Symmetry Analysis in Linear Hydrodynamic Stability Theory: Classical and New Modes in Linear Shear

We present a symmetry classification of the linearised Navier-Stokes equations for a two-dimensional unbounded linear shear flow of an incompressible fluid. The full set of symmetries is employed to systematically derive invariant ansatz functions. The symmetry analysis grasps three approaches. Two of them are existing ones, representing the classical normal modes and the Kelvin modes, while the third is a novel approach and leads to a new closed-form solution of traveling modes, showing qualitatively different behaviour in energetics, shape and kinematics when compared to the classical approaches. The last modes are energy conserving in the inviscid case. They are localized in the cross-stream direction and periodic in the streamwise direction. As for the kinematics, they travel at constant velocity in the cross-stream direction, whilst in the streamwise direction they are accelerated by the base flow. In the viscous case, the modes break down due to damping of high wavenumber contributions

Распознавание изображений лиц на основе кластеризации

This article describes the use of clustering for face recognition image. Clustering was performed using a recurrent neural network used at two stages of the recognition process. The algorithm includes the recognition process itself perform clustering pixel brightness image, calculating image information close proximity and clustering measures to in order to obtain the cluster containing the original similar images

Study of structure and composition of micro arc lantanum-siliconincorporated calcium phosphate coatings

The lanthanum- silicon-incorporated calcium phosphate coatings on the titanium have porous X-Ray amorphous structure. The increase of the process voltage leads to the growth of thickness and structural elements and to the formation in the coatings of crystalline phases CaHPO4 and β-Ca2P2O7

DNS of a turbulent Couette flow at constant wall transpiration up to Re-tau=1000

[EN] We present a new set of direct numerical simulation data of a turbulent plane Couette flow with constant wall-normal transpiration velocity V-0, i.e. permeable boundary conditions, such that there is blowing on the lower side and suction on the upper side. Hence, there is no net change in flux to preserve periodic boundary conditions in the streamwise direction. Simulations were performed at Re-tau = 250; 500; 1000 with varying transpiration rates in the range V-0(+) approximate to 0.03 to 0.085. Additionally, a classical Couette flow case at Re-tau = 1000 is presented for comparison. As a first key result we found a considerably extended logarithmic region of the mean velocity profile, with constant indicator function kappa = 0.77 as transpiration increases. Further, turbulent intensities are observed to decrease with increasing transpiration rate. Mean velocities and intensities collapse only in the cases where the transpiration rate is kept constant, while they are largely insensitive to friction Reynolds number variations. The long and wide characteristic stationary rolls of classical turbulent Couette flow are still present for all present DNS runs. The rolls are affected by wall transpiration, but they are not destroyed even for the largest transpiration velocity case. Spectral information indicates the prevalence of the rolls and the existence of wide structures near the blowing wall. The statistics of all simulations can be downloaded from the webpage of the Chair of Fluid Dynamics.This work was supported by the German Science Foundation (DFG) under grant number OB96/39-1. S.H. was partially supported by project ENE2015-71333-R. The work of S.K. is partially supported by the 'Excellence Initiative' of the German Federal and State Governments under the umbrella of the Graduate School of Computational Engineering at TU Darmstadt. The computations of the new simulations were made possible by a generous grant of computing time from the SuperMUC Petascale System at the Leibniz Supercomputing Centre (LRZ) under project-ID pr92la.Kraheberger, S.; Hoyas, S.; Oberlack, M. (2018). DNS of a turbulent Couette flow at constant wall transpiration up to Re-tau=1000. Journal of Fluid Mechanics. 835:421-443. https://doi.org/10.1017/jfm.2017.757S421443835Komminaho, J., Lundbladh, A., & Johansson, A. V. (1996). Very large structures in plane turbulent Couette flow. Journal of Fluid Mechanics, 320(-1), 259. doi:10.1017/s0022112096007537Avsarkisov, V., Oberlack, M., & Hoyas, S. (2014). New scaling laws for turbulent Poiseuille flow with wall transpiration. Journal of Fluid Mechanics, 746, 99-122. doi:10.1017/jfm.2014.98Hamilton, J. M., Kim, J., & Waleffe, F. (1995). Regeneration mechanisms of near-wall turbulence structures. Journal of Fluid Mechanics, 287, 317-348. doi:10.1017/s0022112095000978Pope, S. B. (2000). Turbulent Flows. doi:10.1017/cbo9780511840531Kametani, Y., Fukagata, K., Örlü, R., & Schlatter, P. (2015). Effect of uniform blowing/suction in a turbulent boundary layer at moderate Reynolds number. International Journal of Heat and Fluid Flow, 55, 132-142. doi:10.1016/j.ijheatfluidflow.2015.05.019Hoyas, S., & Jiménez, J. (2006). Scaling of the velocity fluctuations in turbulent channels up to Reτ=2003. Physics of Fluids, 18(1), 011702. doi:10.1063/1.2162185Schlatter, P., & Örlü, R. (2011). Turbulent asymptotic suction boundary layers studied by simulation. Journal of Physics: Conference Series, 318(2), 022020. doi:10.1088/1742-6596/318/2/022020Moser, R. D., Kim, J., & Mansour, N. N. (1999). Direct numerical simulation of turbulent channel flow up to Reτ=590. Physics of Fluids, 11(4), 943-945. doi:10.1063/1.869966Avsarkisov, V., Hoyas, S., Oberlack, M., & García-Galache, J. P. (2014). Turbulent plane Couette flow at moderately high Reynolds number. Journal of Fluid Mechanics, 751. doi:10.1017/jfm.2014.323Kim, J., Moin, P., & Moser, R. (1987). Turbulence statistics in fully developed channel flow at low Reynolds number. Journal of Fluid Mechanics, 177, 133-166. doi:10.1017/s0022112087000892Bech, K. H., Tillmark, N., Alfredsson, P. H., & Andersson, H. I. (1995). An investigation of turbulent plane Couette flow at low Reynolds numbers. Journal of Fluid Mechanics, 286, 291-325. doi:10.1017/s0022112095000747Lam, K., & Banerjee, S. (1992). On the condition of streak formation in a bounded turbulent flow. Physics of Fluids A: Fluid Dynamics, 4(2), 306-320. doi:10.1063/1.858306Bobke, A., Örlü, R., & Schlatter, P. (2015). Simulations of turbulent asymptotic suction boundary layers. Journal of Turbulence, 17(2), 157-180. doi:10.1080/14685248.2015.1083574CHAKRABORTY, P., BALACHANDAR, S., & ADRIAN, R. J. (2005). On the relationships between local vortex identification schemes. Journal of Fluid Mechanics, 535, 189-214. doi:10.1017/s0022112005004726Hoyas, S., & Jiménez, J. (2008). Reynolds number effects on the Reynolds-stress budgets in turbulent channels. Physics of Fluids, 20(10), 101511. doi:10.1063/1.3005862Hutchins, N., & Marusic, I. (2007). Large-scale influences in near-wall turbulence. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 365(1852), 647-664. doi:10.1098/rsta.2006.1942Jeong, J., & Hussain, F. (1995). On the identification of a vortex. Journal of Fluid Mechanics, 285(-1), 69. doi:10.1017/s0022112095000462JIMÉNEZ, J., UHLMANN, M., PINELLI, A., & KAWAHARA, G. (2001). Turbulent shear flow over active and passive porous surfaces. Journal of Fluid Mechanics, 442, 89-117. doi:10.1017/s0022112001004888KITOH, O., NAKABYASHI, K., & NISHIMURA, F. (2005). Experimental study on mean velocity and turbulence characteristics of plane Couette flow: low-Reynolds-number effects and large longitudinal vortical structure. Journal of Fluid Mechanics, 539(-1), 199. doi:10.1017/s0022112005005641Lee, M., & Moser, R. D. (2015). Direct numerical simulation of turbulent channel flow up to. Journal of Fluid Mechanics, 774, 395-415. doi:10.1017/jfm.2015.268Lele, S. K. (1992). Compact finite difference schemes with spectral-like resolution. Journal of Computational Physics, 103(1), 16-42. doi:10.1016/0021-9991(92)90324-rPIROZZOLI, S., BERNARDINI, M., & ORLANDI, P. (2011). Large-scale motions and inner/outer layer interactions in turbulent Couette–Poiseuille flows. Journal of Fluid Mechanics, 680, 534-563. doi:10.1017/jfm.2011.186Spalart, P. R., Moser, R. D., & Rogers, M. M. (1991). Spectral methods for the Navier-Stokes equations with one infinite and two periodic directions. Journal of Computational Physics, 96(2), 297-324. doi:10.1016/0021-9991(91)90238-gTsukahara, T., Kawamura, H., & Shingai, K. (2006). DNS of turbulent Couette flow with emphasis on the large-scale structure in the core region. Journal of Turbulence, 7, N19. doi:10.1080/14685240600609866Zhapbasbaev, U. K., & Isakhanova, G. Z. (1998). Developed turbulent flow in a plane channel with simultaneous injection through one porous wall and suction through the other. Journal of Applied Mechanics and Technical Physics, 39(1), 53-59. doi:10.1007/bf02467997DEL LAMO, J. C., JIMNEZ, J., ZANDONADE, P., & MOSER, R. D. (2004). Scaling of the energy spectra of turbulent channels. Journal of Fluid Mechanics, 500, 135-144. doi:10.1017/s002211200300733xKitoh, O., & Umeki, M. (2008). Experimental study on large-scale streak structure in the core region of turbulent plane Couette flow. Physics of Fluids, 20(2), 025107. doi:10.1063/1.2844476Del ÁLAMO, J. C., JIMÉNEZ, J., ZANDONADE, P., & MOSER, R. D. (2006). Self-similar vortex clusters in the turbulent logarithmic region. Journal of Fluid Mechanics, 561, 329. doi:10.1017/s0022112006000814Sumitani, Y., & Kasagi, N. (1995). Direct numerical simulation of turbulent transport with uniform wall injection and suction. AIAA Journal, 33(7), 1220-1228. doi:10.2514/3.12363Tillmark, N. 1995 Experiments on transition and turbulence in plane Couette flow. PhD thesis, KTH, Royal Institute of Technology.Pirozzoli, S., Bernardini, M., & Orlandi, P. (2014). Turbulence statistics in Couette flow at high Reynolds number. Journal of Fluid Mechanics, 758, 327-343. doi:10.1017/jfm.2014.52

Прибор для измерения параметров магнитопровода бетатрона

В данной выпускной квалификационной работе рассмотрен способ контроля параметров центральных вкладышей малогабаритного бетатрона. На основании теоретических данных и экспериментально полученных зависимостей был разработан прибор, позволяющий оценивать качество изготовления центральных вкладышей магнитопроводящей системы бетатрона. В основе принципа работы прибора лежит способ определение добротности колебательного контура по скорости затухания его электрических колебаний.The method of controlling the parameters of the central inserts block of a betatron was considered in this final qualifying work. The device, which can measure the quality of manufacturing of central inserts block of the magnetic system of the betatron, was developed on the basis of theoretical data and experimentally obtained dependences. The principle of operation of the device is based on the method for determining the quality factor of an oscillating circuit in terms of the rate of damping of its electric oscillations

On Endogenous Fissility of Argillites within Carbonous Deposits Of Donbass

Based on direct numerical simulations of forced turbulence, shear turbulence, decaying turbulence, a turbulent channel flow as well as a Kolmogorov flow with Taylor-based Reynolds numbers Reλ between 69 and 295, the normalized probability density function of the length distribution P(l) of dissipation elements, the conditional mean scalar difference Δkl at the extreme points as well as the scaling of the two-point velocity difference along gradient trajectories Δun are studied. Using the field of the instantaneous turbulent kinetic energy k as a scalar, we find good agreement between the model equation for P(l) as proposed by Wang and Peters (2008 J. Fluid Mech. 608 113–38) and the results obtained in the different direct numerical simulation cases. This confirms the independence of the model solution from both the Reynolds number and the type of turbulent flow, so that it can be considered universally valid. In addition, we show a 2/3 scaling for the mean conditional scalar difference. In the second part of the paper, we examine the scaling of the conditional two-point velocity difference along gradient trajectories. In particular, we compare the linear s/τ scaling, where τ denotes an integral time scale and s the separation arclength along a gradient trajectory in the inertial range as derived by Wang (2009 Phys. Rev. E 79 046325) with the sa∞ scaling, where a∞ denotes the asymptotic value of the conditional mean strain rate of large dissipation elements

Letter: The link between the Reynolds shear stress and the large structures of turbulent Couette-Poiseuille flow

[EN] The length and width of the long and wide structures appearing in turbulent Couette flows are studied by means of a new dataset of direct numerical simulation covering a stepped transition from pure Couette flow to pure Poiseuille one, at Re-tau approximate to 130, based on the stationary wall. The existence of these structures is linked to the averaged Reynolds stress, (uv) over bar : as soon as in any part of the channel (uv) over bar changes its sign, the structures disappear. The length and width of the rolls are found to be, approximately, 50h and 2.5h, respectively. For this Reynolds number, simulations with a domain shorter than 100h cannot properly describe the behaviour of the longest structures of the flow.This work was supported by MINECO, under Project No. ENE2015-71333-R. The work of M. Oberlack was supported by the German Research Foundation (DFG) under the Grant No. OB96/39-1. The computations of the new simulations were made possible by a generous grant of computing time from the Supercomputing centre of the Universitat Politecnica de Valencia. We are grateful to Mr. Simon Hoyas for fruitful conversations about the paper.Gandía-Barberá, S.; Hoyas, S.; Oberlack, M.; Kraheberger, S. (2018). Letter: The link between the Reynolds shear stress and the large structures of turbulent Couette-Poiseuille flow. Physics of Fluids. 30(4):1-4. https://doi.org/10.1063/1.5028324S1430

Wall turbulence at high friction Reynolds numbers

[EN] A new direct numerical simulation of a Poiseuille channel flow has been conducted for a friction Reynolds number of 10000, using the pseudospectral code LISO. The mean streamwise velocity presents a long logarithmic layer, extending from 400 to 2500 wall units, longer than it was thought. The maximum of the intensity of the streamwise velocity increases with the Reynolds number, as expected. Also, the elusive second maximum of this intensity has not appeared yet. In case it exists, its location will be around y(+) approximate to 120, for a friction Reynolds number extrapolated to approximately 13 500. The small differences in the near-wall gradient of this intensity for several Reynolds numbers are related to the scaling failure of the dissipation, confirming this hypothesis. The scaling of the turbulent budgets in the center of the channel is almost perfect above 1000 wall units. Finally, the peak of the pressure intensity grows with the Reynolds number and does not scale in wall units. If the pressure at the wall is modeled as an inverse quadratic power of Re-tau, then p(infinity)'(+) approximate to 4.7 at the limit of infinite Reynolds number.The authors gratefully acknowledge computing time provided by the Gauss Centre for Supercomputing e.V. on the GCS Supercomputer SuperMUC-NG at Leibniz Supercomputing Centre under Project No. pr92la, on the supercomputer Lichtenberg II at TU Darmstadt under Project No. project00072, and on the supercomputer CLAIX-2018 at RWTH-Aachen, Project No. bund0008. We are thankful to Mr. Monkewitz for providing us a copy of his model. S.K. and M.O. acknowledge funding by the German Research Foundation (DFG) through the Project No. OB96/39-1 and OB96/48-1. S.H. and F.A.A. were supported by Contract No. RTI2018-102256-B-I00 of MINECO/FEDER. F.A.A. is partially funded by GVA/FEDER Project No. ACIF2018. Finally, the authors thank Paul Hollmann for corrections with Latex.Hoyas, S.; Oberlack, M.; Alcántara-Ávila, F.; Kraheberger, SV.; Laux, J. (2022). Wall turbulence at high friction Reynolds numbers. Physical Review Fluids. 7(1):1-10. https://doi.org/10.1103/PhysRevFluids.7.0146021107