Sat, 26 Jul 2008 07:34:46 BST CiteULike: l-alex's Tsinober http://www.citeulike.org/user/l-alex/author/Tsinober CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/l-alex/article/3015770 <i>Physics of Fluids, Vol. 19, No. 7. (2007)</i><br /><br />View This Record in Scopus Small-scale aspects of flows in proximity of the turbulent/nonturbulent interface M Holzner A Liberzon N Nikitin W Kinzelbach A Tsinober Physics of Fluids, Vol. 19, No. 7. (2007) 2008-07-17T20:41:45-00:00 2007 Physics of Fluids 19 7 AIP entrainment experiment interface small-scale http://www.citeulike.org/user/l-alex/article/3015768 <i>Journal of Fluid Mechanics, Vol. 574, No. -1. (2007), pp. 405-427.</i><br /><br />Lagrangian auto- and cross-correlation functions of the rate of strain <em>s</em>², enstrophy ω², their respective production terms −<em>s_ijs_jks_ki</em> and ω_iω_j<em>s</em>_ij, and material derivatives, D<em>s</em>²/D<em>t</em> and Dω²/D<em>t</em> are estimated using experimental results obtained through three-dimensional particle tracking velocimetry (three-dimensional-PTV) in homogeneous turbulence at <em>Re</em>_λ=50. The autocorrelation functions are used to estimate the Lagrangian time scales of different quantities, while the cross-correlation functions are used to clarify some aspects of the interaction mechanisms between vorticity ω and the rate of strain tensor <em>s_ij</em>, that are responsible for the statistically stationary, in the Eulerian sense, levels of enstrophy and rate of strain in homogeneous turbulent flow. Results show that at the Reynolds number of the experiment these quantities exhibit different time scales, varying from the relatively long time scale of ω² to the relatively shorter time scales of <em>s</em>², ω_iω_j<em>s</em>_ij and −<em>s_ijs_jks_ki</em>. Cross-correlation functions suggest that the dynamics of enstrophy and strain, in this flow, is driven by a set of different-time-scale processes that depend on the local magnitudes of <em>s</em>² and ω². In particular, there are indications that, in a statistical sense, (i) strain production anticipates enstrophy production in low-strain–low-enstrophy regions (ii) strain production and enstrophy production display high correlation in high-strain–high-enstrophy regions, (iii) vorticity dampening in high-enstrophy regions is associated with weak correlations between −<em>s_ijs_jks_ki</em> and <em>s</em>² and between −<em>s_ijs_jks_ki</em> and D<em>s</em>²/D<em>t</em>, in addition to a marked anti-correlation between ω_iω_j<em>s</em>_ij and D<em>s</em>²/D<em>t</em>. Vorticity dampening in high-enstrophy regions is thus related to the decay of <em>s</em>² and its production term, −<em>s_ijs_jks_ki</em>. An experimental investigation on Lagrangian correlations of small-scale turbulence at low Reynolds number Michele Guala Alexander Liberzon Arkady Tsinober Wolfgang Kinzelbach doi:10.1017/S0022112006004204 Journal of Fluid Mechanics, Vol. 574, No. -1. (2007), pp. 405-427. 2008-07-17T20:39:52-00:00 2007 Journal of Fluid Mechanics 574 -1 405 427 correlation experiment lagrangian small-scale http://www.citeulike.org/user/l-alex/article/2722256 <i>Physics of Fluids, Vol. 20, No. 4. (2008)</i> Kolmogorov 4/5 law, nonlocality, and sweeping decorrelation hypothesis M Kholmyansky A Tsinober Physics of Fluids, Vol. 20, No. 4. (2008) 2008-04-26T17:48:17-00:00 2008 Physics of Fluids 20 4 AIP nonlocality small-scales http://www.citeulike.org/user/l-alex/article/1751873 <i>J. Fluid Mech, Vol. 589 (2007), pp. 103-123.</i> Velocity and temperature derivatives in high- Reynolds-number turbulent flows in the atmospheric surface layer. Part 3. Temperature and joint statistics of temperature and velocity derivatives G Gulitski M Kholmyansky W Kinzelbach B Luthi A Tsinober S Yorish J. Fluid Mech, Vol. 589 (2007), pp. 103-123. 2007-10-10T19:06:52-00:00 2007 J. Fluid Mech 589 103 123 atmospheric derivatives hot-wire http://www.citeulike.org/user/l-alex/article/1686104 <i>(June 2007), pp. 271-284.</i> Simultaneous measurements of the fluid and the solid phases in homogeneous turbulence: preliminary results at $Re_λ$=250 M Guala A Liberzon K Hoyer A Tsinober W Kinzelbach (June 2007), pp. 271-284. 2007-09-22T21:41:54-00:00 2007 271 284 Springer 3d-ptv clustering two-phase http://www.citeulike.org/user/l-alex/article/1567824 <i>Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 76, No. 2. (2007)</i><br /><br />We find actual evidence, relying upon vorticity time series taken in a high-Reynolds-number atmospheric experiment, that to a very good approximation the surface boundary layer flow may be described, in a statistical sense and under certain regimes, as an advected ensemble of homogeneous turbulent systems, characterized by a log-normal distribution of fluctuating intensities. Our analysis suggests that the usual direct numerical simulations of homogeneous and isotropic turbulence, performed at moderate Reynolds numbers, may play an important role in the study of turbulent boundary layer flows, if supplemented with appropriate statistical information concerned with the structure of large-scale fluctuations. Large-scale intermittency in the atmospheric boundary layer M Kholmyansky L Moriconi A Tsinober doi:10.1103/PhysRevE.76.026307 Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 76, No. 2. (2007) 2007-08-16T00:02:41-00:00 2007 Physical Review E (Statistical, Nonlinear, and Soft Matter Physics) 76 2 APS boundary-layer hot-wire http://www.citeulike.org/user/l-alex/article/1282094 <i>(4 May 2007)</i><br /><br />The work reported below is a first of its kind study of the properties of turbulent flow without strong mean shear in a Newtonian fluid in proximity of the turbulent/non-turbulent interface, with emphasis on the small scale aspects. The main tools used are a three-dimensional particle tracking system (3D-PTV) allowing to measure and follow in a Lagrangian manner the field of velocity derivatives and direct numerical simulations (DNS). The comparison of flow properties in the turbulent (A), intermediate (B) and non-turbulent (C) regions in the proximity of the interface allows for direct observation of the key physical processes underlying the entrainment phenomenon. The differences between small scale strain and enstrophy are striking and point to the definite scenario of turbulent entrainment via the viscous forces originating in strain. Small scale aspects of flows in proximity of the turbulent/non-turbulent interface M Holzner A Liberzon N Nikitin W Kinzelbach A Tsinober (4 May 2007) 2007-05-07T17:20:21-00:00 2007 entrainment http://www.citeulike.org/user/l-alex/article/1031266 <i>Physics of Fluids, Vol. 13, No. 1. (2001), pp. 311-314.</i><br /><br />We report first results of an experiment in which explicit information is obtained on the field of velocity derivatives (all the nine components of the tensor ui/xj) along with all the three components of velocity fluctuations at Reynolds number as high as Re~104. This includes information on such basic processes as enstrophy and strain production, geometrical statistics, the role of concentrated vorticity and strain, and the reduction of nonlinearity. ©2001 American Institute of Physics. Velocity derivatives in the atmospheric surface layer at Re[sub lambda ] = 10[sup 4] M Kholmyansky A Tsinober S Yorish doi:10.1063/1.1328358 Physics of Fluids, Vol. 13, No. 1. (2001), pp. 311-314. 2007-01-09T09:14:33-00:00 2001 Physics of Fluids 13 1 311 314 AIP 3d vorticity http://www.citeulike.org/user/l-alex/article/977107 <i>Physics of Fluids, Vol. 18, No. 12. (2006), 125101.</i><br /><br />Drag reduction by dilute polymer solutions is the most recognized phenomenon in wall-bounded turbulent flows, which is associated with large scales (e.g., velocity scales) in spite of a consensus that polymers act mainly on much smaller scales of velocity derivatives. We demonstrate that drag reduction is only one sort of polymers' effect on a turbulent flow and show how turbulent velocity and velocity derivatives are altered in the presence of dilute polymers, irrespective of drag reduction phenomena. This is an experimental study on the interaction of dilute polymers with a complex three-dimensional turbulent flow with small mean velocity gradients. Lagrangian data (e.g., velocities and velocity gradients) of flow tracers were obtained by using three-dimensional particle tracking velocimetry in an observational volume in the turbulent bulk region, far from the boundaries. The focus is on aspects related to the turbulent kinetic energy (TKE) production, −uiujSij (ui is the fluctuating velocity, uiuj is the Reynolds stress tensor, and Sij is the mean rate-of-strain tensor), such as an anisotropy of Reynolds stresses and the alignment of the velocity vector field with respect to the eigenframe of Sij, among others. We base our study on the comparison of turbulent quantities in flows of water and of dilute polymer solution, forced in two distinct ways: frictional forcing by smooth rotating disks and inertial forcing by disks with baffles. The comparison of the results from the water and from the dilute polymer solution flows allows a critical examination of the influence of polymers on the TKE production, viscous dissipation, and the related turbulent properties. We conclude with (i) quantification of the direct effect of polymers on the small scales of velocity derivatives, (ii) evidence of an additional dissipation mechanism by the polymers, which is the main reason for the strong inhibition of the viscous dissipation, 2s2, in a turbulent bulk, (iii) verification that TKE production does not change if the energy input to the flow is at the scales that are not affected by polymers (e.g., inertial forcing or a very rough wall), and last, (iv) evidence for qualitative modification of the turbulent structure, which is not exhausted by the additional dissipation mechanism. ©2006 American Institute of Physics On turbulent kinetic energy production and dissipation in dilute polymer solutions A Liberzon M Guala W Kinzelbach A Tsinober doi:10.1063/1.2397536 Physics of Fluids, Vol. 18, No. 12. (2006), 125101. 2006-12-06T21:21:54-00:00 2006 Physics of Fluids 18 12 125101 AIP drag-reduction polymers ptv http://www.citeulike.org/user/l-alex/article/909964 <i>Experiments in Fluids</i> Generalized detection of a turbulent front generated by an oscillating grid Markus Holzner Alexander Liberzon Michele Guala Arkady Tsinober Wolfgang Kinzelbach doi:10.1007/s00348-006-0193-y Experiments in Fluids 2006-10-22T17:42:29-00:00 Experiments in Fluids entrainment http://www.citeulike.org/user/l-alex/article/909941 <i>Phys.~Fluids, Vol. 13 (2001), pp. 1974-1984.</i> Random Taylor hypothesis and the behavior of local and convective accelerations in isotropic turbulence A Tsinober P Vedula PK Yeung Phys.~Fluids, Vol. 13 (2001), pp. 1974-1984. 2006-10-22T17:20:14-00:00 2001 Phys.~Fluids 13 1974 1984 no-tag http://www.citeulike.org/user/l-alex/article/909940 <i>Fluid Dyn.~Res., Vol. 21 (1997), pp. 477-494.</i> A study of vortex stretching and enstrophy generation in numerical and laboratory turbulence A Tsinober L Shtilman H Vaisburd Fluid Dyn.~Res., Vol. 21 (1997), pp. 477-494. 2006-10-22T17:20:14-00:00 1997 Fluid Dyn.~Res. 21 477 494 no-tag http://www.citeulike.org/user/l-alex/article/909939 <i>Phys.~Fluids, Vol. 11 (1999), pp. 2291-2297.</i> On depression of nonlinearity in turbulence A Tsinober M Ortenberg L Shtilman Phys.~Fluids, Vol. 11 (1999), pp. 2291-2297. 2006-10-22T17:20:13-00:00 1999 Phys.~Fluids 11 2291 2297 no-tag http://www.citeulike.org/user/l-alex/article/909938 <i>J.~Fluid Mech., Vol. 242 (1992), pp. 169-192.</i> Experimental investigation of the field of velocity gradients in turbulent flows A Tsinober E Kit T Dracos J.~Fluid Mech., Vol. 242 (1992), pp. 169-192. 2006-10-22T17:20:13-00:00 1992 J.~Fluid Mech. 242 169 192 no-tag http://www.citeulike.org/user/l-alex/article/909937 <i>Phys.~Fluids, Vol. 15 (2003), pp. 3514-3531.</i> Exploratory numerical experiments on the differences between genuine and "passive" turbulence A Tsinober B Galanti Phys.~Fluids, Vol. 15 (2003), pp. 3514-3531. 2006-10-22T17:20:13-00:00 2003 Phys.~Fluids 15 3514 3531 no-tag http://www.citeulike.org/user/l-alex/article/909936 <i>(2001)</i> Numerical experiments on geometrical statistics of passive objects in turbulent flows A Tsinober B Galanti (2001) 2006-10-22T17:20:13-00:00 2001 no-tag http://www.citeulike.org/user/l-alex/article/909935 <i>(2005), pp. 31-36.</i> On how different are genuine and `passive' turbulence A Tsinober (2005), pp. 31-36. 2006-10-22T17:20:13-00:00 2005 31 36 Springer no-tag http://www.citeulike.org/user/l-alex/article/909934 <i>(2001), pp. 389-395.</i> Nonlocality in turbulence A Tsinober (2001), pp. 389-395. 2006-10-22T17:20:13-00:00 2001 389 395 Springer no-tag http://www.citeulike.org/user/l-alex/article/909933 <i>(2001)</i> An informal introduction to turbulence A Tsinober (2001) 2006-10-22T17:20:13-00:00 2001 Kluwer no-tag http://www.citeulike.org/user/l-alex/article/909932 <i>(2000)</i> Vortex stretching versus production of strain/dissipation A Tsinober (2000) 2006-10-22T17:20:13-00:00 2000 Cambr. Univ. Press no-tag http://www.citeulike.org/user/l-alex/article/909931 <i>(1998), pp. 85-143.</i> Turbulence - Beyond Phenomenology A Tsinober (1998), pp. 85-143. 2006-10-22T17:20:13-00:00 1998 85 143 Springer no-tag http://www.citeulike.org/user/l-alex/article/909930 <i>Eur. J. Mech., Vol. 17 (1998), pp. 421-449.</i> Is concentrated vorticity that important? A Tsinober Eur. J. Mech., Vol. 17 (1998), pp. 421-449. 2006-10-22T17:20:13-00:00 1998 Eur. J. Mech. 17 421 449 no-tag http://www.citeulike.org/user/l-alex/article/909912 <i>Advances in turbulence, Vol. 8 (2000), pp. 407-410.</i> Kinetic energy, enstrophy and strain rate in near-wall turbulence N Sandham A Tsinober Advances in turbulence, Vol. 8 (2000), pp. 407-410. 2006-10-22T17:20:12-00:00 2000 Advances in turbulence 8 407 410 no-tag http://www.citeulike.org/user/l-alex/article/909901 <i>Phys.~Fluids, Vol. 12 (2000), pp. 3195-3204.</i> Accelerations in isotropic and homogeneous turbulence and Taylor's hypothesis M Pinsky A Khain A Tsinober Phys.~Fluids, Vol. 12 (2000), pp. 3195-3204. 2006-10-22T17:20:11-00:00 2000 Phys.~Fluids 12 3195 3204 no-tag http://www.citeulike.org/user/l-alex/article/909897 <i>(2005)</i> Numerical study of turbulent entrainment in a simple configuration NV Nikitin A Tsinober (2005) 2006-10-22T17:20:11-00:00 2005 no-tag http://www.citeulike.org/user/l-alex/article/909881 <i>J.~Fluid Mech., Vol. 528 (2005), pp. 87-118.</i> Lagrangian measurement of vorticity dynamics in turbulent flow B Lüthi A Tsinober W Kinzelbach J.~Fluid Mech., Vol. 528 (2005), pp. 87-118. 2006-10-22T17:20:10-00:00 2005 J.~Fluid Mech. 528 87 118 no-tag http://www.citeulike.org/user/l-alex/article/909880 <i>Vol. II (2001), pp. 123-128.</i> Velocity derivatives in turbulent flow from 3D-PTV measurements B Luethi U Burr A Gyr W Kinzelbach A Tsinober Vol. II (2001), pp. 123-128. 2006-10-22T17:20:10-00:00 2001 II 123 128 derivatives ptv http://www.citeulike.org/user/l-alex/article/909872 <i>Vol. I (2001), pp. 109-113.</i> Velocity derivatives in the atmospheric surface layer at $\mboxRe_λ =10^4$. Further results M Kholmyansky A Tsinober S Yorish Vol. I (2001), pp. 109-113. 2006-10-22T17:20:10-00:00 2001 I 109 113 no-tag http://www.citeulike.org/user/l-alex/article/909871 <i>Phys.~Fluids, Vol. 13 (2001), pp. 311-314.</i> Velocity derivatives in the atmospheric surface layer at $\mboxRe_λ =10^4$ M Kholmyansky A Tsinober S Yorish Phys.~Fluids, Vol. 13 (2001), pp. 311-314. 2006-10-22T17:20:09-00:00 2001 Phys.~Fluids 13 311 314 no-tag http://www.citeulike.org/user/l-alex/article/909870 <i>Advances in Turbulence, Vol. 8 (2000), pp. 895-898.</i> Geometrical statistics in the atmospheric turbulent flow at $\mboxRe_λ =10^4$ M Kholmyansky A Tsinober S Yorish Advances in Turbulence, Vol. 8 (2000), pp. 895-898. 2006-10-22T17:20:09-00:00 2000 Advances in Turbulence 8 895 898 no-tag http://www.citeulike.org/user/l-alex/article/909869 <i>(2000)</i> On the origins of intermittency in real turbulent flows M Kholmyansky A Tsinober (2000) 2006-10-22T17:20:09-00:00 2000 Cambr. Univ. Press no-tag http://www.citeulike.org/user/l-alex/article/909858 <i>J.~Fluid Mech. (2006)</i> Velocity and temperature derivatives in high Reynolds number turbulent flows in the atmospheric surface layer. Part III. Temperature and joint statistics of temperature and velocity derivatives G Gulitski M Kholmyansky W Kinzelbach B Lüthi A Tsinober S Yorish J.~Fluid Mech. (2006) 2006-10-22T17:20:08-00:00 2006 J.~Fluid Mech. no-tag http://www.citeulike.org/user/l-alex/article/909857 <i>J.~Fluid Mech. (2006)</i> Velocity and temperature derivatives in high Reynolds number turbulent flows in the atmospheric surface layer. Part II. Accelerations and related matters G Gulitski M Kholmyansky W Kinzelbach B Lüthi A Tsinober S Yorish J.~Fluid Mech. (2006) 2006-10-22T17:20:08-00:00 2006 J.~Fluid Mech. no-tag http://www.citeulike.org/user/l-alex/article/909856 <i>J.~Fluid Mech. (2006)</i> Velocity and temperature derivatives in high Reynolds number turbulent flows in the atmospheric surface layer. Part I. Facilities, methods and some general results G Gulitski M Kholmyansky W Kinzelbach B Lüthi A Tsinober S Yorish J.~Fluid Mech. (2006) 2006-10-22T17:20:08-00:00 2006 J.~Fluid Mech. no-tag http://www.citeulike.org/user/l-alex/article/909855 <i>J.~Fluid Mech., Vol. 533 (2005), pp. 339-359.</i> On the evolution of material lines and vorticity in homogeneous turbulence M Guala B Lüthi A Liberson A Tsinober W Kinzelbach J.~Fluid Mech., Vol. 533 (2005), pp. 339-359. 2006-10-22T17:20:08-00:00 2005 J.~Fluid Mech. 533 339 359 no-tag http://www.citeulike.org/user/l-alex/article/909846 <i>Vol. X (2004), pp. 267-270.</i> Joint statistical properties of fine structure of velocity and passive scalar in high Reynolds number flows B Galanti G Gulitsky M Kholmyansky A Tsinober S Yorish Vol. X (2004), pp. 267-270. 2006-10-22T17:20:07-00:00 2004 X 267 270 CIMNE no-tag http://www.citeulike.org/user/l-alex/article/909845 <i>Vol. II (2003), pp. 745-750.</i> Velocity derivatives in turbulent flow in an atmospheric boundary layer without Taylor hypothesis B Galanti G Gulitsky M Kholmyansky A Tsinober S Yorish Vol. II (2003), pp. 745-750. 2006-10-22T17:20:07-00:00 2003 II 745 750 no-tag http://www.citeulike.org/user/l-alex/article/909844 <i>Phys.~Fluids, Vol. 12 (2000), pp. 3097-3099.</i> Self-amplification of the field of velocity derivatives in quasi-isotropic turbulence B Galanti A Tsinober Phys.~Fluids, Vol. 12 (2000), pp. 3097-3099. 2006-10-22T17:20:07-00:00 2000 Phys.~Fluids 12 3097 3099 no-tag http://www.citeulike.org/user/l-alex/article/909827 <i>(2001)</i> An airborne experiment on turbulent velocity derivatives R Busen G Gulitsky M Kholmyansky U Schumann A Tsinober S Yorish (2001) 2006-10-22T17:20:04-00:00 2001 no-tag http://www.citeulike.org/user/l-alex/article/890211 <i>J. Fluid Mech., Vol. 528 (2005), pp. 87-118.</i> Lagrangian measurement of vorticity dynamics in turbulent flow B Lüthi A Tsinober W Kinzelbach J. Fluid Mech., Vol. 528 (2005), pp. 87-118. 2006-10-09T15:03:25-00:00 2005 J. Fluid Mech. 528 87 118 no-tag http://www.citeulike.org/user/l-alex/article/890195 <i>(2001)</i> An informal introduction to turbulence A Tsinober (2001) 2006-10-09T15:03:22-00:00 2001 Kluwer book http://www.citeulike.org/user/l-alex/article/890192 <i>Phys. Fluids, Vol. 12 (2000), pp. 3097-3099.</i> Self-amplification of the field of velocity derivatives in quasi-istropic turbulence B Galanti A Tsinober Phys. Fluids, Vol. 12 (2000), pp. 3097-3099. 2006-10-09T15:03:22-00:00 2000 Phys. Fluids 12 3097 3099 no-tag http://www.citeulike.org/user/l-alex/article/890187 <i>Advances in Turbulence, Vol. 9 (2002), pp. 461-464.</i> Growth of error in quasi-isotropic turbulent flow U Burr M Kolmyansky W Kinzelbach B Lüthi M Ortenberg A Tsinober Advances in Turbulence, Vol. 9 (2002), pp. 461-464. 2006-10-09T15:03:21-00:00 2002 Advances in Turbulence 9 461 464 no-tag http://www.citeulike.org/user/l-alex/article/890186 <i>Physics of Fluids, Vol. 15 (2003), pp. 2313-2320.</i> Is turbulent `wind' in convective flows driven by fluctuations? U Burr W Kinzelbach A Tsinober Physics of Fluids, Vol. 15 (2003), pp. 2313-2320. 2006-10-09T15:03:20-00:00 2003 Physics of Fluids 15 2313 2320 no-tag http://www.citeulike.org/user/l-alex/article/854499 <i>European Journal of Mechanics - B/Fluids, Vol. 17, No. 4. ( 1998), pp. 421-449.</i><br /><br />The main purpose of this paper is to bring about a better balance between views of the exaggerated importance of concentrated vorticity, on one hand, and the underestimated role of three kinds of regions other than concentrated vorticity: i -- `structureless' background, ii -- regions of strong vorticity/strain (self) interaction and strong enstrophy generation, and iii -- regions with negative enstrophy production, on the other hand, with the emphasis on the latter. Results of experiments on turbulent grid flow and DNS of decaying turbulent flow in a periodic `box' at the same Reynolds number (Re[lambda] [approximate] 75) are used in order to demonstrate that all these regions are strongly non-Gaussian, dynamically significant and possess structure. It is argued that due to the strong nonlocality of turbulence in physical space all the four regions are in continuous interaction and are strongly correlated.Thus the answer to the question posed in the title is that -- though important -- regions of concentrated vorticity are not as important as is commonly believed. Is concentrated vorticity that important? A Tsinober doi:10.1016/S0997-7546(98)80003-4 European Journal of Mechanics - B/Fluids, Vol. 17, No. 4. ( 1998), pp. 421-449. 2006-09-22T15:00:12-00:00 1998 European Journal of Mechanics - B/Fluids 17 4 421 449 strain vorticity http://www.citeulike.org/user/l-alex/article/853068 <i>Physics of Fluids, Vol. 13, No. 7. (2001), pp. 1974-1984.</i><br /><br />The properties of acceleration fluctuations in isotropic turbulence are studied in direct numerical simulations (DNS) by decomposing the acceleration as the sum of local and convective contributions (aL = u/t and aC = u·u), or alternatively as the sum of irrotational and solenoidal contributions [aI = –(p/) and aS = 2u]. The main emphasis is on the nature of the mutual cancellation between aL and aC which must occur in order for the acceleration (a) to be small as predicted by the "random Taylor hypothesis" [Tennekes, J. Fluid Mech. 67, 561 (1975)] of small eddies in turbulent flow being passively "swept" past a stationary Eulerian observer. Results at Taylor-scale Reynolds number up to 240 show that the random-Taylor scenario a2" align="middle">aC2" align="middle">" align="middle">aL2" align="middle">" align="middle">, accompanied by strong antialignment between the vectors aL and aC, is indeed increasingly valid at higher Reynolds number. Mutual cancellation between aL and aC also leads to the solenoidal part of a being small compared to its irrotational part. Results for spectra in wave number space indicate that, at a given Reynolds number, the random Taylor hypothesis has greater validity at decreasing scale sizes. Finally, comparisons with DNS data in Gaussian random fields show that the mutual cancellation between aL and aC is essentially a kinematic effect, although the Reynolds number trends are made stronger by the dynamics implied in the Navier–Stokes equations. ©2001 American Institute of Physics. Random Taylor hypothesis and the behavior of local and convective accelerations in isotropic turbulence Arkady Tsinober Prakash Vedula PK Yeung doi:10.1063/1.1375143 Physics of Fluids, Vol. 13, No. 7. (2001), pp. 1974-1984. 2006-09-21T13:41:09-00:00 2001 Physics of Fluids 13 7 1974 1984 AIP acceleration taylor-hypothesis http://www.citeulike.org/user/l-alex/article/853054 <i>Physics of Fluids, Vol. 12, No. 12. (2000), pp. 3195-3204.</i><br /><br />The validity of Taylor's hypothesis is analyzed by comparing the root mean square (rms) values of full (Lagrangian) and inertial accelerations in an isotropic and homogeneous turbulent flow. Full, local, and inertial accelerations in turbulence were decomposed into solenoidal and potential components, which made it possible to avoid dealing, at least directly, with the pressure-gradient term in the Navier–Stokes equation. The evaluations of the correlation functions and spectra of the accelerations are presented. These evaluations have been obtained using the Batchelor [Proc. Cambridge Philos. Soc. 47, 359 (1951)] longitudinal structure function that describes statistical properties of the turbulent velocity field. This function is equally valid for both inertial and dissipative subranges. It was shown that the ratio of the rms values of the full and inertial accelerations depends on the Reynolds number R only and decreases at large R as Rlambda-1/2" align="middle">. At R of about 20 this ratio is close to 0.72. At R of 1000 the ratio is less than 0.1. The validity of Taylor's hypothesis depends on the ratio of the rms values of the accelerations. The results indicate that Taylor's hypothesis is valid for large R (exceeding about 1000) and becomes questionable at R below 100. At large R the full acceleration in homogeneous and isotropic turbulence turned out to be independent of the Reynolds number. ©2000 American Institute of Physics. Accelerations in isotropic and homogeneous turbulence and Taylor's hypothesis M Pinsky A Khain A Tsinober doi:10.1063/1.1290278 Physics of Fluids, Vol. 12, No. 12. (2000), pp. 3195-3204. 2006-09-21T13:37:52-00:00 2000 Physics of Fluids 12 12 3195 3204 AIP acceleration http://www.citeulike.org/user/l-alex/article/852712 <i>App. Sci. Res, Vol. 55 (1996), pp. 289-295.</i> On the mechanism of drag reduction in dilute polymer solutions K Hoyer A Gyr A Tsinober App. Sci. Res, Vol. 55 (1996), pp. 289-295. 2006-09-21T12:44:28-00:00 1996 App. Sci. Res 55 289 295 drag-reduction polymers http://www.citeulike.org/user/l-alex/article/778998 <i>Physics of Fluids, Vol. 16, No. 7. (2004), pp. 2704-2707.</i><br /><br />The main point of this Brief Communication is that the turbulent energy production is due to the compressing of material elements rather than stretching. This is understood in the sense that the positiveness of the turbulent energy production is due to the contribution of the term associated with the compressive (negative) eigenvalue/eigenvector of the mean strain. ©2004 American Institute of Physics. On turbulent energy production in wall bounded flows R Gurka G Hetsroni A Liberzon N Nikitin A Tsinober doi:10.1063/1.1736692 Physics of Fluids, Vol. 16, No. 7. (2004), pp. 2704-2707. 2006-07-28T22:59:59-00:00 2004 Physics of Fluids 16 7 2704 2707 AIP turbulence http://www.citeulike.org/user/l-alex/article/778996 <i>Physics of Fluids, Vol. 17, No. 9. (2005)</i><br /><br />Regions of negative turbulent kinetic energy (TKE) production are observed and studied in two different flows, namely in turbulent thermal Rayleigh-Bénard convection in a cubic cell, and in a mechanically agitated shear flow in absence of buoyancy, with a main focus on the small scale structure of the flow. The experimental investigation is performed using three-dimensional (3D) particle tracking velocimetry, which allows for measuring the three velocity components and the full tensor of velocity derivatives in a finite 3D volume. The capability to compute the TKE production term in its complete form P=–uiujSij is crucial due to the three dimensionality of the flows. A comparative analysis of four different flow situations is performed in regions with positive and negative TKE production with and without buoyancy effects. In both, convective shear flow and shear flow without buoyancy, negative TKE production is associated with the unusual, more pronounced alignment of the velocity vector u with the first eigenvector 1S" align="middle"> of the mean rate-of-strain tensor, related to the stretching eigenvalue, 1S" align="middle">, in contrast to the positive TKE production associated with the alignment with the third eigenvector (i.e., related to the negative, compressing eigenvalue). In the negative TKE production region of convective flow we find (i) increased values for mean strain, (ii) increased values of the first contribution P1 in the eigenframe of the mean rate-of-strain tensor, and decreased values of the vertical contribution to the production term in a fixed frame of reference, (iii) stronger anisotropy of u, (iv) higher levels of fluctuating strain s2 and enstrophy 2, as well as (v) higher rates of their production, –sijsjkski and ijsij, compared to the respective values in positive TKE production region. In the shear flow without buoyancy, all the mentioned quantities are lower in the negative TKE production region than in the positive TKE production region. From this we conclude that the inverse energy transfer in the shear flow case without buoyancy is associated with depletion of the field of velocity derivatives. This does not occur in the cubic Rayleigh-Bénard convection cell. In this flow, buoyancy is observed to have an effect on three levels: the field of velocity derivatives, velocity fluctuations, and the mean flow field. It is inferred that buoyancy is able to maintain a region with the negative TKE production by acting on all these levels simultaneously. ©2005 American Institute of Physics Experimental study of the structure of flow regions with negative turbulent kinetic energy production in confined three-dimensional shear flows with and without buoyancy A Liberzon B Luethi M Guala W Kinzelbach A Tsinober doi:10.1063/1.2055447 Physics of Fluids, Vol. 17, No. 9. (2005) 2006-07-28T22:58:08-00:00 2005 Physics of Fluids 17 9 AIP convection experiment