scholarly journals Experimental study of the turbulent boundary layer in acceleration-skewed oscillatory flow

2011 ◽  
Vol 684 ◽  
pp. 251-283 ◽  
Author(s):  
Dominic A. van der A ◽  
Tom O’Donoghue ◽  
Alan G. Davies ◽  
Jan S. Ribberink
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Reynolds Stress ◽  
Oscillatory Flow ◽  
Bed Shear Stress ◽  
Flow Conditions ◽  
Oscillatory Boundary Layer ◽  
Layer Flow ◽  
Momentum Integral ◽  
Good Agreement

AbstractExperiments have been conducted in a large oscillatory flow tunnel to investigate the effects of acceleration skewness on oscillatory boundary layer flow over fixed beds. As well as enabling experimental investigation of the effects of acceleration skewness, the new experiments add substantially to the relatively few existing detailed experimental datasets for oscillatory boundary layer flow conditions that correspond to full-scale sea wave conditions. Two types of bed roughness and a range of high-Reynolds-number, $\mathit{Re}\ensuremath{\sim} O(1{0}^{6} )$, oscillatory flow conditions, varying from sinusoidal to highly acceleration-skewed, are considered. Results show the structure of the intra-wave velocity profile, the time-averaged residual flow and boundary layer thickness for varying degrees of acceleration skewness, $\ensuremath{\beta} $. Turbulence intensity measurements from particle image velocimetry (PIV) and laser Doppler anemometry (LDA) show very good agreement. Turbulence intensity and Reynolds stress increase as the flow accelerates after flow reversal, are maximum at around maximum free-stream velocity and decay as the flow decelerates. The intra-wave turbulence depends strongly on $\ensuremath{\beta} $ but period-averaged turbulent quantities are largely independent of $\ensuremath{\beta} $. There is generally good agreement between bed shear stress estimates obtained using the log-law and using the momentum integral equation, and flow acceleration skewness leads to high bed shear stress asymmetry between flow half-cycles. Turbulent Reynolds stress is much less than the shear stress obtained from the momentum integral; analysis of the stress contributors shows that significant phase-averaged vertical velocities exist near the bed throughout the flow cycle, which lead to an additional shear stress, $\ensuremath{-} \rho \tilde {u} \tilde {w} $; near the bed this stress is at least as large as the turbulent Reynolds stress.

Non-Newtonian oscillatory layer flow, approximate solution

1979 ◽  
Vol 44 (10) ◽  
pp. 2908-2914 ◽  
Author(s):  
Ondřej Wein
Keyword(s):  
Boundary Layer ◽  
Approximate Solution ◽  
Galerkin Method ◽  
Horizontal Plane ◽  
Oscillatory Flow ◽  
Oscillatory Boundary Layer ◽  
Layer Flow ◽  
Pseudoplastic Liquid ◽  
The Galerkin Method

The problem of the oscillatory flow of pseudoplastic liquid in vicinity of the infinitely long horizontal plane is formulated in stresses. For Re i.e. for conditions of oscillatory boundary layer the problem is solved approximately by the Galerkin method.

Boundary-layer flow and bed shear stress under a solitary wave: revision

2014 ◽  
Vol 753 ◽  
pp. 554-559 ◽  
Author(s):  
Yong Sung Park ◽  
Joris Verschaeve ◽  
Geir K. Pedersen ◽  
Philip L.-F. Liu
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Solitary Wave ◽  
Boundary Layer Flow ◽  
Bottom Boundary Layer ◽  
Bed Shear Stress ◽  
Bottom Boundary ◽  
Layer Flow

AbstractWe address two shortcomings in the article by Liu, Park & Cowen (J. Fluid Mech., vol. 574, 2007, pp. 449–463), which gave a theoretical and experimental treatise of the bottom boundary-layer under a solitary wave.

Boundary layer flow and bed shear stress under a solitary wave

2007 ◽  
Vol 574 ◽  
pp. 449-463 ◽  
Author(s):  
PHILIP L.-F. LIU ◽  
YONG SUNG PARK ◽  
EDWIN A. COWEN
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Solitary Wave ◽  
Analytical Solutions ◽  
Boundary Layer Flow ◽  
Inertia Force ◽  
Bed Shear Stress ◽  
Viscous Boundary Layer ◽  
Layer Flow ◽  
Viscous Boundary

Liu & Orfila (J. Fluid Mech. vol. 520, 2004, p. 83) derived analytical solutions for viscous boundary layer flows under transient long waves. Their analytical solutions were obtained with the assumption that the nonlinear inertia force was negligible in the momentum equations. In this paper, using Liu & Orfila's solution and the solutions for the nonlinear boundary layer equations, we examine the boundary layer flow characteristics under a solitary wave. It is found that while the horizontal component of the free-stream velocity outside the boundary layer always moves in the direction of wave propagation, the fluid particle velocity near the bottom inside the boundary layer reverses direction as the wave decelerates. Consequently, the bed shear stress also changes sign during the deceleration phase. Laboratory measurements, including the free-surface displacement, particle image velocimetry (PIV) resolved velocity fields of the viscous boundary layer, and the calculated bed shear stress were also collected to check the theoretical results. Excellent agreement is observed.

scholarly journals LABORATORY STUDY ON OSCILLATORY BOUNDARY LAYER FLOW

1968 ◽  
Vol 1 (11) ◽  
pp. 29 ◽  
Author(s):  
Kiyoshi Horikawa ◽  
Akira Watanabe
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Oscillatory Flow ◽  
Fluid Motion ◽  
Senior Author ◽  
Theoretical Treatment ◽  
Sand Ripples ◽  
Oscillatory Boundary Layer ◽  
Sediment Particles ◽  
Layer Flow

The characteristics of oscillatory boundary layer flow have been treated with keen interest during the last decade from the various aspects. Among the previous results the theoretical treatment by K. Kajiura must be the most important and fruitful one to advance in our knowledge on the present phenomena. On the other hand the senior author has had a real interest in the behaviour of sediment particles due to oscillatory fluid motion, and has conducted his systematic investigations on the sediment movement in nearshore area. The aim of this paper is to introduce some results of the recent investigations conducted at the Coastal Engineering Laboratory, University of Tokyo, with the intention of investigating the applicability of Kajiura's theory to the oscillatory flow in the vicinity of bottom with sand ripples.

Experimental investigation of wave boundary layers with a sudden change in roughness

1993 ◽  
Vol 252 ◽  
pp. 117-145 ◽  
Author(s):  
J. Fredsøe ◽  
B. M. Sumer ◽  
T. S. Laursen ◽  
C. Pedersen
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Sudden Change ◽  
Maximum Velocity ◽  
Velocity Variation ◽  
Bed Shear Stress ◽  
Mean Flow ◽  
Boundary Layer Flows ◽  
Oscillatory Boundary Layer ◽  
Wave Boundary

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.

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

2010 ◽  
Vol 646 ◽  
pp. 207-231 ◽  
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.

scholarly journals Mean flow structure and velocity–bed shear stress maxima phase difference in smooth wall, transitionally turbulent oscillatory boundary layers: direct numerical simulations

2021 ◽  
Vol 928 ◽  
Author(s):  
Dimitrios K. Fytanidis ◽  
Marcelo H. García ◽  
Paul F. Fischer
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Numerical Simulations ◽  
Phase Difference ◽  
Free Stream ◽  
Direct Numerical Simulations ◽  
Stream Velocity ◽  
Phase Lag ◽  
Bed Shear Stress ◽  
Oscillatory Boundary Layer

Direct numerical simulations of oscillatory boundary-layer flows in the transitional regime were performed to explain discrepancies in the literature regarding the phase difference ${\rm \Delta} \phi$ between the bed-shear stress and free-stream velocity maxima. Recent experimental observations in smooth bed oscillatory boundary-layer (OBL) flows, showed a significant change in the widely used ${\rm \Delta} \phi$ diagram (Mier et al., J. Fluid Mech., vol. 922, 2021, A29). However, the limitations of the point-wise measurement technique did not allow us to associate this finding with the turbulent kinetic energy budget and to detect the approach to a ‘near-equilibrium’ condition, defined in a narrow sense herein. Direct numerical simulation results suggest that a phase lag occurs as the result of a delayed and incomplete transition of OBL flows to a stage that mimics the fully turbulent regime. Data from the literature were also used to support the presence of the phase lag and propose a new ${\rm \Delta} \phi$ diagram. Simulations performed for ${\textit {Re}}_{\delta }=671$ confirmed the sensitivity in the development of self-sustained turbulence on the background disturbances ( $\textit{Re}_{\delta}=U_{o}\delta/\nu$ , where $\delta=[2\nu/\omega]^{1/2}$ is the Stokes' length, $U_{o}$ is the maximum free stream velocity of the oscillation, $\nu$ is the kinematic viscosity and $\omega=2{\rm \pi}/T$ is the angular velocity based on the period of the oscillation T). Variations of the mean velocity slope and intersect values for oscillatory flows are also explained in terms of the proximity to near-equilibrium conditions. Relaminarization and transition effects can significantly delay the development of OBL flows, resulting in an incomplete transition. The shape and defect factors are examined as diagnostic parameters for conditions that allow the formation of a logarithmic profile with the universal von Kármán constant and intersect. These findings are of relevance for environmental fluid mechanics and coastal morphodynamics/engineering applications.

Coherent structures in wave boundary layers. Part 1. Oscillatory motion

2010 ◽  
Vol 646 ◽  
pp. 169-206 ◽  
Author(s):  
STEFAN CARSTENSEN ◽  
B. MUTLU SUMER ◽  
JØRGEN FREDSØE
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Boundary Layers ◽  
Flow Structures ◽  
Bed Shear Stress ◽  
Turbulent Spots ◽  
Onset Of Turbulence ◽  
Stress Signal ◽  
Coherent Flow Structures ◽  
Layer Flow

This work concerns oscillatory boundary layers over smooth beds. It comprises combined visual and quantitative techniques including bed shear stress measurements. The experiments were carried out in an oscillating water tunnel. The experiments reveal two significant coherent flow structures: (i) Vortex tubes, essentially two-dimensional vortices close to the bed extending across the width of the boundary-layer flow, caused by an inflectional-point shear layer instability. The imprint of these vortices in the bed shear stress is a series of small, insignificant kinks and dips. (ii) Turbulent spots, isolated arrowhead-shaped areas close to the bed in an otherwise laminar boundary layer where the flow ‘bursts’ with violent oscillations. The emergence of the turbulent spots marks the onset of turbulence. Turbulent spots cause single or multiple violent spikes in the bed shear stress signal, which has profound implications for sediment transport (in both the laboratory and the field). The experiments also show that similar coherent flow structures exist in the case of combined oscillatory flow and current.

Sign in / Sign up

Export Citation Format

Share Document