The wall region in turbulent shear flow

1972 ◽  
Vol 54 (1) ◽  
pp. 39-48 ◽  
Author(s):  
James M. Wallace ◽  
Helmut Eckelmann ◽  
Robert S. Brodkey
Keyword(s):  
Turbulent Flows ◽  
Reynolds Stress ◽  
Time Scales ◽  
High Speed ◽  
Turbulent Energy ◽  
Turbulent Shear ◽  
Wall Region ◽  
Turbulent Shear Flow ◽  
Sequence Of Events ◽  
Hot Film

Hot-film measurements in a fully developed channel flow have been made in an attempt to gain more insight into the process of Reynolds stress production. The background for this effort is the observation of a certain sequence of events (deceleration, ejection and sweep) in the wall region of turbulent flows by Corino (1965) and Corino & Brodkey (1969). The instantaneous product signal uv was classified according to the sign of its components u and v, and these classified portions were then averaged to obtain their contributions to the Reynolds stress $-\rho\overline{uv} $. The signal was classified into four categories; the two main ones were that with u negative and v positive, which can be associated with the ejection-type motion of Corino & Brodkey (1969), and that with u positive and v negative, associated with the sweep-type motion. It was found that over the wall region investigated, 3·5 [les ] y [les ] 100, these two types of motion give rise to a stress considerably greater than the total Reynolds stress. Two other types of motion, (i) u negative, v negative, corresponding to low-speed fluid deflected towards the wall, and (ii) u positive, v positive, corresponding to high-speed fluid reflected outwards from the wall, were found to account for the ‘excess’ stress produced by the first two categories, which give contributions of opposite sign.The autocorrelations of the classified portions of uv were obtained to determine the relative time scales of these four types of motion. The positive stress producing motions (u < 0, v > 0 and u > 0, v < 0) were found to have significantly larger time scales than the negative stress producing motions (u < 0, v < 0 and u > 0, v > 0). It was further surmised that turbulent energy dissipation is associated with the Reynolds stress producing motions, since these result in localized shear regions in which the dissipation is several orders of magnitude greater than the average dissipation at the wall.

Streamwise vortices associated with the bursting phenomenon

1979 ◽  
Vol 94 (3) ◽  
pp. 577-594 ◽  
Author(s):  
Ron F. Blackwelder ◽  
Helmut Eckelmann
Keyword(s):  
High Speed ◽  
Vortex Pair ◽  
Turbulent Shear ◽  
Sampling Techniques ◽  
Wall Region ◽  
Turbulent Shear Flow ◽  
Streamwise Vortices ◽  
Defect Region ◽  
Low Speed ◽  
Hot Film

The streamwise and spanwise velocity components and the gradients of these components normal to the wall were examined by using hot-film sensors and flush-mounted wall elements to study the vortex structures associated with the bursting phenomenon. Quadrant probability analysis and conditional sampling techniques indicated that pairs of counter-rotating streamwise vortices occur frequently in the wall region of a bounded turbulent shear flow. A streamwise momentum defect occurred between the vortices as low-speed fluid was ‘pumped’ away from the wall by the vortex pair. The defect region was long and narrow and possibly forms the low-speed streak as observed in visualization studies. The velocity defect was terminated by a strong acceleration followed by a high speed region.

scholarly journals A visual study of turbulent shear flow

1973 ◽  
Vol 61 (3) ◽  
pp. 513-540 ◽  
Author(s):  
Stavros G. Nychas ◽  
Harry C. Hershey ◽  
Robert S. Brodkey
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Outer Region ◽  
Solid Particles ◽  
Turbulent Shear ◽  
Small Scale ◽  
Wall Region ◽  
Wall Area ◽  
Sequence Of Events ◽  
Local Mean

The outer region of a turbulent boundary layer along a flat plate was photographed and analysed; in addition, limited observations of the wall area were also made. The technique involved suspending very small solid particles in water and photographing their motion with a high-speed camera moving with the flow.The single most important event observed in the outer region was fluid motion which in the convected view of the travelling camera appeared as a transverse vortex. This was a large-scale motion transported downstream almost parallel to the wall with an average velocity slightly smaller than the local mean. It appeared to be the result of an instability interaction between accelerated and decelerated fluid, and it is believed to be closely associated with the wall-region ejections. The transverse vortex was part of a deterministic sequence of events; although these events occurred randomly in space and time. The first of these events was a decelerated flow exhibiting velocities considerably smaller than the local mean. It was immediately followed by an accelerated flow. Both these events extended from near the wall to the far outer region. Their interaction resulted in the formation of one or more transverse vortices. While the transverse vortex was transported downstream, small-scale fluid elements, originating in the wall area of the decelerated flow, were ejected outwards (ejection event). After travelling some distance outwards the ejected elements interacted with the oncoming accelerated fluid in the wall region and were subsequently swept downstream (sweep event). The sequence of events closed with two large-scale motions.Estimated positive and negative contributions to the instantaneous Reynolds stress during the events were many times higher than the local mean values.

Experimental investigation of coherent structures in turbulent boundary layers

1991 ◽  
Vol 230 ◽  
pp. 183-208 ◽  
Author(s):  
C. E. Wark ◽  
H. M. Nagib
Keyword(s):  
Reynolds Stress ◽  
Coherent Structures ◽  
Three Dimensional ◽  
Wall Layer ◽  
Space Time ◽  
Turbulent Shear ◽  
Wall Region ◽  
Turbulent Shear Flow ◽  
Outer Flow ◽  
Probability Density Distributions

The events which are responsible for strong Reynolds-stress production in the near-wall region of a bounded turbulent shear flow have been investigated in a turbulent boundary layer at a Reynolds number based on momentum thickness of Reθ = 4650. The coherent structures associated with the production process have been studied using the quadrant detection technique. All three velocity components were measured in a three-dimensional sampling volume about the point of detection. The conditional ensemble-averaged velocity field associated with the detection of a sweep or an ejection is presented and compared with non-conditioned space–time correlations. Conditional space–time probability density distributions were calculated at all measurement locations based on the occurrence of a Reynolds-stress-producing event at the detection point. The resulting three-dimensional representation of the conditional probability demonstrates that a significant fraction of the events are relatively large in scale, that a hierarchy of sizes exists and that there is a link between the outer flow and the ’bursting’ process. However, many investigators have shown that the ’bursting’ frequency scales with wall variables. Therefore all indications suggest that the scales are generated by a wall-layer mechanism but grow to sizes and convect with velocities scaling with the outer layer.

Calculation of Developing Turbulent Flows in a Rotating Pipe

1991 ◽  
Vol 113 (1) ◽  
pp. 34-41 ◽  
Author(s):  
G. J. Yoo ◽  
R. M. C. So ◽  
B. C. Hwang
Keyword(s):  
Turbulent Flows ◽  
Reynolds Stress ◽  
Circumferential Strain ◽  
Three Dimensional ◽  
Wall Region ◽  
Boundary Layer Flows ◽  
Viscous Effects ◽  
Wide Range ◽  
Turbulence Closures ◽  
Rotating Boundary

Internal rotating boundary-layer flows are strongly influenced by large circumferential strain and the turbulence field is anisotropic. This is especially true in the entry region of a rotating pipe where the flow is three dimensional, the centrifugal force due to fluid rotation is less important, and the circumferential strain created by surface rotation has a significant effect on the turbulence field near the wall. Consequently, viscous effects cannot be neglected in the near-wall region. Several low-Reynolds-number turbulence closures are proposed for the calculation of developing rotating pipe flows. Some are two-equation closures with and without algebraic stress correction, while others are full Reynolds-stress closures. It is found that two-equation closures with and without algebraic stress correction are totally inadequate for this three-dimensional flow, while Reynolds-stress closures give results that are in good agreement with measurements over a wide range of rotation numbers.

Experimental assessment of fractal scale similarity in turbulent flows. Part 4. Effects of Reynolds and Schmidt numbers

1998 ◽  
Vol 377 ◽  
pp. 169-187 ◽  
Author(s):  
RICHARD D. FREDERIKSEN ◽  
WERNER J. A. DAHM ◽  
DAVID R. DOWLING
Keyword(s):  
Turbulent Flows ◽  
Dissipation Rate ◽  
Single Point ◽  
Energy Dissipation Rate ◽  
Scalar Dissipation ◽  
Turbulent Shear ◽  
Turbulent Shear Flow ◽  
Outer Scale ◽  
Scale Invariant ◽  
Scale Similarity

Experimental results are presented for the influence of Reynolds number on multifractal scale similarity in turbulent flows. These are obtained from single-point measurements of a dynamically passive Sc≈1 conserved scalar quantity ζ(t) in a turbulent shear flow at outer-scale Reynolds numbers of 14000[les ]Reδ[les ]110000. Statistical criteria based on the maximum allowable scale-to-scale variation L1(ε) in multiplier distributions P(Mε) from multifractal gauge sets allow accurate discrimination between multifractal and non-multifractal scaling. Results show that the surrogate scalar energy dissipation rate χs(t)≡(dζ/dt)2is found to display a scale-invariant similarity consistent with a random multiplicative cascade characterized by a bilinear multiplier distribution P(Mε) over a range of scales extending downward from the outer scaleTδ. For a range of scales extending upward from the inner (diffusive) scale TD, the dissipation rate displays a different scale-invariant similarity characterized by a uniform multiplier distribution. The former scale-invariance becomes evident in the present Sc≈1 data only when Reδ is sufficiently large. Comparisons with results from Sc 1 data indicate that this scale-invariant similarity applies when the outer-to-inner scale ratio Tδ/TD≈0.09 Re3/4δSc1/2 is greater than about 400. In contrast to the scalar dissipation rate field, the scalar field is found to lack any multifractal scale similarity.

Evaluation of fish-injury mechanisms during exposure to turbulent shear flow

2005 ◽  
Vol 62 (7) ◽  
pp. 1513-1522 ◽  
Author(s):  
Zhiqun Deng ◽  
Gregory R Guensch ◽  
Craig A McKinstry ◽  
Robert P Mueller ◽  
Dennis D Dauble ◽  
...  
Keyword(s):  
High Speed ◽  
Motion Tracking ◽  
Oncorhynchus Tshawytscha ◽  
Three Dimensional ◽  
Turbulent Shear ◽  
Control Group ◽  
Similar Data ◽  
Turbulent Shear Flow ◽  
Eye Injuries ◽  
Injury Mechanisms

Understanding the factors that injure or kill turbine-passed fish is important to the operation and design of the turbines. Motion-tracking analysis was performed on high-speed, high-resolution digital videos of juvenile salmonids exposed to a laboratory-generated shear environment to isolate injury mechanisms. Hatchery-reared fall chinook salmon (Oncorhynchus tshawytscha, 93–128 mm in length) were introduced into a submerged, 6.35-cm-diameter water jet at velocities ranging from 12.2 to 19.8 m·s–1, with a reference control group released at 3 m·s–1. Injuries typical of turbine-passed fish were observed and recorded. Three-dimensional trajectories were generated for four locations on each fish released. Time series of velocity, acceleration, force, jerk, and bending angle were computed from the three-dimensional trajectories. The onset of minor, major, and fatal injuries occurred at nozzle velocities of 12.2, 13.7, and 16.8 m·s–1, respectively. Opercle injuries occurred at 12.2 m·s–1 nozzle velocity, while eye injuries, bruising, and loss of equilibrium were common at velocities of 16.8 m·s–1 and above. Of the computed dynamic parameters, acceleration showed the strongest predictive power for eye and opercle injuries and overall injury level, and it may provide the best potential link between laboratory studies of fish injury, field studies designed to collect similar data in situ, and numerical modeling.

Spatial and statistical analysis of coherent vortical structures within a stress-driven free-surface turbulent shear flow

2020 ◽  
Author(s):  
Po-Chen Chen ◽  
Wu-ting Tsai
Keyword(s):  
Free Surface ◽  
High Speed ◽  
Surface Friction ◽  
Turbulent Shear ◽  
Wind Condition ◽  
Turbulent Shear Flow ◽  
Streamwise Vortices ◽  
Vortical Structures ◽  
Horseshoe Vortices ◽  
Low Speed Streaks

&lt;p&gt;The water surface under high wind condition is characterized by elongated high-speed streaks and randomly emerged low-speed streaks, which are attributed to underneath coherent vortical motions. These vortical structures within aqueous turbulent boundary layer plays a critical role in turbulent exchange, their characteristics and statistics are therefore of interest in this study. Direct numerical simulation of an aqueous turbulent flow bounded by a stress-driven flat free surface was performed. Simulation results of cases with high wind condition (surface friction velocity = 1.22 cm/s) as well as weak wind condition (surface friction velocity = 0.71 cm/s) are analyzed. To identify the underlying vortical structures, an indicator of swirling strength derived from local velocity-gradient tensor is adopted. A formal classification scheme, based on the topological geometry of the vortex core, is then applied to classify the identified structures. Surface layers with the two wind conditions reveal similar results in statistics and spatial distribution of vortical structures. Two types of characteristic vortices which induce the surface streaks are extracted, including quasi-streamwise vortex and&amp;#160;reversed horseshoe vortex (head pointing upstream), most inclining at about 10 to 20 degrees. Quasi-streamwise vortices are the dominant structure, and both high- and low-speed streaks are fringed with such vortices; they adjoin the surface streaks as counter-rotating arrays in either staggered or side-by-side spatial arrangement. The length of quasi-streamwise vortices, however, are significantly shorter than the corresponding surface streaks, only 10% of the extracted quasi-streamwise vortices are longer than 150 wall units. Reversed horseshoe vortices, associated with downwelling motions and surface convergence, are located beneath the high-speed streaks. In contrast to the turbulent boundary layer next to a flat wall, typical forward horseshoe vortices (head pointing downstream) associated with upwelling motions are barely found within the free-surface turbulent shear flow.&lt;/p&gt;&lt;p&gt;This work was supported by the Taiwan Ministry of Science and Technology (MOST 107-2611-M-002 -014 -MY3).&lt;/p&gt;

The Development of the Reynolds Stress Tensor in a Turbulent Shear Flow

1970 ◽  
Vol 92 (4) ◽  
pp. 836-842
Author(s):  
S. J. Shamroth ◽  
H. G. Elrod
Keyword(s):  
Shear Flow ◽  
Stress Tensor ◽  
Linear Model ◽  
Reynolds Stress ◽  
Experimental Results ◽  
Turbulent Shear ◽  
Turbulent Shear Flow ◽  
Reynolds Stress Tensor ◽  
Theoretical Predictions

The development of the normalized Reynolds stress tensor, uiuj/q2, in the region upstream of a fully developed, turbulent shear flow is investigated. An inviscid, linear model is used to predict values of the normalized Reynolds stress tensor as a function of position. The theoretical predictions are then compared with experimental results.

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