Beatriz M. Marino

Measurements of free-surface profile in transient flow with a simple light-slicing method.

A simple light-slicing technique for the direct measurement of the free-surface shape h(x) in onedirectional transient liquid flows is studied. The method is used to determine h(x) with a precision of the order of 10(-2) mm along a line several centimeters long, allowing for height differences of some millimeters. It is useful for transient flows in rectangular channels in which capillarity and liquid adhesion at walls perturb lateral observations; the method can also be used for nondiffusive fluids in cases in which it is not advisable to add diffusive particles.

Droplet profiles obtained from the intensity distribution of refraction patterns

A noninterferometric method for obtaining profiles of axially symmetric transparent liquid droplets is described. The drops are illuminated along the symmetry axis by a uniform parallel beam whose intensity distribution is recorded at the focal plane of a lens placed behind the drop. In some conditions and within the geometrical optics approach, it is possible to reconstruct the profile of the drop from this intensity distribution except for the length scale factor, which, if necessary, may be provided by an additional simple measurement. Because of CCD cameras and digital image processing, this method is an interesting alternative technique for measuring drop profile shapes with considerable accuracy when interferometry is unwieldy. We also analyze the diffraction features of the intensity distribution to clarify the extent that they affect the approach that we used and to establish additional information that they may provide.

Holographic investigation of residual deformations induced by a pulsed ion implanter

A new use of holographic interferometry to investigate the residual deformations induced in nitrogen implanted specimens by a plasma focus device is reported. The method is simple and nondestructive. Experimental results obtained for AISI 304 stainless steel specimens are presented.

Buoyancy-driven flow between two rooms coupled by two openings at different levels

The stack-driven flow between two interconnected rooms produced by a single heat source is studied. In particular, the features of the transient flow for different positions and areas of two openings in the shared vertical wall are analysed. An analytical model provides the time evolution of the stratified flows in rooms of any size. The concept of an equivalent layer representing a non-uniform density profile, which is useful in other contexts, is included in the theoretical approach and provides physical insight and aids the mathematical solution of the problem. New salt-bath experiments are performed to simulate the thermal forcing between the rooms, to validate the model and to analyse the mixing generated and the effects of a source of volume in the configuration studied.

Lock-Exchange Flows in Non-Rectangular Cross-Section Channels

Lock-exchange flows driven by density differences in non-rectangular cross-section channels are investigated in situations that resemble estuaries, navigation canals and hydraulic engineering structures. A simple analytical model considering stratified flows suggests practical relationships corroborated by results of laboratory experiments carried out in a straight channel of triangular cross-section

Hydrodynamics and sediment transport in an estuary with an abrupt depth step

ABSTRACT The hydrodynamic patterns resulting from the combination of tide flow, riverine discharge and bathymetry and their effects on water circulation and sediment transport are studied to assess the impact of geomorphic changes in the Quequén Grande River estuary (Buenos Aires, Argentina). A depth step located at about 2 km from the sea, created by dredging to provide favourable navigational conditions in the harbour, induces different flow patterns in the deeper and shallow estuarine parts, creating an attractive system to study. The main purpose of this paper is to report key physical features of this water system and the results of detailed longitudinal and transverse measurements of velocity and backscatter intensity. The data reveal the selective settling of suspended sediments in the harbour and a net loss of sediments to the sea. The effects of local severe storms that cause an intense tidal intrusion and mixing as well as a stronger ebb flow and seiches are also described.

Convection generated by a small heat source in a box with a cooled upper contour at constant temperature

The flow generated by a linear heat source inside a thermally insulated box with the upper boundary maintained at constant temperature is analyzed by means of a series of experiments. The attention is focused on the steady state during which the heat provided by the source is absorbed by the upper boundary giving place to a particular convective process in two well defined zones. One of them occupies most part of the box from the lower boundary and is characterized by a turbulent convective flow; the other is the thermal boundary layer developed below the cooled top contour where strong fluctuations are detected. Special interest is found in the analogies with the results obtained employing a configuration similar to that used to research the Rayleigh-Benard convection with lower and upper boundaries at constant temperatures but without internal sources. This study has particular relevance to understanding and predicting the use of the cooled-ceiling systems in buildings as a passive solution to enhance the comfort of its inhabitants during hot days with the consequential energy savings.

Thermal Plume and Stratification

Visualization by synthetic schlieren of the filling box process with fluid heated by a thermal source located on the floor. A constant power of 73 W is released in a 25 cm tall, closed, insulated box filled with water. The initial temperature of the fluid is uniform and equal to the environment.

Profilometry of a liquid-free surface with large slope variations

We describe and test a refractive method for determining the height profile of an unsteady liquid-free surface, which is adequate for regions where the slope of the surface changes strongly, as for example the head of a spreading current. The method is developed for situations in which the height depends on a single Cartesian coordinate (plane flows); however, the underlying idea could be applied to more general cases. As a test, we obtained the profiles of a transparent solid object (a cylindrical lens) and of an actual liquid flow. These profiles are determined with high accuracy even if the direction of the normal to the free surface changes approximately 150 degrees within the probed region.