Study on multiple ring-like vortex formation and small vortex generation in late flow transition on a flat plate

2011 ◽  
Vol 27 (1-2) ◽  
pp. 41-70 ◽  
Author(s):  
Chaoqun Liu ◽  
Lin Chen ◽  
Ping Lu ◽  
Xiaobing Liu
Keyword(s):  
Flat Plate ◽  
Vortex Formation ◽  
Flow Transition ◽  
Vortex Generation ◽  
Small Vortex ◽  
Multiple Ring

scholarly journals New Findings by High-Order DNS for Late Flow Transition in a Boundary Layer

2011 ◽  
Vol 2011 ◽  
pp. 1-16 ◽  
Author(s):  
Chaoqun Liu ◽  
Lin Chen ◽  
Ping Lu
Keyword(s):  
Boundary Layer ◽  
Vortex Breakdown ◽  
Solid Wall ◽  
Vortex Formation ◽  
Ring Structure ◽  
Flow Transition ◽  
New Findings ◽  
Coherent Vortex ◽  
Coherent Vortex Structure ◽  
Multiple Ring

This paper serves as a summary of new discoveries by DNS for late stages of flow transition in a boundary layer. The widely spread concept “vortex breakdown” is found theoretically impossible and never happened in practice. The ring-like vortex is found the only form existing inside the flow field. The ring-like vortex formation is the result of the interaction between two pairs of counter-rotating primary and secondary streamwise vortices. Following the first Helmholtz vortex conservation law, the primary vortex tube rolls up and is stretched due to the velocity gradient. In order to maintain vorticity conservation, a bridge must be formed to link two Λ-vortex legs. The bridge finally develops as a new ring. This process keeps going on to form a multiple ring structure. The U-shaped vortices are not new but existing coherent vortex structure. Actually, the U-shaped vortex, which is a third level vortex, serves as a second neck to supply vorticity to the multiple rings. The small vortices can be found on the bottom of the boundary layer near the wall surface. It is believed that the small vortices, and thus turbulence, are generated by the interaction of positive spikes and other higher level vortices with the solid wall. The mechanism of formation of secondary vortex, second sweep, positive spike, high shear distribution, downdraft and updraft motion, and multiple ring-circle overlapping is also investigated.

Flow in a meandering channel

2015 ◽  
Vol 770 ◽  
pp. 52-84 ◽  
Author(s):  
J. M. Floryan
Keyword(s):  
Vortex Formation ◽  
Comprehensive Analysis ◽  
Linear Stability Theory ◽  
Vortex Generation ◽  
Centrifugal Forces ◽  
Streamwise Vortices ◽  
Meandering Channel ◽  
Channel Narrowing ◽  
Effective Channel ◽  
Wall Geometry

A comprehensive analysis of the pressure-gradient driven flow in a meandering channel has been presented. This geometry is of interest as it can be used for the creation of streamwise vortices which magnify the transverse transport of scalar quantities, e.g. heat transfer. The linear stability theory has been used to determine the meandering wavelengths required for the vortex formation. It has been demonstrated that reduction of the wavelength results in the onset of flow separation which, when combined with the wall geometry, results in an effective channel narrowing: the stream ‘lifts up’ above the wall and becomes nearly rectilinear, thus eliminating vortex-generating centrifugal forces. Increase of the wavelength also leads to a nearly rectilinear stream, as the slope of the wall modulations becomes negligible. As shear-driven instability may interfere with the formation of vortices, the conditions leading to the onset of such instability have also been investigated. The attributes of the geometry which lead to the most effective vortex generation without any interference from the shear instabilities and with the smallest drag penalty have been identified.

Numerical Simulation of Flow in a Photocatalytic Reactor Containing Baffles

2011 ◽  
Author(s):  
Saber Ahmed ◽  
M. G. Rasul ◽  
R. J. Brown ◽  
J. Esteban Duran
Keyword(s):  
Fluid Dynamics ◽  
Wastewater Treatment ◽  
Flat Plate ◽  
Vortex Formation ◽  
Underlying Mechanism ◽  
Valuable Insight ◽  
Photocatalytic Reactor ◽  
Flow Features ◽  
Computational Fluid Dynamics Cfd ◽  
Stream Lines

In this study a new immobilized flat plate photocatalytic reactor for wastewater treatment has been investigated using computational fluid dynamics (CFD). The reactor consists of a reactor inlet, a reactive section where the catalyst is coated, and outlet parts. For simulation, the reactive section of the reactor was modelled with an array of baffles. In order to optimize the fluid mixing and reactor design, this study attempts to investigate the influence of baffles with differing heights on the flow field of the flat plate reactor. The results obtained from the simulation of a baffled flat plate reactor hydrodynamics for differing baffle heights for certain positions are presented. Under the conditions simulated, the qualitative flow features, such as the distribution of local stream lines, velocity contours, and high shear region, boundary layers separation, vortex formation, and the underlying mechanism are examined. At low and high Re numbers, the influence of baffle heights on the distribution of species mass fraction of a model pollutant are also highlighted. The simulation of qualitative and quantitative properties of fluid dynamics in a baffled reactor provides valuable insight to fully understand the effect of baffles and their role on the flow pattern, behaviour, and features of wastewater treatment using a photocatalytic reactor.

Vortex formation and saturation for low-aspect-ratio rotating flat-plate fins

2011 ◽  
Vol 52 (2) ◽  
pp. 441-462 ◽  
Author(s):  
Adam C. DeVoria ◽  
Matthew J. Ringuette
Keyword(s):  
Aspect Ratio ◽  
Flat Plate ◽  
Vortex Formation ◽  
Low Aspect Ratio
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