A. F. Charwat

Bio: A. F. Charwat is an academic researcher from University of California, Los Angeles. The author has contributed to research in topics: Wetting & Flow velocity. The author has an hindex of 2, co-authored 2 publications receiving 100 citations.

The flow and stability of thin liquid films on a rotating disk

Abstract: Measurements of the thickness and the stability of thin films of liquid (1–150 μmthick) formed on a rotating horizontal disk are presented and correlated in terms of an asymptotic-expansion solution of the thin-film equations. Water, various alcohols and water with wetting activities were used to cover a range of viscosity (1-2.5cP) and surface tension (20-72 dynes/cm). Smooth flow was found to occur in a region defined by the flow rate, rotational speed and physical properties of the liquid. Outside this region various wave patterns were observed (concentric, spiral and irregular waves). A linear theory of the stability of the film based on an extension of classical stability theories for plane films on inclined planes is given and contrasted with the experimental results. Surface phenomena associated with the use of wetting agents were found to have a strong effect on the stability of the film.

The velocity perturbations above the orifice of an acoustically excited cavity in grazing flow

Abstract: Detailed measurements of the time-dependent velocities induced inside and outside the opening of an acoustically excited, two-dimensional Helmholtz resonator imbedded in a grazing flow are presented. The remarkably clear structure of the perturbation field which evokes a pulsating source and a coherently pulsating vortex-image pair is described.

Dynamics and stability of thin liquid films

Abstract: The dynamics and stability of thin liquid films have fascinated scientists over many decades: the observations of regular wave patterns in film flows down a windowpane or along guttering, the patterning of dewetting droplets, and the fingering of viscous flows down a slope are all examples that are familiar in daily life. Thin film flows occur over a wide range of length scales and are central to numerous areas of engineering, geophysics, and biophysics; these include nanofluidics and microfluidics, coating flows, intensive processing, lava flows, dynamics of continental ice sheets, tear-film rupture, and surfactant replacement therapy. These flows have attracted considerable attention in the literature, which have resulted in many significant developments in experimental, analytical, and numerical research in this area. These include advances in understanding dewetting, thermocapillary- and surfactant-driven films, falling films and films flowing over structured, compliant, and rapidly rotating substrates, and evaporating films as well as those manipulated via use of electric fields to produce nanoscale patterns. These developments are reviewed in this paper and open problems and exciting research avenues in this thriving area of fluid mechanics are also highlighted.

Effect of Grazing Flow on the Acoustic Impedance of an Orifice

Abstract: A linearized potential flow model is developed to study the effect of grazing flow on the acoustic behavior of an orifice. In accordance with the previous flow visualization and measurements, this model uses the particle velocity continuity boundary condition rather than the widely used displacement to match the flow-fields separated by the shear layer over the orifice. An experiment is also carried out to validate the present theory in the case of circular or rectangular orifices. The theory agrees well with the experiment. In addition, further comparison is made between the present and two existing impedance models. One major objective of the present investigation is to make a tentative judgement on the two boundary conditions for a sound wave transmitting through a turbulent boundary layer over an orifice. It is found that, compared to the particle displacement continuity boundary condition, the use of the particle velocity continuity boundary condition results in a much better agreement between the theoretical predictions and the experimental data. Finally, there is a discussion on the influence of plate thickness on orifice impedance in the presence of grazing flow.