Frictional drag reduction by bubble injection

2014 ◽  
Vol 55 (7) ◽  
Author(s):  
Yuichi Murai
Keyword(s):  
Drag Reduction ◽  
Frictional Drag

Air Layer on Superhydrophobic Surface for Frictional Drag Reduction

2020 ◽  
Vol 64 (02) ◽  
pp. 118-126
Author(s):  
Bradley C. Peifer ◽  
Christopher Callahan-Dudley ◽  
Simo A. Makiharju
Keyword(s):  
Drag Reduction ◽  
Superhydrophobic Surface ◽  
Energy Savings ◽  
Surface Hydrophobicity ◽  
Net Energy ◽  
Frictional Drag ◽  
Gas Flux ◽  
Still Images ◽  
Painted Surface ◽  
Air Layer Drag Reduction

We examined the feasibility of combining a superhydrophobic surface (SHS) and air layer drag reduction (ALDR) to achieve the frictional drag reduction (DR) shown achievable with traditional ALDR, but at a reduced gas flux to increase the achievable net energy savings. The effect of a commercial SHS coating on the gas flux required to maintain a stable air layer (AL) for DR was investigated and compared with that of a painted non-SHS at Reynolds numbers up to 5.1 X 106. Quantitative electrical impedance measurements and more qualitative image analysis were used to characterize surface coverage and to determine whether a stable AL was formed and maintained over the length of the model. Analysis of video and still images for both the SHS and painted surface gives clear indications that the SHS is able to maintain AL consistency at significantly lower gas flux than required on the non-SHS painted surface. Hydrophobicity of the surfaces was characterized through droplet contact angle measurements, and roughness of all the flow surfaces was measured. The results from these preliminary experiments seem to indicate that for conditions explored (up to Rex = 5.1 X 106), there is a significant decrease in the amount of gas required to establish a uniform AL (and hence presumably achieve ALDR) on the SHS when compared with a hydraulically smooth painted non-SHS.

Frictional Drag Reduction: Review and Numerical Simulation of Microbubble Drag Reduction in a Channel Flow

2018 ◽  
Vol Vol 160 (A2) ◽  
Author(s):  
S Sindagi ◽  
R Vijayakumar ◽  
B K Saxena
Keyword(s):  
Numerical Simulation ◽  
Drag Reduction ◽  
Channel Flow ◽  
Void Fraction ◽  
Rectangular Channel ◽  
Air Injection ◽  
Spanwise Direction ◽  
Flat Plates ◽  
Frictional Drag ◽  
Injection Point

The reduction of ship’s resistance is one of the most effective way to reduce emissions, operating costs and to improve EEDI. It is reported that, for slow moving vessels, the frictional drag accounts for as much as 80% of the total drag, thus there is a strong demand for the reduction in the frictional drag. The use of air as a lubricant, known as Micro Bubble Drag Reduction, to reduce that frictional drag is an active research topic. The main focus of authors is to present the current scenario of research carried out worldwide along with numerical simulation of air injection in a rectangular channel. Latest developments in this field suggests that, there is a potential reduction of 80% & 30% reduction in frictional drag in case of flat plates and ships respectively. Review suggests that, MBDR depends on Gas or Air Diffusion which depends on, Bubble size distributions and coalescence and surface tension of liquid, which in turn depends on salinity of water, void fraction, location of injection points, depth of water in which bubbles are injected. Authors are of opinion that, Microbubbles affect the performance of Propeller, which in turn decides net savings in power considering power required to inject Microbubbles. Moreover, 3D numerical investigations into frictional drag reduction by microbubbles were carried out in Star CCM+ on a channel for different flow velocities, different void fraction and for different cross sections of flow at the injection point. This study is the first of its kind in which, variation of coefficient of friction both in longitudinal as well as spanwise direction were studied along with actual localised variation of void fraction at these points. From the study, it is concluded that, since it is a channel flow and as the flow is restricted in confined region, effect of air injection is limited to smaller area in spanwise direction as bubbles were not escaping in spanwise direction.

Frictional Drag Reduction Using Microbubbles

2012 ◽  
Vol 115 (1127) ◽  
pp. 688-691 ◽  
Author(s):  
Yuichi MURAI
Keyword(s):  
Drag Reduction ◽  
Frictional Drag

Frictional drag reduction by microbubbles and change of turbulent structure

2003 ◽  
Vol 2003.2 (0) ◽  
pp. 53-54
Author(s):  
Masato HAMADA ◽  
Noriaki OHTA ◽  
Hiroharu KATO
Keyword(s):  
Drag Reduction ◽  
Turbulent Structure ◽  
Frictional Drag

A Critical Review of Drag Reduction in Channel Flows and Numerical Study of Forced Convective Transport in a Channel With Conducting-Lubricating (CO-LUB) Surfaces

2015 ◽  
Author(s):  
Jessica Reyes ◽  
Krishna Kota
Keyword(s):  
Heat Transfer ◽  
Drag Reduction ◽  
Liquid Flow ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Narrow Channel ◽  
Convective Transport ◽  
Bulk Liquid ◽  
Frictional Drag ◽  
Ansys Fluent

Addressing the traditionally contradictory problem of obtaining considerable drag reduction without negatively impacting heat transfer as much is an arduous scientific challenge. In this paper, prior efforts on frictional drag reduction and the associated issues are discussed in relevant detail, and the effectiveness of Conducting-Lubricating (CO-LUB) surfaces as one of the potential options to address this challenge for single phase forced convection of liquids is numerically pursued. CO-LUB surfaces have exceptionally high wetting characteristics, and when saturated with a liquid microlayer, provide remarkable lubrication to bulk liquid flow and simultaneously facilitate heat transfer by conduction through the microlayer. In the simulations, the side walls of a high aspect ratio rectangular channel were assumed as CO-LUB surfaces and flow and heat transfer of bulk liquid flow were modeled using ANSYS FLUENT 14.5. Volume-of-Fluid (VOF) method was used to model the two phases with a free surface interface, with water as the microlayer liquid and oil as the bulk liquid, in a narrow channel of 5 mm width and 50 mm length under laminar flow, constant wall heat flux conditions. The results were compared with a regular channel of the same dimensions (without CO-LUB surfaces) and it was found that pressure drop decreased remarkably by ∼23 times for some cases but without any heat transfer attenuation (actually, improved heat transfer performance was observed) leading to highly energy-efficient convective transport.

Microstructured Surfaces for Drag Reduction Purposes: Experiments and Simulations on Rectangular 2D Riblets

2005 ◽  
Vol 899 ◽  
Author(s):  
Håkan Rapp ◽  
Igor Zoric ◽  
Bengt Kasemo
Keyword(s):  
Drag Reduction ◽  
Plane Channel ◽  
Viscous Sublayer ◽  
Friction Drag ◽  
Frictional Drag ◽  
Navier Stokes Equation ◽  
Number Range ◽  
Structured Surfaces ◽  
Structured Surface ◽  
Wall Unit

AbstractIt is well established that properly structured surface exhibits a lower friction drag, when exposed to a turbulent boundary layer, than a smooth surface under the same flow conditions. The observed drag decrease is usually attributed to an increased thickness of the viscous sublayer. In this work we examine the friction drag reducing mechanism. Two parallel approaches towards achieving this goal are presented. Photolithography was used to manufacture rectangular riblets in the 10∝m range on a standard 4” silicon wafer. A special compact plane channel system was designed and used for measurements of the frictional drag on structured surfaces in the turbulent flow covering a wide Reynolds number range. Navier-Stokes equation, for the examined drag reducing geometry, was solved in the laminar regime with appropriate boundary conditions. The resulting velocity field was used to extract the protrusion heights difference for streamwise and spanwise flows over the structured surface. The latter was then related to the experimentally measured drag reduction slope. We show that in case of a rectangular riblet, with a size of the order of one wall unit, the observed drag reduction can be accounted for within the above model.

Frictional drag reduction in bubbly Couette–Taylor flow

2008 ◽  
Vol 20 (3) ◽  
pp. 034101 ◽  
Author(s):  
Yuichi Murai ◽  
Hiroshi Oiwa ◽  
Yasushi Takeda
Keyword(s):  
Drag Reduction ◽  
Frictional Drag ◽  
Taylor Flow

scholarly journals Superhydrophobic drag reduction in turbulent flows: a critical review

2021 ◽  
Vol 62 (11) ◽  
Author(s):  
Hyungmin Park ◽  
Chang-Hwan Choi ◽  
Chang-Jin Kim
Keyword(s):  
Drag Reduction ◽  
Turbulent Flows ◽  
Large Scale ◽  
Water Environment ◽  
Experimental Studies ◽  
Open Water ◽  
Laminar Flows ◽  
Turbulent Regime ◽  
Frictional Drag ◽  
Factors Affecting

AbstractSuperhydrophobic (SHPo) surfaces have been investigated vigorously since around 2000 due in large part to their unique potential for hydrodynamic frictional drag reduction without any energy or material input. The mechanisms and key factors affecting SHPo drag reduction have become relatively well understood for laminar flows by around 2010, as has been reviewed before [Lee et al. Exp Fluids 57:176 (2016)], but the progress for turbulent flows has been rather tortuous. While improved flow tests made positive SHPo drag reduction in fully turbulent flows more regular since around 2010, such a success in a natural, open water environment was reported only in 2020 [Xu et al. Phys Rev Appl 13:034056 (2020b)]. In this article, we review studies from the literature about turbulent flows over SHPo surfaces, with a focus on experimental studies. We summarize the key knowledge obtained, including the drag-reduction mechanism in the turbulent regime, the effect of the surface roughness morphology, and the fate and role of the plastron. This review is aimed to help guide the design and application of SHPo surfaces for drag reduction in the large-scale turbulent flows of field conditions. Graphic abstract

A Controllable Microbubble Emitter

2005 ◽  
Author(s):  
Neal A. Brown ◽  
Martin Wosnik
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Water Flow ◽  
Bubble Diameter ◽  
Proof Of Concept ◽  
Surface Drag ◽  
Frictional Drag ◽  
Micro Holes ◽  
Bubble Number ◽  
Theoretical Analyses

Controlled emission of microbubbles into a water flow boundary layer appears to be a promising means to significant reduction of frictional drag on ships. Theoretical analyses and hypotheses require that particularly small (∼ 100 micrometers or less) gas bubbles be emitted and retained in particular laminae close to the wetted surface. Drag reduction economy requires that the quantity of gas emitted be very small. Here a design of a controllable microbubble emitter which meets both demands above is put forth. The two key requirements governing the design are pulsed operation, which expels a known volume of air during each cycle, and a known number of uniformly-sized micro-holes, which determines bubble number and therefore bubble diameter. A first, proof-of-concept experiment with a modified pulsed-pressure design of the proposed microbubble emitter was carried out and shows promise.

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