Carbonate Disequilibrium in the External Boundary Layer of Freshwater Chrysophytes: Implications for Contaminant Uptake

2018 ◽  
Vol 52 (16) ◽  
pp. 9403-9411 ◽  
Author(s):  
Michel Lavoie ◽  
Jérôme F. L. Duval ◽  
John A. Raven ◽  
Frédéric Maps ◽  
Béchir Béjaoui ◽  
...  
Keyword(s):  
Boundary Layer ◽  
External Boundary ◽  
Contaminant Uptake

The nonlinear interaction of Tollmien–Schlichting waves and Taylor-Görtler vortices in curved channel flows

1988 ◽  
Vol 417 (1853) ◽  
pp. 255-282 ◽  
Keyword(s):  
Boundary Layer ◽  
Finite Time ◽  
Practical Importance ◽  
Layer Growth ◽  
Longitudinal Vortex ◽  
External Boundary ◽  
Linear Mode ◽  
Curved Channels ◽  
Tollmien Schlichting ◽  
Laminar Flow Control

It is known that a viscous fluid flow with curved streamlines can support both Tollmien-Schlichting and Taylor-Görtler instabilities. The question of which linear mode is dominant at finite values of the Reynolds numbers was discussed by Gibson & Cooke ( Q. Jl Mech. appl. Math . 27, 149 (1974)). In a situation where both modes are possible on the basis of linear theory a nonlinear theory must be used, however, to determine the effect of the interaction of the instabilities. The details of this interaction are of practical importance because of its possible catastrophic effects on mechanisms used for laminar flow control. Here this interaction is studied in the context of fully developed flows in curved channels. Apart from technical differences associated with boundary-layer growth the structures of the instabilities in this flow can be very similar to those in the practically more important external boundary-layer situation. The interaction is shown to have two distinct phases depending on the size of the input disturbances. At very low amplitudes two oblique Tollmien–Schlichting waves interact with a Görtler vortex in such a manner that the scaled amplitudes become infinite at a finite time. This type of interaction is described by ordinary differential amplitude equations with quadratic nonlinearities. A stronger type of interaction occurs at larger input disturbance amplitudes and leads to a more complicated type of evolution equation. The solution of these equations now depends critically on the orientation of the wavefronts of the Tollmien–Schlichting waves to the Görtler vortex. Thus, if the angle between the directions of the vortex and the waves is greater than 41.6° this stronger interaction again terminates in a singularity at a finite time; otherwise the breakdown is exponential, taking an infinite time. Moreover, the stronger interaction can take place in the absence of curvature, in which case the longitudinal vortex is entirely driven by the Tollmien–Schlichting waves.

scholarly journals Modelling dimethylsulfide diffusion in the algal external boundary layer: implications for mutualistic and signalling roles

2018 ◽  
Vol 20 (11) ◽  
pp. 4157-4169 ◽  
Author(s):  
Michel Lavoie ◽  
Martí Galí ◽  
Caroline Sévigny ◽  
David J. Kieber ◽  
William G. Sunda ◽  
...  
Keyword(s):  
Boundary Layer ◽  
External Boundary

Symmetric Sink Flow and Heat Transfer Between Two Parallel Disks

2003 ◽  
Author(s):  
Marco Aure´lio dos Santos Bernardes
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Friction Factor ◽  
Volumetric Flow Rate ◽  
Internal Boundary ◽  
External Boundary ◽  
Radial Coordinate ◽  
Flow And Heat Transfer ◽  
Disk Spacing

The k-ε model are performed to investigate numerically the steady, turbulent, incompressible flow and heat transfer converging radially between two stationary disks, which is as a continuously developing flow problem under the internal boundary layer approximations. The effect of relaminarization was considered. This present study has presented a good agreement with the laminar investigation of Murphy et al [1], where no heat transfer was considered. At large values of the dimensionless radii (>> 1) the velocity profile becomes parabolic and invariant and the friction factor approaches the classic value obtained for fully developed flow between infinite plates, 24/Re0, where Re0 is an overall Reynolds number based on the volumetric flow rate and the disk spacing and is independent of radius. At radii less than one a typical external boundary layer evolves close to the wall with an approximately uniform core region, the boundary layer thickness decreases from one-half the disk spacing to values proportional to the local radii as the flow accelerates and the friction factor approaches the constant 2.17/Re0. A local Nusselt number, Nu = 230(r/R)0.650(1 − r/R)−0.386, where r is radial coordinate and R the radius of the disk, was estimated. A large overall Reynolds number was imposed and a relaminarization of the flow was observed. It was suggested that these results can be applicable for laminar and turbulent flow under Re0 = 106.

Simulating Boundary Layer Transition With Low-Reynolds-Number k–ε Turbulence Models: Part 1—An Evaluation of Prediction Characteristics

1991 ◽  
Vol 113 (1) ◽  
pp. 10-17 ◽  
Author(s):  
R. C. Schmidt ◽  
S. V. Patankar
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Free Stream ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Boundary Layer Transition ◽  
External Boundary ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Low Reynolds

An analysis and evaluation of the capability of k–ε low-Reynolds-number turbulence models to predict transition in external boundary-layer flows subject to free-stream turbulence is presented. The similarities between the near-wall cross-stream regions in a fully turbulent boundary layer and the progressive stages through which developing boundary layers pass in the streamwise direction are used to describe the mechanisms by which the models simulate the transition process. Two representative models (Jones and Launder, 1972; Lam and Bremhorst, 1981) are employed in a series of computational tests designed to answer some specific practical questions about the ability of these models to yield accurate, reliable answers over a range of free-stream turbulence conditions.

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