Large-scale flow in turbulent convection: a mathematical model

1986 ◽  
Vol 170 ◽  
pp. 385-410 ◽  
Author(s):  
L. N. Howard ◽  
R. Krishnamurti
Keyword(s):  
Mathematical Model ◽  
Large Scale ◽  
Laboratory Experiments ◽  
Boussinesq Equations ◽  
Time Dependent ◽  
Heteroclinic Orbits ◽  
Turbulent Convection ◽  
Mean Flow ◽  
Dependent Flow ◽  
Large Scale Flow

A mathematical model of convection, obtained by truncation from the two-dimensional Boussinesq equations, is shown to exhibit a bifurcation from symmetrical cells to tilted non-symmetrical ones. A subsequent bifurcation leads to time-dependent flow with similarly tilted transient plumes and a large-scale Lagrangian mean flow. This change of symmetry is similar to that occurring with the advent of a large-scale flow and transient tilted plumes seen in laboratory experiments on turbulent convection at high Rayleigh number. Though not intended as a description of turbulent convection, the model does bring out in a theoretically tractable context the possibility of the spontaneous change of symmetry suggested by the experiments.Further bifurcations of the model lead to stable chaotic phenomena as well. These are numerically found to occur in association with heteroclinic orbits. Some mathematical results clarifying this association are also presented.

Coherent large–scale flow structures in turbulent convection

2008 ◽  
pp. 606-608
Author(s):  
C. Resagk ◽  
R. du Puits ◽  
E. Lobutova ◽  
A. Maystrenko ◽  
A. Thess
Keyword(s):  
Large Scale ◽  
Turbulent Convection ◽  
Flow Structures ◽  
Large Scale Flow

scholarly journals Large-Scale Flow in Micro Electrokinetic Turbulent Mixer

Micromachines ◽  
2020 ◽  
Vol 11 (9) ◽  
pp. 813 ◽  
Author(s):  
Keyi Nan ◽  
Zhongyan Hu ◽  
Wei Zhao ◽  
Kaige Wang ◽  
Jintao Bai ◽  
...  
Keyword(s):  
Flow Field ◽  
Electric Conductivity ◽  
Large Scale ◽  
Three Dimensional ◽  
Mixing Process ◽  
Mean Flow ◽  
Velocity Fluctuations ◽  
Two Fluids ◽  
Large Scale Flow ◽  
Particle Imaging

In the present work, we studied the three-dimensional (3D) mean flow field in a micro electrokinetic (μEK) turbulence based micromixer by micro particle imaging velocimetry (μPIV) with stereoscopic method. A large-scale solenoid-type 3D mean flow field has been observed. The extraordinarily fast mixing process of the μEK turbulent mixer can be primarily attributed to two steps. First, under the strong velocity fluctuations generated by μEK mechanism, the two fluids with different conductivity are highly mixed near the entrance, primarily at the low electric conductivity sides and bias to the bottom wall. Then, the well-mixed fluid in the local region convects to the rest regions of the micromixer by the large-scale solenoid-type 3D mean flow. The mechanism of the large-scale 3D mean flow could be attributed to the unbalanced electroosmotic flows (EOFs) due to the high and low electric conductivity on both the bottom and top surface.

scholarly journals Experimental and Computational Study of the Unsteady Flow in a 1.5 Stage Axial Turbine With Emphasis on the Secondary Flow in the Second Stator

1998 ◽  
Author(s):  
Ralf E. Walraevens ◽  
Heinz E. Gallus ◽  
Alexander R. Jung ◽  
Jürgen F. Mayer ◽  
Heinz Stetter
Keyword(s):  
Unsteady Flow ◽  
Secondary Flow ◽  
Computational Study ◽  
Three Dimensional ◽  
Cross Flow ◽  
Axial Flow ◽  
Time Dependent ◽  
Flow Structures ◽  
Mean Flow ◽  
Dependent Flow

A study of the unsteady flow in an axial flow turbine stage with a second stator blade row is presented. The low aspect ratio blades give way to a highly three-dimensional flow which is dominated by secondary flow structures. Detailed steady and unsteady measurements throughout the machine and unsteady flow simulations which include all blade rows have been carried out. The presented results focus on the second stator flow. Secondary flow structures and their origins are identified and tracked on their way through the passage. The results of the time-dependent secondary velocity vectors as well as flow angles and Mach number distributions as perturbation from the time-mean flow field are shown in cross-flow sections and azimuthal cuts throughout the domain of the second stator. At each location the experimental and numerical results are compared and discussed. A good overall agreement in the time-dependent flow behaviour as well as in the secondary flow structures is stated.

scholarly journals Approximation of potential-driven flow dynamics in large-scale self-similar tree networks

2011 ◽  
Vol 467 (2134) ◽  
pp. 2810-2824 ◽  
Author(s):  
Jason Mayes ◽  
Mihir Sen
Keyword(s):  
Mathematical Model ◽  
Analytical Solutions ◽  
Large Scale ◽  
Differential Algebraic Equations ◽  
Flow Dynamics ◽  
Algebraic Equations ◽  
Tree Networks ◽  
Self Similar ◽  
Large Scale Flow ◽  
The Mathematical Model

Dynamic analysis of large-scale flow networks is made difficult by the large system of differential-algebraic equations resulting from its modelling. To simplify analysis, the mathematical model must be sufficiently reduced in complexity. For self-similar tree networks, this reduction can be made using the network’s structure in way that can allow simple, analytical solutions. For very large, but finite, networks, analytical solutions are more difficult to obtain. In the infinite limit, however, analysis is sometimes greatly simplified. It is shown that approximating large finite networks as infinite not only simplifies the analysis, but also provides an excellent approximate solution.

EFFECTS OF A LARGE-SCALE MEAN FLOW IN A SHELL MODEL OF TURBULENT CONVECTION

2007 ◽  
Vol 21 (23n24) ◽  
pp. 4178-4183 ◽  
Author(s):  
EMILY S. C. CHING ◽  
H. GUO
Keyword(s):  
Shell Model ◽  
Large Scale ◽  
Temperature Fluctuations ◽  
Scaling Behavior ◽  
The Other ◽  
Turbulent Convection ◽  
Mean Flow ◽  
Mean Velocity ◽  
Other Hand ◽  
Flow Reversals

The possible effects of a large-scale mean flow, represented as a non-zero mean velocity in the shell of the largest scale, are studied using a shell model of turbulent convection. In the regime where buoyancy is dynamically important, flow reversals are not observed. On the other hand, flow reversals are found in the regime where buoyancy is not dynamically important. In both regimes, the presence of such a large-scale mean flow does not change the scaling behavior of the velocity and temperature fluctuations.

Prediction of time-dependent channel meander migration based on large-scale laboratory experiments

2011 ◽  
Vol 49 (5) ◽  
pp. 617-629 ◽  
Author(s):  
Po-Hung Yeh ◽  
Namgyu Park ◽  
Kuang-An Chang ◽  
Hamn-Ching Chen ◽  
Jean-Louis Briaud
Keyword(s):  
Large Scale ◽  
Laboratory Experiments ◽  
Time Dependent ◽  
Meander Migration

scholarly journals Convective self–aggregation in a mean flow

2020 ◽  
Author(s):  
Hyunju Jung ◽  
Ann Kristin Naumann ◽  
Bjorn Stevens
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Surface Flux ◽  
Horizontal Wind ◽  
Convective System ◽  
Mean Flow ◽  
Near Surface ◽  
Tropical Deep Convection ◽  
Large Scale Flow ◽  
Self Aggregation

Abstract. Convective self-aggregation is an atmospheric phenomenon found in numerical simulations in a radiative convective equilibrium framework of which configuration captures the main characteristics of the real-world convection in the deep tropics. As tropical deep convection is typically embedded in a large-scale flow, we impose a background mean wind flow on convection-permitting simulations through the surface flux calculation. The simulations show that with imposing mean flow, the organized convective system propagates in the direction of the flow but slows down compared to what pure advection would suggest, and eventually becomes stationary relative to the surface after 15 simulation days. The termination of the propagation arises from momentum flux, which acts as a drag on the near-surface horizontal wind. In contrast, the thermodynamic response through the wind-induced surface heat exchange feedback is a relatively small effect, which slightly retards (by about 15 %) the convection relative to the mean wind.

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