scholarly journals Generation, Evolution, and Characterization of Turbulence Coherent Structures

2019 ◽  
Author(s):  
Zambri Harun ◽  
Eslam Reda Lotfy
Keyword(s):  
Coherent Structures

Characterization of Geometrical and Temporal Properties of Large-scale Motions in Turbulent Flows

2021 ◽  
Author(s):  
Christina Tsai ◽  
Kuang-Ting Wu
Keyword(s):  
Turbulent Flow ◽  
Turbulent Flows ◽  
Coherent Structures ◽  
Large Scale ◽  
Streamwise Velocity ◽  
Turbulent Structures ◽  
Temporal Properties ◽  
Turbulent Statistics ◽  
Spatial Locations

<p>It is demonstrated that turbulent boundary layers are populated by a hierarchy of recurrent structures, normally referred to as the coherent structures. Thus, it is desirable to gain a better understanding of the spatial-temporal characteristics of coherent structures and their impact on fluid particles. Furthermore, the ejection and sweep events play an important role in turbulent statistics. Therefore, this study focuses on the characterizations of flow particles under the influence of the above-mentioned two structures.</p><div><span>With regard to the geometry of turbulent structures, </span><span>Meinhart & Adrian (1995) </span>first highlighted the existence of large and irregularly shaped regions of uniform streamwise momentum zone (hereafter referred to as a uniform momentum zone, or UMZs), regions of relatively similar streamwise velocity with coherence in the streamwise and wall-normal directions.  <span>Subsequently, </span><span>de Silva et al. (2017) </span><span>provided a detection criterion that had previously been utilized to locate the uniform momentum zones (UMZ) and demonstrated the application of this criterion to estimate the spatial locations of the edges that demarcates UMZs.</span></div><div> </div><div>In this study, detection of the existence of UMZs is a pre-process of identifying the coherent structures. After the edges of UMZs are determined, the identification procedure of ejection and sweep events from turbulent flow DNS data should be defined. As such, an integrated criterion of distinguishing ejection and sweep events is proposed. Based on the integrated criterion, the statistical characterizations of coherent structures from available turbulent flow data such as event durations, event maximum heights, and wall-normal and streamwise lengths can be presented.</div>

scholarly journals Characterization of Coherent Structures in the Cardiovascular System

2008 ◽  
Vol 36 (7) ◽  
pp. 1152-1162 ◽  
Author(s):  
Shawn C. Shadden ◽  
Charles A. Taylor
Keyword(s):  
Cardiovascular System ◽  
Coherent Structures

Nonlinear Fourier transform for characterization of the coherent structures in optical microresonators

2020 ◽  
Vol 45 (11) ◽  
pp. 3059
Author(s):  
Sergei K. Turitsyn ◽  
Igor S. Chekhovskoy ◽  
Mikhail P. Fedoruk
Keyword(s):  
Fourier Transform ◽  
Coherent Structures ◽  
Optical Microresonators ◽  
Nonlinear Fourier Transform

scholarly journals Characterization of Disturbed Hemodynamics due to Stenosed Aortic Jets with a Lagrangian Coherent Structures Technique

2018 ◽  
Vol 11 (2) ◽  
pp. 375-384 ◽  
Author(s):  
A. Olcay ◽  
A. Amindari ◽  
K. Kirkkopru ◽  
H. Yalcin ◽  
◽  
...  
Keyword(s):  
Coherent Structures ◽  
Lagrangian Coherent Structures

Characterization of Flow Structures in a Diesel Injector for Different Needle Lifts and a Fluctuating Injection Pressure

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Alexandre Pelletingeas ◽  
Louis Dufresne ◽  
Patrice Seers
Keyword(s):  
Steady State ◽  
Coherent Structures ◽  
Injection Pressure ◽  
Internal Flow ◽  
Orthogonal Decomposition ◽  
Navier Stokes ◽  
Flow Structures ◽  
Single Hole ◽  
Proper Orthogonal

This paper aims at analyzing the needle lift's influence on the internal flow of single-hole diesel injector to identify flow structures. A numerical Reynolds-Averaged Navier–Stokes (RANS) model of a single-hole diesel injector was developed and validated to study the flow's dynamic for different needle's lifts and subjected to realistic injection pressure. The main findings are: (1) under steady injection pressure, flow coefficients reached a steady-state value and maximum injected fuel mass flow rate is reached at intermediate needle's lifts. (2) The sac volume is the area with several vortex structures due to the throttling between the needle body and the injector body. (3) The frequency of the fluctuating injection pressure can excite the initial jet entering the sac volume similarly to the Coanda effect. Finally, using a proper orthogonal decomposition (POD) allowed extracting coherent structures within the sac volume and putting in evidence a reorganization of the flow.

Experimental Characterization of the Flow-Field Downstream of an Innovative Ultra Low NOx Injection System

2014 ◽  
Author(s):  
Marco Berrino ◽  
Francesca Satta ◽  
Marina Ubaldi ◽  
Pietro Zunino ◽  
Salvatore Colantuoni ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Coherent Structures ◽  
Particle Image ◽  
Flow Region ◽  
Experimental Results ◽  
Injection System ◽  
Hot Wire ◽  
Mean Velocity ◽  
Image Velocimetry

The present paper is focused on the characterization of the aerodynamics of the nonreacting flow downstream of an innovative Ultra Low NOx (ULN) injection system. The system is aimed at reducing NOx emissions and combustor axial length, to obtain a more compact and lighter low-emission combustor. The flow path downstream of the injection system has been investigated by means of Particle Image Velocimetry (PIV) and Hot Wire Anemometry (HWA). Particle Image Velocimetry measurements have been carried out in the meridional plane and in three frontal planes, in order to measure mean velocity components and their fluctuations, as well as to identify the coherent structures that characterize the time-varying flow. Hot Wire Anemometry has been used to investigate the unsteady behavior of the flow and to detect the presence of velocity fluctuation frequencies at different radial and axial positions downstream of the injection system. The HWA technique allowed the identification of the frequencies associated with the precession motion due to the vortex breakdown and with the coherent structures at the interface between the inverse flow region and the jets. The experimental results show a large reverse flow region at the exit, without any back-flow within the injection system, hence offering the evidence that the injection system may be able to stabilize the flame, without inducing risks of flash-back or auto-ignition phenomena. Moreover, the mean velocity distributions show the injection system ability of keeping separated the two jets coming out from the internal and external swirlers, with the consequent possibility of applying fuel-staging. Furthermore, the experimental results have been compared to CFD RANS calculations and used for the validation of the numerical procedure.

scholarly journals Characterization of turbulent coherent structures in square duct flow

2018 ◽  
Vol 1001 ◽  
pp. 012008 ◽  
Author(s):  
Marco Atzori ◽  
Ricardo Vinuesa ◽  
Adrián Lozano-Durán ◽  
Philipp Schlatter
Keyword(s):  
Coherent Structures ◽  
Duct Flow ◽  
Square Duct ◽  
Turbulent Coherent Structures
Sign in / Sign up

Export Citation Format

Share Document