Wall Suction Effects on the Structure of Fully Developed Turbulent Pipe Flow

1996 ◽  
Vol 118 (1) ◽  
pp. 33-39 ◽  
Author(s):  
D. Sofialidis ◽  
P. Prinos
Keyword(s):  
Shear Stress ◽  
Pipe Flow ◽  
Stokes Equations ◽  
Turbulent Pipe Flow ◽  
Turbulent Shear ◽  
Experimental Measurements ◽  
Wall Region ◽  
Wall Suction ◽  
Law Of The Wall ◽  
Near Wall

The effects of wall suction on the structure of fully developed pipe flow are studied numerically by solving the Reynolds averaged Navier-Stokes equations. Linear and nonlinear k-ε or k-ω low-Re models of turbulence are used for “closing” the system of the governing equations. Computed results are compared satisfactorily against experimental measurements. Analytical results, based on boundary layer assumptions and the mixing length concept, provide a law of the wall for pipe flow under the influence of low suction rates. The analytical solution is found in satisfactory agreement with computed and experimental data for a suction rate of A = 0.46 percent. For the much higher rate of A = 2.53 percent the above assumptions are not valid and analytical velocities do not follow the computed and experimental profiles, especially in the near-wall region. Near-wall velocities, as well as the boundary shear stress, are increased with increasing suction rates. The excess wall shear stress, resulting from suction, is found to be 1.5 to 5.5 times the respective one with no suction. The turbulence levels are reduced with the presence of the wall suction. Computed results of the turbulent shear stress uv are in close agreement with experimental measurements. The distribution of the turbulent kinetic energy k is predicted better by the k-ω model of Wilcox (1993). Nonlinear models of the k-ε and k-ω type predict the reduction of the turbulence intensities u’, v’, w’, and the correct levels of v’ and w’ but they underpredict the level of u’.

The Effects of Adverse Pressure Gradients on Momentum and Thermal Structures in Transitional Boundary Layers: Part 2—Fluctuation Quantities

1996 ◽  
Vol 118 (4) ◽  
pp. 728-736 ◽  
Author(s):  
S. P. Mislevy ◽  
T. Wang
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Transition Region ◽  
Boundary Layers ◽  
Reynolds Shear Stress ◽  
Turbulent Shear ◽  
Wall Region ◽  
Pressure Gradients ◽  
Baseline Case ◽  
Near Wall

The effects of adverse pressure gradients on the thermal and momentum characteristics of a heated transitional boundary layer were investigated with free-stream turbulence ranging from 0.3 to 0.6 percent. Boundary layer measurements were conducted for two constant-K cases, K1 = −0.51 × 10−6 and K2 = −1.05 × 10−6. The fluctuation quantities, u′, ν′, t′, the Reynolds shear stress (uν), and the Reynolds heat fluxes (νt and ut) were measured. In general, u′/U∞, ν′/U∞, and νt have higher values across the boundary layer for the adverse pressure-gradient cases than they do for the baseline case (K = 0). The development of ν′ for the adverse pressure gradients was more actively involved than that of the baseline. In the early transition region, the Reynolds shear stress distribution for the K2 case showed a near-wall region of high-turbulent shear generated at Y+ = 7. At stations farther downstream, this near-wall shear reduced in magnitude, while a second region of high-turbulent shear developed at Y+ = 70. For the baseline case, however, the maximum turbulent shear in the transition region was generated at Y+ = 70, and no near-wall high-shear region was seen. Stronger adverse pressure gradients appear to produce more uniform and higher t′ in the near-wall region (Y+ < 20) in both transitional and turbulent boundary layers. The instantaneous velocity signals did not show any clear turbulent/nonturbulent demarcations in the transition region. Increasingly stronger adverse pressure gradients seemed to produce large non turbulent unsteadiness (or instability waves) at a similar magnitude as the turbulent fluctuations such that the production of turbulent spots was obscured. The turbulent spots could not be identified visually or through conventional conditional-sampling schemes. In addition, the streamwise evolution of eddy viscosity, turbulent thermal diffusivity, and Prt, are also presented.

The Law of the Wall for Swirling Flow in Annular Ducts

1989 ◽  
Vol 111 (2) ◽  
pp. 160-164 ◽  
Author(s):  
R. J. Kind ◽  
F. M. Yowakim ◽  
S. A. Sjolander
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Swirling Flow ◽  
Tangential Velocity ◽  
Wall Region ◽  
Law Of The Wall ◽  
Resultant Velocity ◽  
The Law ◽  
Wall Shear ◽  
Near Wall

Expressions for the logarithmic portion of the law of the wall are derived for the axial and tangential velocity components of swirling flow in annular ducts. These expressions involve new shear-velocity scales and curvature terms. They are shown to agree well with experiment over a substantial portion of the flow near both walls of an annulus. The resultant velocity data also agree with the law of the wall. The success of the proposed logarithmic expressions implies that the mixing-length model used in deriving them correctly describes flow-velocity behavior. This model indicates that the velocity gradient at any height y in the near-wall region is determined by the wall shear stress, not by the local shear stress. This suggests that the influence of wall shear stress is dominant and that it determines the near-wall wall flow even in flows with curvature and pressure gradient. A physical explanation is suggested for this.

scholarly journals Effect of reverse flow on the pattern of wall shear stress near arterial branches

2011 ◽  
Vol 8 (64) ◽  
pp. 1594-1603 ◽  
Author(s):  
A. Kazakidi ◽  
A. M. Plata ◽  
S. J. Sherwin ◽  
P. D. Weinberg
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Steady Flow ◽  
Stokes Equations ◽  
Reverse Flow ◽  
Side Branch ◽  
Navier Stokes ◽  
Wall Region ◽  
Wall Shear ◽  
Near Wall

Atherosclerotic lesions have a patchy distribution within arteries that suggests a controlling influence of haemodynamic stresses on their development. The distribution near aortic branches varies with age and species, perhaps reflecting differences in these stresses. Our previous work, which assumed steady flow, revealed a dependence of wall shear stress (WSS) patterns on Reynolds number and side-branch flow rate. Here, we examine effects of pulsatile flow. Flow and WSS patterns were computed by applying high-order unstructured spectral/hp element methods to the Newtonian incompressible Navier–Stokes equations in a geometrically simplified model of an aorto-intercostal junction. The effect of pulsatile but non-reversing side-branch flow was small; the aortic WSS pattern resembled that obtained under steady flow conditions, with high WSS upstream and downstream of the branch. When flow in the side branch or in the aortic near-wall region reversed during part of the cycle, significantly different instantaneous patterns were generated, with low WSS appearing upstream and downstream. Time-averaged WSS was similar to the steady flow case, reflecting the short duration of these events, but patterns of the oscillatory shear index for reversing aortic near-wall flow were profoundly altered. Effects of reverse flow may help explain the different distributions of lesions.

Turbulent flow

2018 ◽  
Author(s):  
Marcel Escudier
Keyword(s):  
Turbulent Flow ◽  
Stokes Equations ◽  
Turbulent Shear ◽  
Complex Nature ◽  
Time Averaging ◽  
Surface Shear Stress ◽  
Law Of The Wall ◽  
Wide Range ◽  
Log Law ◽  
Near Wall

In this chapter the principal characteristics of a turbulent flow are outlined and the way that Reynolds’ time-averaging procedure, applied to the Navier-Stokes equations, leads to a set of equations (RANS) similar to those governing laminar flow but including additional terms which arise from correlations between fluctuating velocity components and velocity-pressure correlations. The complex nature of turbulent motion has led to an empirical methodology based upon the RANS and turbulence-transport equations in which the correlations are modelled. An important aspect of turbulent flows is the wide range of scales involved. It is also shown that treating near-wall turbulent shear flow as a Couette flow leads to the Law of the Wall and the log law. The effect of surface roughness on both the velocity distribution and surface shear stress is discussed. It is shown that the distribution of mean velocity within a turbulent boundary layer can be represented by a linear combination of the near-wall log law and an outer-layer Law of the Wake.

The structure of Reynolds stress in the near-wall region of a fully developed turbulent pipe flow

1992 ◽  
Vol 13 (6) ◽  
pp. 405-413 ◽  
Author(s):  
P. -A. Chevrin ◽  
H. L. Petrie ◽  
S. Deutsch
Keyword(s):  
Reynolds Stress ◽  
Pipe Flow ◽  
Turbulent Pipe Flow ◽  
Wall Region ◽  
Near Wall

Effects of an axisymmetric contraction on a turbulent pipe flow

2011 ◽  
Vol 687 ◽  
pp. 376-403 ◽  
Author(s):  
Seong Jae Jang ◽  
Hyung Jin Sung ◽  
Per-Åge Krogstad
Keyword(s):  
Pipe Flow ◽  
Core Region ◽  
Turbulent Pipe Flow ◽  
Wall Region ◽  
Mean Flow ◽  
The Core ◽  
Thin Region ◽  
Local Mean ◽  
The Mean ◽  
Near Wall

AbstractThe flow in an axisymmetric contraction fitted to a fully developed pipe flow is experimentally and numerically studied. The reduction in turbulence intensity in the core region of the flow is discussed on the basis of the budgets for the various turbulent stresses as they develop downstream. The contraction generates a corresponding increase in energy in the near-wall region, where the sources for energy production are quite different and of opposite sign compared to the core region, where these effects are caused primarily by vortex stretching. The vortices in the pipe become aligned with the flow as the stretching develops through the contraction. Vortices which originally have a spanwise component in the pipe are stretched into pairs of counter-rotating vortices which become disconnected and aligned with the mean flow. The structures originating in the pipe which are inclined at an angle with respect to the wall are rotated towards the local mean streamlines. In the very near-wall region and the central part of the contraction the flow tends towards two-component turbulence, but these structures are different. The streamwise and azimuthal stresses are dominant in the near-wall region, while the lateral components dominate in the central part of the flow. The two regions are separated by a rather thin region where the flow is almost isotropic.

scholarly journals The Effects of Adverse Pressure Gradients on Momentum and Thermal Structures in Transitional Boundary Layers: Part 2 — Fluctuation Quantities

1995 ◽  
Author(s):  
Scott P. Mislevy ◽  
Ting Wang
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Transition Region ◽  
Boundary Layers ◽  
Reynolds Shear Stress ◽  
Turbulent Shear ◽  
Wall Region ◽  
Pressure Gradients ◽  
Baseline Case ◽  
Near Wall

The effects of adverse pressure gradients on the thermal and momentum characteristics of a heated transitional boundary layer were investigated with free-stream turbulence ranging from 0.3 to 0.6%. Boundary layer measurements were conducted for two constant K cases, K1=−0.51 × 10−6 and K2=−1.05 × 10−6. The fluctuation quantities, u′, v′, t′, the Reynolds shear stress (uv¯), and the Reynolds heat fluxes (vt¯ and ut¯) were measured. In general, u′/U∞, v′/U∞, and vt¯ have higher values across the boundary layer for the adverse pressure-gradient cases than they do for the baseline case (K=0). The development of v′ for the adverse pressure gradients was more actively involved than that of the baseline. In the early transition region, the Reynolds shear stress distribution for the K2 case showed a near-wall region of high-turbulent shear generated at Y+=7. At stations farther downstream, this near-wall shear reduced in magnitude, while a second region of high-turbulent shear developed at Y+=70. For the baseline case, however, the maximum turbulent shear in the transition region was generated at Y+=70, and no near-wall high-shear region was seen. Stronger adverse pressure gradients appear to produce more uniform and higher t′ in the near-wall region (Y,+<20) in both transitional and turbulent boundary layers. The instantaneous velocity signals did not show any clear turbulent/non-turbulent demarcations in the transition region. Increasingly stronger adverse pressure gradients seemed to produce large non-turbulent unsteadiness (or instability waves) at a similar magnitude as the turbulent fluctuations such that the production of turbulent spots was obscured. The turbulent spots could not be identified visually or through conventional conditional-sampling schemes. In addition, the streamwise evolution of eddy viscosity, turbulent thermal diffusivity, and Prt are also presented.

Resistance Reduction in Pulsating Turbulent Pipe Flows

2003 ◽  
Author(s):  
Marcello Manna ◽  
Andrea Vacca
Keyword(s):  
Large Scale ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Turbulent Pipe Flow ◽  
Navier Stokes ◽  
Recent Experimental Data ◽  
Wall Region ◽  
Navier Stokes Equations ◽  
Oscillating Motion ◽  
Near Wall

The paper describes the effects of a forced harmonic oscillations of fixed frequency and amplitudes in the range Λ = Um/Ub = 1 ÷ 11 on the characteristics of a turbulent pipe flow with a bulk Reynolds number of 5900. The resulting Stokes layer δ is a fraction of the pipe radius (χ = R/δ = 53) so that the vorticity associated to the oscillating motion is generated in a small near wall region. The analysis is carried out processing a set of statistically independent samples obtained from wall resolved Large Eddy Simulations; time and space averaged global quantities, extracted for the sake of comparison with recent experimental data, confirm the presence of a non negligible drag reduction phenomenon. Phase averaged profiles of the Reynolds stress tensor components provide valuable material for the comprehension of the effects of the time varying mean shear upon the near wall turbulent flow structures. The large scale of motion are directly computed through numerical integration of the space filtered three dimensional Navier-Stokes equations with a spectrally accurate code; the subgrid scale terms are parametrized with a dynamic procedure.

Experiments on the structure of turbulence in fully developed pipe flow. Part 2. A statistical procedure for identifying ‘bursts’ in the wall layers and some characteristics of flow during bursting periods

1977 ◽  
Vol 82 (4) ◽  
pp. 705-723 ◽  
Author(s):  
T. R. Heidrick ◽  
S. Banerjee ◽  
R. S. Azad
Keyword(s):  
Shear Stress ◽  
Pipe Flow ◽  
Axial Velocity ◽  
High Energy ◽  
Turbulent Pipe Flow ◽  
Wall Turbulence ◽  
Wall Region ◽  
Velocity Fluctuations ◽  
Sequence Of Events ◽  
The Mean

This paper is the second of a pair describing two-point velocity measurements in fully developed pipe flow. A method of processing hot-film anemometer signals to identify intervals of high energy production (‘bursts’) in wall turbulence is presented. The method uses filtered cross-stream spatial derivatives of the axial velocity fluctuations. It is demonstrated to be more sensitive to ‘bursts’ than several other methods of indentification. The bursts identified in this manner are shown to have similar characteristics to those observed in visual studies.The technique has been applied to the wall region of turbulent pipe flow. Mean burst rates have been obtained at various distances from the wall for three Reynolds numbers. It is shown that the mean burst rate cannot be reliably obtained from a previously used technique based on the autocorrelation of the axial velocity fluctuations.On the basis of our experiments, the mean burst rate and the turbulent shear stress have been found to vary similarly with distance from the wall. In the region near the wall where the shear stress is constant the mean burst rate is independent of the kinematic viscosity.Some characteristics of the velocity fluctuations during burst intervals have been studied. All the bursts began with a relative minimum in the axial velocity fluctuations followed by a peak in the cross-stream spatial derivative. A second peak always occurred midway through the burst. The sequence of events is somewhat similar to that in the last stage of laminar-to-turbulent transition.

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