An advanced experimental investigation of quasi-two-dimensional shear flow

1992 ◽  
Vol 241 ◽  
pp. 705-722 ◽  
Author(s):  
F. V. Dolzhanskii ◽  
V. A. Krymov ◽  
D. Yu. Manin
Keyword(s):  
Experimental Investigation ◽  
Shear Flow ◽  
Viscous Fluid ◽  
Thin Layer ◽  
Driving Force ◽  
Flow Characteristics ◽  
Vortical Flow ◽  
Two Dimensional ◽  
Dimensional Approximation ◽  
The Stability

Forced shear flows in a thin layer of an incompressible viscous fluid are studied experimentally. Streak photographs are used to obtain the stream function of vortical flow patterns arising after the primary shear flow loses stability. Various flow characteristics are determined and results are compared to the stability theory of quasi-two-dimensional flows. The applicability of the quasi-two-dimensional approximation is directly verified and the possibility of reconstruction of the driving force from the secondary flow pattern is demonstrated.

The stability of filamentary vorticity in two-dimensional geophysical vortex-dynamics models

1991 ◽  
Vol 231 ◽  
pp. 575-598 ◽  
Author(s):  
D. W. Waugh ◽  
D. G. Dritschel
Keyword(s):  
Green Function ◽  
Shear Flow ◽  
Stream Function ◽  
Potential Vorticity ◽  
Two Dimensional ◽  
Interaction Range ◽  
Inversion Operator ◽  
The Green Function ◽  
The Stability ◽  
Background Shear

The linear stability of filaments or strips of ‘potential’ vorticity in a background shear flow is investigated for a class of two-dimensional, inviscid, non-divergent models having a linear inversion relation between stream function and potential vorticity. In general, the potential vorticity is not simply the Laplacian of the stream function – the case which has received the greatest attention historically. More general inversion relationships between stream function and potential vorticity are geophysically motivated and give an impression of how certain classic results, such as the stability of strips of vorticity, hold under more general circumstances.In all models, a strip of potential vorticity is unstable in the absence of a background shear flow. Imposing a shear flow that reverses the total shear across the strip, however, brings about stability, independent of the Green-function inversion operator that links the stream function to the potential vorticity. But, if the Green-function inversion operator has a sufficiently short interaction range, the strip can also be stabilized by shear having the same sense as the shear of the strip. Such stabilization by ‘co-operative’ shear does not occur when the inversion operator is the inverse Laplacian. Nonlinear calculations presented show that there is only slight disruption to the strip for substantially less adverse shear than necessary for linear stability, while for co-operative shear, there is major disruption to the strip. It is significant that the potential vorticity of the imposed flow necessary to create shear of a given value increases dramatically as the interaction range of the inversion operator decreases, making shear stabilization increasingly less likely. This implies an increased propensity for filaments to ‘roll-up’ into small vortices as the interaction range decreases, a finding consistent with many numerical calculations performed using the quasi-geostrophic model.

Two-dimensional wave regimes in a thin layer of a viscous fluid

1985 ◽  
Vol 20 (3) ◽  
pp. 389-394 ◽  
Author(s):  
E. A. Demekhin ◽  
V. Ya. Shkadov
Keyword(s):  
Viscous Fluid ◽  
Thin Layer ◽  
Two Dimensional ◽  
Dimensional Wave

Shear flow instability in a conducting viscous fluid

1973 ◽  
Vol 57 (3) ◽  
pp. 481-490
Author(s):  
B. Roberts
Keyword(s):  
Magnetic Field ◽  
Shear Flow ◽  
Viscous Fluid ◽  
Flow Instability ◽  
Approximate Solutions ◽  
Viscous Fluids ◽  
Neutral Stability ◽  
Parallel Magnetic Field ◽  
The Stability ◽  
Shear Flow Instability

The effect of a parallel magnetic field upon the stability of the plane interface between two conducting viscous fluids in uniform relative motion is considered. A parameter reduction, which has not previously been noted, is employed to facilitate the solution of the problem. Neutral stability curves for unrestricted ranges of the governing parameters are found, and the approximate solutions of other authors are examined in this light.

Aggregation and stability in parasite—host models

Parasitology ◽  
1992 ◽  
Vol 104 (2) ◽  
pp. 199-205 ◽  
Author(s):  
F. R. Adler ◽  
M. Kretzschmar
Keyword(s):  
Equilibrium Distribution ◽  
Empirical Studies ◽  
Dimensional System ◽  
Two Dimensional ◽  
Full System ◽  
Dimensional Approximation ◽  
Approximate System ◽  
The Mean ◽  
Two Dimensional System ◽  
The Stability

SUMMARYThis paper generalizes the two-dimensional approximation of models of macroparasites on homogeneous populations developed by Anderson & May (1978), focusing on how the dispersion (the variance to mean ratio) of the equilibrium distribution of parasites on hosts is related to the stability of the equilibrium. We show in the approximate system that the equilibrium is stabilized not by aggregation, but by dispersion which increases as a function of the mean. Computer simulations indicate, however, that this analysis fails to capture properly the dynamics of the full system, raising the question of whether any two-dimensional system could produce an adequate approximation. We discuss the relevance of our results to several empirical studies which have examined the relation of dispersion to the mean.

An experimental investigation of the instability of a two-dimensional jet at low Reynolds numbers

1964 ◽  
Vol 20 (2) ◽  
pp. 337-352 ◽  
Author(s):  
Hiroshi Sato ◽  
Fujihiko Sakao
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Maximum Velocity ◽  
Reynolds Numbers ◽  
Two Dimensional ◽  
Low Reynolds Numbers ◽  
Laminar Jet ◽  
Artificial Disturbance ◽  
Low Reynolds ◽  
The Stability

An experimental investigation was made of the stability of a two-dimensional jet at low Reynolds numbers with extremely small residual disturbances both in and around the jet. The velocity distribution of a laminar jet is in agreement with Bickley's theoretical result. The stability and transition of a laminar jet are characterized by the Reynolds number based on the slit width and the maximum velocity of the jet. When the Reynolds number is less than 10, the whole jet is laminar. When the Reynolds number is between 10 and around 50, periodic velocity fluctuations are found in the jet. They die out as they travel downstream without developing into irregular fluctuations. When the Reynolds number exceeds about 50, periodic fluctuations develop into irregular, turbulent fluctuations. The frequency of the periodic fluctuation is roughly proportional to the square of the jet velocity.The stability of the jet against an artificially imposed disturbance was also investigated. Sound was used as an artificial disturbance. The disturbance is either amplified or damped in the jet depending on its frequency. The conventional stability theory was modified by considering the streamwise increase of Reynolds number. The experimental results are in agreement with the theoretical results.

scholarly journals Experimental Investigation on the Arc Characteristics and Arc Quenching Capabilities of C5F10O-CO2 Mixtures

2019 ◽  
Vol 6 (3) ◽  
pp. 231-234
Author(s):  
Z. Guo ◽  
F. Tang ◽  
Q. Lv ◽  
X. Li ◽  
B. Zhang ◽  
...  
Keyword(s):  
Experimental Investigation ◽  
High Speed ◽  
Inverse Transformation ◽  
High Speed Camera ◽  
Two Dimensional ◽  
Circuit Breakers ◽  
Arc Voltage ◽  
Arc Characteristics ◽  
Dimensional Distribution ◽  
The Stability

C<sub>5</sub>F<sub>10</sub>O-CO<sub>2</sub> mixtures are possible alternatives to SF<sub>6</sub> - which has a high global warming potential - as the interruption medium in gas circuit breakers. This paper experimentally studies the arcing characteristics of C<sub>5</sub>F<sub>10</sub>O-CO<sub>2</sub> mixture, with an experimental model with viewing windows, and measures the arc voltage, current and emission spectrum. The arc evolution process is captured with a high speed camera through an inspection window. The two-dimensional distribution of arc is obtained and analyzed by the inverse transformation of Abel. The results show that, the C<sub>5</sub>F<sub>10</sub>O-CO<sub>2</sub> mixture arc is more volatile than SF<sub>6</sub> gas, and adding C<sub>5</sub>F<sub>10</sub>O into CO<sub>2</sub> improves the stability of the arc, and significantly reduces the arc temperature.

Flow structures downstream of the horizontal cylinder laid on a plane surface

2008 ◽  
Vol 223 (2) ◽  
pp. 397-413 ◽  
Author(s):  
M Sami Akoz
Keyword(s):  
Flow Structure ◽  
Plane Surface ◽  
Water Channel ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Horizontal Cylinder ◽  
Vortical Flow ◽  
Cylinder Surface ◽  
Stress Concentrations ◽  
The Stability

The complex vortical flow structure arises from the interaction between the flow and a pipeline on seabed, causing erosion scour around the pipeline, which is a threat to the stability of the structure. The viscous flow past a circular cylinder laid on a horizontal bed is analysed experimentally using the particle image velocimetry image technique to understand the vortical flow characteristics downstream of the cylinder. The experiments were conducted in a closed-loop water channel with Reynolds numbers, in the range of 1000 ≤ ReD ≤ 7000 based on the cylinder diameter. To provide a detailed evaluation of the properties of the flow structure behind the cylinder, instantaneous and time-averaged patterns of velocity vector field, corresponding vorticity contours, streamline topology, and Reynolds stress concentrations were presented. The point of the boundary layer detachment from the cylinder surface and the lengths of the primary and secondary downstream separation regions were determined as a function of Reynolds numbers. Instantaneous velocity fields clearly indicate the scour mechanism downstream of the horizontal cylinder.

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