Extension of POD Analysis Toward the Three-Dimensional Coherent Structure

2018 ◽  
pp. 39-50
Author(s):  
R. Gurka ◽  
A. Liberzon ◽  
G. Hetsroni
Keyword(s):  
Coherent Structure ◽  
Three Dimensional ◽  
Pod Analysis

scholarly journals A note on the mirror-symmetric coherent structure in plane Couette flow

2013 ◽  
Vol 727 ◽  
Author(s):  
M. Nagata
Keyword(s):  
Couette Flow ◽  
Coherent Structure ◽  
Rotation Rate ◽  
Symmetric Solution ◽  
Three Dimensional ◽  
Plane Couette Flow ◽  
System Rotation ◽  
The Way

AbstractWe note that the mirror-symmetric solution in plane Couette flow, found recently by Gibson, Halcrow & Cvitanović (J. Fluid Mech., vol. 611, 2009, pp. 107–130) and Itano & Generalis (Phys. Rev. Lett., vol. 102, 2009, p. 114501), belongs to the solution group classified as ‘ribbon’ in rotating-plane Couette flow (RPCF). It represents a subcritical (in terms of the system rotation) solution at zero rotation rate on the three-dimensional tertiary flow branch which bifurcates from thesecondstreamwise-independent flow in RPCF. The way of its appearance is similar to that of the Nagata solution (J. Fluid Mech., vol. 217, 1990, pp. 519–527), which lies on the subcritical three-dimensional tertiary flow branch bifurcating from thefirststreamwise-independent flow in RPCF.

Lagrangian Analysis of Unsteady Partial Cavitating Flow Around a Three-Dimensional Hydrofoil

2020 ◽  
Author(s):  
Tingyun Yin ◽  
Giorgio Pavesi ◽  
Ji Pei ◽  
Shouqi Yuan ◽  
Giovanna Cavazzini ◽  
...  
Keyword(s):  
Coherent Structure ◽  
Cavity Growth ◽  
Three Dimensional ◽  
Adverse Pressure Gradient ◽  
Buffer Zone ◽  
Cavitating Flow ◽  
Lagrangian Analysis ◽  
Lagrangian Coherent Structure ◽  
Cavity Development ◽  
Unsteady Cavitating Flow

Abstract This study employs an incompressible homogeneous flow framework with a transport-equation-based cavitation model and shear stress transport turbulence model to successfully reproduce the unsteady cavitating flow around a three-dimensional hydrofoil. Cavity growth, development, and break-off during the periodic shedding process are adequately reproduced and match experimental observations. The predicted shedding frequency is very close to the experimental value of 23 ms. By monitoring the motions of the seeding trackers, growth-up of attached cavity and dynamic evolution of U-type cavity are clearly displayed, which indicating the trackers could serve as an effective tool to visualize the cavitating field. Repelling Lagrangian Coherent Structure (RLCS) is so complex that abundant flow patterns are highlighted, reflecting the intricacy of cavity development. The formation of cloud cavities is clearly characterized by the Attracting Lagrangian Coherent Structure (ALCS), where bumbling wave wrapping the whole shedding cavities indicates the rotating transform of cavities and stretching of the wave eyes shows the distortion of vortices. Generation of the re-entrant jet is considered to be not only associated with the adverse pressure gradient due to the positive attack angle, but also the contribution of cloud cavitating flow, based on the observation of a buffer zone between the attached and cloud cavities.

scholarly journals A network-based perspective on coherent structure detection from very-sparse Lagrangian data

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Giovanni Iacobello ◽  
David E. Rival
Keyword(s):  
Coherent Structure ◽  
Measurement Techniques ◽  
Three Dimensional ◽  
Coherent Motion ◽  
Modeling And Control ◽  
Structure Detection ◽  
Spatio Temporal ◽  
Lagrangian Data ◽  
And Control ◽  
Lagrangian Flow

Coherent structure detection (CSD) is a long-lasting issue in fluid mechanics research as the presence of spatio-temporal coherent motion enables simpler ways to characterize the flow dynamics. Such reducedorder representation, in fact, has significant implications for the understanding of the dynamics of flows, as well as their modeling and control (Hussain, 1986). While the Eulerian framework has been extensively adopted for CSD, Lagrangian coherent structures have recently received increasing attention, mainly driven by advancements in Lagrangian flow measurement techniques (Haller, 2015; Hadjighasem et al., 2017). Lagrangian particle tracking (LPT), in particular, is widely used nowadays due to its ability to quantity fluid-parcel trajectories in three-dimensional volumes (Schanz et al., 2016).

Elliptic jets. Part 3. Dynamics of preferred mode coherent structure

1993 ◽  
Vol 248 ◽  
pp. 315-361 ◽  
Author(s):  
Hyder S. Husain ◽  
Fazle Hussain
Keyword(s):  
Coherent Structure ◽  
Near Field ◽  
Three Dimensional ◽  
Mixing Enhancement ◽  
Hot Wire ◽  
Vortical Structures ◽  
Mass Entrainment ◽  
Time Average ◽  
And Control ◽  
Made In

The dynamics of the preferred mode structure in the near field of an elliptic jet have been investigated using hot-wire measurements. A 2:1 aspect ratio jet with an initially turbulent boundary layer and a constant momentum thickness all around the nozzle exit perimeter was used for this study. Measurements were made in air at a Reynolds number ReDe (≡ UeDe/v) = 3.5 × 104. Controlled longitudinal excitation at the preferred mode frequency (StDe ≡ fDe/Ue = 0.4) induced periodic formation of structures, allowing phase-locked measurements with a local trigger hot wire. The dynamics of the organized structure are examined from educed fields of coherent vorticity and incoherent turbulence in the major and minor symmetry planes at five successive phases of evolution, and are also compared with corresponding data for a circular jet. Unlike in a circular jet, azimuthally fixed streamwise vortices (ribs) form without the aid of azimuthal forcing. The three-dimensional deformation of elliptic vortical structures and the rib formation mechanism have also been studied through direct numerical simulation. Differential self-induced motions due to non-uniform azimuthal curvature and the azimuthally fixed ribs produce greater mass entrainment in the elliptic jet than in a circular jet. The turbulence production mechanism, entrainment and mixing enhancement, and time-average measures and their modification by excitation are also discussed in terms of coherent structure dynamics and the rib-roll interaction. Various phase-dependent and time-average turbulence measures documented in this paper should serve as target data for validation of numerical simulations and turbulence modelling, and for design and control purposes in technological applications. Further details are given by Husain (1984).

Corner Separation Dynamics in a Linear Compressor Cascade

2016 ◽  
Author(s):  
Gherardo Zambonini ◽  
Xavier Ottavy ◽  
Jochen Kriegseis
Keyword(s):  
Three Dimensional ◽  
Recirculation Region ◽  
Spanwise Direction ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Time Resolved ◽  
Piv Measurements ◽  
Blade Section ◽  
Pod Analysis ◽  
Linear Compressor Cascade

This paper considers the inherent unsteady behavior of the three dimensional separation in the corner region of a subsonic linear compressor cascade equipped of thirteen NACA 65-009 profile blades. Detailed experimental measurements were carried out at different sections in spanwise direction achieving, simultaneously, unsteady wall pressure signals on the surface of the blade and velocity fields by time-resolved PIV measurements. Two configurations of the cascade were investigated with an incidence of 4° and 7°, both at Re = 3.8 * 105 and Ma = 0.12 at the inlet of the facility. The intermittent switch between the two statistical preferred sizes of separation, large and almost suppressed, is called bimodal behaviour. The existence of such oscillation, reported at first in previous experimental and numerical works on the same test rig, is confirmed for both incidences. Additionally, the present PIV measurements provide, for the first time, time-resolved flow visualizations of the size switch of the separation with an extended field of view covering the entire blade section. The interaction of random large structures of the incoming boundary layer with the blade is found to be a predominant element that destabilizes the separation boundary. The recirculation region enlarges when these high vorticity perturbations blend with larger eddies situated in the aft part of the blade. Such massive separation persists until the blockage in the passage causes the breakdown of the largest structures in the aft part of the blade. The flow starts again to accelerate and the separation is almost suppressed. Finally, POD analysis is carried out to decompose flow modes and to contribute to the clarification of underlying cause-effect-relations, which predominate the dynamics of the present flow scenario.

scholarly journals Microscopic Effect on Filamentary Coherent Structure Dynamics in Boundary Layer Plasmas

Plasma ◽  
2018 ◽  
Vol 1 (1) ◽  
pp. 61-67 ◽  
Author(s):  
Hiroki Hasegawa ◽  
Seiji Ishiguro
Keyword(s):  
Boundary Layer ◽  
Symmetry Breaking ◽  
Electron Temperature ◽  
Coherent Structure ◽  
Three Dimensional ◽  
Temperature Ratio ◽  
Pic Simulation ◽  
Particle In Cell ◽  
Plasma Filament ◽  
Potential Structure

This study has demonstrated kinetic behaviors on the plasma filament propagation with the three-dimensional (3D) Particle-in-Cell (PIC) simulation. When the ion-to-electron temperature ratio T i / T e is higher, the poloidal symmetry breaking in the filament propagation occurs. The poloidal symmetry breaking is thought to be induced by the unbalanced potential structure that arises from the effect of the gyro motion of plasma particles.

PIV Study of Mildly Controlled Flow Over a Wing Model Using a Synthetic Jet Array

2016 ◽  
Author(s):  
Pramod B. Salunkhe ◽  
Hui Tang ◽  
Yanhua Wu
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Separated Flow ◽  
Synthetic Jet ◽  
Particle Image Velocimetry System ◽  
Wing Model ◽  
Subsonic Wind Tunnel ◽  
Discrete Structures ◽  
Controlled Flow ◽  
Pod Analysis

This work describes the use of a synthetic jet (SJ) array for mild control of flow separation over a straight wing model. Experiments were performed in a subsonic wind tunnel to show improvement of the wing aerodynamic performance. A tomographic particle image velocimetry system was used to measure and analyze the three-dimensional flow-field with and without the SJ actuation. It was observed that, although the SJ array is relatively weak, it can still made impacts on the separated flow. After the SJ actuation, the large-scale vortex structures in the shear layer were broken into small discrete structures and the near-wall flow was substantially improved. Subsequently, Proper Orthogonal Decomposition (POD) analysis was also conducted and the effectiveness of the present SJ array was further discussed.

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