scholarly journals The evolution of large-scale motions in turbulent pipe flow

2015 ◽  
Vol 779 ◽  
pp. 701-715 ◽  
Author(s):  
Leo H. O. Hellström ◽  
Bharathram Ganapathisubramani ◽  
Alexander J. Smits
Keyword(s):  
Pipe Flow ◽  
Large Scale ◽  
Complex Structure ◽  
Turbulent Pipe Flow ◽  
Large Scale Structures ◽  
Large Structures ◽  
Scale Structures ◽  
The Cross ◽  
Spatio Temporal ◽  
Temporal Extent

A dual-plane snapshot proper orthogonal decomposition (POD) analysis of turbulent pipe flow at a Reynolds number of 104 000 is presented. The high-speed particle image velocimetry data were simultaneously acquired in two planes, a cross-stream plane (2D–3C) and a streamwise plane (2D–2C) on the pipe centreline. The cross-stream plane analysis revealed large structures with a spatio-temporal extent of $1{-}2R$, where $R$ is the pipe radius. The temporal evolution of these large-scale structures is examined using the time-shifted correlation of the cross-stream snapshot POD coefficients, identifying the low-energy intermediate modes responsible for the transition between the large-scale modes. By conditionally averaging based on the occurrence/intensity of a given cross-stream snapshot POD mode, a complex structure consisting of wall-attached and -detached large-scale structures is shown to be associated with the most energetic modes. There is a pseudo-alignment of these large structures, which together create structures with a spatio-temporal extent of approximately $6R$, which appears to explain the formation of the very-large-scale motions previously observed in pipe flow.

Spectral Analysis of Large Scale Structures in Fully Developed Turbulent Pipe Flow

PAMM ◽  
2017 ◽  
Vol 17 (1) ◽  
pp. 647-650
Author(s):  
El-Sayed Zanoun ◽  
Emir Öngüner ◽  
Amir Shahirpour ◽  
Sebastian Merbold ◽  
Christoph Egbers
Keyword(s):  
Spectral Analysis ◽  
Pipe Flow ◽  
Large Scale ◽  
Turbulent Pipe Flow ◽  
Large Scale Structures ◽  
Scale Structures

A direct numerical simulation study on the mean velocity characteristics in turbulent pipe flow

2008 ◽  
Vol 608 ◽  
pp. 81-112 ◽  
Author(s):  
XIAOHUA WU ◽  
PARVIZ MOIN
Keyword(s):  
Reynolds Number ◽  
Pipe Flow ◽  
Large Scale ◽  
Turbulent Pipe Flow ◽  
Bulk Velocity ◽  
Mean Velocity ◽  
Large Scale Structures ◽  
Narrow Region ◽  
The Mean ◽  
Scale Structures

Fully developed incompressible turbulent pipe flow at bulk-velocity- and pipe-diameter-based Reynolds number ReD=44000 was simulated with second-order finite-difference methods on 630 million grid points. The corresponding Kármán number R+, based on pipe radius R, is 1142, and the computational domain length is 15R. The computed mean flow statistics agree well with Princeton Superpipe data at ReD=41727 and at ReD=74000. Second-order turbulence statistics show good agreement with experimental data at ReD=38000. Near the wall the gradient of $\mbox{ln}\overline{u}_{z}^{+}$ with respect to ln(1−r)+ varies with radius except for a narrow region, 70 < (1−r)+ < 120, within which the gradient is approximately 0.149. The gradient of $\overline{u}_{z}^{+}$ with respect to ln{(1−r)++a+} at the present relatively low Reynolds number of ReD=44000 is not consistent with the proposition that the mean axial velocity $\overline{u}_{z}^{+}$ is logarithmic with respect to the sum of the wall distance (1−r)+ and an additive constant a+ within a mesolayer below 300 wall units. For the standard case of a+=0 within the narrow region from (1−r)+=50 to 90, the gradient of $\overline{u}_{z}^{+}$ with respect to ln{(1−r)++a+} is approximately 2.35. Computational results at the lower Reynolds number ReD=5300 also agree well with existing data. The gradient of $\overline{u}_{z}$ with respect to 1−r at ReD=44000 is approximately equal to that at ReD=5300 for the region of 1−r > 0.4. For 5300 < ReD < 44000, bulk-velocity-normalized mean velocity defect profiles from the present DNS and from previous experiments collapse within the same radial range of 1−r > 0.4. A rationale based on the curvature of mean velocity gradient profile is proposed to understand the perplexing existence of logarithmic mean velocity profile in very-low-Reynolds-number pipe flows. Beyond ReD=44000, axial turbulence intensity varies linearly with radius within the range of 0.15 < 1−r < 0.7. Flow visualizations and two-point correlations reveal large-scale structures with comparable near-wall azimuthal dimensions at ReD=44000 and 5300 when measured in wall units. When normalized in outer units, streamwise coherence and azimuthal dimension of the large-scale structures in the pipe core away from the wall are also comparable at these two Reynolds numbers.

scholarly journals Photographic Wide-Field Imaging from Schmidt Plates — I

1994 ◽  
Vol 161 ◽  
pp. 141-145
Author(s):  
H.H. Heyer ◽  
J. Quebatte ◽  
H. Zodet
Keyword(s):  
Large Scale ◽  
Wide Field ◽  
Clear Trend ◽  
Observational Astronomy ◽  
Large Scale Structures ◽  
Large Structures ◽  
Scale Structures ◽  
Field Imaging ◽  
Wide Field Imaging ◽  
Individual Objects

The recent years have seen a clear trend in observational astronomy towards digital detectors, but they are only able to cover sky fields which are significantly smaller than what is possible with photographic plates. In consequence, there has been a tendency to concentrate on small sky areas and individual objects. Nevertheless, many large-scale structures can only be well comprehended if the observed fields are much larger than such CCD-frames. Similarly, the use of more than one passband adds important information for a better understanding of the nature of large structures. We demonstrate this by showing here a two-field composite of IC 1396 (Palomar/ESO Atlas), and a four-field composite from the ESO R-Atlas, covering an area of more than 100 square degrees around IC 4628 in Scorpius/Ara.

scholarly journals Identification of Extremely Large Scale Structures in SDSS-III

2014 ◽  
Vol 11 (S308) ◽  
pp. 299-300
Author(s):  
Shishir Sankhyayan ◽  
J. Bagchi ◽  
P. Sarkar ◽  
V. Sahni ◽  
J. Jacob
Keyword(s):  
Large Scale ◽  
Sloan Digital Sky Survey ◽  
Limited Sample ◽  
Large Scale Structures ◽  
Large Structures ◽  
Density Peaks ◽  
Redshift Surveys ◽  
Sky Survey ◽  
Scale Structures ◽  
The Universe

AbstractWe have initiated the search and detailed study of large scale structures present in the universe using galaxy redshift surveys. In this process, we take the volume-limited sample of galaxies from Sloan Digital Sky Survey III and find very large structures even beyond the redshift of 0.2. One of the structures is even greater than 600 Mpc which raises a question on the homogeneity scale of the universe. The shapes of voids-structures (adjacent to each other) seem to be correlated, which supports the physical existence of the observed structures. The other observational supports include galaxy clusters' and QSO distribution's correlation with the density peaks of the volume limited sample of galaxies.

Direct numerical simulation of a 30R long turbulent pipe flow at R+ = 685: large- and very large-scale motions

2012 ◽  
Vol 698 ◽  
pp. 235-281 ◽  
Author(s):  
Xiaohua Wu ◽  
J. R. Baltzer ◽  
R. J. Adrian
Keyword(s):  
Spatial Data ◽  
Pipe Flow ◽  
Large Scale ◽  
Single Point ◽  
Complex Structure ◽  
Turbulent Pipe Flow ◽  
Bulk Velocity ◽  
Experimental Measurements ◽  
Flow Profile ◽  
Taylor’S Hypothesis

AbstractFully developed incompressible turbulent pipe flow at Reynolds number ${\mathit{Re}}_{D} = 24\hspace{0.167em} 580$ (based on bulk velocity) and Kármán number ${R}^{+ } = 684. 8$ is simulated in a periodic domain with a length of $30$ pipe radii $R$. While single-point statistics match closely with experimental measurements, questions have been raised of whether streamwise energy spectra calculated from spatial data agree with the well-known bimodal spectrum shape in premultiplied spectra produced by experiments using Taylor’s hypothesis. The simulation supports the importance of large- and very large-scale motions (VLSMs, with streamwise wavelengths exceeding $3R$). Wavenumber spectral analysis shows evidence of a weak peak or flat region associated with VLSMs, independent of Taylor’s hypothesis, and comparisons with experimental spectra are consistent with recent findings (del Álamo & Jiménez, J. Fluid Mech., vol. 640, 2009, pp. 5–26) that the long-wavelength streamwise velocity energy peak is overestimated when Taylor’s hypothesis is used. Yet, the spectrum behaviour retains otherwise similar properties to those documented based on experiment. The spectra also reveal the importance of motions of long streamwise length to the $uu$ energy and $uv$ Reynolds stress and support the general conclusions regarding these quantities formed using experimental measurements. Space–time correlations demonstrate that low-level correlations involving very large scales persist over $40R/ {U}_{\mathit{bulk}} $ in time and indicate that these motions convect at approximately the bulk velocity, including within the region approaching the wall. These very large streamwise motions are also observed to accelerate the flow near the wall based on force spectra, whereas smaller scales tend to decelerate the mean streamwise flow profile, in accordance with the behaviour observed in net force spectra of prior experiments. Net force spectra are resolved for the first time in the buffer layer and reveal an unexpectedly complex structure.

Effect of large-scale structures on wall shear stress fluctuations in pipe flow

2020 ◽  
Vol 5 (10) ◽  
Author(s):  
Tong Tong ◽  
Kovid Bhatt ◽  
Tatsuya Tsuneyoshi ◽  
Yoshiyuki Tsuji
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Pipe Flow ◽  
Large Scale ◽  
Large Scale Structures ◽  
Scale Structures ◽  
Wall Shear

scholarly journals Extreme-scale motions in turbulent plane Couette flows

2018 ◽  
Vol 842 ◽  
pp. 128-145 ◽  
Author(s):  
Myoungkyu Lee ◽  
Robert D. Moser
Keyword(s):  
Reynolds Number ◽  
Large Scale ◽  
Reynolds Shear Stress ◽  
Streamwise Vortices ◽  
Streamwise Direction ◽  
Large Scale Structures ◽  
Large Structures ◽  
Scale Structures ◽  
Turbulent Plane ◽  
Extreme Scale

We study the large-scale motions in turbulent plane Couette flows at moderate friction Reynolds number up to $Re_{\unicode[STIX]{x1D70F}}=500$. Direct numerical simulation (DNS) domains were as large as $100\unicode[STIX]{x03C0}\unicode[STIX]{x1D6FF}\times 2\unicode[STIX]{x1D6FF}\times 5\unicode[STIX]{x03C0}\unicode[STIX]{x1D6FF}$, where $\unicode[STIX]{x1D6FF}$ is half the distance between the walls. The results indicate that there are streamwise vortices filling the space between the walls that remain correlated over distances in the streamwise direction and that increase strongly with the Reynolds number, so that for the largest Reynolds number studied here, they are correlated across the entire $100\unicode[STIX]{x03C0}\unicode[STIX]{x1D6FF}$ length of the domain. The presence of these very long structures is apparent in the spectra of all three velocity components and the Reynolds stress. In DNS using a smaller domain, the large structures are constrained, eliminating the streamwise variations present in the larger domain. Near the centre of the domain, these large-scale structures contribute as much as half of the Reynolds shear stress.

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.

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