The Dynamics of the Large-Scale Turbulent Structures in the Impinging Round Jet

2003 ◽  
Author(s):  
Joseph W. Hall ◽  
Dan Ewing ◽  
Zhuyun Xu ◽  
Horia Hangan
Keyword(s):  
Large Scale ◽  
Wall Jet ◽  
Turbulent Structures ◽  
Azimuthal Mode ◽  
Large Scale Structures ◽  
Preferred Direction ◽  
Plate Spacing ◽  
Ring Structures ◽  
Instantaneous Pressure ◽  
Scale Structures

Experiments were performed to characterize the development of the large-scale structures in the stagnation and wall-jet regions of a turbulent impinging jet with a nozzle-to-plate spacing of 2 diameters and a Reynolds number of 20000. In particular, the instantaneous pressure was measured at 137 points on the wall using 6 concentric rings of pressure taps located 0.25, 0.5, 1.0, 1.5, 2.0 and 2.5 pipe diameters from the jet centreline. The 6 rings respectively contained 8, 16, 16, 32, 32 and 32 equally spaced taps as well as a single pressure tap placed at the jet centerline. The fluctuating pressure was decomposed into azimuthal modes and it was found that a significant portion of the field was contained in azimuthal mode 0 associated with the axisymmetric ring structures and azimuthal mode 1, often associated with jet precessing. The instantaneous pressure was filtered so that only azimuthal modes 0, 1 and −1 remained, and the dynamics of the large-scale structures associated with these modes was examined. These structures were found to be convected radially outward, were highly intermittent, and found to not rotate in a preferred direction.

The Three-Dimensional Evolution of the Large-Scale Structures in the Impinging Round Jet

2002 ◽  
Author(s):  
J. W. Hall ◽  
N. Gao ◽  
D. Ewing
Keyword(s):  
Large Scale ◽  
Dominant Role ◽  
Three Dimensional ◽  
Convection Velocity ◽  
Fluctuating Pressure ◽  
Round Jet ◽  
Large Scale Structures ◽  
Plate Spacing ◽  
Ring Structures ◽  
Scale Structures

The evolution of the large-scale structures in the impinging round jet were studied by measuring the fluctuating pressure on the impingement surface for nozzle-to-plate distances of 2.0, 3.0 and 4.0 nozzle diameters. It is found that the large-scale vortex ring structures played a much more dominant role when the nozzle-to-plate spacing was 2.0 diameters than for either 3.0 or 4.0 diameters. The results for a nozzle-to-plate spacing of 3.0 nozzle diameters more closely resembles the spacing of 4.0 diameters. The convection velocity of the different azimuthal modes were deduced from radial cross-spectra measurements. It was found that the convection velocity of all the azimuthal modes were similar and the convection speed for the structures measured with the fluctuating pressure were independent of nozzle-to-plate distance.

The meandering behaviour of large-scale structures in turbulent boundary layers

2019 ◽  
Vol 865 ◽  
Author(s):  
Kevin Kevin ◽  
Jason Monty ◽  
Nicholas Hutchins
Keyword(s):  
Boundary Layers ◽  
Large Scale ◽  
Flow Direction ◽  
Main Flow ◽  
Turbulent Structures ◽  
Velocity Fluctuations ◽  
Large Scale Structures ◽  
Main Flow Direction ◽  
Scale Structures ◽  
Spanwise Velocity

This paper quantifies the instantaneous form of large-scale turbulent structures in canonical smooth-wall boundary layers, demonstrating that they adhere to a form that is consistent with the self-sustaining streak instability model suggested by Flores & Jiménez (Phys. Fluids, vol. 22, 2010, 071704) and Hwang & Cossu (Phys. Fluids, vol. 23, 2011, 061702). Our motivation for this study stems from previous observations of large-scale streaks that have been spatially locked in position within spanwise-heterogeneous boundary layers. Here, using similar tools, we demonstrate that the randomly occurring large-scale structures in canonical layers show similar behaviour. Statistically, we show that the signature of large-scale coherent structures exhibits increasing meandering behaviour with distance from the wall. At the upper edge of the boundary layer, where these structures are severely misaligned from the main-flow direction, the induced velocities associated with the strongly yawed vortex packets/clusters yield a significant spanwise-velocity component leading to an apparent oblique coherence of spanwise-velocity fluctuations. This pronounced meandering behaviour also gives rise to a dominant streamwise periodicity at a wavelength of approximately $6\unicode[STIX]{x1D6FF}$. We further statistically show that the quasi-streamwise roll-modes formed adjacent to these very large wavy motions are often one-sided (spanwise asymmetric), in stark contrast to the counter-rotating form suggested by conventional conditionally averaged representations. To summarise, we sketch a representative picture of the typical large-scale structures based on the evidence gathered in this study.

Large-scale motions in a plane wall jet

2019 ◽  
Vol 877 ◽  
pp. 239-281 ◽  
Author(s):  
Ebenezer P. Gnanamanickam ◽  
Shibani Bhatt ◽  
Sravan Artham ◽  
Zheng Zhang
Keyword(s):  
Reynolds Number ◽  
Shear Layer ◽  
Large Scale ◽  
Plane Wall ◽  
Shear Stresses ◽  
Wall Jet ◽  
Wall Region ◽  
Free Shear Layer ◽  
Large Scale Structures ◽  
Scale Structures

The plane wall jet (PWJ) is a wall-bounded flow in which a wall shear layer develops in the presence of extremely energetic flow structures of the outer free-shear layer. The structure of a PWJ, developing in still air, was studied with the focus on the large scales in the flow. Wall-normal hot-wire anemometry (HWA) measurements along with double-frame particle image velocimetry (PIV) measurements (wall-normal–streamwise plane) were carried out at streamwise distances up to $162b$, where $b$ is the slot width of the PWJ exit. The nominal PWJ Reynolds number based on exit parameters was $Re_{j}\approx 5940$. Comparisons with a zero-pressure-gradient boundary layer (ZPGBL) at nominally matched friction Reynolds number $Re_{\unicode[STIX]{x1D70F}}$ were also carried out as appropriate, to highlight key features of the PWJ structure. Consistent with previous work, the PWJ showed a dependence of the peak turbulent stresses on the jet exit Reynolds number. The turbulent production showed a peak corresponding to the near-wall cycle similar to the peak seen in the ZPGBL. However, another turbulent production peak was observed in the outer free-shear layer that was an order of magnitude larger than the inner one. Along with the change in sign of the viscous and Reynolds shear stresses, the PWJ was shown to have a region of very low turbulent production between these two peaks. The dissipation rate increased over the PWJ layer with a peak also in the outer region. Visualizations of the flow and two-point correlations reveal that the most energetic large-scale structures within a PWJ are vortical motions in the wall-normal–streamwise plane similar to those structures seen in free-shear layers. These structures are referred to as J (for jet) type structures. In addition two-point correlations reveal the existence of large-scale structures in the wall region which have a signature similar to those structures seen in canonical boundary layers. These structures are referred to as W (for wall) type structures. Instantaneous PIV realizations and flow visualizations reveal that these W type large-scale features are consistent with the paradigm of hairpin vortex packets in the wall region. The J type structures were seen to intrude well into the wall region while the W type structures were also seen to extend into the outer shear layer. Further, these large-scale structures were shown to modulate the amplitude of the finer scales of the flow.

scholarly journals Large-scale structures of scalar and velocity in a turbulent jet flow

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Jesse Reijtenbagh ◽  
Jerry Westerweel ◽  
Willem Van de Water
Keyword(s):  
Velocity Field ◽  
Finite Time ◽  
Large Scale ◽  
Concentration Field ◽  
Turbulent Jet ◽  
Moving Frame ◽  
Mean Flow ◽  
Turbulent Structures ◽  
Large Scale Structures ◽  
Scale Structures

We study the relation between large-scale structures in the concentration field with those in the velocity field in a dye-seeded turbulent jet. The scalar concentration in a plane is measured using laser-induced fluorescence. Uniform concentration zones of an advected scalar are identified using cluster analysis. We simultaneously measure the two-dimensional velocity field using particle image velocimetry. The structures in the velocity field are characterized by finite-time Lyapunov exponents. The measurement of the scalarand velocity fields moves with the mean flow. In this moving frame, turbulent structures remain in focus long enough to observe well-defined ridges of the finite-time Lyapunov field. This field gauges the rate of point separation along Lagrangian trajectories; it was measured both for future and past times since the instant of observation. The edges of uniform concentration zones are correlated with the ridges of the past-time Lyapunov field, but not with those of the future-time Lyapunov field.

Development of the Large-Scale Structures in the Intermediate Region of the Three-Dimensional Wall Jet

2002 ◽  
Author(s):  
Hongguang Sun ◽  
Dan Ewing
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Horseshoe Vortex ◽  
Lateral Spread ◽  
Wall Jet ◽  
Intermediate Region ◽  
Streamwise Vorticity ◽  
Large Scale Structures ◽  
Intermediate Field ◽  
Scale Structures

The development of the large-scale structures in the intermediate region of the three-dimensional wall jet was examined using measurements of the mean streamwise vorticity and the two-point, two-time correlations of the streamwise fluctuating velocity in the vertical and lateral directions. It was found that a dominant large-scale double horse-shoe structure persisted to 40 diameters downstream of the jet exit. It was also found that the structure continued to evolve throughout the intermediate field. In particular, the inner horse-shoe vortex was induced toward the wall, while the position of the outer horseshoe vortex relative to the half-width moved toward the centerline. The inclination of this structure relative to the wall also increased as the flow evolved downstream. These changes in the structure combined to cause the lateral spread rate of the jet to aprroximately double in the intermediate field.

Some comments about observations and image processing of comet 29P/Schwassmann-Wachmann 1

1999 ◽  
Vol 173 ◽  
pp. 243-248
Author(s):  
D. Kubáček ◽  
A. Galád ◽  
A. Pravda
Keyword(s):  
Image Processing ◽  
Large Scale ◽  
Harvard College ◽  
Oak Ridge ◽  
Large Scale Structures ◽  
Short Period Comet ◽  
Short Period ◽  
Scale Structures ◽  
Harvard College Observatory ◽  
Period Comet

AbstractUnusual short-period comet 29P/Schwassmann-Wachmann 1 inspired many observers to explain its unpredictable outbursts. In this paper large scale structures and features from the inner part of the coma in time periods around outbursts are studied. CCD images were taken at Whipple Observatory, Mt. Hopkins, in 1989 and at Astronomical Observatory, Modra, from 1995 to 1998. Photographic plates of the comet were taken at Harvard College Observatory, Oak Ridge, from 1974 to 1982. The latter were digitized at first to apply the same techniques of image processing for optimizing the visibility of features in the coma during outbursts. Outbursts and coma structures show various shapes.

scholarly journals The organization and control of an evolving interdependent population

2015 ◽  
Vol 12 (108) ◽  
pp. 20150044 ◽  
Author(s):  
Dervis C. Vural ◽  
Alexander Isakov ◽  
L. Mahadevan
Keyword(s):  
Evolutionary Game Theory ◽  
Large Scale ◽  
Social Evolution ◽  
Evolutionary Game ◽  
Large Scale Structures ◽  
External Perturbations ◽  
Emergence Of Cooperation ◽  
Scale Structures ◽  
And Control ◽  
Evolutionarily Stable

Starting with Darwin, biologists have asked how populations evolve from a low fitness state that is evolutionarily stable to a high fitness state that is not. Specifically of interest is the emergence of cooperation and multicellularity where the fitness of individuals often appears in conflict with that of the population. Theories of social evolution and evolutionary game theory have produced a number of fruitful results employing two-state two-body frameworks. In this study, we depart from this tradition and instead consider a multi-player, multi-state evolutionary game, in which the fitness of an agent is determined by its relationship to an arbitrary number of other agents. We show that populations organize themselves in one of four distinct phases of interdependence depending on one parameter, selection strength. Some of these phases involve the formation of specialized large-scale structures. We then describe how the evolution of independence can be manipulated through various external perturbations.

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