Small-Scale Phenomena in Reactive Bubbly Flows: Experiments, Numerical Modeling, and Applications

2021 ◽  
Vol 12 (1) ◽  
pp. 625-643
Author(s):  
Michael Schlüter ◽  
Sonja Herres-Pawlis ◽  
Ulrich Nieken ◽  
Ute Tuttlies ◽  
Dieter Bothe
Keyword(s):  
Bubbly Flows ◽  
Small Scale ◽  
Joint Research ◽  
Mixing Processes ◽  
Wake Structure ◽  
Local Bubble ◽  
Reaction Systems ◽  
Process Improvements ◽  
Consecutive Reactions ◽  
Challenging Tasks

Improving the yield and selectivity of chemical reactions is one of the challenging tasks in paving the way for a more sustainable and climate-friendly economy. For the industrially highly relevant gas–liquid reactions, this can be achieved by tailoring the timescales of mixing to the requirements of the reaction. Although this has long been known for idealized reactors and time- and space-averaged processes, considerable progress has been made recently on the influence of local mixing processes. This progress has become possible through joint research between chemists, mathematicians, and engineers. We present the reaction systems with adjustable kinetics that have been developed, which are easy to handle and analyze. We show examples of how the selectivity of competitive-consecutive reactions can be controlled via local bubble wake structures. This is demonstrated for Taylor bubbles and bubbly flows under technical conditions. Highly resolvednumerical simulations confirm the importance of the bubble wake structure for the performance of a particular chemical reaction and indicate tremendous potential for future process improvements.

scholarly journals Physical Transport Processes that Affect the Distribution of Oil in the Gulf of Mexico: Observations and Modeling

Oceanography ◽  
2021 ◽  
Vol 34 (1) ◽  
pp. 58-75
Author(s):  
Michel Boufadel ◽  
◽  
Annalisa Bracco ◽  
Eric Chassignet ◽  
Shuyi Chen ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Physical Environment ◽  
Large Scale ◽  
Transport Processes ◽  
Small Scale ◽  
Surface Mixed Layer ◽  
Physical Processes ◽  
Mixing Processes ◽  
Near Surface ◽  
Wide Range

Physical transport processes such as the circulation and mixing of waters largely determine the spatial distribution of materials in the ocean. They also establish the physical environment within which biogeochemical and other processes transform materials, including naturally occurring nutrients and human-made contaminants that may sustain or harm the region’s living resources. Thus, understanding and modeling the transport and distribution of materials provides a crucial substrate for determining the effects of biological, geological, and chemical processes. The wide range of scales in which these physical processes operate includes microscale droplets and bubbles; small-scale turbulence in buoyant plumes and the near-surface “mixed” layer; submesoscale fronts, convergent and divergent flows, and small eddies; larger mesoscale quasi-geostrophic eddies; and the overall large-scale circulation of the Gulf of Mexico and its interaction with the Atlantic Ocean and the Caribbean Sea; along with air-sea interaction on longer timescales. The circulation and mixing processes that operate near the Gulf of Mexico coasts, where most human activities occur, are strongly affected by wind- and river-induced currents and are further modified by the area’s complex topography. Gulf of Mexico physical processes are also characterized by strong linkages between coastal/shelf and deeper offshore waters that determine connectivity to the basin’s interior. This physical connectivity influences the transport of materials among different coastal areas within the Gulf of Mexico and can extend to adjacent basins. Major advances enabled by the Gulf of Mexico Research Initiative in the observation, understanding, and modeling of all of these aspects of the Gulf’s physical environment are summarized in this article, and key priorities for future work are also identified.

3-D tomographic observations of Rossby wave breaking over the Northern Atlantic during the WISE aircraft campaign in 2017

2021 ◽  
Author(s):  
Lukas Krasauskas ◽  
Jörn Ungermann ◽  
Peter Preusse ◽  
Felix Friedl-Vallon ◽  
Andreas Zahn ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Water Vapour ◽  
Rossby Wave ◽  
Wave Breaking ◽  
Thin Filament ◽  
Small Scale ◽  
Data Sets ◽  
Mixing Processes ◽  
Air Masses ◽  
Rossby Wave Breaking

<p>We present measurements of ozone, water vapour and nitric acid in the upper troposphere/lower stratosphere (UTLS) over North Atlantic and Europe. The measurements were acquired with the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) during the Wave Driven Isentropic Exchange (WISE) campaign in October 2017. GLORIA is an airborne limb imager capable of acquiring both 2-D data sets (curtains along the flight path) and, when the carrier aircraft is flying around the observed air mass, spatially highly resolved 3-D tomographic data. We show a case study of a Rossby wave (RW) breaking event observed during two subsequent flights two days apart. RW breaking is known to steepen tracer gradients and facilitate stratosphere-troposphere exchange (STE). Our measurements reveal complex spatial structures in stratospheric tracers (ozone and nitric acid) with multiple vertically stacked filaments. Backward trajectory analysis is used to demonstrate that these features are related to several previous Rossby wave breaking events and that the small-scale structure of the UTLS in the Rossby wave breaking region, which is otherwise very hard to observe, can be understood as stirring and mixing of air masses of tropospheric and stratospheric origin. It is also shown that a strong nitric acid enhancement observed just above the tropopause is likely a result of NO<sub>x</sub> production by lightning activity. The measurements showed signatures of enhanced mixing between stratospheric and tropospheric air near the polar jet with some transport of water vapour into the stratosphere. Some of the air masses seen in 3-D data were encountered again two days later, stretched to very thin filament (horizontal thickness down to 30 km at some altitudes) rich in stratospheric tracers. This repeated measurement allowed us to directly observe and analyse the progress of mixing processes in a thin filament over two days. Our results provide direct insight into small-scale dynamics of the UTLS in the Rossby wave breaking region, witch is of great importance to understanding STE and poleward transport in the UTLS.</p>

Fractal reconstruction of the subgrid scales in turbulence models in applications to cloud microphysics

2020 ◽  
Author(s):  
Emmanuel Akinlabi ◽  
Marta Waclawczyk ◽  
Szymon Malinowski
Keyword(s):  
Climate Models ◽  
A Priori ◽  
Turbulence Models ◽  
Random Variable ◽  
Fractal Model ◽  
Cloud Microphysics ◽  
Small Scale ◽  
Mixing Processes ◽  
Subgrid Scales ◽  
Scale Turbulence

<p>Modelling of small-scale turbulence in the atmosphere play a significant role in improving our understanding of cloud processes, thereby contributing to the development of better parameterization of climate models. One of the important problems is related to the transport of cloud particles, their activation and growth, which are influenced by small-scale turbulence motions. The idea presented in this work is to use fractal interpolation to reconstruct structures which are typically not resolved in the Large Eddy Simulations (LES) of clouds. Known filtered values of velocities on LES are basis of the reconstruction. The reconstructed small scales depend on the stretching parameter <em>d</em>, which is related to the fractal dimension of the signal. In many previous studies, the stretching parameter values were assumed to be constant in space and time. We modify this approach by treating the stretching parameter as a random variable with a prescribed probability density function (pdf). This function can be determined from <em>a priori</em> analysis of numerical or experimental data and within a certain range of wavenumbers it has a universal form, independent of the Reynolds number. We show, such modification leads to improvement in terms of reconstruction of two-point statistics of turbulent velocities. Preliminary results of simulations with Lagrangian particles (superdroplets) in the reconstructed field show the fractal model properly mimics the turbulent mixing processes at subgrid scales.</p>

Flow Physics and Vortex Evolution in Annular Turbine Cascades

2002 ◽  
Author(s):  
M. Treiber ◽  
R. S. Abhari ◽  
M. Sell
Keyword(s):  
Leading Edge ◽  
Operating Conditions ◽  
Experimental Results ◽  
Small Scale ◽  
Test Case ◽  
Mixing Processes ◽  
Substantial Impact ◽  
Aerodynamic Loss ◽  
Spatially Resolved ◽  
Exit Mach Number

The evolution of flow vortices downstream of annular cascades with a specific focus upon the association between vorticity and the mechanisms of aerodynamic loss generation has been experimentally investigated. Spatially-resolved experimental results on an unstructured measurement pattern is used to identify small scale flow structures on the surface of the investigated blades and downstream of two different cascades. The test case comparison is based upon two moderately loaded turbine blade profiles, one stacked prismatically and the other on a bowed stacking line. The design operating conditions for both cascade is at a nominal exit Mach number of 0.5. The measurements were made using an ultra miniature (0.9 mm Dia) 5-hole probe. The measurement were made on 4 planes behind and one plane in front of the trailing and leading edge of the cascade respectively. The experimental results clearly show the influence of the flow structure on the evolution of the stream wise vorticities behind the blading. Detailed measurements are used to compare and evaluate the mixing processes downstream of these two cascades. It is shown that the interaction of the different vortices with the endwall boundary layer has a substantial impact on the overall total pressure loss generation.

scholarly journals The Thinness of the Ocean in S–Θ–p Space and the Implications for Mean Diapycnal Advection

2007 ◽  
Vol 37 (6) ◽  
pp. 1714-1732 ◽  
Author(s):  
Trevor J. McDougall ◽  
David R. Jackett
Keyword(s):  
Dimensional Space ◽  
World Ocean ◽  
Three Dimensional ◽  
Small Scale ◽  
Lateral Motion ◽  
Hydrographic Data ◽  
Mixing Processes ◽  
The World ◽  
The Mean ◽  
Three Dimensional Space

Abstract It is shown that the ocean’s hydrography occupies little volume in the three-dimensional space defined by salinity–temperature–pressure (S–Θ–p), and the implications of this observation for the mean vertical transport across density surfaces are discussed. Although ocean data have frequently been analyzed in the two-dimensional temperature–salinity (S–Θ) diagram where casts of hydrographic data are often locally tight in S–Θ space, the relatively empty nature of the World Ocean in the three-dimensional S–Θ–p space seems not to have received attention. The World Ocean’s data lie close to a single surface in this three-dimensional space, and it is shown that this explains the known smallness of the ambiguity in defining neutral surfaces. The ill-defined nature of neutral surfaces means that lateral motion along neutral trajectories leads to mean vertical advection through density surfaces, even in the absence of small-scale mixing processes. The situation in which the ocean’s hydrography occupies a large volume in S–Θ–p space is also considered, and it is suggested that the consequent vertical diapycnal advection would be sufficiently large that the ocean would not be steady.

scholarly journals Effcts of smooth divergence-free flows on tracer gradients and spectra: Eulerian prognosis description

2021 ◽  
Author(s):  
Valentin Resseguier ◽  
Bertrand Chapron ◽  
Etienne Mémin
Keyword(s):  
Growth Rate ◽  
Finite Time ◽  
Eddy Diffusivity ◽  
Spectral Energy ◽  
Optimal Time ◽  
Small Scale ◽  
Coarse Scale ◽  
Mixing Processes ◽  
Finite Time Lyapunov Exponents ◽  
Flow Gradients

AbstractOcean eddies play an important role in the transport of heat, salt, nutrients or pollutants. During a finite-time advection, the gradients of these tracers can increase or decrease, depending on a growth rate and the angle between flow gradients and initial tracer gradients. The growth rate is directly related to finite-time Lyapunov exponents. Numerous studies on mixing and/or tracer downscaling methods rely on satellite altimeter-derived ocean velocities. Filtering most oceanic small-scale eddies, the resulting smooth Eulerian velocities are often stationary during the characteristic time of tracer gradient growth. While smooth, these velocity fields are still locally misaligned, and thus uncorrelated, to many coarse-scale tracers observations amendable to downscaling (e.g. SST, SSS). Using finite-time advections, the averaged squared norm of tracer gradients can then only increase, with local growth rate independent of the initial coarse-scale tracer distribution. The key mixing processes are then only governed by locally uniform shears and foldings around stationary convective cells. To predict the tracer deformations and the evolution of their 2nd-order statistics, an effcient proxy is proposed. Applied to a single velocity snapshot, this proxy extends the Okubo-Weiss criterion. For the Lagrangian-advection-based downscaling methods, it further successfully predicts the evolution of tracer spectral energy density after a finite time, and the optimal time to stop the downscaling operation. A practical estimation can then be proposed to define an effective parameterization of the horizontal eddy diffusivity.

scholarly journals A Thermohaline Inverse Method for Estimating Diathermohaline Circulation and Mixing

2014 ◽  
Vol 44 (10) ◽  
pp. 2681-2697 ◽  
Author(s):  
Sjoerd Groeskamp ◽  
Jan D. Zika ◽  
Bernadette M. Sloyan ◽  
Trevor J. McDougall ◽  
Peter C. McIntosh
Keyword(s):  
Diffusion Coefficient ◽  
Inverse Method ◽  
Climate Model ◽  
Salinity Gradient ◽  
Surface Flux ◽  
Volume Transport ◽  
Heat Fluxes ◽  
Small Scale ◽  
Mixing Processes ◽  
Turbulent Diffusion Coefficient

Abstract The thermohaline inverse method (THIM) is presented that provides estimates of the diathermohaline streamfunction , the downgradient along-isopycnal diffusion coefficient K, and the isotropic downgradient turbulent diffusion coefficient D of small-scale mixing processes. This is accomplished by using the water mass transformation framework in two tracer dimensions: here in Absolute Salinity SA and Conservative Temperature Θ coordinates. The authors show that a diathermal volume transport down a Conservative Temperature gradient is related to surface heating and cooling and mixing, and a diahaline volume transport down an Absolute Salinity gradient is related to surface freshwater fluxes and mixing. Both the diahaline and diathermal flows can be calculated using readily observed parameters that are used to produce climatologies, surface flux products, and mixing parameterizations for K and D. Conservation statements for volume, salt, and heat in (SA, Θ) coordinates, using the diahaline and diathermal volume transport expressed as surface freshwater and heat fluxes and mixing, allow for the formulation of a system of equations that is solved by an inverse method that can estimate the unknown diathermohaline streamfunction and the diffusion coefficients K and D. The inverse solution provides an accurate estimate of , K, and D when tested against a numerical climate model for which all these parameters are known.

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