces in engineering applications and in nature are in general not symmetric, resulting in complex interactions between the flow and the asymmetric roughness elements. Examples are wind blowing over a landscape with asymmetric slopes and ocean flows over an asymmetric sea-bed, etc. Other examples include marine animals which can actively change the asymmetric roughness for maneuverability.In this work, we aim to study the influences of ratchetlike wall structures on the flow organization and heat transfer in fully developed convective thermal turbulence. Indeed, building on the classical Feynman-Smoluchowski ratchet, in various contexts researchers have proposed ratchet-type mechanisms and devices that operate outside of thermal equilibrium [21]. Examples include the so-called 'capillary-ratchet' in zoology [22], a rotational ratchet in a granular gas [23], self-propelled Leidenfrost droplets and solids on ratchet sur...

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Massive heat transfer enhancement of Rayleigh-Bénard turbulence over rough surfaces and under horizontal vibration

Wang

Zhou

2022

Acta Mech. Sin.

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Thermal boundary layer near roughnesses in turbulent Rayleigh-Bénard convection: Flow structure and multistability

Cited by 53 publications

References 52 publications

Boundary layer structure in a rough Rayleigh–Bénard cell filled with air

Boundary layer structure in a rough Rayleigh–Bénard cell filled with air

Controlling Heat Transport and Flow Structures in Thermal Turbulence Using Ratchet Surfaces

Massive heat transfer enhancement of Rayleigh-Bénard turbulence over rough surfaces and under horizontal vibration

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