Quasi-periodic cylinder wakes and the Ginzburg–Landau model

1995 ◽  
Vol 291 ◽  
pp. 191-222 ◽  
Author(s):  
Pierre Albarède ◽  
Michel Provansal
Keyword(s):  
Three Dimensional ◽  
Reynolds Numbers ◽  
Model Parameters ◽  
Ginzburg Landau ◽  
Phase Measurements ◽  
Low Reynolds Numbers ◽  
Aspect Ratios ◽  
Second Mode ◽  
Time Periodic

The time-periodic phenomena occurring at low Reynolds numbers (Re [lsim ] 180) in the wake of a circular cylinder (finite-length section) are well modelled by a Ginzburg–Landau (GL) equation with zero boundary conditions (Albarède & Monkewitz 1992). According to the GL model, the wake is mainly governed by a rescaled length, based on the aspect ratio and the Reynolds number. However, the determination of coefficients is not complete: we correct a former evaluation of the nonlinear Landau coefficient, we show difficulties in obtaining a consistent set of coefficients for different Reynolds numbers or end configurations, and we propose the use of an ‘influential’ length. New two-point velocimetry results are presented: phase measurements show that a subtle property is shared by the three-dimensional wake and the GL model.Two time-quasi-periodic phenomena – the second mode observed for smaller aspect ratios, and the dislocated chevron observed for larger aspect ratios – are presented and precisely related to the GL model. Only the linear characteristics of the second mode are readily explained; its existence depends on the end conditions. Moreover, through a quasi-static variation of the length, the second mode evolves continuously to end cells (and vice versa). Observations of the dislocated chevron are recalled. A very similar instability is found on the chevron solution of the GL equation, when the model parameters (c1, c2) move towards the phase diffusion unstable region. The early stages of this instability are qualitatively similar to the observed patterns.

The Effect of Reynolds Number on the Performance of a Tangential-Flow Turbine

1965 ◽  
Author(s):  
Robert G. Adams
Keyword(s):  
Reynolds Number ◽  
Power Systems ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Theoretical Determination ◽  
Low Reynolds Numbers ◽  
Tangential Flow ◽  
Circulatory Flow ◽  
Reasonable Prediction

The tangential-flow turbine, which was developed from the drag turbine in an effort to take advantage of the circulatory flow in the drag-turbine passages, frequently has been proposed for use in power systems characterized by low specific speeds. Since such systems often operate with low exhaust pressures which lead to low Reynolds numbers in turbine passages, it is of interest to determine the effect of Reynolds number on the performance of this type of machine. Theoretical determination of the effect is made difficult by the complex three-dimensional nature of the flow in this type of turbine. This paper describes a program of tests which was run on a tangential-flow turbine to investigate the effect of Reynolds number, and presents a simplified theoretical approach to the Reynolds-number effect which is shown to give a reasonable prediction of the trend of the effect.

scholarly journals Diffusive dynamics and stochastic models of turbulent axisymmetric wakes

2015 ◽  
Vol 778 ◽  
Author(s):  
G. Rigas ◽  
A. S. Morgans ◽  
R. D. Brackston ◽  
J. F. Morrison
Keyword(s):  
Three Dimensional ◽  
Reynolds Numbers ◽  
Axisymmetric Body ◽  
Wake Flow ◽  
Model Parameters ◽  
Low Reynolds Numbers ◽  
Turbulent Fluctuations ◽  
Broken Symmetries ◽  
Diffusive Dynamics ◽  
Modelling Methodology

A modelling methodology to reproduce the experimental measurements of a turbulent flow in the presence of symmetry is presented. The flow is a three-dimensional wake generated by an axisymmetric body. We show that the dynamics of the turbulent wake flow can be assimilated by a nonlinear two-dimensional Langevin equation, the deterministic part of which accounts for the broken symmetries that occur in the laminar and transitional regimes at low Reynolds numbers and the stochastic part of which accounts for the turbulent fluctuations. Comparison between theoretical and experimental results allows the extraction of the model parameters.

Experimental and Numerical Determination of Micropropulsion Device Efficiencies at Low Reynolds Numbers

2004 ◽  
Author(s):  
Andrew D. Ketsdever ◽  
Michael T. Clabough ◽  
Sergey F. Gimelshein ◽  
Alina Alexeenko
Keyword(s):  
Reynolds Numbers ◽  
Numerical Determination ◽  
Low Reynolds Numbers ◽  
Low Reynolds

3D simulation of emulsion flow using the boundary element method on the heterogeneous computational systems

2012 ◽  
Vol 9 (1) ◽  
pp. 142-146
Author(s):  
O.A. Solnyshkina
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Problem Size ◽  
Low Reynolds Numbers ◽  
Infinite Domains ◽  
The Matrix ◽  
Computational Systems ◽  
Element Method

In this work the 3D dynamics of two immiscible liquids in unbounded domain at low Reynolds numbers is considered. The numerical method is based on the boundary element method, which is very efficient for simulation of the three-dimensional problems in infinite domains. To accelerate calculations and increase the problem size, a heterogeneous approach to parallelization of the computations on the central (CPU) and graphics (GPU) processors is applied. To accelerate the iterative solver (GMRES) and overcome the limitations associated with the size of the memory of the computation system, the software component of the matrix-vector product

Cylinder rolling on a wall at low Reynolds numbers

2011 ◽  
Vol 685 ◽  
pp. 461-494 ◽  
Author(s):  
Alain Merlen ◽  
Christophe Frankiewicz
Keyword(s):  
Three Dimensional ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Flow Around A Cylinder ◽  
Low Reynolds Numbers ◽  
Initial Location ◽  
Upstream Pressure ◽  
Small Reynolds Numbers ◽  
Onset Of Cavitation

AbstractThe flow around a cylinder rolling or sliding on a wall was investigated analytically and numerically for small Reynolds numbers, where the flow is known to be two-dimensional and steady. Both prograde and retrograde rotation were analytically solved, in the Stokes regime, giving the values of forces and torque and a complete description of the flow. However, solving Navier–Stokes equation, a rotation of the cylinder near the wall necessarily induces a cavitation bubble in the nip if the fluid is a liquid, or compressible effects, if it is a gas. Therefore, an infinite lift force is generated, disconnecting the cylinder from the wall. The flow inside this interstice was then solved under the lubrication assumptions and fully described for a completely flooded interstice. Numerical results extend the analysis to higher Reynolds number. Finally, the effect of the upstream pressure on the onset of cavitation is studied, giving the initial location of the phenomenon and the relation between the upstream pressure and the flow rate in the interstice. It is shown that the flow in the interstice must become three-dimensional when cavitation takes place.

scholarly journals Three-dimensional wake transition in the flow over four square cylinders at low Reynolds numbers

AIP Advances ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 015142
Author(s):  
Yuhang Zhang ◽  
Rui Wang ◽  
Yaoran Chen ◽  
Yan Bao ◽  
Zhaolong Han ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Square Cylinders ◽  
Low Reynolds ◽  
Four Square ◽  
Wake Transition

Experimental characterization of three-dimensional corner flows at low Reynolds numbers

2012 ◽  
Vol 707 ◽  
pp. 37-52 ◽  
Author(s):  
J. Sznitman ◽  
L. Guglielmini ◽  
D. Clifton ◽  
D. Scobee ◽  
H. A. Stone ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Channel Cross Section ◽  
Experimental Characterization ◽  
Low Reynolds Numbers ◽  
Low Reynolds

AbstractWe investigate experimentally the characteristics of the flow field that develops at low Reynolds numbers ($\mathit{Re}\ll 1$) around a sharp $9{0}^{\ensuremath{\circ} } $ corner bounded by channel walls. Two-dimensional planar velocity fields are obtained using particle image velocimetry (PIV) conducted in a towing tank filled with a silicone oil of high viscosity. We find that, in the vicinity of the corner, the steady-state flow patterns bear the signature of a three-dimensional secondary flow, characterized by counter-rotating pairs of streamwise vortical structures and identified by the presence of non-vanishing transverse velocities (${u}_{z} $). These results are compared to numerical solutions of the incompressible flow as well as to predictions obtained, for a similar geometry, from an asymptotic expansion solution (Guglielmini et al., J. Fluid Mech., vol. 668, 2011, pp. 33–57). Furthermore, we discuss the influence of both Reynolds number and aspect ratio of the channel cross-section on the resulting secondary flows. This work represents, to the best of our knowledge, the first experimental characterization of the three-dimensional flow features arising in a pressure-driven flow near a corner at low Reynolds number.

scholarly journals Tomography-based determination of permeability and Dupuit–Forchheimer coefficient of characteristic snow samples

2011 ◽  
Vol 57 (205) ◽  
pp. 811-816 ◽  
Author(s):  
Emilie Zermatten ◽  
Sophia Haussener ◽  
Martin Schneebeli ◽  
Aldo Steinfeld
Keyword(s):  
Mass Transport ◽  
Effective Properties ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Momentum Conservation ◽  
Micro Computed Tomography ◽  
Wide Range ◽  
Snow Microstructure ◽  
Semi Empirical

AbstractA tomography-based methodology for the mass transport characterization of snow is presented. Five samples, characteristic for a wide range of seasonal snow, are considered. Their three-dimensional (3-D) geometrical representations are obtained by micro-computed tomography and used in direct pore-level simulations to numerically solve the governing mass and momentum conservation equations, allowing for the determination of their effective permeability and Dupuit–Forchheimer coefficient. The extension to the Dupuit–coefficient is useful near the snow surface, where Reynolds numbers higher than unity can appear. Simplified semi-empirical models of porous media are also examined. The methodology presented allows for the determination of snow’s effective mass transport properties, which are strongly dependent on the snow microstructure and morphology. These effective properties can, in turn, readily be used in snowpack volume-averaged (continuum) models such as strongly layered samples with macroscopically anisotropic properties.

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