Hairpin Structures in a Turbulent Boundary Layer under Stalled-Airfoil-Type Flow Conditions

This article discusses the problems of determining the friction parameter and non-eroding conditions in a wave flow are considered from the standpoint of an approach using a critical dynamic speed. In the first stage of research, the question of the formation of an unsteady turbulent boundary layer is substantiated. Because of the research, dependences were obtained for the most important value from the point of view of sediment transport - the friction parameter. Based on the data of these measurements, a plot of dependence was built, which differs from the previously obtained analytical relationships. For the convenience of practical use of the obtained empirical connection approximated. The second stage of research is the development of a method for calculating the critical tangential stresses corresponding to the beginning of the movement of bottom sediments. Based on the Shilds method, a curve similar to the Shilds curve for wave flow conditions was constructed, which was approximated for the convenience of practical use.

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Direct intervention of hairpin structures for turbulent boundary-layer control

Physics of Fluids ◽

10.1063/1.3006346 ◽

2008 ◽

Vol 20 (10) ◽

pp. 101517 ◽

Cited By ~ 11

Author(s):

Yong-Duck Kang ◽

Kwing-So Choi ◽

Ho Hwan Chun

Keyword(s):

Boundary Layer ◽

Turbulent Boundary Layer ◽

Boundary Layer Control ◽

Hairpin Structures ◽

Layer Control

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Passive bristling of mako shark scales in reversing flows

Journal of The Royal Society Interface ◽

10.1098/rsif.2018.0473 ◽

2018 ◽

Vol 15 (147) ◽

pp. 20180473 ◽

Cited By ~ 5

Author(s):

Kevin T. Du Clos ◽

Amy Lang ◽

Sean Devey ◽

Philip J. Motta ◽

Maria Laura Habegger ◽

...

Keyword(s):

Boundary Layer ◽

Turbulent Boundary Layer ◽

Drag Reduction ◽

High Speed ◽

Scale Up ◽

Control Mechanisms ◽

Flow Conditions ◽

Boundary Layer Flows ◽

Mako Shark ◽

Shortfin Mako

Shark skin has been shown to reduce drag in turbulent boundary layer flows, but the flow control mechanisms by which it does so are not well understood. Drag reduction has generally been attributed to static effects of scale surface morphology, but possible drag reduction effects of passive or active scale actuation, or ‘bristling’, have been recognized more recently. Here, we provide the first direct documentation of passive scale bristling due to reversing, turbulent boundary layer flows. We recorded and analysed high-speed videos of flow over the skin of a shortfin mako shark, Isurus oxyrinchus . These videos revealed rapid scale bristling events with mean durations of approximately 2 ms. Passive bristling occurred under flow conditions representative of cruise swimming speeds and was associated with two flow features. The first was a downward backflow that pushed a scale-up from below. The second was a vortex just upstream of the scale that created a negative pressure region, which pulled up a scale without requiring backflow. Both flow conditions initiated bristling at lower velocities than those required for a straight backflow. These results provide further support for the role of shark scale bristling in drag reduction.

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Interacting Turbulent Boundary Layer over a Wavy Wall

Journal of Heat Transfer ◽

10.1115/1.3450876 ◽

1978 ◽

Vol 100 (4) ◽

pp. 678-683 ◽

Cited By ~ 2

Author(s):

A. Polak ◽

M. J. Werle

Keyword(s):

Boundary Layer ◽

Turbulent Boundary Layer ◽

Eddy Viscosity ◽

Relaxation Method ◽

Inviscid Flow ◽

Reynolds Numbers ◽

Flow Conditions ◽

Boundary Layer Equations ◽

Eddy Viscosity Model ◽

Turbulence Effects

This paper is concerned with the two-dimensional supersonic flow of a thick turbulent boundary layer over a train of relatively small wave-like protuberances. The flow conditions and the geometry are such that there exists a strong interaction between the viscous and inviscid flow. Here the interacting boundary layer equations are solved numerically using a time-like relaxation method with turbulence effects represented by the inclusion of the eddy viscosity model of Cebeci and Smith. Results are presented for flow over a train of up to six waves for Mach numbers of 2.5 and 3.5, Reynolds numbers of 10 and 32 × 106/meter, and wall temperature ratios Tw/T0 of 0.4 and 0.8. Limited comparisons with independent experimental and analytical results are also given.

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