Fiber-optic probe measurements of void fraction and bubble size distributions beneath breaking waves

Rojas, Gabriela; Loewen, Mark

doi:10.1007/s00348-007-0356-5

Cited by 71 publications

(53 citation statements)

References 25 publications

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“…3.7) can be applied to the experimental data of Deane & Stokes (2002) shown in the inset of Figure 1. Figure 7e shows the time-averaged bubble size distributionN (r) over the active breaking time τ b .N (r) is found to follow a power law,N (r) ∝ r −m , with 3 m 3.5 compatible with various experimental results (Terrill et al 2001;Deane & Stokes 2002;Rojas & Loewen 2007;Blenkinsopp & Chaplin 2010). The bubble inertial subrange, i.e.…”

Section: Time Evolution Of the Bubble Size Distribution And Integral supporting

confidence: 75%

“…Several experimental studies (Loewen et al 1996;Terrill et al 2001;Deane & Stokes 2002;Leifer & de Leeuw 2006;Rojas & Loewen 2007;Blenkinsopp & Chaplin 2010) have identified a bubble size distribution following a power law of the bubble radius N (r) ∝ r −m with m ∈ [2.5 : 3.5], roughly compatible with Eq. (1.1) when considering the difficulty of the experiments.…”

Section: Bubble Size Distribution Models and Observationssupporting

confidence: 53%

“…From Figure 1 it is hard to make a clear statement on the exact value of the power law exponent m. Data from Deane & Stokes (2002) and Loewen et al (1996) are closer to the m = 10/3 value while data from more recent experiments shows values closer to m = 3 (Rojas & Loewen 2007;Blenkinsopp & Chaplin 2010). Moreover, the experiments by Deane & Stokes (2002) and Blenkinsopp & Chaplin (2010) give very different shapes for N (r) below the Hinze scale.…”

Section: Bubble Size Distribution Models and Observationsmentioning

confidence: 89%

“…(1.1) when considering the difficulty of the experiments. Figure 1 shows the bubble size distribution from various laboratory studies, using different measurement methods: cameras and bubble interface detection technique (Deane & Stokes 2002), fiber optical probes (Rojas & Loewen 2007; Blenkinsopp & Chaplin (2010), (×) L1996 for Loewen et al (1996), ( ) RL2007 for Rojas & Loewen (2007) and (•) DS2002 for Deane & Stokes (2002). (Inset) Experimental bubble size distributions N (r, t) from Deane & Stokes (2002), during the active breaking stage (+) and later during the decay (•).…”

Section: Bubble Size Distribution Models and Observationsmentioning

confidence: 99%

“…Experimentally, the local void fraction α(x, z, t) (volume of air per unit volume of water) is measured using conductivity (Lamarre & Melville 1991) or optical probes (Blenkinsopp & Chaplin 2007;Rojas & Loewen 2007). A spatial map of the void fraction is then obtained by repeating this measure at various locations.…”

Section: Air Entrainment and Void Fractionmentioning

confidence: 99%

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Air entrainment and bubble statistics in breaking waves

2016

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We investigate air entrainment and bubble statistics in three-dimensional breaking waves through novel direct numerical simulations of the two-phase air-water flow, resolving the length scales relevant for the bubble formation problem, the capillary length and the Hinze scale. The dissipation due to breaking is found to be in good agreement with previous experimental observations and inertial-scaling arguments. The air-entrainment properties and bubble-size statistics are investigated for various initial characteristic wave slopes. For radii larger than the Hinze scale, the bubble size distribution, can be described by N (r, t) = B(V 0 /2π)(ε(t − ∆τ )/W g)r −10/3 r −2/3 m during the active breaking stages, where ε(t − ∆τ ) is the time dependent turbulent dissipation rate, with ∆τ the collapse time of the initial air pocket entrained by the breaking wave, W a weighted vertical velocity of the bubble plume, r m the maximum bubble radius, g gravity, V 0 the initial volume of air entrained, r the bubble radius and B a dimensionless constant. The active breaking time-averaged bubble size distribution is described bȳ N (r) = B(1/2π)( l L c /W gρ)r −10/3 r −2/3 m , where l is the wave dissipation rate per unit length of breaking crest, ρ the water density and L c the length of breaking crest. Finally, the averaged total volume of entrained air,V , per breaking event can be simply related to l byV = B( l L c /W gρ), which leads to a relationship to a characteristic slope, S, of V ∝ S 5/2 . We propose a phenomenological turbulent bubble break-up model, based on earlier models and the balance between mechanical dissipation and work done against buoyancy forces. The model is consistent with the numerical results and existing experimental results.

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Section: Time Evolution Of the Bubble Size Distribution And Integral supporting

confidence: 75%

Section: Bubble Size Distribution Models and Observationssupporting

confidence: 53%

Section: Bubble Size Distribution Models and Observationsmentioning

confidence: 89%

Section: Bubble Size Distribution Models and Observationsmentioning

confidence: 99%

Section: Air Entrainment and Void Fractionmentioning

confidence: 99%

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Air entrainment and bubble statistics in breaking waves

2016

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Experimental study on plunging breaking waves in deep water

et al. 2015

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This study presents a unique data set that combines measurements of velocities and void fraction under an unsteady deep water plunging breaker in a laboratory. Flow properties in the aerated crest region of the breaking wave were measured using modified particle image velocimetry (PIV) and bubble image velocimetry (BIV). Results show that the maximum velocity in the plunging breaker reached 1.68C at the first impingement of the overturning water jet with C being the phase speed of the primary breaking wave, while the maximum velocity reached 2.14C at the beginning of the first splash-up. A similarity profile of void fraction was found in the successive impinging and splash-up rollers. In the highly foamy splashing roller, the increase of turbulent level and vorticity level were strongly correlated with the increase of void fraction when the range of void fraction was between 0 and 0.4 (from the trough level to approximately the center of the roller). The levels became constant when void fraction was greater than 0.5. The mass flux, momentum flux, kinetic energy, potential energy, and total energy were computed and compared with and without the void fraction being accounted for. The results show that all the mean and turbulence properties related to the air-water mixture are considerably overestimated unless void fraction is considered. When including the density variation due to the air bubbles, the wave energy dissipated exponentially a short distance after breaking; about 54% and 85% of the total energy dissipated within one and two wavelengths beyond the breaking wave impingement point, respectively.

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Turbulent flow field and air entrainment in laboratory plunging breaking waves

Chang

Huang

et al. 2016

JGR Oceans

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This paper presents laboratory measurements of turbulent flow fields and void fraction in deep‐water plunging breaking waves using imaging and optical fiber techniques. Bubble‐size distributions are also determined based on combined measurements of velocity and bubble residence time. The most excited mode of the local intermittency measure of the turbulent flow and its corresponding length scale are obtained using a wavelet‐based method and found to correlate with the swirling strength and vorticity. Concentrated vortical structures with high intermittency are observed near the lower boundaries of the aerated rollers where the velocity shear is high; the length scale of the deduced eddies ranges from 0.05 to 0.15 times the wave height. The number of bubbles with a chord length less than 2 mm demonstrates good correlation with the swirling strength. The power‐law scaling and the Hinze scale of the bubbles determined from the bubble chord length distribution compare favorably with existing measurements. The turbulent dissipation rate, accounting for void fraction, is estimated using mixture theory. When void fraction is not considered, the turbulent dissipation rate is underestimated by more than 70% in the initial impinging and the first splash‐up roller. A significant discrepancy of approximately 67% between the total energy dissipation rate and the turbulence dissipation rate is found. Of this uncounted dissipation, 23% is caused by bubble‐induced dissipation.

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Fiber-optic probe measurements of void fraction and bubble size distributions beneath breaking waves

Cited by 71 publications

References 25 publications

Air entrainment and bubble statistics in breaking waves

Air entrainment and bubble statistics in breaking waves

Experimental study on plunging breaking waves in deep water

Turbulent flow field and air entrainment in laboratory plunging breaking waves

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