An Experimental Study of Passive Drag Reduction in a Turbulent Boundary Layer by a Riblet Surface PDF Download
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Author: Seong-Ryong Park
Publisher:
ISBN:
Category : Aerodynamics
Languages : en
Pages : 410
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Book Description
Author: Seong-Ryong Park
Publisher:
ISBN:
Category : Aerodynamics
Languages : en
Pages : 410
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Book Description
Author: E. Coustols
Publisher: Springer
ISBN: 9789401074711
Category : Technology & Engineering
Languages : en
Pages : 182
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Book Description
Proceedings of the 4th European Drag Reduction Meeting
Author: Abdolrahim Hooshmand
Publisher:
ISBN:
Category : Aerodynamics
Languages : en
Pages : 418
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Book Description
Author:
Publisher: AIAA
ISBN: 9781600863783
Category : Boundary layer
Languages : en
Pages : 542
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Book Description
Author: Shabnam Raayai Ardakani
Publisher:
ISBN:
Category :
Languages : en
Pages : 291
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Book Description
The surfaces of many plants and animals are covered with a variety of micro-textures such as ribs or 3D tubules which can control surface-mediated properties such as skin friction. Inspired by the drag reducing ability of these natural structures, especially the ribbed features on shark denticles, passive drag reduction strategies such as micro-fabricated riblet surfaces have been developed and studied. Microgroove textures on the surface of objects such as hulls, wings or inner surface of pipes which are aligned in the stream-wise direction have been shown to reduce the wall friction by 4 − 8%. The mechanisms suggested for this form of drag reduction are viscous retardation of the flow in the grooves (both laminar and turbulent) and the displacement of vortical structures away from the wall in turbulent flows. Due to their effectiveness in altering the boundary layer structure and reducing the viscous drag force, use of riblets have been banned in various competitions such as the America’s Cup. The current thesis work is partly focused on theoretical and numerical modelling (using the open source CFD package OpenFOAM) of the evolution of viscous boundary layers in the presence of various-shaped riblets (V-grooves as well as sinusoidal wrinkled surfaces) in high Reynolds laminar flow. We explore the effect of the dimensionless height to spacing of the grooves (aspect ratio) as well as the length of the wetted surface in the streamwise direction and how these change the total drag compared with a corresponding flat wall. We show that riblets retard the viscous flow inside the grooves and reduce the shear stress inside the grooves. But for this reduction to result in overall drag reduction, the riblet wall needs to be longer than a critical length. The total drag reduction achieved is a non-monotonic function of the aspect ratio of the riblets, with aspect ratios of order unity offering the largest reduction in the total drag. To eliminate the role of entrance effects, we additionally investigate the effect of stream-wise aligned riblet structures on fully-developed Taylor-Couette flow. We perform both experimental studies as well as time-dependent numerical simulations in both the laminar Couette and the Taylor vortex regime. We again explore the effect of the size of the riblets with respect to the geometry of the Taylor-Couette cell, as well as the aspect ratio of the riblet grooves and the shape of the grooves (V-groove, Rectangular, semi-circular, etc.). For the experiments, the cylindrical textured rotors are fabricated using 3D printing techniques and the rest of the Taylor-Couette cell is custom built using CNC machining. The test cell is then aligned and mounted on a stress-controlled rheometer to measure the velocity and the torque on the rotating inner cylinder. The numerical studies are performed using the open source CFD software package OpenFOAM to compare results and understand the physical mechanisms contributing to this drag reduction phenomenon. Again we observe a non-monotonic behavior for the reduction in torque as a function of the aspect ratio of the riblets tested, similar to the trend observed in the boundary layer analysis and we discuss the effect of changing the geometry of the flow as well as the riblet spacing on the changes in the total torque. When viewed holistically the results of these two studies show that, through careful design, a net reduction in viscous drag force can be robustly realized on micro-textured surfaces in high Reynolds number laminar flows through complex changes in near-wall stream-wise velocity profiles even in the absence of turbulent effects. The understanding of these changes can be effective in guiding the design of internal flows (pipes or ducts) and external flows (such as ship hulls, micro air vehicles or unmanned underwater vehicles) that are tailored and optimized to result in low frictional drag over the entire wetted surface in both laminar and turbulent regions.
Author: C. Sinclair Wells
Publisher: Springer
ISBN: 1489955798
Category : Technology & Engineering
Languages : en
Pages : 497
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Book Description
Author: L. Gaudet
Publisher:
ISBN:
Category : Aerodynamics
Languages : en
Pages : 13
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Book Description
An assessment is given of the performance of riblets in reducing skin friction in turbulent flow. The data of Sawyer and Winter is used to develop skin-friction relationships derived from the velocity profile for a turbulent boundary layer as modified by a riblet surface. The maximum percentage drag reduction is shown to vary with Reynolds number R sub x. At large values of the non-dimensional riblet height the riblet surface acts as a uniform roughness and a value for the equivalent sand-grain roughness height is given. Examples of the estimated drag reductions which might be achieved for two current aircraft by incorporating riblet surfaces are presented.
Author: Haecheon Choi
Publisher:
ISBN:
Category :
Languages : en
Pages : 318
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Author: Dean R. Chapman
Publisher:
ISBN:
Category : Aerodynamics
Languages : en
Pages : 92
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Summary: Tests were conducted to determine the effects of viscosity on the drag and base pressure characteristics of various bodies of revolution at a Mach number of 1.5. The models were tested both with smooth surfaces and with roughness added to evaluate the effects of Reynolds number for both laminar and turbulent boundary layers. The principal geometric variables investigated were after-body shape and length-diameter ratio. For most models, force tests and base pressure measurements were made over a range of Reynolds numbers, based on model length, from 0.6 million to 5.0 millions. Schlieren photographs were used to analyze the effects of viscosity on flow separation and shock-wave configuration near the base and to verify the condition of the boundary layer as deduced from force tests. The results are discussed and compared with theoretical calculations.
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 704
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Book Description
