A New Measure for Direct Measurement of the Bed Shear Stress of Wave Boundary Layer in Wave Flume

This study deals with turbulent oscillatory boundary-layer flows over a plane bed with a sudden spatial change in roughness. Two kinds of ‘change in the roughness’ were investigated: in one, the roughness changed from a smooth-wall roughness to a roughness equal to 4.8 mm, and in the other, it changed from a roughness equal to 0.35 mm to the same roughness as in the previous experiment (4.8 mm). The free-stream flow was a purely oscillating flow with sinusoidal velocity variation. Mean flow and turbulence properties were measured. The Reynolds number was 6 × 106 for the major part of the experiments, with a maximum velocity of approximately 2 m/s and the stroke of the motion about 6 m. The response of the boundary layer to the sudden change in roughness was found to occur over a transitional length of the flow. The bed shear stress over this transitional length attains a peak value over the bed section with the larger roughness. It was found that the amplification in the bed shear stress due to this peak could be up to 2.5 times its asymptotic value. Also, it was found that the turbulence is quantitatively different in the two half periods; a much stronger turbulence is experienced in the half period where the flow is towards the less-rough section. The present experiments further showed that a constant streaming occurs near the bed in the neighbourhood of the junction between the two bed sections. This streaming is directed towards the section with the larger roughness.

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Comment on "Wall Shear Stress Measurements in a Shock-Wave Boundary-Layer Interaction"

AIAA Journal ◽

10.2514/3.61200 ◽

1979 ◽

Vol 17 (6) ◽

pp. 670-671

Author(s):

Robert D. Kirchner

Keyword(s):

Boundary Layer ◽

Shock Wave ◽

Shear Stress ◽

Wall Shear Stress ◽

Stress Measurements ◽

Layer Interaction ◽

Wave Boundary Layer ◽

Boundary Layer Interaction ◽

Wall Shear ◽

Wave Boundary

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Coherent structures in wave boundary layers. Part 2. Solitary motion

Journal of Fluid Mechanics ◽

10.1017/s0022112009992837 ◽

2010 ◽

Vol 646 ◽

pp. 207-231 ◽

Cited By ~ 59

Author(s):

B. MUTLU SUMER ◽

PALLE M. JENSEN ◽

LONE B. SØRENSEN ◽

JØRGEN FREDSØE ◽

PHILIP L.-F. LIU ◽

...

Keyword(s):

Boundary Layer ◽

Shear Stress ◽

Boundary Layers ◽

Bed Shear Stress ◽

Laminar Regime ◽

Short Period ◽

Flow Features ◽

Layer Flow ◽

Wave Boundary ◽

Flow Experiences

This study continues the investigation of wave boundary layers reported by Carstensen, Sumer & Fredsøe (J. Fluid Mech., 2010, part 1 of this paper). The present paper summarizes the results of an experimental investigation of turbulent solitary wave boundary layers, simulated by solitary motion in an oscillating water tunnel. Two kinds of measurements were made: bed shear stress measurements and velocity measurements. The experiments show that the solitary-motion boundary layer experiences three kinds of flow regimes as the Reynolds number is increased: (i) laminar regime; (ii) laminar regime where the boundary-layer flow experiences a regular array of vortex tubes near the bed over a short period of time during the deceleration stage; and (iii) transitional regime characterized with turbulent spots, revealed by single/multiple, or, sometimes, quite dense spikes in the bed shear stress traces. Supplementary synchronized flow visualization tests confirmed the presence of the previously mentioned flow features. Information related to flow resistance are also given in the paper.

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WAVE BOUNDARY LAYER HYDRODYNAMICS DURING ONSHORE BAR MIGRATION

Coastal Engineering Proceedings ◽

10.9753/icce.v32.sediment.2 ◽

2011 ◽

Vol 1 (32) ◽

pp. 2 ◽

Cited By ~ 1

Author(s):

Martijn Henriquez ◽

Ad Reniers ◽

Gerben Ruessink ◽

Marcel Stive

Keyword(s):

Boundary Layer ◽

Sediment Transport ◽

Bottom Boundary Layer ◽

Flume Experiment ◽

Bottom Boundary ◽

Bottom Stress ◽

Wave Boundary Layer ◽

Wave Flume ◽

Wave Boundary ◽

Wave Flume Experiment

To study onshore bar migration and the accompanying intra-wave sediment transport a wave flume experiment was conducted. The wave flume had a rigid bottom with a single bar profile. The focus of the experiment was to measure the hydrodynamics in the wave bottom boundary layer. The results show that the skewness of bottom stress is not only related to wave skewness but also to wave asymmetry.

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