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 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 Effect of Aspect-Ratio on the Development of the Large-Scale Structures in the Three-Dimensional Wall Jet

2005 ◽  
Author(s):  
Joseph W. Hall ◽  
Daniel Ewing
Keyword(s):  
Aspect Ratio ◽  
Large Scale ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Decomposition Analysis ◽  
Wall Pressure ◽  
Symmetric Mode ◽  
Large Scale Structures ◽  
Aspect Ratios ◽  
Scale Structures

The development of the large-scale structures in three-dimensional wall jets exiting rectangular nozzles with aspect-ratios of 1 and 4 was investigated using simultaneous measurements of the fluctuating wall pressure across the jet. The pressure fluctuations in the jets were asymmetric and caused the fluctuating wall pressure to be poorly correlated across the jet centerline. A Proper Orthogonal Decomposition analysis indicated that both the first and second modes make similar contributions to the variance of the fluctuating pressure, and were symmetric and antisymmetric, respectively, and the interplay between these modes caused the asymmetry in the instantaneous pressure fluctuations across the jet centreline. A wavelet analysis of the instantaneously reconstructed pressure fields indicated that the fluctuations were predominantly in two frequency bands near the jet centerline, but were only contained in one band on the outer lateral edges of the jet, indicating there were two different large-scale motions present. The development of large-scale structures in the two jets initially differed in the intermediate field with the antisymmetric mode being more prominent in the square jet and the symmetric mode being more prominent in the larger aspect-ratio jet. Further downstream, the symmetric mode was more prominent in both jets.

Three-dimensional conditional structure of a high-Reynolds-number turbulent boundary layer

2011 ◽  
Vol 673 ◽  
pp. 255-285 ◽  
Author(s):  
N. HUTCHINS ◽  
J. P. MONTY ◽  
B. GANAPATHISUBRAMANI ◽  
H. C. H. NG ◽  
I. MARUSIC
Keyword(s):  
Skin Friction ◽  
High Reynolds Number ◽  
Large Scale ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Small Scale ◽  
Large Scale Structures ◽  
Local Mean ◽  
Scale Structures ◽  
High Reynolds

An array of surface hot-film shear-stress sensors together with a traversing hot-wire probe is used to identify the conditional structure associated with a large-scale skin-friction event in a high-Reynolds-number turbulent boundary layer. It is found that the large-scale skin-friction events convect at a velocity that is much faster than the local mean in the near-wall region (the convection velocity for large-scale skin-friction fluctuations is found to be close to the local mean at the midpoint of the logarithmic region). Instantaneous shear-stress data indicate the presence of large-scale structures at the wall that are comparable in scale and arrangement to the superstructure events that have been previously observed to populate the logarithmic regions of turbulent boundary layers. Conditional averages of streamwise velocity computed based on a low skin-friction footprint at the wall offer a wider three-dimensional view of the average superstructure event. These events consist of highly elongated forward-leaning low-speed structures, flanked on either side by high-speed events of similar general form. An analysis of small-scale energy associated with these large-scale events reveals that the small-scale velocity fluctuations are attenuated near the wall and upstream of a low skin-friction event, while downstream and above the low skin-friction event, the fluctuations are significantly amplified. In general, it is observed that the attenuation and amplification of the small-scale energy seems to approximately align with large-scale regions of streamwise acceleration and deceleration, respectively. Further conditional averaging based on streamwise skin-friction gradients confirms this observation. A conditioning scheme to detect the presence of meandering large-scale structures is also proposed. The large-scale meandering events are shown to be a possible source of the strong streamwise velocity gradients, and as such play a significant role in modulating the small-scale motions.

The Asymmetry of the Large-Scale Structures in Turbulent Three-Dimensional Wall Jets Exiting Long Rectangular Channels

2007 ◽  
Vol 129 (7) ◽  
pp. 929-941 ◽  
Author(s):  
J. W. Hall ◽  
D. Ewing
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Wall Pressure ◽  
Mode Shapes ◽  
Wall Jets ◽  
Frequency Dependent ◽  
Large Scale Structures ◽  
Intermediate Field ◽  
Rectangular Channels ◽  
Scale Structures

The development of the large-scale structures in three-dimensional wall jets formed using long rectangular channels with aspect ratios of 1 and 4 was investigated using measurements of the fluctuating wall pressure and point measurements of the turbulent velocity throughout the near and intermediate field. The instantaneous pressure fluctuations in both jets were laterally asymmetric causing the fluctuating wall pressure to be poorly correlated across the jet centerline. A frequency-dependent proper orthogonal decomposition (POD) of the fluctuating pressure measurements indicated that the first two mode shapes were opposite and each mode made similar contributions to the mean square fluctuations at all frequencies in order to capture the instantaneous asymmetry of the pressure field. The mode shapes in the intermediate field of both jets were strongly frequency dependent, and a subsequent wavelet analysis indicated that there are both large-scale horseshoe structures that span one-half of the jet and separate, smaller, near-wall structures located near the jet centerline. The initial development of the large-scale structures in the two jets differed, with the most energetic fluctuations being more antisymmetric in the square jet.

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