The Okubo-Weiss criterion in hydrodynamic flows:Geometric aspects and further extension

2022 ◽  
Author(s):  
Bhimsen Shivamoggi ◽  
G Heijst ◽  
Leon Kamp
Keyword(s):  
Flow Field ◽  
Polar Coordinates ◽  
Coriolis Parameter ◽  
Laminar Jet ◽  
Type Criterion ◽  
Burgers Vortex ◽  
2D Flow ◽  
Flow Configurations ◽  
Elliptic Regions ◽  
Oseen Vortex

Abstract The Okubo [5]-Weiss [6] criterion has been extensively used as a diagnostic tool to divide a two-dimensional (2D) hydrodynamical flow field into hyperbolic and elliptic regions and to serve as a useful qualitative guide to the complex quantitative criteria. The Okubo-Weiss criterion is frequently validated on empirical grounds by the results ensuing its application. So, we will explore topological implications into the Okubo-Weiss criterion and show the Okubo-Weiss parameter is, to within a positive multiplicative factor, the negative of the Gaussian curvature of the underlying vorticity manifold. The Okubo-Weiss criterion is reformulated in polar coordinates, and is validated via several examples including the Lamb- Oseen vortex, and the Burgers vortex. These developments are then extended to 2D quasi- geostrophic (QG) flows. The Okubo-Weiss parameter is shown to remain robust under the -plane approximation to the Coriolis parameter. The Okubo-Weiss criterion is shown to be able to separate the 2D flow-field into coherent elliptic structures and hyperbolic flow configurations very well via numerical simulations of quasi-stationary vortices in QG flows. An Okubo-Weiss type criterion is formulated for 3D axisymmetric flows, and is validated via application to the round Landau-Squire Laminar jet flow.

Suppression of Baroclinic Instabilities in Buoyancy-Driven Flow over Sloping Bathymetry

2017 ◽  
Vol 47 (1) ◽  
pp. 49-68 ◽  
Author(s):  
Robert D. Hetland
Keyword(s):  
Growth Rate ◽  
Linear Instability ◽  
Linear Stability Theory ◽  
Buoyancy Frequency ◽  
Bottom Slope ◽  
Coriolis Parameter ◽  
Plume Front ◽  
Instability Theory ◽  
Instability Growth ◽  
Flow Configurations

AbstractBaroclinic instabilities are ubiquitous in many types of geostrophic flow; however, they are seldom observed in river plumes despite strong lateral density gradients within the plume front. Supported by results from a realistic numerical simulation of the Mississippi–Atchafalaya River plume, idealized numerical simulations of buoyancy-driven flow are used to investigate baroclinic instabilities in buoyancy-driven flow over a sloping bottom. The parameter space is defined by the slope Burger number S = Nf−1α, where N is the buoyancy frequency, f is the Coriolis parameter, and α is the bottom slope, and the Richardson number Ri = N2f2M−4, where M2 = |∇Hb| is the magnitude of the lateral buoyancy gradients. Instabilities only form in a subset of the simulations, with the criterion that SH ≡ SRi−1/2 = Uf−1W−1 = M2f−2α 0.2, where U is a horizontal velocity scale and SH is a new parameter named the horizontal slope Burger number. Suppression of instability formation for certain flow conditions contrasts linear stability theory, which predicts that all flow configurations will be subject to instabilities. The instability growth rate estimated in the nonlinear 3D model is proportional to ωImaxS−1/2, where ωImax is the dimensional growth rate predicted by linear instability theory, indicating that bottom slope inhibits instability growth beyond that predicted by linear theory. The constraint SH 0.2 implies a relationship between the inertial radius Li = Uf−1 and the plume width W. Instabilities may not form when 5Li > W; that is, the plume is too narrow for the eddies to fit.

Shock formation in the presence of entropy gradients

2001 ◽  
Vol 431 ◽  
pp. 161-188 ◽  
Author(s):  
HAO LIN ◽  
ANDREW J. SZERI
Keyword(s):  
Flow Field ◽  
Sound Speed ◽  
Compression Wave ◽  
Method Of Characteristics ◽  
Principal Result ◽  
Polar Coordinates ◽  
Shock Formation ◽  
Analytical Criterion ◽  
Energy Focusing ◽  
Normal Compression

The steepening of a normal compression wave into a shock in a homentropic flow field is understood well through the method of characteristics. In a non-homentropic flow field, however, shock formation from a compression wave is more complex. The effects of entropy (or sound speed) gradients on shock formation from a compression wave are determined using a wave front expansion in Cartesian and in spherical polar coordinates. The latter problem has application to the intense energy focusing of sonoluminescence, particularly when applied to a spherically collapsing gas. The principal result is an analytical criterion for the time and place of shock formation, for a wave propagating into a field of smoothly varying entropy.

Low Analysis of Steady Flow Field in Mechanical Seal Based on ANSYS

2011 ◽  
Vol 121-126 ◽  
pp. 3352-3355
Author(s):  
Yue Feng Zhu ◽  
De Lin Chen
Keyword(s):  
Flow Field ◽  
Steady Flow ◽  
Mechanical Seal ◽  
The Press ◽  
2D Flow ◽  
Comparison And Analysis ◽  
Velocity Contour

Simulation and analysis of steady and 2D flow field by using ANSYS8.0 and getting the press and velocity contour. omulate the leakage. then through comparison and analysis offering theory evidence for controlling leakage effectively.

New Radial-Based Flow Configurations for PEMFCs

2009 ◽  
Author(s):  
Isaac Perez-Raya ◽  
Abel Hernandez-Guerrero ◽  
Daniel Juarez-Robles ◽  
M. Ernesto Gutierrez-Rivera ◽  
J. C. Rubio-Arana
Keyword(s):  
Fuel Cell ◽  
Flow Field ◽  
Gas Flow ◽  
Previous Analysis ◽  
Pem Fuel Cell ◽  
Cell Performance ◽  
Fuel Cell Performance ◽  
Flow Configurations ◽  
Gas Flow Field

This work presents the results of a study of a new radial configuration proposed for the gas flow field for a PEM fuel cell. The objective of this study is to understand the effects of this configuration on the fuel cell performance. The results are compared with the radial designs proposed in previous analysis. The proposed designs on this work show an improvement on the cell performance, with a better use of the reaction area compared with a flow free radial design. The results also show that the effect of channeling the flow inside these radial configurations helps to improve the fuel cell performance.

Experimental Analysis and Numerical Simulation of the Flow Field in Turbine Scrolls

1998 ◽  
Author(s):  
Uwe W. Menter ◽  
Thomas Klima ◽  
Heiner Pfost
Keyword(s):  
Numerical Simulation ◽  
Finite Element ◽  
Flow Field ◽  
Cross Sections ◽  
Theoretical Calculations ◽  
Two Dimensional ◽  
3D Finite Element ◽  
Non Invasive ◽  
Flow Configurations ◽  
Selection Of

A large selection of one- and two-dimensional methods can be used to calculate the scroll geometries. This paper examines the consequences of different scroll geometry parameters under various flow configurations, including the influence of components in the scroll flow field. A combination of arrangements of the various components was investigated, (scroll/nozzle/rotor, scroll/nozzle/stator, scroll/vane support/rotor, scroll/vane support/stator), to see how the flow varied. In this particular case a frictionless scroll was designed. The turbine operates with a gas fluid. Using a non-invasive laser two-focus technique and wall pressure drillings the flow field was measured over three scroll cross sections and over its extent at φ = 186° up to φ = 211°. The theoretical analysis was performed on a computer using a commercial 3D finite element programme. Using the programme enables the theoretical flow fields of various scroll geometries to be calculated. The validity of the calculations can be assessed by comparing the theoretical calculations with the above mentioned measurements. The measurements show that by using a rotor the flow field inside the scroll remains uninfluenced by the vane support and nozzle. Measurable differences appear when the rotor is replaced by a stator, these results are confirmed by the computer program. The calculations also show that the scroll geometry has an important effect on the development of the flow field.

scholarly journals Impact of flow configuration on electrosorption performance and energy consumption of CDI systems

2020 ◽  
Vol 69 (2) ◽  
pp. 134-144 ◽  
Author(s):  
Lutfi Agartan ◽  
Bilen Akuzum ◽  
Ertan Agar ◽  
E. Caglan Kumbur
Keyword(s):  
Flow Field ◽  
Flow Rate ◽  
Poor Performance ◽  
Peak Performance ◽  
Carbon Cloth ◽  
Activated Carbon Cloth ◽  
Flow Configuration ◽  
Flow Configurations ◽  
Parallel Configuration ◽  
Adsorption Rates

Abstract The flow configuration selected for a capacitive deionization (CDI) system can impact the desalination performance due to drastic changes to the ion transport. Herein, a zero-gap CDI cell fixture with various flow configurations was utilized to investigate the effects of flow directionality on the CDI performance of activated carbon cloth (ACC) electrodes. Salt adsorption capacities and salt adsorption rates were determined for three commonly studied flow field designs (parallel (PFF), interdigitated (IDFF), and serpentine (SFF)) at various flow rates (2–128 mL/min). Increasing the flow rate was found to result in decreasing CDI performance for SFF and IDFF designs. On the other hand, the peak performance was observed for the parallel flow field at 32 mL/min flow rate. Additionally, the pressure drop values for different flow configurations were measured, and the energy consumptions were calculated. Overall, the findings showed that the performance of CDI systems strongly depends on the selected flow field geometry. Among the tested flow fields, the parallel configuration offered the best balance between CDI performance and energy efficiency. However, the designs that exert high hydrodynamic forces on the electrode plane showed poor performance due to rip-off of ions from the double layer causing a significant capacity loss for ACC electrodes.

scholarly journals Continental Shelf Baroclinic Instability. Part II: Oscillating Wind Forcing

2016 ◽  
Vol 46 (2) ◽  
pp. 569-582 ◽  
Author(s):  
K. H. Brink ◽  
H. Seo
Keyword(s):  
Flow Field ◽  
Continental Shelf ◽  
Large Scale ◽  
Baroclinic Instability ◽  
Wind Forcing ◽  
Develop Model ◽  
Bottom Slope ◽  
Coriolis Parameter ◽  
Wide Range ◽  
Eddy Field

AbstractContinental shelf baroclinic instability energized by fluctuating alongshore winds is treated using idealized primitive equation numerical model experiments. A spatially uniform alongshore wind, sinusoidal in time, alternately drives upwelling and downwelling and so creates highly variable, but slowly increasing, available potential energy. For all of the 30 model runs, conducted with a wide range of parameters (varying Coriolis parameter, initial stratification, bottom friction, forcing period, wind strength, and bottom slope), a baroclinic instability and subsequent eddy field develop. Model results and scalings show that the eddy kinetic energy increases with wind amplitude, forcing period, stratification, and bottom slope. The dominant alongshore length scale of the eddy field is essentially an internal Rossby radius of deformation. The resulting depth-averaged alongshore flow field is dominated by the large-scale, periodic wind forcing, while the cross-shelf flow field is dominated by the eddy variability. The result is that correlation length scales for alongshore flow are far greater than those for cross-shelf velocity. This scale discrepancy is qualitatively consistent with midshelf observations by Kundu and Allen, among others.

Inviscid waves on a Lamb–Oseen vortex in a rotating stratified fluid: consequences for the elliptic instability

2008 ◽  
Vol 597 ◽  
pp. 283-303 ◽  
Author(s):  
STÉPHANE LE DIZÈS
Keyword(s):  
Plane Waves ◽  
Stratified Fluid ◽  
Lagrangian Description ◽  
Small Range ◽  
Local Approach ◽  
Coriolis Parameter ◽  
Centrifugal Instability ◽  
Local Plane ◽  
Core Modes ◽  
Oseen Vortex

The inviscid waves propagating on a Lamb–Oseen vortex in a rotating medium for an unstratified fluid and for a strongly stratified fluid are analysed using numerical and asymptotic approaches. By a local Lagrangian description, we first provide the characteristics of the local plane waves (inertia–gravity waves) as well as the local growth rate associated with the centrifugal instability when the vortex is unstable. A global WKBJ approach is then used to determine the frequencies of neutral core modes and neutral ring modes. We show that these global Kelvin modes only exist in restricted domains of the parameters. The consequences of these domain limitations for the occurrence of the elliptic instability are discussed. We argue that in an unstratified fluid the elliptic instability should be active in a small range of the Coriolis parameter which could not have been predicted from a local approach. The wavenumbers of the sinuous modes of the elliptic instability are provided as a function of the Coriolis parameter for both an unstratified fluid and a strongly stratified fluid.

scholarly journals 2D Flow in a Wall-Bounded Porous Medium

2013 ◽  
Vol 334-335 ◽  
pp. 359-364 ◽  
Author(s):  
P.J.S.A. Ferreira de Sousa ◽  
Isabel Malico ◽  
Gérson Fernandes
Keyword(s):  
Boundary Conditions ◽  
Drag Coefficient ◽  
Cross Sections ◽  
Porous Matrix ◽  
Finite Differences Method ◽  
2D Flow ◽  
Compact Finite Differences ◽  
Flow Through ◽  
Flow Configurations ◽  
Immersed Boundaries

A compact finite differences method is used to calculate two-dimensional viscous flows through complex geometries. The immersed boundaries are set through body forces that allow for the imposition of boundary conditions that coincide with the computational grid. Two different flow configurations are simulated. First, the flow through a row of cylinders with square cross-sections is calculated and used as a validation study. The computed average drag coefficient and Strouhal number are compared to data available in the literature, showing a good agreement between the results. The second flow configuration analyzed is the flow through a porous matrix composed of equal size staggered square cylinders. Flow visualization results are shown and various flow regimes identified. Different inlet boundary conditions are compared. The drag coefficient is larger when a uniform inlet velocity is prescribed and the variability between cylinders is lower.

Sign in / Sign up

Export Citation Format

Share Document