Turbulent Boundary-Layer Separation

Simpson, Robert W.

doi:10.1146/annurev.fluid.21.1.205

Cited by 120 publications

(193 citation statements)

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“…5b). These variations are coherent with the separated sheltering hypothesis, which suggests the presence of recirculations past the point of separation (e.g., Simpson 1989). The spanwise vorticity field, plotted in Fig.…”

Section: Instantaneous 2d Fieldssupporting

confidence: 74%

“…This suggests that, over the crest, the viscous boundary layer is very thin, and the near surface shear is large. In aerodynamics, boundary layer thinning is known to occur in a similar fashion in favorable pressure gradient conditions, on the leading edge of an airplane wing or the upwind side of a hill for example (Baskaran et al 1987;Simpson 1989). Just past the wave crest, the shear layer appears to detach from the water surface, and the near surface streamwise velocity drops dramatically.…”

Section: Instantaneous 2d Fieldsmentioning

confidence: 99%

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Airflow measurements at a wavy air–water interface using PIV and LIF

Buckley

Véron

2017

Exp Fluids

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geophysical sphere, which largely motivates this study, fluxes of momentum and scalars across the wavy air-sea interface provide boundary conditions for both the atmosphere and the oceans and are therefore, pivotal in controlling the evolution of weather and climate. These fluxes are affected by fine-scale, coupled dynamics above and below the wavy ocean surface. In fact, the surface waves significantly modify the boundary layers on both sides of the interface and it is now well established that it is through waverelated dynamical processes that the air and water boundary layers are coupled (see Sullivan and McWilliams (2010) for a review on the topic).On the water side, for example, it has been shown that the interaction between the wave-induced Lagrangian mass transport, i.e. the Stokes drift, and the surface shear current, leads to the generation of Langmuir circulations, causing significant mixing of the water column (Skyllingstad and Denbo 1995;McWilliams et al. 1997;Noh et al. 2005;Li et al. 2005;Harcourt and D'Asaro 2008; Grant and E 2009;Veron et al. 2009;Kukulka et al. 2010;Belcher et al. 2012;D'Asaro 2014). When surface waves break, the turbulence injected into the water column also significantly enhances surface mixing Melville et al. 1998;Veron and Melville 1999;Melville et al. 2002;Thorpe et al. 2003;Gemmrich and Farmer 2004) and leads to substantial deviations from the classical theories (Agrawal et al. 1992;Thorpe 1993;Melville 1994;Anis and Moum 1995;Melville 1996;Terray et al. 1996; Veron and Melville 2001) and causes significant energy dissipation (Banner et al. 2014;Thomson et al. 2016;Schwendeman et al. 2014;Zappa et al. 2016; Melville 2013, 2015).On the air side, it is clear that surface wave processes also play an important role in the kinematics and dynamics of the boundary layer (e.g. Janssen 1989; Komen et al. 1994;Belcher and Hunt 1998;Hristov et al. 1998; Abstract Physical phenomena at an air-water interface are of interest in a variety of flows with both industrial and natural/environmental applications. In this paper, we present novel experimental techniques incorporating a multi-camera multi-laser instrumentation in a combined particle image velocimetry and laser-induced fluorescence system. The system yields accurate surface detection thus enabling velocity measurements to be performed very close to the interface. In the application presented here, we show results from a laboratory study of the turbulent airflow over wind driven surface waves. Accurate detection of the wavy air-water interface further yields a curvilinear coordinate system that grants practical and easy implementation of ensemble and phase averaging routines. In turn, these averaging techniques allow for the separation of mean, surface wave coherent, and turbulent velocity fields. In this paper, we describe the instrumentation and techniques and show several data products obtained on the air-side of a wavy air-water interface.

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Section: Instantaneous 2d Fieldssupporting

confidence: 74%

Section: Instantaneous 2d Fieldsmentioning

confidence: 99%

Airflow measurements at a wavy air–water interface using PIV and LIF

Buckley

Véron

2017

Exp Fluids

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“…The resulting extrapolated measurement volume has a typical aspect ratio of about 10 (length in xdirection divided by typical width along y-or z-directions). Such an aspect ratio is reasonable compared with, although greater than, the coherent structure length-scale ratios in the near-wall turbulent boundary layer (Simpson 1989;Jeong et al 1997), but strongly affects the gradient estimation variance. The effect of this aspect ratio on the uncertainties for the final result is evident in a couple of ways.…”

Section: Quantification Ofperformance Of the Direct Estimation Proceduresmentioning

confidence: 94%

Application of a Novel Laser-Doppler Velocimeter for Turbulence: Structural Measurements in Turbulent Boundary Layers

Lowe¹

2006

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“…Previously, experimental investigation by Shugar et al (2010) showed that stacked series of wavelet plots indicated that clusters of low-frequency coherent flow structures initiated close to the bed, grew with height above the bed, and then broke up as they were advected downstream, with their decay possibly being linked to topographically induced flow acceleration. The frequency at which these structures were generated was suitably predicted by the models of Driver et al (1987) and Simpson (1989) for variation in separation zone size and wake flapping, respectively. Our measured data in BMCV runs were consistent with AMCV runs as well as with previous investigations.…”

Section: Discussionmentioning

confidence: 99%

The influence of turbulent bursting on sediment resuspension under unidirectional currents

et al. 2017

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Abstract. Laboratory experiments were conducted in an open channel flume with a flat sandy bed to examine the role of turbulence on sediment resuspension. An acoustic Doppler velocimeter (ADV) was used to measure the instantaneous three-dimensional velocity components and acoustic backscatter as a proxy to suspended sediment concentration. Estimates of sediment transport assume that there is a mean critical velocity that needs to be exceeded before sediment transport is initiated. This approach does not consider the turbulent flow field that may initiate sediment resuspension through event-based processes such as the "bursting" phenomenon. In this paper, laboratory measurements were used to examine the sediment resuspension processes below and above the mean critical velocity. The results within a range above and below the measured mean critical velocity suggested that (1) the contribution of turbulent bursting events remained identical in both experimental conditions, (2) ejection and sweep events contributed more to the total sediment flux than up-acceleration and down-deceleration events, and (3) wavelet transform revealed a correlation between the momentum and sediment flux in both test conditions. Such similarities in conditions above and below the measured mean critical velocity highlight the need to re-evaluate the accuracy of a single time-averaged mean critical velocity for the initiation of sediment entrainment.

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Turbulent Boundary-Layer Separation

Cited by 120 publications

References 0 publications

Airflow measurements at a wavy air–water interface using PIV and LIF

Airflow measurements at a wavy air–water interface using PIV and LIF

Application of a Novel Laser-Doppler Velocimeter for Turbulence: Structural Measurements in Turbulent Boundary Layers

The influence of turbulent bursting on sediment resuspension under unidirectional currents

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