Measurements Of Air Entrainment Research Articles

Measurement of Air Entrainment and its Effect on the Microstructure and Mechanical Properties of a A356 Aluminum Alloy

Measurement of Air Entrainment and its Effect on the Microstructure and Mechanical Properties of a A356 Aluminum Alloy

Three‐Dimensional Measurements of Air Entrainment and Enhanced Bubble Transport During Wave Breaking

AbstractWe experimentally investigate the depth distributions and dynamics of air bubbles entrained by breaking waves in a wind‐wave channel over a range of breaking wave conditions using high‐resolution imaging and three‐dimensional bubble tracking. Below the wave troughs, the bubble concentration decays exponentially with depth. Patches of entrained bubbles are identified for each breaking wave, and statistics describing the horizontal and vertical transport are presented. Aggregating our results, we find a stream‐wise transport faster than the associated Stokes drift and modified Stokes drift for buoyant particles, which is an effect not accounted for in current models of bubble transport. This enhancement in transport is attributed to the flow field induced by the breaking waves and is relevant for the transport of bubbles, oil droplets, and microplastics at the ocean surface.

Measurements of Air Entrainment into Diesel Spray by Laser Induced Fluorescence-Particle Image Velocimetry Method

Measurements of Air Entrainment into Diesel Spray by Laser Induced Fluorescence-Particle Image Velocimetry Method

Measurement of Air Entrainment During Pouring of an Aluminum Alloy

Measurement of Air Entrainment During Pouring of an Aluminum Alloy

Air entrainment characteristics of artificial supercavities for free and constrained closure models

Artificial supercavitation is a promising technology for the drag reduction of high-speed underwater vehicles, whereby a cavity is generated through air entrainment to encompass the entire vehicle. Supercavitation experiments are conventionally conducted in closed wall water tunnels. In order to properly extend these results to the operation of underwater vehicles in the ocean, it is imperative to understand the underlying physics governing these processes. The current study focuses upon the factors that govern the ventilation demand of a supercavitating vehicle operating under artificial supercavitation mode. Systematic artificial supercavitation experiments are carried out in a high-speed water tunnel with two different experimental models and high-speed visualization and measurements of air entrainment are carried out at different stages of supercavity formation, sustenance and collapse. Our measurements suggest a marked difference between the two experimental models for formation, sustenance and critical air entrainments of supercavities. Such differences are explained based on the understanding of fundamental physical factors governing the process, such as bubble breakup, coalescence and the effect of the presence of a body inside the supercavity.

0514 吸込水槽ポンプへの空気吸込の3次元計測(OS03-3 熱・流体の可視化と計測,オーガナイズドセッション 3:「熱・流体の可視化と計測」)

0514 吸込水槽ポンプへの空気吸込の3次元計測(OS03-3 熱・流体の可視化と計測,オーガナイズドセッション 3:「熱・流体の可視化と計測」)

A sub-grid air entrainment model for breaking bow waves and naval surface ships

Direct numerical simulations (DNS) of air entrainment by the breaking bow waves of naval surface ships are outside of the computational reach of the most powerful computers in the foreseeable future. This creates a need for physically-based models of air entrainment for applications in numerical simulations for ship design. Due to the non-linear dependence of the terminal bubble velocity with diameter most air entrainment flows have a high void fraction region immediately below the free surface. We present a model that locates this region employing the local liquid velocity and the distance to the interface. Using this model and the bubble size distributions measured by Deane and Stokes [Deane BD, Stokes MD. Scale dependence of bubble creation mechanisms in breaking waves. Nature 2002;418:839–44] we have simulated the air entrainment in the breaking wave experiments of Wanieski et al. [Waniewski TA, Brennen CE, Raichlen F. Measurement of air entrainment by bow waves. J Fluids Eng 2001;123:57–63]. Comparison against these experimental data is good. We then apply this model to simulate the flow around naval combatant DTMB 5415 and the research vessel Athena. The model predicts air entrainment in regions where it was actually observed at sea, namely the breaking bow wave, along the water/air/hull contact line and in the near-wake. To the best of our knowledge this is the first model of air entrainment that compares favorably with data at laboratory scale and also presents the right trends at full-scale.

Measurements of air entrainment by vertical plunging liquid jets

This paper addresses the issue of the air-entrainment process by a vertical plunging liquid jet. A non-dimensional physical analysis, inspired by the literature on the stability of free jets submitted to an aerodynamic interaction, was developed and yielded two correlation equations for the laminar and the turbulent plunging jets. These correlation equations allow the volumetric flow rate of the air carryunder represented by the Weber number of entrainment Wen to be predicted. The plunging jets under consideration issued from circular tubes long enough to achieve a fully developed flow at the outlet. A sensitive technique based on a rising soap meniscus was developed to measure directly the volumetric flow rate of the air carryunder. Our data are compared with other experimental data available in the literature; they also stand as a possible database for future theoretical modelling.

Measurement of air-entrainment from a stationary Taylor bubble in a vertical tube

To get insight into the air entrainment process from a Taylor bubble in a vertical tube, we measured the gas loss from a Taylor bubble that was held stationary in a downward liquid flow. Also, we measured the void fraction in the downward bubbly flow below the Taylor bubble, as well as the radial void fraction distribution in this region. We varied the Taylor bubble length, the liquid flow rate approaching the bubble, and the turbulence level of this flow. The experiments strongly indicate that the entrainment flux is related to the presence of turbulence in the liquid film surrounding the Taylor bubble.

Buoyant diffusion flames: Some measurements of air entrainment, heat transfer, and flame merging

Thistledown has been used as a tracer to measure the flow of air toward ethyl alcohol and wood fires 91 cm in diameter, and a smaller town gas fire. The total quantity of air below the mean flame height is approximately one order times the stoichiometric requirements, a substantial part of the air flowing upwards around the flame. The total flow also exceeds that estimated from entrainment theory and measurements of flame tip velocity. The mean concentration of oxygen on the flame axis and the heat transfer back towards the fuel surface have also been measured. The convection transfer at 1–2 cm above the fuel surface was found to be about 1/5 of the total heat transfer at the center increasing to about 1/2 at the edge. The measured mean axial temperature rise at the mean flame height was about 300°–350°C for wood and alcohol and 500°C for town gas. The average period of the eddies outside the flame and the corresponding length were about 0.7 sec and 15 cm, respectively. No variation was found with height above the base. Elementary considerations of entrainment and the motion of flames have been applied to the merging of the flames from two nearby rectilinear fuel beds and there is reasonable agreement between theory and experiment.