Wall pressure and coherent structures in a turbulent boundary layer on a cylinder in axial flow

1995 ◽  
Vol 286 ◽  
pp. 137-171 ◽  
Author(s):  
Stephen R. Snarski ◽  
Richard M. Lueptow
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Streamwise Velocity ◽  
Wall Pressure ◽  
Small Scale ◽  
Fluctuating Pressure ◽  
Large Scale Structures ◽  
Transverse Curvature ◽  
Scale Structures

Measurements of wall pressure and streamwise velocity fluctuations in a turbulent boundary layer on a cylinder in an axial air flow (δ/a = 5.04, Reθ = 2870) have been used to investigate the turbulent flow structures in the cylindrical boundary layer that contribute to the fluctuating pressure at the wall in an effort to deduce the effect of transverse curvature on the structure of boundary layer turbulence. Wall pressure was measured at a single location with a subminiature electret condenser microphone, and the velocity was measured throughout a large volume of the boundary layer with a hotwire probe. Auto- and cross-spectral densities, cross-correlations, and conditional sampling of the pressure and streamwise velocity indicate that two primary groups of flow disturbances contribute to the fluctuating pressure at the wall: (i) low-frequency large-scale structures with dynamical significance across the entire boundary layer that are consistent with a pair of large-scale spanwise-oriented counter-rotating vortices and (ii) higher frequency small-scale disturbances concentrated close to the wall that are associated with the burst-sweep cycle and are responsible for the short-duration large-amplitude wall pressure fluctuations. A bidirectional relationship was found to exist between both positive and negative pressure peaks and the temporal derivative of u near the wall. Because the frequency of the large-scale disturbance observed across the boundary layer is consistent with the bursting frequency deduced from the average time between bursts, the burst-sweep cycle appears to be linked to the outer motion. A stretching of the large-scale structures very near the wall, as suggested by space-time correlation convection velocity results, may provide the coupling mechanism. Since the high-frequency disturbance observed near the wall is consistent with the characteristic frequency deduced from the average duration of bursting events, the bursting process provides the two characteristic time scales responsible for the bimodal distribution of energy near the wall. Because many of the observed structural features of the cylindrical boundary layer are similar to those observed in flat-plate turbulent boundary layers, transverse curvature appears to have little effect on the fundamental turbulent structure of the boundary layer for the moderate transverse curvature ratio used in this investigation. From differences that exist between the turbulence intensity, skewness, and spectra of the streamwise velocity, however, it appears that transverse curvature may enhance (i.e. energize) the large-scale motion owing to the reduced constraint imposed on the flow by the smaller cylindrical wall.

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.

A supersonic turbulent boundary layer in an adverse pressure gradient

1990 ◽  
Vol 211 ◽  
pp. 285-307 ◽  
Author(s):  
Emerick M. Fernando ◽  
Alexander J. Smits
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Pressure Distribution ◽  
Large Scale ◽  
Adverse Pressure Gradient ◽  
Large Scale Structures ◽  
Streamline Curvature ◽  
The Mean ◽  
Scale Structures

This investigation describes the effects of an adverse pressure gradient on a flat plate supersonic turbulent boundary layer (Mf ≈ 2.9, βx ≈ 5.8, Reθ, ref ≈ 75600). Single normal hot wires and crossed wires were used to study the Reynolds stress behaviour, and the features of the large-scale structures in the boundary layer were investigated by measuring space–time correlations in the normal and spanwise directions. Both the mean flow and the turbulence were strongly affected by the pressure gradient. However, the turbulent stress ratios showed much less variation than the stresses, and the essential nature of the large-scale structures was unaffected by the pressure gradient. The wall pressure distribution in the current experiment was designed to match the pressure distribution on a previously studied curved-wall model where streamline curvature acted in combination with bulk compression. The addition of streamline curvature affects the turbulence strongly, although its influence on the mean velocity field is less pronounced and the modifications to the skin-friction distribution seem to follow the empirical correlations developed by Bradshaw (1974) reasonably well.

Mechanisms of Turbulence Transport in a Turbine Blade Coolant Passage With a Rib Turbulator

1999 ◽  
Vol 121 (1) ◽  
pp. 152-159 ◽  
Author(s):  
P. K. Panigrahi ◽  
S. Acharya
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Turbulent Boundary Layer ◽  
Shear Layer ◽  
Large Scale ◽  
Turbulence Models ◽  
Turbulent Shear ◽  
Large Scale Structures ◽  
Turbulent Shear Stress ◽  
Scale Structures

This paper provides detailed measurements of the flow in a ribbed coolant passage, and attempts to delineate the important mechanisms that contribute to the production of turbulent shear stress and the normal stresses. It is shown that the separated flow behind the rib is dictated by large-scale structures, and that the dynamics of the large-scale structures, associated with sweep, ejection, and inward and outward interactions, all play an important role in the production of the turbulent shear stress. Unlike the turbulent boundary layer, in a separated shear flow past the rib, the inward and outward interaction terms are both important, accounting for a negative stress production that is nearly half of the positive stress produced by the ejection and sweep mechanisms. It is further shown that the shear layer wake persists well past the re-attachment location of the shear layer, implying that the flow between ribbed passages never recovers to that of a turbulent boundary layer. Therefore, even past re-attachment, the use of statistical turbulence models that ignore coherent structure dynamics is inappropriate.

scholarly journals Wall-Normal Variation of Spanwise Streak Spacing in Turbulent Boundary Layer With Low-to-Moderate Reynolds Number

Entropy ◽  
2018 ◽  
Vol 21 (1) ◽  
pp. 24 ◽  
Author(s):  
Wenkang Wang ◽  
Chong Pan ◽  
Jinjun Wang
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Buffer Layer ◽  
Large Scale ◽  
Normal Growth ◽  
Small Scale ◽  
Piv Measurement ◽  
Moderate Reynolds Number ◽  
Scale Structures ◽  
Log Normal

Low-speed streaks in wall-bounded turbulence are the dominant structures in the near-wall turbulent self-sustaining cycle. Existing studies have well characterized their spanwise spacing in the buffer layer and below. Recent studies suggested the existence of these small-scale structures in the higher layer where large-scale structures usually receive more attention. The present study is thus devoted to extending the understanding of the streak spacing to the log layer. An analysis is taken on two-dimensional (2D) wall-parallel velocity fields in a smooth-wall turbulent boundary layer with Ret = 4402400, obtained via either 2D Particle Image Velocimetry (PIV) measurement taken here or public Direct Numerical Simulation (DNS). Morphological-based streak identification analysis yields a Re-independent log-normal distribution of the streak spacing till the upper bound of the log layer, based on which an empirical model is proposed to account for its wall-normal growth. The small-scale part of the spanwise spectra of the streamwise fluctuating velocity below y? = 100 is reasonably restored by a synthetic simulation that distributes elementary streak units based on the proposed empirical streak spacing model, which highlights the physical significance of streaks in shaping the small-scale part of the velocity spectra beyond the buffer layer.

scholarly journals Mechanisms of Turbulence Transport in a Turbine Blade Coolant Passage With a Rib-Turbulator

1997 ◽  
Author(s):  
P. K. Panigrahi ◽  
S. Acharya
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Turbulent Boundary Layer ◽  
Shear Layer ◽  
Large Scale ◽  
Turbulence Models ◽  
Turbulent Shear ◽  
Large Scale Structures ◽  
Turbulent Shear Stress ◽  
Scale Structures

This paper provides detailed measurements of the flow in a ribbed coolant passage, and attempts to delineate the important mechanisms that contribute to the production of turbulent shear stress and the normal stresses. It is shown that the separated flow behind the rib is dictated by large scale structures, and that the dynamics of the large scale structures, associated with sweep, ejection, and inward and outward interactions all play an important role in the production of the turbulent shear stress. Unlike the turbulent boundary layer, in a separated shear flow past the rib, the inward and outward interaction terms are both important accounting for a negative stress production that is nearly half of the positive stress produced by the ejection and sweep mechanisms. It is further shown, that the shear layer wake persists well past the re-attachment location of the shear layer, implying that the flow between ribbed passages never recovers to that of a turbulent boundary layer. Therefore, even past re-attachment, the use of statistical turbulence models that ignore coherent structure dynamics is inappropriate.

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