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Titolo:
COHERENT STRUCTURES NEAR THE WALL IN A TURBULENT CHANNEL FLOW
Autore:
JEONG J; HUSSAIN F; SCHOPPA W; KIM J;
Indirizzi:
UNIV HOUSTON,DEPT MECH ENGN HOUSTON TX 77204 UNIV CALIF LOS ANGELES,DEPT AEROSP & MECH ENGN LOS ANGELES CA 90095
Titolo Testata:
Journal of Fluid Mechanics
, volume: 332, anno: 1997,
pagine: 185 - 214
SICI:
0022-1120(1997)332:<185:CSNTWI>2.0.ZU;2-H
Fonte:
ISI
Lingua:
ENG
Soggetto:
BOUNDARY-LAYER; REYNOLDS STRESS; CORE DYNAMICS; VORTEX; VORTICES; VELOCITY; EDDIES; WAKE;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Science Citation Index Expanded
Citazioni:
45
Recensione:
Indirizzi per estratti:
Citazione:
J. Jeong et al., "COHERENT STRUCTURES NEAR THE WALL IN A TURBULENT CHANNEL FLOW", Journal of Fluid Mechanics, 332, 1997, pp. 185-214

Abstract

Coherent structures (CS) near the wall (i.e. y(+) less than or equal to 60) in a numerically simulated turbulent channel flow are educed using a conditional sampling scheme which extracts the entire extent of dominant vortical structures. Such structures are detected from the instantaneous flow field using our newly developed vortex definition (Jeong & Hussain 1995) - a region of negative lambda(2), the second largest eigenvalue of the tensor SikSkj + Omega(ik)Omega(kj) - which accurately captures the structure details (unlike velocity-, vorticity- or pressure-based eduction). Extensive testing has shown that lambda(2) correctly captures vortical structures, even in the presence of the strong shear occurring near the wall of a boundary layer. We have shown that the dominant near-wall educed (i.e. ensemble averaged after proper alignment) CS are highly elongated quasi-streamwise vortices; the CS are inclined 9 degrees in the vertical (x,y)-plane and tilted +/- 4 degrees in the horizontal (x,z)-plane. The vortices of alternating sign overlap in x as a staggered array; there is no indication near the wallof hairpin vortices, not only in the educed data but also in instantaneous fields. Our model of the CS array reproduces nearly all experimentally observed events reported in the literature, such as VITA, Reynolds stress distribution, wall pressure variation, elongated low-speed streaks, spanwise shear, etc. In particular, a phase difference (in space) between streamwise and normal velocity fluctuations created by CSadvection causes Q4 ('sweep') events to dominate Q2 ('ejection') and also creates counter-gradient Reynolds stresses (such as Q1 and Q3 events) above and below the CS. We also show that these effects are adequately modelled by half of a Batchelor's dipole embedded in (and decoupled from) a background shear U(y). The CS tilling (in the (x,z)-plane)is found to be responsible for sustaining CS through redistribution of streamwise turbulent kinetic energy to normal and spanwise components via coherent pressure-strain effects.

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Documento generato il 02/04/20 alle ore 06:17:51