Artykuły w czasopismach: „Transitional channel flow”

1

Hager, Willi H. "Transitional Flow in Channel Junctions". Journal of Hydraulic Engineering 115, nr 2 (luty 1989): 243–59. http://dx.doi.org/10.1061/(asce)0733-9429(1989)115:2(243).

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Kumar, Sampath G. "Transitional flow in channel junctions". Journal of Hydraulic Research 31, nr 5 (wrzesień 1993): 601–4. http://dx.doi.org/10.1080/00221689309498773.

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ELSNAB, J., J. KLEWICKI, D. MAYNES i T. AMEEL. "Mean dynamics of transitional channel flow". Journal of Fluid Mechanics 678 (3.05.2011): 451–81. http://dx.doi.org/10.1017/jfm.2011.120.

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The redistribution of mean momentum and vorticity, along with the mechanisms underlying these redistribution processes, is explored for post-laminar flow in fully developed, pressure driven, channel flow. These flows, generically referred to as transitional, include an instability stage and a nonlinear development stage. The central focus is on the nonlinear development stage. The present analyses use existing direct numerical simulation data sets, as well as recently reported high-resolution molecular tagging velocimetry measurements. Primary considerations stem from the emergence of the effects of turbulent inertia as represented by the Reynolds stress gradient in the mean differential statement of dynamics. The results describe the flow evolution following the formation of a non-zero Reynolds stress peak that is known to first arise near the critical layer of the most unstable disturbance. The positive and negative peaks in the Reynolds stress gradient profile are observed to undergo a relative movement toward both the wall and centreline for subsequent increases in Reynolds number. The Reynolds stress profiles are shown to almost immediately exhibit the same sequence of curvatures that exists in the fully turbulent regime. In the transitional regime, the outer inflection point in this profile physically indicates a localized zone within which the mean dynamics are dominated by inertia. These observations connect to recent theoretical findings for the fully turbulent regime, e.g. as described by Fife, Klewicki & Wei (J. Discrete Continuous Dyn. Syst., vol. 24, 2009, p. 781) and Klewicki, Fife & Wei (J. Fluid Mech., vol. 638, 2009, p. 73). In accord with momentum equation analyses at higher Reynolds number, the present observations provide evidence that a logarithmic mean velocity profile is most rapidly approximated on a sub-domain located between the zero in the Reynolds stress gradient (maximum in the Reynolds stress) and the outer region location of the maximal Reynolds stress gradient (inflection point in the Reynolds stress profile). Overall, the present findings provide evidence that the dynamical processes during the post-laminar regime and those operative in the high Reynolds number regime are connected and describable within a single theoretical framework.

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4

Manneville, Paul, i Masaki Shimizu. "Transitional Channel Flow: A Minimal Stochastic Model". Entropy 22, nr 12 (29.11.2020): 1348. http://dx.doi.org/10.3390/e22121348.

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In line with Pomeau’s conjecture about the relevance of directed percolation (DP) to turbulence onset/decay in wall-bounded flows, we propose a minimal stochastic model dedicated to the interpretation of the spatially intermittent regimes observed in channel flow before its return to laminar flow. Numerical simulations show that a regime with bands obliquely drifting in two stream-wise symmetrical directions bifurcates into an asymmetrical regime, before ultimately decaying to laminar flow. The model is expressed in terms of a probabilistic cellular automaton of evolving von Neumann neighborhoods with probabilities educed from a close examination of simulation results. It implements band propagation and the two main local processes: longitudinal splitting involving bands with the same orientation, and transversal splitting giving birth to a daughter band with an orientation opposite to that of its mother. The ultimate decay stage observed to display one-dimensional DP properties in a two-dimensional geometry is interpreted as resulting from the irrelevance of lateral spreading in the single-orientation regime. The model also reproduces the bifurcation restoring the symmetry upon variation of the probability attached to transversal splitting, which opens the way to a study of the critical properties of that bifurcation, in analogy with thermodynamic phase transitions.

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5

Sahan, R. A., H. Gunes i A. Liakopoulos. "A modeling approach to transitional channel flow". Computers & Fluids 27, nr 1 (styczeń 1998): 121–36. http://dx.doi.org/10.1016/s0045-7930(97)00016-9.

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6

Piomelli, Ugo, i Thomas A. Zang. "Large-eddy simulation of transitional channel flow". Computer Physics Communications 65, nr 1-3 (kwiecień 1991): 224–30. http://dx.doi.org/10.1016/0010-4655(91)90175-k.

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Kashyap, Pavan, Yohann Duguet i Olivier Dauchot. "Flow Statistics in the Transitional Regime of Plane Channel Flow". Entropy 22, nr 9 (8.09.2020): 1001. http://dx.doi.org/10.3390/e22091001.

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The transitional regime of plane channel flow is investigated above the transitional point below which turbulence is not sustained, using direct numerical simulation in large domains. Statistics of laminar-turbulent spatio-temporal intermittency are reported. The geometry of the pattern is first characterized, including statistics for the angles of the laminar-turbulent stripes observed in this regime, with a comparison to experiments. High-order statistics of the local and instantaneous bulk velocity, wall shear stress and turbulent kinetic energy are then provided. The distributions of the two former quantities have non-trivial shapes, characterized by a large kurtosis and/or skewness. Interestingly, we observe a strong linear correlation between their kurtosis and their skewness squared, which is usually reported at much higher Reynolds number in the fully turbulent regime.

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8

Zagarola, Mark V., Alexander J. Smits i George E. Karniadakis. "Heat transfer enhancement in a transitional channel flow". Journal of Wind Engineering and Industrial Aerodynamics 49, nr 1-3 (grudzień 1993): 257–67. http://dx.doi.org/10.1016/0167-6105(93)90021-f.

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9

He, S., i M. Seddighi. "Turbulence in transient channel flow". Journal of Fluid Mechanics 715 (9.01.2013): 60–102. http://dx.doi.org/10.1017/jfm.2012.498.

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AbstractDirect numerical simulations (DNS) are performed of a transient channel flow following a rapid increase of flow rate from an initially turbulent flow. It is shown that a low-Reynolds-number turbulent flow can undergo a process of transition that resembles the laminar–turbulent transition. In response to the rapid increase of flow rate, the flow does not progressively evolve from the initial turbulent structure to a new one, but undergoes a process involving three distinct phases (pre-transition, transition and fully turbulent) that are equivalent to the three regions of the boundary layer bypass transition, namely, the buffeted laminar flow, the intermittent flow and the fully turbulent flow regions. This transient channel flow represents an alternative bypass transition scenario to the free-stream-turbulence (FST) induced transition, whereby the initial flow serving as the disturbance is a low-Reynolds-number turbulent wall shear flow with pre-existing streaky structures. The flow nevertheless undergoes a ‘receptivity’ process during which the initial structures are modulated by a time-developing boundary layer, forming streaks of apparently specific favourable spacing (of about double the new boundary layer thickness) which are elongated streamwise during the pre-transitional period. The structures are stable and the flow is laminar-like initially; but later in the transitional phase, localized turbulent spots are generated which grow spatially, merge with each other and eventually occupy the entire wall surfaces when the flow becomes fully turbulent. It appears that the presence of the initial turbulent structures does not promote early transition when compared with boundary layer transition of similar FST intensity. New turbulent structures first appear at high wavenumbers extending into a lower-wavenumber spectrum later as turbulent spots grow and join together. In line with the transient energy growth theory, the maximum turbulent kinetic energy in the pre-transitional phase grows linearly but only in terms of ${u}^{\ensuremath{\prime} } $, whilst ${v}^{\ensuremath{\prime} } $ and ${w}^{\ensuremath{\prime} } $ remain essentially unchanged. The energy production and dissipation rates are very low at this stage despite the high level of ${u}^{\ensuremath{\prime} } $. The pressure–strain term remains unchanged at that time, but increases rapidly later during transition along with the generation of turbulent spots, hence providing an unambiguous measure for the onset of transition.

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10

Wirtz, R. A., i Weiming Chen. "Laminar-Transitional Convection From Repeated Ribs in a Channel". Journal of Electronic Packaging 114, nr 1 (1.03.1992): 29–34. http://dx.doi.org/10.1115/1.2905438.

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Velocimetry, heat transfer, and pressure drop experiments are reported for laminar/transitional air flow in a channel containing rectangular transverse ribs located along one channel wall. The geometry is intended to represent an array of low profile electronic packages. At fixed pumping power per unit channel volume, the heat transfer rate per unit volume is independent of rib-to-rib spacing and increases with decreasing wall-to-wall spacing. The fully developed, rib-average heat transfer coefficient is found to be linearly related to the maximum streamwise rms turbulence measured above the rib-tops. Linear correlations, in terms of a descriptor of the rms streamwise turbulence, are shown to unify heat transfer/pressure drop data for channels containing either two-or three-dimensional protrusions.

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11

Ligrani, P. M., i C. R. Hedlund. "Experimental Surface Heat Transfer and Flow Structure in a Curved Channel With Laminar, Transitional, and Turbulent Flows". Journal of Turbomachinery 126, nr 3 (1.07.2004): 414–23. http://dx.doi.org/10.1115/1.1738119.

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Heat transfer and flow structure are described in a channel with a straight portion followed by a portion with mild curvature at Dean numbers from 100 to 1084. The channel aspect ratio is 40, radius ratio is 0.979, and the ratio of shear layer thickness to channel inner radius is 0.011. The data presented include flow visualizations, and spanwise-averaged Nusselt numbers. Also included are time-averaged turbulence structural data, time-averaged profiles of streamwise velocity, spectra of longitudinal velocity fluctuations, and a survey of the radial time-averaged vorticity component. Different flow events are observed including laminar two-dimensional flow, Dean vortex flow, wavy Dean vortex flow (in both undulating and twisting modes), splitting and merging of Dean vortex pairs, transitional flow with arrays of Dean vortex pairs, and fully turbulent flow with arrays of Dean vortex pairs. Transitional events generally first appear in the curved portion of the channel at Dean numbers less than 350 in the form of arrays of counterrotating Dean vortex pairs. At Dean numbers greater than 350, transitional events occur in the upstream straight portion of the channel but then continue to cause important variations in the downstream curved portion. The resulting Nusselt number variations with curvature, streamwise development, and Dean number are described as they are affected by these different laminar, transitional, and turbulent flow phenomena.

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12

Garretón, Gonzalo, Lindley Maxwell i Iván Cornejo. "Transition of the Flow Regime Inside of Monolith Microchannel Reactors Fed with Highly Turbulent Flow". Catalysts 13, nr 6 (26.05.2023): 938. http://dx.doi.org/10.3390/catal13060938.

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This paper investigates the flow behaviour of monolith microchannels. Specifically, the study characterizes the flow regime within in-series monolith channels where highly turbulent flow approaches them but inside of the channels, the Reynolds number is subcritical. Results from LES and a transitional RANS model are compared to those obtained when directly assuming laminar flow inside of the channels. A space-resolved model of channels placed in series and channel Reynolds numbers ranging from 50 to 300 are considered. The results show that the flow pattern in is almost identical in the two channels and that the frequency of fluctuations tends to increase with the Reynolds number. The flow regime in both channels is unsteady laminar, containing a wide spectrum of frequencies. The tested transitional RANS model (k-kL-ω) is unable to capture the velocity fluctuations predicted by LES. Despite the differences in the velocity field prediction, the pressure drop estimation from all models is practically the same. This study provides insights into the flow behaviour of monolith reactors and is useful for reactor design and optimization.

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13

Majumdar, D., i C. H. Amon. "Oscillatory Momentum Transport Mechanisms in Transitional Complex Geometry Flows". Journal of Fluids Engineering 119, nr 1 (1.03.1997): 29–35. http://dx.doi.org/10.1115/1.2819114.

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This work reports direct numerical simulations of transitional flows in communicating channels. Above a critical Reynolds number, the flow becomes fluctuating and self-sustained with vortical motions temporally synchronized with channel traveling waves. The energy transfer mechanism between the mean and the fluctuating flow is investigated along with the distributions of oscillatory shear stress and transitional viscosity. The kinetic energy equation for the fluctuating velocity is solved from DNS data to evaluate the contributions of the production term, viscous dissipation, work of dynamic pressure and work of viscous shear stresses.

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14

Sahan, R. A., A. Liakopoulos i H. Gunes. "Reduced dynamical models of nonisothermal transitional grooved-channel flow". Physics of Fluids 9, nr 3 (marzec 1997): 551–65. http://dx.doi.org/10.1063/1.869218.

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15

Wang, Sung-Ning, Ashwin Shekar i Michael D. Graham. "Spatiotemporal dynamics of viscoelastic turbulence in transitional channel flow". Journal of Non-Newtonian Fluid Mechanics 244 (czerwiec 2017): 104–22. http://dx.doi.org/10.1016/j.jnnfm.2017.04.008.

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16

Masaharu, Matsubara, Miyazaki Makoto, Watanabe Kenta, Kvick Mathias, Lundell Fredrik i Soderberg Daniel. "1222 Effect of nano-fibrillated cellulose suspension on transitional two-dimensional channel flow". Proceedings of the International Conference on Jets, Wakes and Separated Flows (ICJWSF) 2013.4 (2013): _1222–1_—_1222–5_. http://dx.doi.org/10.1299/jsmeicjwsf.2013.4._1222-1_.

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17

Guzmán, A. M., i C. H. Amon. "Dynamical flow characterization of transitional and chaotic regimes in converging–diverging channels". Journal of Fluid Mechanics 321 (25.08.1996): 25–57. http://dx.doi.org/10.1017/s002211209600763x.

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Numerical investigation of laminar, transitional and chaotic flows in converging–diverging channels are performed by direct numerical simulations in the Reynolds number range 10 < Re < 850. The temporal flow evolution and the onset of turbulence are investigated by combining classical fluid dynamics representations with dynamical system flow characterizations. Modern dynamical system techniques such as timedelay reconstructions of pseudophase spaces, autocorrelation functions, fractal dimensions and Eulerian Lyapunov exponents are used for the dynamical flow characterization of laminar, transitional and chaotic flow regimes. As a consequence of these flow characterizations, it is verified that the transitional flow evolves through intermediate states of periodicity, two-frequency quasi-periodicity, frequency-locking periodicity, and multiple-frequency quasi-periodicity before reaching a non-periodic unpredictable behaviour corresponding to low-dimensional deterministic chaos.Qualitative and quantitative differences in Eulerian dynamical flow parameters are identified to determine the predictability of transitional flows and to characterize chaotic, weak turbulent flows in converging–diverging channels. Autocorrelation functions, pseudophase space representations and Poincaré maps are used for the qualitative identification of chaotic flows, assertion of their unpredictable nature, and recognition of the topological structure of the attractors for different flow regimes. The predictability of transitional flows is determined by analysing the autocorrelation functions and by representing their attractors in the reconstructed pseudophase spaces. The transitional flow behaviour is examined by the geometric visualization of the evolution of the attractors and Poincaré maps until the appearance of a strange attractor at the onset of chaos. Eulerian Lyapunov exponents and fractal dimensions are quantitative parameters to establish the onset of chaos, the persistence of chaotic flow behaviour, and the long-term persistent unpredictability of chaotic Eulerian flow regimes. Lastly, three-dimensional simulations for converging–diverging channel flow are performed to determine the effect of the spanwise direction on the route of transition to chaos.

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Ilak, Miloš, i Clarence W. Rowley. "Modeling of transitional channel flow using balanced proper orthogonal decomposition". Physics of Fluids 20, nr 3 (marzec 2008): 034103. http://dx.doi.org/10.1063/1.2840197.

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19

Ting, D. S. K. "TEMPERATURE FLUCTUATION MEASUREMENTS FOR TRANSITIONAL FLOW IN A SQUARE CHANNEL". Experimental Heat Transfer 9, nr 4 (październik 1996): 357–70. http://dx.doi.org/10.1080/08916159608946530.

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Baker, James, i Panagiotis D. Christofides. "Drag reduction in transitional linearized channel flow using distributed control". International Journal of Control 75, nr 15 (styczeń 2002): 1213–18. http://dx.doi.org/10.1080/00207170210163631.

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ISHIBASHI, Tomohiro, Genta KAWAHARA, Masaki SHIMIZU i Shingo MOTOKI. "Dissimilarity between heat and momentum transfer in transitional channel flow". Proceedings of Mechanical Engineering Congress, Japan 2019 (2019): J05117P. http://dx.doi.org/10.1299/jsmemecj.2019.j05117p.

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NISHIMURA, TATSUO, YOSHIHIKO KAJIMOTO, ATSUSHI TARUMOTO i YUJI KAWAMURA. "Flow structure and mass transfer for a wavy channel in transitional flow regime." Journal of Chemical Engineering of Japan 19, nr 5 (1986): 449–55. http://dx.doi.org/10.1252/jcej.19.449.

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SCHÄFER, F., M. BREUER i F. DURST. "The dynamics of the transitional flow over a backward-facing step". Journal of Fluid Mechanics 623 (6.03.2009): 85–119. http://dx.doi.org/10.1017/s0022112008005235.

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The internal flow over a backward-facing step in the transitional regime (ReD = 6000) was studied based on direct numerical simulations. The predictions were carried out with the help of a finite-volume Navier–Stokes solver equipped with a co-visualization facility which allows one to investigate the flow dynamics at high temporal resolution. First, grid-induced oscillations were precluded by a careful grid design. Second, the strong influence of the velocity profile approaching the step was studied and outlined. The main objective, however, was to provide a comprehensive insight into the dynamic flow behaviour, especially oscillations of the reattachment length of the primary recirculation region. The origin of this well-known flapping behaviour of the reattachment line is not yet completely understood. In the present work, the mechanisms leading to the oscillations of the reattachment length were extensively investigated by analysing the time-dependent flow. Besides the oscillations of the primary recirculation region, oscillations of the separation and the reattachment line of the secondary recirculation bubble at the upper channel wall were also observed. The results clearly show that in the present flow case the flapping of the primary reattachment and the secondary separation line is due to vortical structures in the unstable shear layers between the main flow and the recirculation bubbles. Vortices emerging in the shear layers and sweeping downstream convectively induce small zones of backward-flowing fluid at the channel walls while passing the recirculation regions. In the case of the primary recirculation region, the rotational movement of the shear-layer vortices impinging on the lower channel wall was found to cause zones of negative fluid velocity at the end of the recirculation bubble and thus flapping of the reattachment line. In contrast, in the case of the secondary recirculation region, the shear-layer vortices moved away from the upper channel wall so that their rotational movement did not reach the boundary. In this case, the pressure gradients originating from local pressure minima located in the shear-layer vortices were identified as being responsible for the oscillations of the separation line at the upper channel wall. While moving downstream with the shear-layer vortices, the pressure gradients were found to influence the top boundary of the channel and create alternating zones of forward- and backward-flowing fluid along the wall. All of these unsteady processes can best be seen from animations which are provided on the Journal of Fluid Mechanics website: journals.cambridge.org/FLM.

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Takeishi, Keisuke, Genta Kawahara, Hiroki Wakabayashi, Markus Uhlmann i Alfredo Pinelli. "Localized turbulence structures in transitional rectangular-duct flow". Journal of Fluid Mechanics 782 (8.10.2015): 368–79. http://dx.doi.org/10.1017/jfm.2015.546.

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Direct numerical simulations of transitional flow in a rectangular duct of cross-sectional aspect ratio $A\equiv s/h=1$–9 ($s$ and $h$ being the duct half-span and half-height, respectively) have been performed in the Reynolds number range $\mathit{Re}\equiv u_{b}h/{\it\nu}=650$–1500 ($u_{b}$ and ${\it\nu}$ being the bulk velocity and the kinematic viscosity, respectively) in order to investigate the dependence on the aspect ratio of spatially localized turbulence structures. It was observed that the lowest Reynolds number $\mathit{Re}_{T}$, estimated in a specific way, for localized (transiently sustaining) turbulence decreases monotonically from $\mathit{Re}_{T}=730$ for $A=1$ (square duct) with increasing aspect ratio, and for $A=5$ it nearly attains a minimal value $\mathit{Re}_{T}\approx 670$ that is consistent with the onset Reynolds number of turbulent spots in a plane channel ($A=\infty$). Turbulent states consist of localized structures that undergo a fundamental change around $A=4$. At $\mathit{Re}=\mathit{Re}_{T}$ turbulence for $A=1$–$3$ is streamwise-localized similar to turbulent puffs in pipe flow, while for $A=5$–9 turbulence at $\mathit{Re}=\mathit{Re}_{T}$ is also localized in the spanwise direction, similar to turbulent spots in plane channel flow. This structural change in turbulent states at $\mathit{Re}=\mathit{Re}_{T}$ is attributed to the exclusion of turbulence from the vicinity of the duct sidewalls in the case of a wide duct with $A\gtrsim 4$: here the friction length on the sidewalls is so long that the size (around 100 times the friction length) of a self-sustaining minimal flow unit of streamwise vortices and streaks is larger than the duct height and, therefore, it cannot be accommodated.

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Ma, Jing-Tao, Yuan-Qing Xu i Xiao-Ying Tang. "A Numerical Simulation of Cell Separation by Simplified Asymmetric Pinched Flow Fractionation". Computational and Mathematical Methods in Medicine 2016 (2016): 1–8. http://dx.doi.org/10.1155/2016/2564584.

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As a typical microfluidic cell sorting technique, the size-dependent cell sorting has attracted much interest in recent years. In this paper, a size-dependent cell sorting scheme is presented based on a controllable asymmetric pinched flow by employing an immersed boundary-lattice Boltzmann method (IB-LBM). The geometry of channels consists of 2 upstream branches, 1 transitional channel, and 4 downstream branches (D-branches). Simulations are conducted by varying inlet flow ratio, the cell size, and the ratio of flux of outlet 4 to the total flux. It is found that, after being randomly released in one upstream branch, the cells are aligned in a line close to one sidewall of the transitional channel due to the hydrodynamic forces of the asymmetric pinched flow. Cells with different sizes can be fed into different downstream D-branches just by regulating the flux of one D-branch. A principle governing D-branch choice of a cell is obtained, with which a series of numerical cases are performed to sort the cell mixture involving two, three, or four classes of diameters. Results show that, for each case, an adaptive regulating flux can be determined to sort the cell mixture effectively.

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Zerihun, Yebegaeshet T. "Non-Hydrostatic Transitional Open-Channel Flows from a Supercritical to a Subcritical State". Slovak Journal of Civil Engineering 29, nr 2 (1.06.2021): 39–48. http://dx.doi.org/10.2478/sjce-2021-0012.

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Abstract In this study, a depth-averaged numerical model was employed to investigate the two-dimensional flow features of transitional open-channel flows from a supercritical to a subcritical state. Compared to a shallow-water model, the proposed model incorporates supplementary terms to account for the effects of non-uniform velocity and non-hydrostatic pressure distributions. The model equation was solved numerically by means of the Adams–Bashforth–Moulton scheme. A wide variety of transitional open-channel flow problems such as hydraulic jumps was considered for assessing the suitability of the numerical model. The results of the model for the free-surface profile, pressure distribution, and characteristics of the first wave of an undular jump were compared with the experimental data, and the agreement was found to be satisfactory. Despite the effects of the three-dimensional characteristics of the flow and the bulking of the flow caused by air entrainment, the model performed reasonably well with respect to the simulations of the mean flow characteristics of the curvilinear turbulent flow problems. Furthermore, the results of this investigation confirmed that the model is more suitable for analyzing near-critical turbulent flow problems without cross-channel shock waves.

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Sanvicente, E., S. Giroux-Julien, C. Ménézo i H. Bouia. "Transitional natural convection flow and heat transfer in an open channel". International Journal of Thermal Sciences 63 (styczeń 2013): 87–104. http://dx.doi.org/10.1016/j.ijthermalsci.2012.07.004.

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Dipankar, A., i T. K. Sengupta. "Symmetrized compact scheme for receptivity study of 2D transitional channel flow". Journal of Computational Physics 215, nr 1 (czerwiec 2006): 245–73. http://dx.doi.org/10.1016/j.jcp.2005.10.018.

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Abad, Jorge D., Alejandro Mendoza, Kristin Arceo, Zara Torres, Henry Valverde, Gerles Medina, Christian Frias i Moisés Berezowsky. "Planform Dynamics and Cut-Off Processes in the Lower Ucayali River, Peruvian Amazon". Water 14, nr 19 (28.09.2022): 3059. http://dx.doi.org/10.3390/w14193059.

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The Ucayali River is one of the most dynamic large rivers in the world, with high rates of channel migration regularly producing cutoffs. In the lower portion of the Ucayali River, before its confluence to the Marañon River where the Amazon River is born, the increase in water and sediment discharge triggers bends with secondary channels (transitional stage from purely meandering to anabranching), which influence the planform migration rates and patterns of the sinuous channels. Based on remote sensing analysis, a comparison of planform dynamics of bends with and without secondary channels is presented. For the case of a bend with secondary channels (Jenaro Herrera, JH), detailed field measurements for bed morphology, hydrodynamics, bed and suspended load are performed for low-, transitional- and high-flow conditions (August, February and May, respectively). Additionally, a two-dimensional depth average hydraulic model is utilized to correlate observed migrating patterns with the hydrodynamics. Results indicate that the secondary channels have disrupted typical planform migration rates of the main meandering channel. However, at high amplitudes, these secondary channels reduce their capacity to capture flow and start a narrowing process, which in turn increases migration rates of the main channels (meandering reactivation process), suggesting that an imminent cutoff along the JH bend is underway by pure lateral migration or by the collapse into the existing paleochannels.

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TANAKA, Ichiro, Jiro SUZUKI i Saburo YAMADA. "Heat Transfer and Flow Features of Intermittent Flow Structure Arising in Channel Flow for Transitional Regime". Proceedings of Conference of Kansai Branch 2017.92 (2017): 702. http://dx.doi.org/10.1299/jsmekansai.2017.92.702.

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Guo, Qiaozhen, Jinmiao Tan, Daoqing Li, Hao Lan, Peng Qiu, Tao Xu, Tingbin Sun i Wen Yin. "Grain Size Curve Characteristics of 2nd Member of Sangonghe Formation in Qianshao Area and Its Indicative Significance of Hydrodynamic Environment". Applied Sciences 12, nr 19 (30.09.2022): 9852. http://dx.doi.org/10.3390/app12199852.

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There are mainly two sedimentary types of the 2nd member of Jurassic Sangonghe Formation (J1s2) in the Qianshao area: shallow-water delta and sandy debris flow. In order to accurately understand the characteristics and further identify the difference of sedimentary microfacies, the characteristics of the grain size curve are analyzed. The results show that the cumulative probability curve of sandstone particle size in the research area mainly includes two basic types: tractive current type and sandy debris flow type. The tractive current type is mainly developed in the shallow-water delta front. Among them, the inner front subaqueous distributary channel microfacies develop two patterns: tri-segment pattern and one bouncing segment-one suspension segment-one complex transitional zone pattern. The transitional section is widely developed. There are two patterns in the subaqueous distributary channel microfacies of the outer front (bi-segment pattern and one bouncing segment-one suspension segment-one transitional zone pattern) and two patterns in the estuary bar microfacies (bi-bouncing segment-one suspension segment-one transitional zone pattern and one bouncing segment-one suspension segment-one transitional zone pattern). The main tractive current characteristics are higher bouncing component content and slope and lower suspended component content. The sand debris flow type mainly develops two patterns: one bouncing segment-one suspension segment-one transitional zone pattern and one bouncing segment-one suspension segment-one complex transitional zone pattern with lower jump component content and slope and higher suspended component content.

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Burmistrov, A. V., S. I. Salikeev i A. A. Raykov. "Simulation of Gas Flow in Channels with Variable Cross-Section at Different Flow Modes using Lattice Boltzmann Method (LBM)". Herald of the Bauman Moscow State Technical University. Series Mechanical Engineering, nr 6 (129) (grudzień 2019): 105–15. http://dx.doi.org/10.18698/0236-3941-2019-6-105-115.

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All contact-free vacuum pumps operate in a very wide pressure range. Therefore, the calculation of flows through the slot channels is associated with the need to take into account the laws of all three modes of gas flow: viscous, transitional and molecular. Most of channels of contact-free pumps are formed by curved walls, which are slits of variable cross-section in the direction of gas flow, having a minimum gap in some place. The paper considers the basic methods of calculating flows in channels of variable cross-section: the Monte Carlo method for molecular mode, the numerical solution of Navier --- Stokes equations for viscous mode and the Lattice Boltzmann method (LBM) for a wide range of pressures. The results of gas flow simulation calculated in COMSOL Multiphysics with LBM method are presented. The influence of the gas flow mode on the velocity profile in the channel is discussed. Based on the simulation results, the conductivity of channels of different geometries was calculated at various pressures at the inlet and outlet of the channel. The graphs of conductivity dependence on the Knudsen number for the method of angular coefficients, the model of lattice Boltzmann equations and experimental data are presented. It is shown that for slit channels of variable cross-section, the LBM model agrees well with the experiment under any gas flow modes.

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33

Kordi, E., S. A. Ayyoubzadeh, M. Z. Ahmadi i A. Zahiri. "Prediction of the lateral flow regime and critical depth in compound open channels". Canadian Journal of Civil Engineering 36, nr 1 (styczeń 2009): 1–13. http://dx.doi.org/10.1139/l08-095.

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In this study, the common critical depth calculation in compound channels has been modified considering the effect of momentum transfer between the interface of a main channel and its floodplains. In noncorrected specific energy curves of a given slope, the flow is not necessarily entirely sub- or supercritical as it is in a single cross section and there is a possibility of both flow regimes at a certain stage, called the lateral mixed flow regimes, which makes the application of specific energy equation to determine the critical depth and transitional zone calculations questionable. In the present research, the flow distribution in a main channel and floodplains has been corrected by combining the corrected hydraulic flow in compound cross sections using the coherence method. The specific energy has been subsequently modified in the subsections. The results seem satisfactory when compared with the results based on the available laboratory data.

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Lehmann, G. L., i J. Pembroke. "Forced Convection Air Cooling of Simulated Low Profile Electronic Components: Part 1—Base Case". Journal of Electronic Packaging 113, nr 1 (1.03.1991): 21–26. http://dx.doi.org/10.1115/1.2905361.

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Forced convection cooling of a simulated array of card-mounted electronic components has been investigated. An important feature of the simulated components is their relatively low profile (height/length = 0.058). Laboratory measurements of heat transfer rates resulting from convective air flow through a low aspect ratio channel are reported. The effect of variations in array position, channel spacing and flow rate is discussed. In the flow range considered laminar, transitional and turbulent heat transfer behavior have been observed. The behavior due to variations in flow rate and channel spacing is well correlated using a Reynolds number based on component length.

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Nering, Konrad, i Krzysztof Nering. "Validation of Modified Algebraic Model during Transitional Flow in HVAC Duct". Energies 14, nr 13 (2.07.2021): 3975. http://dx.doi.org/10.3390/en14133975.

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Airflow occurring in a ventilation duct is characterized by low velocity and hence low Reynolds number. In these conditions, either a laminar, transitional or turbulent flow will occur. Different flow conditions result in different values of the friction coefficient. To achieve the transitional flow in numerical simulation, a modified algebraic model for bypass transition (modified k−ω) was used. Numerical simulation was validated using Particle Tracking Velocimetry (PTV) in the circular channel. The modified algebraic model consists of only two partial differential equations, which leads to much faster calculation than the shear stress transport model. Results of the modified algebraic model are largely consistent with either the measurement and shear stress transport model considering laminar and transitional flow. Consistency slightly decreased in turbulent flow in relation to the model using shear stress transport method.

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Yamaguchi, Hiroki, Pierre Perrier, Minh Tuan Ho, J. Gilbert Méolans, Tomohide Niimi i Irina Graur. "Mass flow rate measurement of thermal creep flow from transitional to slip flow regime". Journal of Fluid Mechanics 795 (20.04.2016): 690–707. http://dx.doi.org/10.1017/jfm.2016.234.

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Measurements of the thermal creep flow through a single rectangular microchannel connected to two tanks maintained initially at the same pressure, but at different temperatures, are carried out for five noble gas species, over a large range of pressure and for two temperature differences between the tanks. The time-dependent pressure variations in both cold and hot tanks are investigated, and the temperature-driven (thermal creep) mass flow rate between two tanks is calculated from these data for the rarefaction parameter ranging from the transitional to slip flow regime. The measured mass flow rate is compared with the numerical solution of the S-model kinetic equation, and they show good agreement. A novel approximate expression to calculate the temperature-driven mass flow rate in the transitional and slip flow regimes is proposed. This expression provides results in good agreement with the measured values of the mass flow rate. In the slip flow regime, the thermal slip coefficient is calculated by employing the previously reported methodology, and the influence of the nature of the gas on this coefficient is investigated. The measured values of the thermal slip coefficient agree well with the values available in the literature, indicating that this coefficient is independent of the shape of a channel.

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Beratlis, N., E. Balaras, B. Parvinian i K. Kiger. "A Numerical and Experimental Investigation of Transitional Pulsatile Flow in a Stenosed Channel". Journal of Biomechanical Engineering 127, nr 7 (15.08.2005): 1147–57. http://dx.doi.org/10.1115/1.2073628.

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In the present paper, a closely coupled numerical and experimental investigation of pulsatile flow in a prototypical stenotic site is presented. Detailed laser Doppler velocimetry measurements upstream of the stenosis are used to guide the specification of velocity boundary conditions at the inflow plane in a series of direct numerical simulations (DNSs). Comparisons of the velocity statistics between the experiments and DNS in the post-stenotic area demonstrate the great importance of accurate inflow conditions, and the sensitivity of the post-stenotic flow to the disturbance environment upstream. In general, the results highlight a borderline turbulent flow that sequentially undergoes transition to turbulence and relaminarization. Before the peak mass flow rate, the strong confined jet that forms just downstream of the stenosis becomes unstable, forcing a role-up and subsequent breakdown of the shear layer. In addition, the large-scale structures originating from the shear layer are observed to perturb the near wall flow, creating packets of near wall hairpin vortices.

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Agrawal, Rishav, Henry C. H. Ng, David J. C. Dennis i Robert J. Poole. "Investigating channel flow using wall shear stress signals at transitional Reynolds numbers". International Journal of Heat and Fluid Flow 82 (kwiecień 2020): 108525. http://dx.doi.org/10.1016/j.ijheatfluidflow.2019.108525.

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KLEWICKI, J., R. EBNER i X. WU. "Mean dynamics of transitional boundary-layer flow". Journal of Fluid Mechanics 682 (19.07.2011): 617–51. http://dx.doi.org/10.1017/jfm.2011.253.

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The dynamical mechanisms underlying the redistribution of mean momentum and vorticity are explored for transitional two-dimensional boundary-layer flow at nominally zero pressure gradient. The analyses primarily employ the direct numerical simulation database of Wu & Moin (J. Fluid Mech., vol. 630, 2009, p. 5), but are supplemented with verifications utilizing subsequent similar simulations. The transitional regime is taken to include both an instability stage, which effectively generates a finite Reynolds stress profile, −ρuv(y), and a nonlinear development stage, which progresses until the terms in the mean momentum equation attain the magnitude ordering of the four-layer structure revealed by Wei et al. (J. Fluid Mech., vol. 522, 2005, p. 303). Self-consistently applied criteria reveal that the third layer of this structure forms first, followed by layers IV and then II and I. For the present flows, the four-layer structure is estimated to be first realized at a momentum thickness Reynolds number Rθ = U∞ θ/ν ≃ 780. The first-principles-based theory of Fife et al. (J. Disc. Cont. Dyn. Syst. A, vol. 24, 2009, p. 781) is used to describe the mean dynamics in the laminar, transitional and four-layer regimes. As in channel flow, the transitional regime is marked by a non-negligible influence of all three terms in the mean momentum equation at essentially all positions in the boundary layer. During the transitional regime, the action of the Reynolds stress gradient rearranges the mean viscous force and mean advection profiles. This culminates with the segregation of forces characteristic of the four-layer regime. Empirical and theoretical evidence suggests that the formation of the four-layer structure also underlies the emergence of the mean dynamical properties characteristic of the high-Reynolds-number flow. These pertain to why and where the mean velocity profile increasingly exhibits logarithmic behaviour, and how and why the Reynolds stress distribution develops such that the inner normalized position of its peak value, ym+, exhibits a Reynolds number dependence according to $y_m^+ {\,\simeq\,} 1.9 \sqrt{\delta^+}$.

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RANI, H. P., TONY W. H. SHEU i ERIC S. F. TSAI. "Eddy structures in a transitional backward-facing step flow". Journal of Fluid Mechanics 588 (24.09.2007): 43–58. http://dx.doi.org/10.1017/s002211200700763x.

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In the present study, flow simulation has been carried out in a backward-facing step channel defined by an expansion ratio of 2.02 and a spanwise aspect ratio of 8 to provide the physical insight into the longitudinal and spanwise flow motions and to identify the presence of Taylor–Görtler-like vortices. The Reynolds numbers have been taken as 1000 and 2000, which fall in the category of transitional flow. The present simulated results were validated against the experimental and numerical data and the comparison was found to be satisfactory. The simulated results show that the flow becomes unsteady and exhibits a three-dimensional nature with the Kelvin–Helmholtz instability oscillations and Taylor–Görtler-Like longitudinal vortices. The simulated data were analysed to give an in-depth knowledge of the complex interactions among the floor and roof eddies, and the spiralling spanwise flow motion. Destabilization of the present incompressible flow system, with the amplified Reynolds number due to the Kelvin–Helmholtz and Taylor–Görtler instabilities, is also highlighted. A movie is available with the online version of the paper.

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Khan, Mohammad Amir, Nayan Sharma, Jaan H. Pu, Faisal M. Alfaisal, Shamshad Alam, Rishav Garg i Mohammad Obaid Qamar. "Mid-Channel Braid-Bar-Induced Turbulent Bursts: Analysis Using Octant Events Approach". Water 14, nr 3 (2.02.2022): 450. http://dx.doi.org/10.3390/w14030450.

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In a laboratory, a model of a mid-channel bar is built to study the turbulent flow structures in its vicinity. The present study on the turbulent flow structure around a mid-channel bar is based on unravelling the fluvial fluxes triggered by the bar’s 3D turbulent burst phenomenon. To this end, the three-dimensional velocity components are measured with the help of acoustic doppler velocimetry (ADV). The results indicate that the transverse component of turbulent kinetic energy cannot be neglected when analyzing turbulent burst processes, since the dominant flow is three-dimensional around the mid-channel bar. Due to the three-dimensionality of flow, the octant events approach is used for analyzing the flow in the vicinity of the mid-channel bar. The aim is to develop functional relationships between the stable movements that are modelled in the present study. To find the best Markov chain order to present experimental datasets, the zero-, first-, and second-order Markov chains are analyzed using the Akaike information criterion (AIC) and the Bayesian information criterion (BIC). The parameter transition ratio has evolved in this research to reflect the linkage of streambed elevation changes with stable transitional movements. For a better understanding of the temporal behaviors of stable transitional movements, the residence time vs. frequency graphs are also plotted for scouring as well as for depositional regions. The study outcome herein underlines the usefulness of the octant events approach for characterizing turbulent bursts around mid-channel bar formation, which is a precursor to the initiation of braiding configuration.

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Kuo, Chung-Chin, Wan-Yu Chen i Ya-Chin Yang. "Block of Tetrodotoxin-resistant Na+ Channel Pore by Multivalent Cations". Journal of General Physiology 124, nr 1 (28.06.2004): 27–42. http://dx.doi.org/10.1085/jgp.200409054.

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Tetrodotoxin-resistant (TTX-R) Na+ channels are much less susceptible to external TTX but more susceptible to external Cd2+ block than tetrodotoxin-sensitive (TTX-S) Na+ channels. Both TTX and Cd2+ seem to block the channel near the “DEKA” ring, which is probably part of a multi-ion single-file region adjacent to the external pore mouth and is involved in the selectivity filter of the channel. In this study we demonstrate that other multivalent transitional metal ions such as La3+, Zn2+, Ni2+, Co2+, and Mn2+ also block the TTX-R channels in dorsal root ganglion neurons. Just like Cd2+, the blocking effect has little intrinsic voltage dependence, but is profoundly influenced by Na+ flow. The apparent dissociation constants of the blocking ions are always significantly smaller in inward Na+ currents than those in outward Na+ current, signaling exit of the blocker along with the Na+ flow and a high internal energy barrier for “permeation” of these multivalent blocking ions through the pore. Most interestingly, the activation and especially the inactivation kinetics are slowed by the blocking ions. Moreover, the gating changes induced by the same concentration of a blocking ion are evidently different in different directions of Na+ current flow, but can always be correlated with the extent of pore block. Further quantitative analyses indicate that the apparent slowing of channel activation is chiefly ascribable to Na+ flow–dependent unblocking of the bound La3+ from the open Na+ channel, whereas channel inactivation cannot happen with any discernible speed in the La3+-blocked channel. Thus, the selectivity filter of Na+ channel is probably contiguous to a single-file multi-ion region at the external pore mouth, a region itself being nonselective in terms of significant binding of different multivalent cations. This region is “open” to the external solution even if the channel is “closed” (“deactivated”), but undergoes imperative conformational changes during the gating (especially the inactivation) process of the channel.

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YIMPRASERT, Sattaya, Kentaro KATO, P. Henrik ALFREDSSON i Masaharu MATSUBARA. "Effects of polymer addition on transition and length scales of flow structures in transitional channel flow". Journal of Fluid Science and Technology 18, nr 1 (2023): JFST0021. http://dx.doi.org/10.1299/jfst.2023jfst0021.

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Lehmann, G. L., i R. A. Wirtz. "The Effect of Variations in Stream-Wise Spacing and Length on Convection From Surface Mounted Rectangular Components". Journal of Electronic Packaging 111, nr 1 (1.03.1989): 26–32. http://dx.doi.org/10.1115/1.3226504.

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The effect of variations in stream-wise spacing and component length on convection from rectangular, surface mounted components in a channel flow are reported. Component dimensions are the same order of magnitude as the channel wall-to-wall spacing. The channel Reynolds number, with air as the coolant, ranged from 670 to 3000. Flow visualization showed that under the above conditions the channel flow is transitional. The effect of variations in component stream-wise spacing on the level of turbulence in the channel and on the interaction between the core of the channel flow and the recirculating flow in cavities between components is discussed. Pressure drop measurements show that the dominant loss mechanism is due to form drag caused by the components. Local heat transfer measurements are made using an interferometer. Analysis of the results shows that the overall heat transfer is properly correlated in terms of a flow Reynolds number based on the component length. At small component Reynolds number, the overall conductance tends towards the laminar smooth wall value. An overall correlation is proposed which includes the effect of component Reynolds number, channel wall-to-wall spacing, and component stream-wise spacing.

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KANEKO, Shizuma, Takahiro TSUKAHARA i Yasuo KAWAGUCHI. "G203 DNS study on energy budget for transitional channel flow with turbulent stripe". Proceedings of the Fluids engineering conference 2010 (2010): 545–46. http://dx.doi.org/10.1299/jsmefed.2010.545.

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Xia, Zhenhua, Yipeng Shi i Yaomin Zhao. "Assessment of the shear-improved Smagorinsky model in laminar-turbulent transitional channel flow". Journal of Turbulence 16, nr 10 (28.05.2015): 925–36. http://dx.doi.org/10.1080/14685248.2015.1043131.

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Saito, Namiko, Dale I. Pullin i Michio Inoue. "Large eddy simulation of smooth-wall, transitional and fully rough-wall channel flow". Physics of Fluids 24, nr 7 (lipiec 2012): 075103. http://dx.doi.org/10.1063/1.4731301.

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Marques, Francisco, Alvaro Meseguer, Fernando Mellibovsky i Patrick D. Weidman. "Extensional channel flow revisited: a dynamical systems perspective". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 473, nr 2202 (czerwiec 2017): 20170151. http://dx.doi.org/10.1098/rspa.2017.0151.

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Extensional self-similar flows in a channel are explored numerically for arbitrary stretching–shrinking rates of the confining parallel walls. The present analysis embraces time integrations, and continuations of steady and periodic solutions unfolded in the parameter space. Previous studies focused on the analysis of branches of steady solutions for particular stretching–shrinking rates, although recent studies focused also on the dynamical aspects of the problems. We have adopted a dynamical systems perspective, analysing the instabilities and bifurcations the base state undergoes when increasing the Reynolds number. It has been found that the base state becomes unstable for small Reynolds numbers, and a transitional region including complex dynamics takes place at intermediate Reynolds numbers, depending on the wall acceleration values. The base flow instabilities are constitutive parts of different codimension-two bifurcations that control the dynamics in parameter space. For large Reynolds numbers, the restriction to self-similarity results in simple flows with no realistic behaviour, but the flows obtained in the transition region can be a valuable tool for the understanding of the dynamics of realistic Navier–Stokes solutions.

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Ciptoadi, Prayitno. "PENGARUH JARAK ALUR TERHADAP KESTABILAN ALIRAN FLUIDA BERDENYUT DALAM SALURAN BERPENAMPANG SEGIEMPAT". ALE Proceeding 1 (17.07.2021): 74–79. http://dx.doi.org/10.30598/ale.1.2018.74-79.

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The pulsatile fluid flow in a transverse grooved channel would become self-sustained oscillatory flow at a certain critical Reynold number. The critical Reynold number where laminar unsteady flow changed to unsteady transitional one depends on grooves distances. The objective of this research is to analyze the effect of grooves distances toward the vortex strength and the stability of the fluid flow. This research was done by implementing a closed square cross-section channel, where the bottom surface of the channel was semicircle grooved. The frequency of flow oscillation measurement was done by setting up a resistance manometer and measurement was done at several Reynold numbers. From the research result, it is seen that the largest vortex strength occurs at the smallest groove distance. The flows become instability in all of the grooves distances by seen Phase Plane.

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Rogge, Alexander J., i Jae Sung Park. "On the Underlying Drag-Reduction Mechanisms of Flow-Control Strategies in a Transitional Channel Flow: Temporal Approach". Flow, Turbulence and Combustion 108, nr 4 (18.11.2021): 1001–16. http://dx.doi.org/10.1007/s10494-021-00305-7.

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