A consecutive competitive gas‐liquid reaction is investigated using a Taylor bubble setup regarding the influence of fluid mixing in the bubble wake on yield and selectivity. The concentration fields behind a Taylor bubble are visualized and measured quantitatively with a novel time‐resolved absorption imaging technique based on Beer Lamberts law and an integral selectivity is derived. In addition, the calculation of the local selectivity, often used in numerical approaches, is discussed and the existing experimental limits for its derivation are pointed out. Finally, an increase in selectivity of a competitive consecutive reaction for enhanced mixing is experimentally confirmed.

<p>The ocean surface is, more often than not, riddled with locally generated, growing wind-waves interacting with remotely generated swells. In moderate to high wind speeds, these complex interactions may strongly influence the occurrence of wave breaking as well as airflow separation events, which, in turn, control air-sea fluxes of momentum and scalars.</p><p>We present laboratory measurements of air and water dynamics in the vicinity of wind-modulated mechanically generated waves, at a 10 m fetch, using Particle Image Velocimetry. Using flow vorticity and turbulence estimates above and below the waves, we are able to quantify airflow separation and wave breaking events.</p><p>We observe modulations of the airflow by locally generated wind waves, including small sheltering events downwind of sharp wave crests. We will discuss the influence of local vs peak wind-wave conditions (e.g., wave age, slope), on wind-wave momentum and energy flux mechanisms.</p>

<p>Small-scale processes govern the transfer of energy and momentum at the coupled atmospheric and oceanic wave boundary layers. The physical wind energy input mechanisms by wave growth remain poorly understood (critical layer theory vs sheltering mechanism).</p><p>We conducted laboratory velocity measurements within the first millimeters to centimeters above and below surface waves. A high resolution 2D Particle Image Velocimetry (PIV) system was installed in a wind-wave tunnel at a fetch of approximately 10 m. In addition, wave field properties were captured by Laser-Induced Fluorescence (LIF). Experiments were run with wind waves and wind over mechanical swell. During the measurements, 10-m wind speeds of 5 to 10 m/s were observed, with peak wave ages (<em>c<sub>p</sub>/u<sub>*</sub></em>) ranging from 1 to 7.</p><p>We will focus on the air phase and describe the modulations of the airflow structure. Furthermore, we will discuss the influence of peak wind-wave conditions (e.g., wave age, slope) on the dynamical role of the critical layer.</p>

<p>This study aims to investigate the wave boundary layer and the turbulent<br>airflow above wind waves on slick-free and slick-covered water surfaces. To realize<br>this, we carried out laboratory measurements of the airflow in a wind-wave<br>tank, where we deployed three surfactants of different visco-elastic properties,<br>each at five wind speeds ranging from 4 ms<sup>−1</sup> to 8 ms<sup>−1</sup>. For measurements<br>over slick-free water surfaces, we chose wind speeds, at which we observed the<br>same peak wave frequencies as in the presence of the surfactants. We measured<br>high-resolution single-point profiles of the horizontal and vertical velocity<br>components at different heights above the water surface using a Laser-Doppler-<br>Velocimeter (LDV), wave heights using a wire gauge, and wave slopes using<br>a laser slope gauge. Both wave field parameters were recorded simultaneously<br>with the airflow measurements to investigate the influences of the small-scale<br>wave field on the wave boundary layer. In the airflow turbulence spectra, we<br>found a clear maximum corresponding to the dominant wave frequencies reflecting<br>the influence of the waves on the airflow. However, depending on wind<br>speed and the surfactants’ damping behaviour, the maximum differs in both its<br>strength and its height above the wavy surface, the latter being interpreted as<br>the wave boundary layer height. The LDV achieved mean data rates exceeding<br>2 kHz; hence, it resolved the small-scale turbulence, which manifests in the<br>high-frequency part of the turbulence spectra. For the slick-free cases, we observed<br>a linear decrease in turbulence with increasing height above the surface,<br>and increasing turbulence with increasing friction velocity u∗, which depends<br>on the wind speed and wind-wave interactions. However, we did not find clear<br>trends at any wind speed when the water surface was covered by a surfactant.<br>Here, the turbulence increases with increasing height above the water surface for<br>higher friction velocities. Thus, the surfactants dampen not only the waves, but<br>they also reduce the turbulence in the airflow directly above the waves, within<br>the wave boundary layer.</p>