Light attenuation experiments on double diffusive plumes and fountains

Sutherland, Bruce; Lee, Brace; Ansong, Joseph K.

doi:10.1063/1.4730431

Cited by 13 publications

(16 citation statements)

References 39 publications

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“…The light attenuation measurements gave density fields before, during and after transits of the ridge, at a high spatial resolution limited only by the digital camera sensor [ Allgayer and Hunt , ]. This method has been previously applied to infer dye concentration and density fields from attenuation measurements [e.g., Hacker et al ., ; Sutherland et al ., ]. The light source was an electroluminescent panel, which had maximum emission in the blue part of the visible spectrum.…”

Section: Experimental Methodsmentioning

confidence: 99%

Experiments with mixing in stratified flow over a topographic ridge

et al. 2016

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The interaction of quasi‐steady abyssal ocean flow with submarine topography is expected to generate turbulent mixing in the ocean. This mixing may occur locally, close to topography, or via breaking quasi‐steady lee waves that can carry energy into the ocean interior. There is currently no theoretical, or empirically derived, prediction for the relative amounts of local and interior mixing. We report measurements of the mixing rate in laboratory experiments with a topographic ridge towed through a density stratification. The experiments span three parameter regimes including linear lee waves, nonlinear flow and an evanescent regime in which wave radiation is weak. Full field density measurements provide the depth‐dependence of energy loss to turbulent mixing, allowing separation of the local mixing in the turbulent wake and remote mixing by wave radiation. Remote mixing is significant only for a narrow band of forcing parameters where the flow speed is resonant with internal waves; in all other parameter regimes local mixing close to the topography is dominant. The results suggest that mixing by local nonlinear mechanisms close to abyssal ocean topography may be much greater than the remote mixing by quasi‐steady lee waves.

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Section: Experimental Methodsmentioning

confidence: 99%

Experiments with mixing in stratified flow over a topographic ridge

et al. 2016

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“…The line-of-sight averaged concentration used in the aforementioned papers, however, is not a solution for the nonlinear response we see here. In a pioneering work, Sutherland, Lee & Ansong (2012) analysed the averaged image based on the axisymmetric discretization, converting the depth-integrated recorded image to the concentration field as a function of radius and height, which serves as a very good strategy for our interests to obtain the oversaturation field as a function of radius and height in the domain.…”

Section: Experimental Methodsmentioning

confidence: 99%

Micro-droplet nucleation through solvent exchange in a turbulent buoyant jet

et al. 2022

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Solvent exchange is a process involving mixing between a good solvent with dissolved solute and a poor solvent. The process creates local oversaturation which causes the nucleation of minute solute droplets. Such ternary systems on a macro-scale have remained unexplored in the turbulent regime. We experimentally study the solvent exchange process by injecting mixtures of ethanol and trans-anethole into water, forming a turbulent buoyant jet in the upward direction. Locally, turbulent mixing causes oversaturation of the trans-anethole following turbulent entrainment. We optically measure the concentration of the nucleated droplets using a light attenuation technique and find that the radial concentration profile has a sub-Gaussian kurtosis. In contrast to the entrainment-based models, the spatial evolution of the oversaturation reveals continuous droplet nucleation downstream and radially across the jet, which we attribute to the limited mixing capacity of the jet. Although we are far from a full quantitative understanding, this work extends the knowledge on solvent exchange into the turbulent regime, and brings in a novel type of flow, broadening the scope of multicomponent, multiphase turbulent jets with phase transition.

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“…The light attenuation technique infers local density from absorption measurements at high spatial resolution (Allgayer & Hunt, 1991; Hacker et al, 1996; Sutherland et al, 2012). This method has previously been used to describe the dynamics of IWs generated in the lee of a moving topography as well as the induced mixing (Dossmann, Gamble Rosevear, et al, 2016).…”

Section: Methodsmentioning

confidence: 99%

Asymmetric Internal Tide Generation in the Presence of a Steady Flow

et al. 2020

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The generation of topographic internal waves (IWs) by the sum of an oscillatory and a steady flow is investigated experimentally and with a linear model. The two forcing flows represent the combination of a tidal constituent and a weaker quasi-steady flow interacting with an abyssal hill. The combined forcings cause a coupling between internal tides and lee waves that impacts their dynamics of IWs as well as the energy carried away. An asymmetry is observed in the structure of upstream and downstream IW beams due to a quasi-Doppler shift effect. This asymmetry is enhanced for the narrowest ridge on which a superbuoyancy (> N) downstream beam and an evanescent upstream beam are measured. Energy fluxes are measured and compared with the linear model, that has been extended to account for the coupling mechanism. The structure and amplitude of energy fluxes match well in most regimes, showing the relevance of the linear prediction for IW wave energy budgets, while the energy flux toward IW beams is limited by the generation of periodic vortices in a particular experiment. The upstream-bias energy flux-and consequently net horizontal momentum-described in Shakespeare (2020, https://doi.org/10.1175/JPO-D-19-0179.1) is measured in the experiments. The coupling mechanism plays an important role in the pathway to IW-induced mixing, that has previously been quantified independently for lee waves and internal tides. Hence, future parameterizations of IW processes ought to include the coupling mechanism to quantify its impact on the global distribution of mixing. Plain Language Summary When tides and currents interact with abyssal topographies, such as ridges and hills, they generate internal waves that propagate in the ocean interior. The energy transported by these waves sustains the largest scale oceanic motions. To improve our understanding of how and where energy is transferred to oceanic currents, an important step is to describe the fate of internal waves, from their generation to their breaking. Previous studies have independently described the dynamics of internal waves generated by tides, or by a steady current. Here we combine the two types of currents-a situation that is met at many oceanic sites-using laboratory experiments and a linear model. The combined currents cause an asymmetry in the internal wave structure. Internal waves are more energetic on the upstream side of the ridge, a phenomenon that is amplified when decreasing the ridge width. The measured energy matches the model prediction in all but one experiment. This gap is likely related to the formation of a vertical swirl close to the ridge that limits energy transfers to internal waves. These results contributes to improve our understanding of the internal wave dynamics and to better represent their effects in oceanic models. IWs are predominantly generated either at the surface by wind fluctuations or at the ocean bottom by the interaction of flow with topography. Two seemingly independent classes of topographic IWs have been distinguished in previo...

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Light attenuation experiments on double diffusive plumes and fountains

Cited by 13 publications

References 39 publications

Experiments with mixing in stratified flow over a topographic ridge

Experiments with mixing in stratified flow over a topographic ridge

Micro-droplet nucleation through solvent exchange in a turbulent buoyant jet

Asymmetric Internal Tide Generation in the Presence of a Steady Flow

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