The Experts below are selected from a list of 195 Experts worldwide ranked by ideXlab platform
Joseph W. Hall - One of the best experts on this subject based on the ideXlab platform.
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Reynolds Stress distribution and turbulence generated secondary flow in the turbulent three dimensional wall jet
Journal of Fluid Mechanics, 2016Co-Authors: Lhendup Namgyal, Joseph W. HallAbstract:The lateral half-width of the turbulent three-dimensional wall jet is typically five to eight times larger than the vertical half-width Normal to the wall. Although the reason for this behaviour is not fully understood, it is caused by mean secondary flows that develop in the jet due to the presence of the wall. The origin of the secondary flow has been associated previously with both vorticity reorientation and also gradients in the Reynolds Stresses, although this has not been directly quantified as yet. The present investigation focuses on a wall jet formed using a circular contoured nozzle with exit Reynolds number of 250 000. Stereoscopic particle image velocimetry measurements are used herein to measure the three-component velocity, thereby allowing access to the full Reynolds Stress tensor that contributes to the secondary flow in a turbulent three-dimensional wall jet. Throughout the jet, the Reynolds Normal Stress ( $\overline{u^{2}}$ ) makes the largest contribution to the Reynolds Stress field whereas Reynolds shear Stress ( $\overline{vw}$ ) is found to be negligible when compared with other Stresses. In particular, the differences in the Reynolds Normal Stresses ( $\overline{v^{2}}-\overline{w^{2}}$ ) are found to be significantly larger than $\overline{vw}$ ; these terms are important for the generation of turbulence secondary flow in the wall jet. Above all, the differences in the Reynolds Normal Stresses are oriented to reinforce the near-wall streamwise vorticity, and thus contribute to the large lateral growth of this flow. The contours of the turbulent kinetic budget indicate that the turbulent energy budget obtained on the jet centreline is different from that obtained off of the jet centreline.
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Reynolds Stress distribution and turbulence generated secondary flow in the turbulent three-dimensional wall jet
Journal of Fluid Mechanics, 2016Co-Authors: Lhendup Namgyal, Joseph W. HallAbstract:The lateral half-width of the turbulent three-dimensional wall jet is typically five to eight times larger than the vertical half-width Normal to the wall. Although the reason for this behaviour is not fully understood, it is caused by mean secondary flows that develop in the jet due to the presence of the wall. The origin of the secondary flow has been associated previously with both vorticity reorientation and also gradients in the Reynolds Stresses, although this has not been directly quantified as yet. The present investigation focuses on a wall jet formed using a circular contoured nozzle with exit Reynolds number of 250 000. Stereoscopic particle image velocimetry measurements are used herein to measure the three-component velocity, thereby allowing access to the full Reynolds Stress tensor that contributes to the secondary flow in a turbulent three-dimensional wall jet. Throughout the jet, the Reynolds Normal Stress ( ) makes the largest contribution to the Reynolds Stress field whereas Reynolds shear Stress ( ) is found to be negligible when compared with other Stresses. In particular, the differences in the Reynolds Normal Stresses ( ) are found to be significantly larger than ; these terms are important for the generation of turbulence secondary flow in the wall jet. Above all, the differences in the Reynolds Normal Stresses are oriented to reinforce the near-wall streamwise vorticity, and thus contribute to the large lateral growth of this flow. The contours of the turbulent kinetic budget indicate that the turbulent energy budget obtained on the jet centreline is different from that obtained off of the jet centreline.
Robert J. Poole - One of the best experts on this subject based on the ideXlab platform.
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turbulent pipe flow of a drag reducing rigid rod like polymer solution
Journal of Non-newtonian Fluid Mechanics, 2009Co-Authors: Azuraien Japperjaafar, M. P. Escudier, Robert J. PooleAbstract:Abstract Fully developed turbulent pipe flow of an aqueous solution of a rigid “rod-like” polymer, scleroglucan, at concentrations of 0.005% (w/w) and 0.01% (w/w) has been investigated experimentally. Fanning friction factors were determined from pressure-drop measurements for the Newtonian solvent (water) and the polymer solutions and so levels of drag reduction for the latter. Mean axial velocity u and complete Reynolds Normal Stress data, i.e. u′, v′ and w′, were measured by means of a laser Doppler anemometer at three different Reynolds numbers for each fluid. The measurements indicate that the effectiveness of scleroglucan as a drag-reducing agent is only mildly dependent on Reynolds number. The turbulence structure essentially resembles that of flexible polymer solutions which also lead to low levels of drag reduction.
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Turbulent flow of viscoelastic shear-thinning liquids through a rectangular duct: Quantification of turbulence anisotropy
Journal of Non-Newtonian Fluid Mechanics, 2009Co-Authors: M. P. Escudier, A. K. Nickson, Robert J. PooleAbstract:Abstract We report laser Doppler anemometry (LDA) measurements of mean velocity and turbulence structure for fully-developed turbulent flow through a rectangular duct of aqueous solutions of a xanthan gum and a polyacrylamide both of which are drag-reducing polymer solutions. All three components of the turbulent fluctuations (i.e. the Reynolds Normal Stresses) have been measured as well as the Reynolds shear Stress − ρ u v ¯ . A novel open-slit test-section allows measurement of the component of Reynolds Normal Stress perpendicular to the duct wall and of the Reynolds shear Stress down to values of y+, the distance from the surface in wall units, close to unity. We show that the maximum value of the transverse (or Normal) component of turbulence intensity in wall units v ′ M A X + decreases linearly from about unity for zero drag reduction (DR1) to about 0.6 at DR1 = 80% while the lateral component w M A X + is practically independent of DR1. For levels of drag reduction below 50% the streamwise component u′+MAX increases monotonically but for higher levels of drag reduction the trend is less clear. Anisotropy of the turbulence structure is characterised using Pope's modification [S. Pope, Turbulent flows (2000), Cambridge University Press, New York.] of the triangle plot suggested by Lumley [J.L. Lumley, Computational modelling of turbulent flows, Adv. Appl. Mech. 18 (1978) 123–176] and shown to follow closely the line for axisymmetric turbulence. The detailed LDA measurements are supplemented by particle-image velocimetry observations which reveal how drag reduction changes the near-wall streaky structure.
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Turbulent Pipe Flow of “Rod‐Like” Polymer Solutions
AIP Conference Proceedings, 2008Co-Authors: Azuraien Japper-jaafar, M. P. Escudier, Robert J. PooleAbstract:In this study the drag reduction of an aqueous solution of a rigid “rod‐like” polymer, scleroglucan, at a concentration of 0.01% w/w in a 100‐mm diameter, 23‐m long circular pipe‐flow facility was experimentally investigated. Pressure‐drop measurements were conducted via a differential pressure transducer and compared to that of the Newtonian solvent. Mean axial velocity and complete Reynolds Normal Stress data, i.e. u′, v′ and w′ were measured by means of a laser Doppler anemometer at three different Reynolds numbers, all in the turbulent‐flow regime. Newtonian control runs, also within the turbulent‐flow regime, were also performed for comparison.
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Turbulent flow of viscoelastic shear-thinning liquids through a rectangular duct
Springer Proceedings Physics, 1Co-Authors: M. P. Escudier, A. K. Nickson, Robert J. PooleAbstract:We report LDA measurements of mean velocity and turbulence structure for fullydeveloped turbulent flow through a rectangular duct of two drag-reducing polymers: aqueous solutions of a xanthan gum and a polyacrylamide. All three components of the turbulent fluctuations have been measured as well as the Reynolds shear Stress. A novel open-slit testsection allows measurement of the component of Reynolds Normal Stress perpendicular to the duct wall and of the Reynolds shear Stress down to values of + y , the distance from the surface in wall units, close to unity. Anisotropy of the turbulence structure is characterised using Pope’s (2000) modification of the parameters suggested by Lumley (1978) and shown to follow closely the line for axisymmetric turbulence.
Lhendup Namgyal - One of the best experts on this subject based on the ideXlab platform.
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Reynolds Stress distribution and turbulence generated secondary flow in the turbulent three dimensional wall jet
Journal of Fluid Mechanics, 2016Co-Authors: Lhendup Namgyal, Joseph W. HallAbstract:The lateral half-width of the turbulent three-dimensional wall jet is typically five to eight times larger than the vertical half-width Normal to the wall. Although the reason for this behaviour is not fully understood, it is caused by mean secondary flows that develop in the jet due to the presence of the wall. The origin of the secondary flow has been associated previously with both vorticity reorientation and also gradients in the Reynolds Stresses, although this has not been directly quantified as yet. The present investigation focuses on a wall jet formed using a circular contoured nozzle with exit Reynolds number of 250 000. Stereoscopic particle image velocimetry measurements are used herein to measure the three-component velocity, thereby allowing access to the full Reynolds Stress tensor that contributes to the secondary flow in a turbulent three-dimensional wall jet. Throughout the jet, the Reynolds Normal Stress ( $\overline{u^{2}}$ ) makes the largest contribution to the Reynolds Stress field whereas Reynolds shear Stress ( $\overline{vw}$ ) is found to be negligible when compared with other Stresses. In particular, the differences in the Reynolds Normal Stresses ( $\overline{v^{2}}-\overline{w^{2}}$ ) are found to be significantly larger than $\overline{vw}$ ; these terms are important for the generation of turbulence secondary flow in the wall jet. Above all, the differences in the Reynolds Normal Stresses are oriented to reinforce the near-wall streamwise vorticity, and thus contribute to the large lateral growth of this flow. The contours of the turbulent kinetic budget indicate that the turbulent energy budget obtained on the jet centreline is different from that obtained off of the jet centreline.
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Reynolds Stress distribution and turbulence generated secondary flow in the turbulent three-dimensional wall jet
Journal of Fluid Mechanics, 2016Co-Authors: Lhendup Namgyal, Joseph W. HallAbstract:The lateral half-width of the turbulent three-dimensional wall jet is typically five to eight times larger than the vertical half-width Normal to the wall. Although the reason for this behaviour is not fully understood, it is caused by mean secondary flows that develop in the jet due to the presence of the wall. The origin of the secondary flow has been associated previously with both vorticity reorientation and also gradients in the Reynolds Stresses, although this has not been directly quantified as yet. The present investigation focuses on a wall jet formed using a circular contoured nozzle with exit Reynolds number of 250 000. Stereoscopic particle image velocimetry measurements are used herein to measure the three-component velocity, thereby allowing access to the full Reynolds Stress tensor that contributes to the secondary flow in a turbulent three-dimensional wall jet. Throughout the jet, the Reynolds Normal Stress ( ) makes the largest contribution to the Reynolds Stress field whereas Reynolds shear Stress ( ) is found to be negligible when compared with other Stresses. In particular, the differences in the Reynolds Normal Stresses ( ) are found to be significantly larger than ; these terms are important for the generation of turbulence secondary flow in the wall jet. Above all, the differences in the Reynolds Normal Stresses are oriented to reinforce the near-wall streamwise vorticity, and thus contribute to the large lateral growth of this flow. The contours of the turbulent kinetic budget indicate that the turbulent energy budget obtained on the jet centreline is different from that obtained off of the jet centreline.
Michael P. Schultz - One of the best experts on this subject based on the ideXlab platform.
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Reynolds number scaling of turbulent channel flow
Physics of Fluids, 2013Co-Authors: Michael P. Schultz, Karen A FlackAbstract:Results of an experimental study of smooth-wall, fully developed, turbulent channel flow are presented. The Reynolds number (Rem) based on the channel height and the bulk mean velocity ranged from 10 000 to 300 000. The present results indicate that the skin-friction coefficient (Cf) closely follows a power law for Rem < 62 000. At higher Reynolds numbers, Cf is best described by a log law. Detailed two-component velocity measurements taken at friction Reynolds numbers of Reτ = 1000–6000 indicate that the mean flow and Reynolds shear Stress display little or no Reynolds-number dependence. The streamwise Reynolds Normal Stress (u′2¯+), on the other hand, varies significantly with Reynolds number. The inner peak in u′2¯+ is observed to grow with Reynolds number. Growth in u′2¯+ farther from the wall is documented over the entire range of Reynolds number giving rise to a plateau in the streamwise Reynolds Normal Stress in the overlap region of the profile for Reτ = 6000. The wall-Normal Reynolds Normal stres...
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Turbulence in pipe flows with small relative roughness
IUTAM Symposium on The Physics of Wall-Bounded Turbulent Flows on Rough Walls, 2010Co-Authors: Alexander Smits, Sean C. C. Bailey, Richard L Pepe, Michael P. SchultzAbstract:The Princeton University Superpipe, capable of generating Reynolds numbers from 31 ×103 to 35 ×106, has been used to study the effects of surface roughness on turbulence in fully developed turbulent pipe flow. Mean velocity and pressure gradient results, streamwise Reynolds Stresses, and two point correlations have all been performed on flow through a commercial steel pipe, with k rms ∕ D = 1 ∕ 26, 000 = 38. 5 ×10− 6, where k rms is the rms roughness height and Dis the pipe diameter. The Reynolds number of these studies ranged from 76 ×103 to 20 ×106. It was found that through the transitionally rough flow regime, the friction factor behavior did not follow that predicted by the Colebrook correlation. In addition, when the flow moved into the transitional and fully rough flow regimes, the streamwise Reynolds Normal Stress in the outer layer was found to saturate at a maximum value and did not increase in the same manner as observed for smooth pipes.
Sujit K. Bose - One of the best experts on this subject based on the ideXlab platform.
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Submerged wall jets subjected to injection and suction from the wall
Journal of Fluid Mechanics, 2010Co-Authors: Subhasish Dey, Tushar K. Nath, Sujit K. BoseAbstract:This paper presents an experimental study on turbulent flow characteristics in submerged plane wall jets subjected to injection (upward seepage) and suction (downward seepage) from the wall. The vertical distributions of time-averaged velocity components, turbulence intensity components and Reynolds shear Stress at different horizontal distances are presented. The horizontal distributions of wall shear Stress determined from the Reynolds shear Stress profiles are also furnished. The flow field exhibits a decay of the jet velocity over a horizontal distance. The wall shear Stress and the rate of decay of the jet velocity increase in the presence of injection and decrease with suction. Based on the two-dimensional Reynolds-averaged Navier― Stokes equations of a steady turbulent flow, the velocity and Reynolds shear Stress distributions in the fully developed zone subjected to no seepage, injection and suction are theoretically computed. The response of the turbulent flow characteristics to injection and suction is analysed from the point of view of similarity characteristics, growth of the length scale and decay of the velocity and turbulence characteristics scales. The significant observation is that the velocity, Reynolds shear Stress and turbulence intensities in the fully developed zone are reasonably similar under both injection and suction on applying the appropriate scaling laws. An analysis of the third-order moments of velocity fluctuations reveals that the inner layer of the jet is associated with the arrival of low-speed fluid streaks causing an effect of retardation. On the other hand, the upper layer of the jet is associated with the arrival of highspeed fluid streaks causing an effect of acceleration. Injection influences the near-wall distributions of the third-order moments by increasing the upward turbulent advection of the streamwise Reynolds Normal Stress. In contrast, suction influences the near-wall distributions of the third-order moments by increasing the downward turbulent advection of the streamwise Reynolds Normal Stress. Also, injection and suction change the vertical turbulent flux of the vertical Reynolds Normal Stress in a similar way. The streamwise turbulent energy flux travels towards the jet origin within the jet layer, while it travels away from the origin within the inner layer of the circulatory flow. The turbulent energy budget suggests that the turbulent and pressure energy diffusions oppose each other, and the turbulent dissipation lags the turbulent production. The quadrant analysis of velocity fluctuations reveals that the inward and outward interactions are the primary contributions to the Reynolds shear Stress production in the inner and outer layers of the jet, respectively. However, injection induces feeble ejections in the vicinity of the wall.