scholarly journals Surface drag reduction and flow separation control in pelagic vertebrates, with implications for interpreting scale morphologies in fossil taxa

2015 ◽  
Vol 2 (1) ◽  
pp. 140163
Author(s):  
Colin Palmer ◽  
Mark T. Young
Keyword(s):  
Soft Tissue ◽  
Drag Reduction ◽  
Flow Separation ◽  
The Body ◽  
Surface Drag ◽  
Frictional Drag ◽  
Reduced Pressure ◽  
Flow Separation Control ◽  
Pressure Drag ◽  
Aquatic Vertebrates

Living in water imposes severe constraints on the evolution of the vertebrate body. As a result of these constraints, numerous extant and extinct aquatic vertebrate groups evolved convergent osteological and soft-tissue adaptations. However, one important suite of adaptations is still poorly understood: dermal cover morphologies and how they influence surface fluid dynamics. This is especially true for fossil aquatic vertebrates where the soft tissue of the dermis is rarely preserved. Recent studies have suggested that the keeled scales of mosasaurids (pelagic lizards that lived during the Late Cretaceous) aided in surface frictional drag reduction in a manner analogous to the riblets on shark placoid scales. However, here we demonstrate that mosasaurid scales were over an order of magnitude too large to have this effect. More likely they increased the frictional drag of the body and may have played a role in controlling flow separation by acting as surface roughness that turbulated the boundary layer. Such a role could have reduced pressure drag and enhanced manoeuvrability. We caution those studying fossil aquatic vertebrates from positing the presence of surface drag reducing morphologies, because as we show herein, to be effective such features need to have a spacing of approximately 0.1 mm or less.

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.

Drag reduction by flow separation control on a car after body

2009 ◽  
Vol 60 (11) ◽  
pp. 1222-1240 ◽  
Author(s):  
Mathieu Rouméas ◽  
Patrick Gilliéron ◽  
Azeddine Kourta
Keyword(s):  
Drag Reduction ◽  
Flow Separation ◽  
Separation Control ◽  
Flow Separation Control

Experimental Study of Air Layer Sustainability for Frictional Drag Reduction

2014 ◽  
Vol 58 (01) ◽  
pp. 30-42 ◽  
Author(s):  
Bhat Nikhil Jagdish ◽  
Tay Zhi Xian Brandon ◽  
Tiaw Joo Kwee ◽  
Arun Kr. Dev
Keyword(s):  
Drag Reduction ◽  
Experimental Studies ◽  
Hydrophobic Surface ◽  
Viscous Drag ◽  
Total Resistance ◽  
Frictional Drag ◽  
Form Drag ◽  
Friction Resistance ◽  
Slow Steaming ◽  
Pressure Drag

Frictional drag reduction by microbubbles is a promising engineering method for reducing ship fuel consumption, especially for large, slow steaming vessels. Total resistance can be broken down into frictional drag and form drag (also known as pressure drag or profile drag). Ship's hull form optimization is commonly to reduce the form drag of a ship. Another technique would be required to deal with the frictional (viscous) portion of the total resistance. One such technique that reduces the friction resistance is the air lubrication technique. This research looks at possible enhancement for the microbubbles drag reduction technique with the use of hydrophobic plates to trap and retain an air layer. The hydrophobic surface cannot sustain bubbles by itself. Laser-machined microstructure coupled with hydrophobic coatings allows the rapid formation of air layer rapidly and sustainability of the air layer is recorded. With extensive experimental studies, we have shown that an air layer can be entrained around a moving flat plate thereby reducing friction. This could pave the way for applying this technique around the wall of moving ship hulls thereby minimizing the viscous drag and reducing the shipping costs.

Research on Automobile Aerodynamic Drag Reduction Based on Isobaric Surface of a Blunt Body

2013 ◽  
Vol 328 ◽  
pp. 634-638
Author(s):  
Xing Jun Hu ◽  
Lei Liao ◽  
Xiu Cheng Li ◽  
Chang Hai Yang ◽  
Peng Guo ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Blunt Body ◽  
Aerodynamic Drag ◽  
Simulation Method ◽  
The Body ◽  
Viscous Drag ◽  
Isobaric Surface ◽  
Pressure Drag ◽  
Aerodynamic Drag Reduction ◽  
The Relationship

This paper focuses on a new method of aerodynamic drag reduction. In this paper numerical simulation method is adopted to investigate the relationship between the aerodynamic drag characteristics of a blunt body and the distribution of total pressure around the body. The study shows that when the shape of a blunt body is modified to be close to its isobaric surface, the pressure drag of the body can be reduced largely while the viscous drag increases slightly, and the summary of the drag gets lower as a result. This conclusion will have profound guiding significance in the aerodynamic shape designing and the aerodynamic drag reduction of an automobile.

Flow Separation Control and Drag Reduction for a Two-Dimensional Boat-Tailed Bluff Body Through Transverse Grooves

2018 ◽  
Author(s):  
Alessandro Mariotti ◽  
Guido Buresti ◽  
Maria Vittoria Salvetti
Keyword(s):  
Drag Reduction ◽  
Flow Separation ◽  
Bluff Body ◽  
Boundary Layer Separation ◽  
Control Device ◽  
Recirculation Region ◽  
Two Dimensional ◽  
Flow Separation Control ◽  
Flow Control Device ◽  
Transverse Grooves

The present work focuses on a passive strategy consisting in the introduction of properly contoured transverse grooves to delay the flow separation occurring on a boat-tailed bluff body before its sharp-edged base. We consider a two-dimensional body having a cross-section with a 3:1 elliptical forebody and a rectangular main part followed by a circular-arc boat tail. We carry out Variational Multiscale Large Eddy Simulations at Re = Du∞/v = 9.6 × 104. A boat-tail drag reduction of the order of 9.7% is produced by the significant delay of the flow separation caused by the groove and by the consequent increase of the base pressure. This effect is mainly due to the relaxation of the no-slip condition over the small and steady recirculation region inside the groove, which reduces the momentum losses near the wall and thus delays boundary layer separation. The flow control device is also robust to small variations of the groove location and depth.

scholarly journals Enhanced Fuel Efficiency by Frictional Drag Reduction of Toy Boat Coated with Superhydrophobic Additives comprising Nickel Stearate and AlNiCo Nanoparticles

2021 ◽  
Author(s):  
Kadarkaraithangam Jeyasubramanian ◽  
Silambu Selvan Paranibramma Nayagi ◽  
Gnanadhas Sobhin Osannal Hikku
Keyword(s):  
Drag Reduction ◽  
Buoyancy Force ◽  
Fuel Efficiency ◽  
Layer By Layer ◽  
Surface Drag ◽  
Frictional Drag ◽  
Trapped Air ◽  
Co Precipitation ◽  
Marine Vessels ◽  
Sailing Boat

Surface frictional drag developed by marine vessels utilizes a considerable percentage of fuel for propulsion. Superhydrophobic (SH) surface normally traps a layer of air at the interface and significantly reduces the surface frictional drag. Herein, the efficacy of the SH coating towards the surface drag reduction of the sailing boat is recognized by conducting a facile experiment where the bottom of the toy boat is coated with SH additives. AlNiCo nanoparticles and nickel stearate prepared by ball-milling and co-precipitation methods respectively are drop-casted layer by layer over the surface of the toy boat to impart SH. The fuel efficiency of the SH boat is improved by 51.49% substantiating the reduction in surface drag of the vessel. Further, the trapped air provides extra buoyancy force, enhancing the load-bearing capability of the SH boat by 5.77%.

scholarly journals Numerical Investigation on the Influence of the Streamlined Structures of the High-Speed Train’s Nose on Aerodynamic Performances

2021 ◽  
Vol 11 (2) ◽  
pp. 784
Author(s):  
Zhenxu Sun ◽  
Shuanbao Yao ◽  
Lianyi Wei ◽  
Yongfang Yao ◽  
Guowei Yang
Keyword(s):  
Drag Reduction ◽  
Pressure Distribution ◽  
Flow Separation ◽  
High Speed ◽  
Leeward Side ◽  
Detached Eddy Simulation ◽  
Side Force ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Asymmetrical Design

The structural design of the streamlined shape is the basis for high-speed train aerodynamic design. With use of the delayed detached-eddy simulation (DDES) method, the influence of four different structural types of the streamlined shape on aerodynamic performance and flow mechanism was investigated. These four designs were chosen elaborately, including a double-arch ellipsoid shape, a single-arch ellipsoid shape, a spindle shape with a front cowcatcher and a double-arch wide-flat shape. Two different running scenes, trains running in the open air or in crosswind conditions, were considered. Results reveal that when dealing with drag reduction of the whole train running in the open air, it needs to take into account how air resistance is distributed on both noses and then deal with them both rather than adjust only the head or the tail. An asymmetrical design is feasible with the head being a single-arch ellipsoid and the tail being a spindle with a front cowcatcher to achieve the minimum drag reduction. The single-arch ellipsoid design on both noses could aid in moderating the transverse amplitude of the side force on the tail resulting from the asymmetrical vortex structures in the flow field behind the tail. When crosswind is considered, the pressure distribution on the train surface becomes more disturbed, resulting in the increase of the side force and lift. The current study reveals that the double-arch wide-flat streamlined design helps to alleviate the side force and lift on both noses. The magnitude of side force on the head is 10 times as large as that on the tail while the lift on the head is slightly above that on the tail. Change of positions where flow separation takes place on the streamlined part is the main cause that leads to the opposite behaviors of pressure distribution on the head and on the tail. Under the influence of the ambient wind, flow separation occurs about distinct positions on the train surface and intricate vortices are generated at the leeward side, which add to the aerodynamic loads on the train in crosswind conditions. These results could help gain insight on choosing a most suitable streamlined shape under specific running conditions and acquiring a universal optimum nose shape as well.

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