Elastically driven surface plumes in rimming flow of a non-Newtonian fluid (original) (raw)
Starting laminar plumes: Comparison of laboratory and numerical modeling
Geochemistry, Geophysics, Geosystems, 2009
1] A detailed comparison of starting laminar plumes in viscous fluids is provided using the complementary approaches of laboratory modeling and numerical simulation. In the laboratory experiments the plumes are started in a nearly isoviscous silicone oil with heat supplied through a fixed circular source. The temperature field is measured by differential interferometry and thermochromic liquid crystals. The velocity field is determined by particle image velocimetry. Numerical simulations of the laboratory experiments are performed using a finite element method that employs the measured properties of the physical oil and the heating history. No further adjustments are made to match the laboratory results. For fluids at two different viscosities and for variable power supplied to the plume there is excellent agreement in the temporal evolution and fine spatial detail of the plume. Minor differences remain, particulary in the transient stage of the plume in the low-viscosity fluid, but the differences are within the experimental uncertainties. In contrast, the assumption of constant viscosity in the numerical models leads to differences that are larger than the experimental uncertainties, demonstrating that these near-isoviscous fluids should not be considered to have constant viscosity.
Inviscid and Viscous Models of Axisymmetric Fluid Jets or Plumes
The ANZIAM Journal, 2012
The vertical rise of a round plume of light fluid through a surrounding heavier fluid is considered. An inviscid model is analysed in which the boundary of the plume is taken to be a sharp interface. An efficient spectral method is used to solve this nonlinear free-boundary problem, and shows that the plume narrows as it rises. A generalized condition is also introduced at the boundary, and allows the ambient fluid to be entrained into the rising plume. In this case, the fluid plume first narrows then widens as it rises. These features are confirmed by an asymptotic analysis. A viscous model of the same situation is also proposed, based on a Boussinesq approximation. It qualitatively confirms the widening of the plume due to entrainment of the ambient fluid, but also shows the presence of vortex rings around the interface of the rising plume.
Laminar starting plumes in high-Prandtl-number fluids
Journal of Fluid Mechanics, 2003
Experimental studies of laminar axisymmetric starting plumes are performed to investigate the dependence of the flow on the Prandtl number, focusing on large Prandtl numbers. Thermal plumes are generated by a small electric heater in a glass tank filled with viscous oils. Prandtl numbers in the range of 7-10 4 were investigated. Experimental conditions are such that viscosity variations due to temperature differences are negligible. Plumes ascend in two different regimes as a function of distance to source. At short distances, the plumes accelerate owing to the development of the viscous boundary layer. At distances larger than about five times the heater size, the ascent velocity is constant and increases as a function of the Prandtl number, as predicted by theory for steady plumes. This velocity is, within experimental error, proportional to the steady plume centreline velocity.
The flow in and around air-bubble plumes
International Journal of Multiphase Flow, 2002
- A short review is given of some of the important publications on air-bubble plumes. Two main ways of modelling, using either the entrainment assumption, or the energy balance principle, are presented and briefly compared.
Drag of a Spherical Bubble Rising in Power Law Fluids at Intermediate Reynolds Numbers
Industrial & Engineering Chemistry Research, 2007
The steady rise of a spherical bubble through an incompressible quiescent power law fluid has been studied numerically in the 2-D axisymmetric flow regime using the finite volume method. Based on the present numerical results, a predictive correlation in terms of Reynolds number (Re) and power law index (n) is proposed which enables the prediction of the total drag coefficient for the ranges of conditions as 5 e Re e 500 and 0.5 e n e 2 (hence covering both shear-thinning and shear-thickening type of fluid behavior). For n < 1, the drag is reduced below the corresponding Newtonian value, whereas it increases above its Newtonian value in shear-thickening fluids (n > 1). Thus, the drag coefficient increases with the increasing power law index for all values of the Reynolds number. The contribution of the pressure drag also increases with the increasing Reynolds number, though the shear-thickening behavior (n > 1) seems to suppress this tendency. In addition to the drag behavior, streamline and constant vorticity plots are presented to show the detailed nature of the flow and the effect of Reynolds number and power law index on the flow characteristics.
Numerical Study of Backflow for Nozzle Plumes Expanding into Vacuum
37th AIAA Thermophysics Conference, 2004
This work is prompted by recent experiments on a multiphase (gas/droplets/cooling film) flow expanding from a supersonic nozzle into vacuum. A reverse motion of droplets (in the direction opposite to the flow in the plume core) has been experimentally observed near the nozzle lip. To understand this phenomenon, we have performed a numerical investigation of backflow formation. A hybrid Navier-Stokes/Direct Simulation Monte Carlo approach has been used to simulate the flow in different regimes -from a dense flow inside the nozzle, through very fast expansion near the nozzle lip, to a rarefied, freemolecular flow in the backflow region. A Lagrangian particle algorithm has been employed to trace the droplet motion in the gas flow. It has been shown that the gas backflow constitutes only a small part of the total mass flow rate. As a result, aerodynamic forces are insufficient to turn the droplets around the nozzle lip, and it seems that none of the droplets from the nozzle cannot reach the backflow region. Thus, it can be assumed that all droplets in the backflow originate from the cooling film being destroyed on the nozzle lip. Further, to investigate the viscous expansion flow near the nozzle lip in more detail, a model problem -the flow over a plane wall turning by a large angle (an expansion corner), has been studied using both continuum and kinetic modeling. It has been shown that, due to viscous effects, the flow deviates drastically from the classical Prandtl-Meyer solution. For large deflection angles, the decrease in the flow Mach number and the growth of the flow temperature are observed instead of their increase and fall, respectively. Reasons for such behavior are discussed, and the limits of applicability of the Navier-Stokes solution are analyzed.
Editorial: Introduction to the 37th Annual Gallery of Fluid Motion (Seattle, Washington, USA, 2019)
Physical Review Fluids, 2020
The 37th Annual Gallery of Fluid Motion (GFM) was held at the American Physical Society (APS) Division of Fluid Dynamics Annual Meeting in Seattle, Washington November 23-26, 2019. The meeting featured approximately 3300 technical abstracts with an additional 103 entries to the GFM for display during the meeting (66 video and 37 poster submissions). Submissions were received from 17 countries with approximately 50% of submissions coming from institutions outside the United States. The work submitted represents a broad range of fluid dynamical topics being explored in academia, industry, and national laboratories today. To select winners of the 2019 GFM, two panels of judges (ten for videos and four for posters) were assembled from scholars with a diverse background in fluid mechanics. As in previous years, judges evaluated entries on the basis of the beauty and aesthetic value of the work, the scientific and technical merit of the described research, and the originality and clarity in communication. The panel for the videos was formed by a total of ten judges and each video was ranked by four panelists. From these ratings, the seven top ranked videos were reviewed by all the judges and chosen as winners. Posters were judged in person, with panelists scoring each poster individually, with the five winning entries having the highest average score. As in previous years, the top three winners in each category were designated Milton van Dyke Award winners and received a monetary prize in addition to the certificates and copy of An Album of Fluid Motion given to all winners. The winning entries, as well as many of the other submissions, are visible online at . The 2019 Gallery of Fluid Motion winners are listed below. (1) V0013 Impaled droplets: On the breakup of drops impacting singularities.