Effect of bubble size on the microbubble drag reduction of a turbulent boundary layer

Kawamura, Takafumi; Moriguchi, Yasuhiro; Kato, Hiroharu; Kakugawa, Akira; Kodama, Y.

doi:10.1299/jsmemecjo.2002.7.0_55

Cited by 14 publications

(16 citation statements)

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“…Takahashi et al (2001) examined BDR at Re x as high as 25 million and found that variations in bubble size and boundary-layer thickness did not significantly influence the level of drag reduction. Kawamura et al (2003) found a similar insensitivity to bubble size for bubble radii of 250 to 1000 µm at similar Re x values. BDR studies have also involved axisymmetric bodies (Deutsch & Castano 1986;Clark & Deutsch 1991) and sea trials (Kodama et al 2000).…”

Section: Introductionsupporting

confidence: 53%

Bubble friction drag reduction in a high-Reynolds-number flat-plate turbulent boundary layer

et al. 2006

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Turbulent boundary layer skin friction in liquid flows may be reduced when bubbles are present near the surface on which the boundary layer forms. Prior experimental studies of this phenomenon reached downstream-distance-based Reynolds numbers ($Re_{x}$) of several million, but potential applications may occur at $Re_{x}$ orders of magnitude higher. This paper presents results for $Re_{x}$ as high as 210 million from skin-friction drag-reduction experiments conducted in the USA Navy's William B. Morgan Large Cavitation Channel (LCC). Here, a near-zero-pressure-gradient flat-plate turbulent boundary layer was generated on a 12.9 m long hydraulically smooth flat plate that spanned the 3 m wide test section. The test surface faced downward and air was injected at volumetric rates as high as 0.38 m$^{3}$ s$^{-1}$ through one of two flush-mounted 40 $\mu$m sintered-metal strips that nearly spanned the test model at upstream and downstream locations. Spatially and temporally averaged shear stress and bubble-image-based measurements are reported here for nominal test speeds of 6, 12 and 18 m s$^{-1}$. The mean bubble diameter was $\sim$300 $\mu$m. At the lowest test speed and highest air injection rate, buoyancy pushed the air bubbles to the plate surface where they coalesced to form a nearly continuous gas film that persisted to the end of the plate with near-100% skin-friction drag reduction. At the higher two flow speeds, the bubbles generally remained distinct and skin-friction drag reduction was observed when the bubbly mixture was closer to the plate surface than 300 wall units of the boundary-layer flow without air injection, even when the bubble diameter was more than 100 of these wall units. Skin-friction drag reduction was lost when the near-wall shear induced the bubbles to migrate from the plate surface. This bubble-migration phenomenon limited the persistence of bubble-induced skin-friction drag reduction to the first few metres downstream of the air injector in the current experiments.

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Section: Introductionsupporting

confidence: 53%

Bubble friction drag reduction in a high-Reynolds-number flat-plate turbulent boundary layer

et al. 2006

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“…Recent experimental studies in low-Re TBL flows (Kawamura et al 2003) confirm the importance of bubble size (and number density) in skin-friction drag reduction. Kawamura et al produced bubbles in two different size ranges using different injection methods.…”

Section: Introductionmentioning

confidence: 83%

Bubble-size distributions produced by wall injection of air into flowing freshwater, saltwater and surfactant solutions

et al. 2004

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As air is injected into a flowing liquid, the resultant bubble characteristics depend on the properties of the injector, near-wall flow, and flowing liquid. Previous research has shown that near-wall bubbles can significantly reduce skin-friction drag. Air was injected into the turbulent boundary layer on a test section wall of a water tunnel containing various concentrations of salt and surfactant (Triton-X-100, Union Carbide). Photographic records show that the mean bubble diameter decreased monotonically with increasing salt and surfactant concentrations. Here, 33 ppt saltwater bubbles had one quarter, and 20 ppm Triton-X-100 bubbles had one half of the mean diameter of freshwater bubbles.

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“…The influence of bubble size on BDR has been difficult to ascertain for high-Reynolds number flows. Moriguchi & Kato (2002) and Kawamura et al (2003) reported no change in drag reduction over a range of injected bubble sizes, all of which were much larger than the viscous length. Winkel et al (2004) and Elbing et al (2008) used saltwater and surfactants to reduce the average bubble size with little change far from the injector.…”

Section: Mechanisms and Persistence Of Bubble Drag Reductionmentioning

confidence: 92%

Friction Drag Reduction of External Flows with Bubble and Gas Injection

Ceccio

2010

Annu. Rev. Fluid Mech.

459

248

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The lubrication of external liquid flow with a bubbly mixture or gas layer has been the goal of engineers for many years, and this article presents the underlying principles and recent advances of this technology. It reviews the use of partial and supercavities for drag reduction of axisymmetric objects moving within a liquid. Partial cavity flows can also be used to reduce the friction drag on the nominally two-dimensional portions of a horizontal surface, and the basic flow features of two-dimensional cavities are presented. Injection of gas can lead to the creation of a bubbly mixture near the flow surface that can significantly modify the flow within the turbulent boundary layer, and there have been significant advances in the understanding of the underlying physical process of drag reduction. Moreover, with sufficient gas flux, the bubbles flowing beneath a solid surface can coalesce to form a thin drag-reducing air layer. The current applications of these techniques to underwater vehicles and surface ships are discussed.

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Effect of bubble size on the microbubble drag reduction of a turbulent boundary layer

Cited by 14 publications

References 0 publications

Bubble friction drag reduction in a high-Reynolds-number flat-plate turbulent boundary layer

Bubble friction drag reduction in a high-Reynolds-number flat-plate turbulent boundary layer

Bubble-size distributions produced by wall injection of air into flowing freshwater, saltwater and surfactant solutions

Friction Drag Reduction of External Flows with Bubble and Gas Injection

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