Evaluation of Skin Friction Drag Reduction in the Turbulent Boundary Layer Using Riblets

Takahashi, Hidemi; Iijima, Hidetoshi; Kurita, Minoru; Koga, Shunsaku

doi:10.3390/app9235199

Cited by 12 publications

(15 citation statements)

References 26 publications

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“…The size parameter of the circular concave structure was considered: diameter D, the lateral distance W, the longitudinal distance L, and the depth S. To facilitate the design and arrangement, the depth S of the circular concave structure is half of the circular concave diameter D. The size design of the circular concave structure is shown specifically in Figure 5. The value range of D, W, L and S is given as [10,50], [60, 160], [60, 160], [5,25] respectively; its numeric type is integer and unit is mm. According to many bionics experiments, the soil animal, the dung beetle, can move freely in the soil due to the circular concave shape of its non-smooth surface and the arrangement of its circular concave structure.…”

Section: Size Design and Arrangement Of Circular Concave Structurementioning

confidence: 99%

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Aerodynamic Shape Optimization Method of Non-Smooth Surfaces for Aerodynamic Drag Reduction on A Minivan

Yang

Yong²,

Gu³

2021

Fluids

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To reduce aerodynamic drag of a minivan, non-smooth surfaces are applied to the minivan’s roof panel design. A steady computational fluid dynamics (CFD) method is used to investigate the aerodynamic drag characteristics. The accuracy of the numerical method is validated by wind tunnel test. The drag reduction effects of rectangle, rhombus and arithmetic progression arrangement for circular concaves are investigated numerically, and then the aerodynamic drag coefficient of the rectangle arrangement with a better drag reduction effect is chosen as the optimization objective. Three parameters, that is, the diameter D of the circular concave, the width W and the longitudinal distance L among the circular concaves, are selected as design variables. A 20-level design of an experimental study using a Latin Hypercube scheme is conducted. The responses of 20 groups of sample points are obtained by CFD simulation, based on which a Kriging model is chosen to create the surrogate-model. The multi-island genetic algorithm is employed to find the optimum solution. The result shows that maximum drag reduction effects up to 7.71% can be achieved with a rectangle circular concaves arrangement. The reduction mechanism of the roof with the circular concaves was discussed. The circular concaves decrease friction resistance of the roof and change the flow characteristics of the recirculation area in the wake of the minivan. The roof with the circular concaves reduces the differential pressure drag of the front and rear of the minivan.

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Section: Size Design and Arrangement Of Circular Concave Structurementioning

confidence: 99%

“…The drag reduction research on non-smooth surface structures has received a great deal of attention [4][5][6]. Drag force can be divided into two different types, that is, pressure drag and friction drag.…”

Section: Introductionmentioning

confidence: 99%

Aerodynamic Shape Optimization Method of Non-Smooth Surfaces for Aerodynamic Drag Reduction on A Minivan

Yang

Yong²,

Gu³

2021

Fluids

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“…Here, τ designates the time lag at which the correlation is measured. Since the duration of the sampling has to be finite, the integration is limited to a time lag, τ 0 , for which the absolute value of the auto-correlation coefficient becomes less than 0.0005 and its gradient becomes less than 0.005, i.e., R pp < 0.0005 and dR p p dτ < 0.005 [44].…”

Section: Auto-correlations Of Unsteady Surface Pressurementioning

confidence: 99%

Airfoil Trailing-Edge Noise Reduction by Application of Finlets

et al. 2021

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This experimental study investigates the effect of bio-inspired finlets on the reduction of trailing edge noise of a NACA 0012 airfoil. At a chord-based Reynolds number of 400,000, the far-field noise measurements show that the finlets are capable of reducing the trailing edge noise effectively from 1,000 Hz to 4,000 Hz with up to 6 dB reduction, for effective angles of attack from zero to eight degree. By correlating the far-field noise to the boundary layer measurements, an optimal finlet height to boundary layer thickness ratio to achieve the highest noise reduction is discussed. Static pressure and dynamic pressure fluctuations are examined, particularly within the finlet-treated area, to capture the flow dynamics through the treatments.The unsteady surface pressure fluctuation spectra show strong reduction at frequencies higher than 1,000 Hz in the finlet wake, complying with the far-field measurements. Both the auto-and cross-correlation results of the unsteady surface pressure reveal the formation of large-scale turbulence at the entrance and toward the exit of the finlets. Moreover, they suggest that the formation and subsequent mixing of these large-scale structures with the boundary layer can be beneficial to reducing the unsteady surface pressure fluctuations. The findings will be useful to potential optimization of the finlets.

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“…Turbulent skin friction drag reduction with longitudinal microgrooves and riblets in channel flow is analyzed using lattice Boltzmann method by Rastegary and Akhavan (2018). Turbulent boundary layer characteristics for a flat plate model with riblet surface is examined in wind tunnel experiments by Takahashi et al (2018). The results revealed that skin friction drag is reduced aboaut 3.6% at free stream velocity of 42m/s.…”

Section: Nomenclaturementioning

confidence: 99%

Optimization of Drag Reducing Shark Inspired Blade-Shape Riblet Surfaces in External Flow

Monfared

Alidoostan

2020

JAFM

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The main goal of this research is to study the drag reduction capabilities of blade-shape riblet surfaces in external flows. For this purpose, the ability of riblet surfaces for drag reduction of an underwater hydrodynamic model has been investigated. The surface geometry has been modified by applying shark skin inspired blade-shape riblets on the surface. These riblets have been modeled in various dimensions and applied on the exterior surface of an underwater hydrodynamic model, and their effects on the exerted drag force, at different flow velocities, have been studied numerically. For validating the numerical solution, the simulation results have been compared with the experimental data obtained by testing an underwater hydrodynamic model in a towing tank laboratory; and the validity of the numerical solution results has been confirmed. The results indicated that, riblet spacing has a significant effect on the reduction of drag force. Furthermore, by increasing the riblet spacing, the drag force is increased rather than decreased. Also, as the velocity increases, the performance of riblets in reducing the drag force is enhanced. In order to minimize the drag force applied on the underwater hydrodynamic model, by analyzing the numerical results, the most optimum riblet spacing has been obtained; at which the drag force is reduced by 7%. The achieved distance is a limit value; and at distances smaller or larger than this optimal distance, the effectiveness of the blade-shape riblet surface in reducing the drag force diminishes.

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Evaluation of Skin Friction Drag Reduction in the Turbulent Boundary Layer Using Riblets

Cited by 12 publications

References 26 publications

Aerodynamic Shape Optimization Method of Non-Smooth Surfaces for Aerodynamic Drag Reduction on A Minivan

Aerodynamic Shape Optimization Method of Non-Smooth Surfaces for Aerodynamic Drag Reduction on A Minivan

Airfoil Trailing-Edge Noise Reduction by Application of Finlets

Optimization of Drag Reducing Shark Inspired Blade-Shape Riblet Surfaces in External Flow

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