The objective of this study is to investigate for turbulent flow the fluid motions very near a solid boundary, and to create a physical picture which relates these motions to turbulence generation and transport processes. An experimental technique was developed which permitted detailed observations of the regions very near a pipe wall, including the viscous sublayer, without requiring the introduction of any injection or measuring device into the flow. This technique involved suspending solid particles of colloidal size in a liquid, and photographing their motions with a high-speed motion picture camera moving with the flow. To provide greater detail, the field of view was magnified.Fluid motions were observed to change in character with distance from the wall. The sublayer was continuously disturbed by small-scale velocity fluctuations of low magnitude and periodically disturbed by fluid elements which penetrated into the region from positions further removed from the wall. From a thin region adjacent to the sublayer, fluid elements were periodically ejected outward toward the centreline. Often there was associated with these events a zone of high shear at the interface between the mean flow and the decelerated region that gave rise to the ejected element. When the ejected element entered this shear zone, it interacted with the mean flow and created intense, chaotic velocity fluctuations. These ejections and resulting fluctuations were the most important feature of the wall region, and are believed to be a factor in the generation and maintenance of turbulence.

/pdf/a-visual-investigation-of-the-wall-region-in-turbulent-flow-1or0vrnor1.pdf

A visual investigation of the wall region in turbulent flow

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/jps.2600560302

Diffusional Models Useful in Biopharmaceutics: Drug Release Rate Processes

On gas absorption into a turbulent liquid

Drops in annular two-phase flow

Correlation of entrainment for annular flow in horizontal pipes

The droplets that appear in annular gas-liquid flows are formed by the eruption of wavelets from the surface of the wall layer. Ninety per cent of the volume of this dispersed liquid is carried by only about 10% of the drops. We find, as suggested by Wicks and Dukler, that the distribution of drop sizes can be characterized by an upper limit, log normal function with only one of the three parameters, the volume median diameter, a strong function of flow conditions. A method for predicting the average diameter is suggested which is consistent with a theoretical interpretation based on a Kelvin-Helmholtz mechanism, whereby the destabilizing force is the pressure variation over the wavelets.

Drop sizes in annular gas‐liquid flows

Visual observations by Fage and Townend of the behavior of a turbulent-flow strean near a boundary and experimental data by Lin, Moulton, and Putnam of concentratiol profiles near a boundary contradict the commonly held concept of the “laminar sublayer.” A model developed by Higbie and Danckwerts which is consistent with the visual obser vations of Page and Townend is used to describe the exchange of mass and heat between a turbulent fluid and a solid surface. It is postulated that masses of fluid are contiuously moving to and from the wall. The exchange process then depends on the average contact time of these fluid masses with the wall.

The agreement of the concentration profile predicted on the basis of the proposed model with experimental mass transfer data where the exchange process is rate controlling lends support to the usefulness of the model. No equivalent data are available for velocity profiles. Velocity data represent a condition where the transport process within the fluid is playing an important role; however, in the immediate vicinity of the wall the proposed model might serve as a rough approximation of the profile. Such an approximation is made in this paper, and the agreement obtained is much better than should be expected.

Thomas J. Hanratty

Papers

Drop sizes in annular gas‐liquid flows

Turbulent exchange of mass and momentum with a boundary