Visualization of low Reynolds boundary-driven cavity flows in thin liquid shells

Classic examples of low-Reynolds recirculating cavity flows are typically generated from lid-driven boundary motion at a solid-fluid interface, or alternatively may result from shear flow over cavity openings. Here, we are interested in an original family of boundary-driven cavity flows occurring, in contrast to classic setups, at fluid-fluid interfaces. Particle image velocimetry (PIV) is used to investigate the structure of internal convective flows observed in thin liquid shells. Under the specific configuration investigated, the soap bubble's liquid shell is in fact in motion and exhibits sporadic local "bursts”. These bursts induce transient flow motion within the cavity of order Re ∼ O(1). The combination of PIV and proper orthogonal decomposition (POD) is used to extract dominant flow structures present within bubble cavities. Next, we show that thermally induced Marangoni flows in the liquid shell can lead to forced, (quasi) steady-state, internal recirculating flows. The present findings illustrate a novel example of low-Reynolds boundary-driven cavity flows. Graphical Abstrac

Thermal Flows

Flows of thermal origin and heat transfer problems are central in a variety of disciplines and industrial applications. The present book entitled Thermal Flows consists of a collection of studies by distinct investigators and research groups dealing with different types of flows relevant to both natural and technological contexts. Both reviews of the state-of-the-art and new theoretical, numerical and experimental investigations are presented, which illustrate the structure of these flows, their stability behavior, and the possible bifurcations to different patterns of symmetry and/or spatiotemporal regimes. Moreover, different categories of fluids are considered (liquid metals, gases, common fluids such as water and silicone oils, organic and inorganic transparent liquids, and nanofluids). This information is presented under the hope that it will serve as a new important resource for physicists, engineers and advanced students interested in the physics of non-isothermal fluid systems; fluid mechanics; environmental phenomena; meteorology; geophysics; and thermal, mechanical and materials engineering

Aeronautical Engineering: A special bibliography with indexes, supplement 72, July 1976

This bibliography lists 184 reports, articles, and other documents introduced into the NASA scientific and technical information system in June 1976

Modeling, design, and fabrication of pulsed fluidic micro-actuators

The forced vibration of a thin flexible plate or membrane in a sealed cavity with a small opening can cause fluid to be pumped into and out-of the cavity. At particular frequencies and amplitudes of vibration, a streaming of vortex rings can occur near the orifice. These vortex rings move under their own self-induced momentum. Downstream of the opening the rings ultimately break up and can form a fully developed jet. This work is dedicated to the analysis, design, and fabrication of electrostatic micro fluidic actuators, which use the pulsing mechanism described above to generate a fluid flow. Particle Image Velocimetry (PIV) is used to visualize the jet at various drive frequencies. The complex coupling between the electric field driving the membrane, the deformation of the membrane, and the compressible squeeze film in the cavity are studied in depth. Theoretical modeling, computer simulation (CFD-Computational Fluid Dynamics) and experiments are used to characterize the performance of the actuator. A low dimensional theoretical model, which takes into account the coupled physics of the problem, is derived from the Newton equation. The model is used to predict the membrane motion for varying voltage and frequency inputs. The system response predicted with the model is compared to numerical simulations, and it was found that the model can accurately capture the system response for a given input. Finally, a protocol for fabricating the actuator using Micro Electrical Mechanical Systems(MEMS) processes is presented

CONVECTIVE HEAT TRANSFER ENHANCEMENT OF A CHANNEL-FLOW USING SYNTHETIC JET

A transient numerical simulation was carried out using ANSYS Fluent, to investigate the convection heat transfer enhancement of the air channel flow using the synthetic jet. Keeping the dimensional parameters of the domain fixed, averaged channel flow velocity was varied up to 3m/s. The diaphragm displacement effect on synthetic jet was studied, ranging the peak-to-peak displacement value from 0.4 to 1.2mm with increment of 0.4mm. Three locations were studied to determine the best operating location of the synthetic jet. Also, frequencies were varied up to 200Hz with every 50Hz increment, from initial condition of 50Hz. It was found that the effect of the synthetic jet deteriorates as channel velocity is increased, as vortex structures get degenerated by strong channel flow. The heat transfer rate decreases, as the synthetic jet location is shifted from upstream position to the front end and center of the heated surface, moving further downstream. The maximum diaphragm displacement of 1.2 and maximum frequency increased the heat transfer rate by 97.43%. Finally, Q-criterion was analyzed to observe the interaction between the channel flow and synthetic jet, and their transport mechanism, along with the interaction with the heated surface. It was found that the impingement or sweeping effect of the vortical structures has significant effect on the convective heat transfer rate of the heated surface in the channel

Inertial waves in a laboratory model of the Earth's core

A water-filled three-meter diameter spherical shell built as a model of the Earth's core shows evidence of precessionally forced flows and, when spinning the inner sphere differentially, inertial modes are excited. We identified the precessionally forced flow to be primarily the spin-over inertial mode, i.e., a uniform vorticity flow whose rotation axis is not aligned with the container's rotation axis. A systematic study of the spin-over mode is carried out, showing that the amplitude dependence on the Poincaré number is in qualitative agreement with Busse's laminar theory while its phase differs significantly, likely due to topographic effects. At high rotation rates free shear layers concentrating most of the kinetic energy of the spin-over mode have been observed. When spinning the inner sphere differentially, a total of 12 inertial modes have been identified, reproducing and extending previous experimental results. The inertial modes excited appear ordered according to their azimuthal drift speed as the Rossby number is varied

Thermal Flows

Flows of thermal origin and heat transfer problems are central in a variety of disciplines and industrial applications. The present book entitled Thermal Flows consists of a collection of studies by distinct investigators and research groups dealing with different types of flows relevant to both natural and technological contexts. Both reviews of the state-of-the-art and new theoretical, numerical and experimental investigations are presented, which illustrate the structure of these flows, their stability behavior, and the possible bifurcations to different patterns of symmetry and/or spatiotemporal regimes. Moreover, different categories of fluids are considered (liquid metals, gases, common fluids such as water and silicone oils, organic and inorganic transparent liquids, and nano-fluids). This information is presented under the hope that it will serve as a new important resource for physicists, engineers and advanced students interested in the physics of non-isothermal fluid systems; fluid mechanics; environmental phenomena; meteorology; geophysics; and thermal, mechanical and materials engineering

Experimental study of libration-driven zonal flows in non-axisymmetric containers

International audienceOrbital dynamics that lead to longitudinal libration of celestial bodies also result in an elliptically deformed equatorial core-mantle boundary. The non-axisymmetry of the boundary leads to a topographic coupling between the assumed rigidmantle and the underlying low viscosity fluid.The present experimental study investigates theeffect of non axisymmetric boundaries on the zonal flow driven by longitudinal libration. For large enough equatorial ellipticity, we report intermittent space-filling turbulence in particular bands of resonant frequency correlated with larger amplitude zonal flow. The mechanism underlying the intermittent turbulence has yet to be unambiguously determined. Nevertheless, recent numerical simulations in triaxial and biaxial ellipsoids suggest that it may be associated with the growth and collapse of an elliptical instability (Cebron et al., 2012). Outside of the band of resonance, we find that the background flow is laminar and the zonal flow becomes independent of the geometry at first order, in agreement with a non linear mechanism in the Ekman boundary layer (e.g. Calkins et al.; 2010, Sauret and Le Dizes, 2012b)

Index to NASA Tech Briefs, 1975

This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs