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Artykuły w czasopismach na temat „Laminar breakdown”

Autor: Grafiati

Data publikacji: 5 października 2024

Data aktualizacji: 31 lipca 2025

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1

Li, Ning, and Qi Hong Zeng. "Direct Numerical Simulation on Transition of an Incompressible Boundary Layer on a Flat Plate." Applied Mechanics and Materials 268-270 (December 2012): 1143–47. http://dx.doi.org/10.4028/www.scientific.net/amm.268-270.1143.

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Direct Numerical Simulation(DNS) was carried out for laminar-turbulent transition of an incompressible boundary layer on a flat plate based on disturbance Navier-Stokes(N-S) equation in spatial mode with Massage Passing Interface(MPI) technology. Study on breakdown mechanism of laminar-turbulent transition was carried on. The effect of mean flow distortion on the process of breakdown in laminar-turbulent transition was investigated. Results indicate that change of instability characteristic of mean flow profile plays a key role during process of breakdown.

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2

Zhou, Teng, Zaijie Liu, Yuhan Lu, Ying Wang, and Chao Yan. "Direct numerical simulation of complete transition to turbulence via first- and second-mode oblique breakdown at a high-speed boundary layer." Physics of Fluids 34, no. 7 (2022): 074101. http://dx.doi.org/10.1063/5.0094069.

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Complete transition to turbulence via first- and second-mode oblique breakdown in a high-speed boundary layer at Mach 4.5 is studied by direct numerical simulations (DNS) and linear stability theory (LST). The initial frequency and spanwise wavenumbers for both types of oblique breakdown are determined from LST. Then, DNS is employed to study the main features of the two oblique breakdown types in detail, which has rarely been discussed in previous studies. This includes the main flow structures and evolution of various modes during the linear, nonlinear, and breakdown stages, and both differe

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3

Seifi, Zeinab, Mehrdad Raisee, and Michel J. Cervantes. "Optimal flow control of vortex breakdown in a laminar swirling flow." Journal of Physics: Conference Series 2707, no. 1 (2024): 012129. http://dx.doi.org/10.1088/1742-6596/2707/1/012129.

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Abstract In highly swirling flows, such as hydraulic turbines operating under part-load (PL) conditions, vortex breakdown occurs and performance is impaired. Consequently, it is imperative that mitigation measures are taken. In the present study, a laminar swirling flow with a vortex breakdown at a Reynolds number of 180 is investigated. At the inlet, a swirling velocity profile with a swirl number of 1.095 is set. A stability analysis is conducted to identify unstable modes based on the assumption that vortex breakdown is a global instability. The results indicate that spiral modes with wave

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4

Kadyirov, A. I., and B. R. Abaydullin. "Vortex Breakdown under Laminar Flow of Pseudoplastic Fluid." Journal of Physics: Conference Series 899 (September 2017): 022009. http://dx.doi.org/10.1088/1742-6596/899/2/022009.

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5

Kachanov, Yu S. "On the resonant nature of the breakdown of a laminar boundary layer." Journal of Fluid Mechanics 184 (November 1987): 43–74. http://dx.doi.org/10.1017/s0022112087002805.

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The first part of this paper (§2) briefly reviews the history of the idea of the resonant nature of laminar-boundary-layer breakdown. In the second part a new wave-resonance concept of the breakdown mechanism is proposed. The existing experimental data on the laminar boundary layer (and plane channel flow) breakdown are analysed from the viewpoint of this concept and are compared with the well-known local high-frequency secondary-instability concept. The results testify to the correctness of the proposed wave-resonant concept for the initial stages of breakdown, in particular for the K-regime

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6

Ozdemir, Celalettin E., Tian-Jian Hsu, and S. Balachandar. "Direct numerical simulations of instability and boundary layer turbulence under a solitary wave." Journal of Fluid Mechanics 731 (August 28, 2013): 545–78. http://dx.doi.org/10.1017/jfm.2013.361.

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AbstractA significant amount of research effort has been made to understand the boundary layer instability and the generation and evolution of turbulence subject to periodic/oscillatory flows. However, little is known about bottom boundary layers driven by highly transient and intermittent free-stream flow forcing, such as solitary wave motion. To better understand the nature of the instability mechanisms and turbulent flow characteristics subject to solitary wave motion, a large number of direct numerical simulations are conducted. Different amplitudes of random initial fluctuating velocity f

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7

Bottaro, Alessandro, Inge L. Ryhming, Marc B. Wehrli, Franz S. Rys, and Paul Rys. "Laminar swirling flow and vortex breakdown in a pipe." Computer Methods in Applied Mechanics and Engineering 89, no. 1-3 (1991): 41–57. http://dx.doi.org/10.1016/0045-7825(91)90036-6.

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8

ZAKI, TAMER A., JAN G. WISSINK, WOLFGANG RODI, and PAUL A. DURBIN. "Direct numerical simulations of transition in a compressor cascade: the influence of free-stream turbulence." Journal of Fluid Mechanics 665 (October 27, 2010): 57–98. http://dx.doi.org/10.1017/s0022112010003873.

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The flow through a compressor passage without and with incoming free-stream grid turbulence is simulated. At moderate Reynolds number, laminar-to-turbulence transition can take place on both sides of the aerofoil, but proceeds in distinctly different manners. The direct numerical simulations (DNS) of this flow reveal the mechanics of breakdown to turbulence on both surfaces of the blade. The pressure surface boundary layer undergoes laminar separation in the absence of free-stream disturbances. When exposed to free-stream forcing, the boundary layer remains attached due to transition to turbul

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9

Jost, Dominic, and Kai Nagel. "Probabilistic Traffic Flow Breakdown in Stochastic Car-Following Models." Transportation Research Record: Journal of the Transportation Research Board 1852, no. 1 (2003): 152–58. http://dx.doi.org/10.3141/1852-19.

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Whether traffic displays multiple phases (e.g., laminar, jammed, synchronized) has been much discussed. Computational evidence is presented that a stochastic car-following model can be moved from two phases (laminar and jammed) to one phase by changing one of its parameters. Models with two phases show three states. Two of them are homogeneous and correspond to the two phases. The third state consists of a mix of the two phases (phase coexistence). Although the gas–liquid analogy to traffic models has been widely discussed, no traffic-related model ever displayed a completely understood stocha

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10

Sansica, Andrea, Neil D. Sandham, and Zhiwei Hu. "Instability and low-frequency unsteadiness in a shock-induced laminar separation bubble." Journal of Fluid Mechanics 798 (May 31, 2016): 5–26. http://dx.doi.org/10.1017/jfm.2016.297.

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Three-dimensional direct numerical simulations (DNS) of a shock-induced laminar separation bubble are carried out to investigate the flow instability and origin of any low-frequency unsteadiness. A laminar boundary layer interacting with an oblique shock wave at $M=1.5$ is forced at the inlet with a pair of monochromatic oblique unstable modes, selected according to local linear stability theory (LST) performed within the separation bubble. Linear stability analysis is applied to cases with marginal and large separation, and compared to DNS. While the parabolized stability equations approach a

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11

Incropera, F. P., A. L. Knox, and J. R. Maughan. "Mixed-Convection Flow and Heat Transfer in the Entry Region of a Horizontal Rectangular Duct." Journal of Heat Transfer 109, no. 2 (1987): 434–39. http://dx.doi.org/10.1115/1.3248100.

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Entry-region hydrodynamic and thermal conditions have been experimentally determined for laminar mixed-convection water flow through a horizontal rectangular duct with uniform bottom heating. Direct heating of 0.05 mm stainless steel foil was used to minimize wall conduction, and the foil was instrumented to yield spanwise and longitudinal distributions of the Nusselt number. Flow visualization revealed the existence of four regimes corresponding to laminar forced convection, laminar mixed convection, transitional mixed convection, and turbulent free convection. The laminar mixed-convection re

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12

Zang, Thomas A., and M. Yousuff Hussaini. "Multiple paths to subharmonic laminar breakdown in a boundary layer." Physical Review Letters 64, no. 6 (1990): 641–44. http://dx.doi.org/10.1103/physrevlett.64.641.

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13

SHAIKH, F. N. "Investigation of transition to turbulence using white-noise excitation and local analysis techniques." Journal of Fluid Mechanics 348 (October 10, 1997): 29–83. http://dx.doi.org/10.1017/s0022112097006629.

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Weak free-stream turbulence excites modulated Tollmien–Schlichting (T–S) waves in a laminar boundary layer that grow in magnitude with downstream distance and ultimately lead to the formation of turbulent spots and then fully turbulent flow. Hot-wire experiments have indicated that the development of localized large-amplitude ‘events’ in the velocity records are the essential precursor to the eventual formation of turbulent spots in the flow field. Traditional global Fourier techniques are unable to resolve the localized nature of these events and hence provide little useful information concer

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14

Franko, Kenneth J., and Sanjiva K. Lele. "Breakdown mechanisms and heat transfer overshoot in hypersonic zero pressure gradient boundary layers." Journal of Fluid Mechanics 730 (August 1, 2013): 491–532. http://dx.doi.org/10.1017/jfm.2013.350.

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AbstractA laminar Mach 6 flat plate boundary layer is perturbed using three different types of disturbances introduced through blowing and suction. The linear and nonlinear development and eventual breakdown to turbulence are investigated using direct numerical simulation. The three different transition mechanisms compared are first mode oblique breakdown, second mode oblique breakdown and second mode fundamental resonance. The focus of the present work is to compare the nonlinear development and breakdown to turbulence for the different transition mechanisms and explain the heat transfer over

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15

Nering, Konrad, and Kazimierz Rup. "An improved algebraic model for by-pass transition for calculation of transitional flow in pipe and parallel-plate channels." Thermal Science 23, Suppl. 4 (2019): 1123–31. http://dx.doi.org/10.2298/tsci19s4123n.

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Modified algebraic intermittency model developed by E. Dick and S. Kubacki was used to describe laminar-turbulent transition. In this work a modification of this model was made for simulating internal flows in pipes and parallel-plate channel. In particular, constants present in this model were modified. These modified constants are the same for different flows in pipes and parallel-plate channels. In this work, a dependence of friction factor on Reynolds number and turbulence intensity were determined as well as the localization of laminar breakdown and fully developed flow. Obtained results

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16

Jovanovic, Jovan, and Mira Pashtrapanska. "On the evolution of laminar to turbulent transition and breakdown to turbulence." Thermal Science 7, no. 2 (2003): 59–76. http://dx.doi.org/10.2298/tsci0302059j.

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Starting from the basic conservation laws of fluid flow, we investigated transition and breakdown to turbulence of a laminar flat plate boundary layer exposed to small, statistically stationary, two-component, three-dimensional disturbances. The derived equations for the statistical properties of the disturbances are closed using the two-point correlation technique and invariant theory. By considering the equilibrium solutions of the modeled equations, the transition criterion is formulated in terms of a Reynolds number based on the intensity and the length scale of the disturbances. The deduc

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17

Lopez, J. M. "Axisymmetric vortex breakdown Part 1. Confined swirling flow." Journal of Fluid Mechanics 221 (December 1990): 533–52. http://dx.doi.org/10.1017/s0022112090003664.

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A comparison between the experimental visualization and numerical simulations of the occurrence of vortex breakdown in laminar swirling flows produced by a rotating endwall is presented. The experimental visualizations of Escudier (1984) were the first to detect the presence of multiple recirculation zones and the numerical model presented here, consisting of a numerical solution of the unsteady axisymmetric Navier-Stokes equations, faithfully reproduces these phenomena and all other observed characteristics of the flow. Further, the numerical calculations elucidate the onset of oscillatory fl

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18

Jovanovic, Jovan, and Mina Nishi. "The origin of turbulence in wall-bounded flows." Thermal Science 21, suppl. 3 (2017): 565–72. http://dx.doi.org/10.2298/tsci160413184j.

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The motion of liquids and gases can be either laminar, flowing slowly in orderly parallel and continuous layers of fluid that cannot mix, or turbulent in which motion exhibits disorder in time and space with the ability to promote mixing. Breakdown of ordered to disordered motion can follow different scenarios so that no universal mechanism can be identified even in similar flow configurations [1]. Only under very special circumstances can the mechanism associated with the appearance of turbulence be studied within the deterministic theory of hydrodynamic stability [2] or employing direct nume

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19

Wu, Xiaohua, Parviz Moin, Ronald J. Adrian, and Jon R. Baltzer. "Osborne Reynolds pipe flow: Direct simulation from laminar through gradual transition to fully developed turbulence." Proceedings of the National Academy of Sciences 112, no. 26 (2015): 7920–24. http://dx.doi.org/10.1073/pnas.1509451112.

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The precise dynamics of breakdown in pipe transition is a century-old unresolved problem in fluid mechanics. We demonstrate that the abruptness and mysteriousness attributed to the Osborne Reynolds pipe transition can be partially resolved with a spatially developing direct simulation that carries weakly but finitely perturbed laminar inflow through gradual rather than abrupt transition arriving at the fully developed turbulent state. Our results with this approach show during transition the energy norms of such inlet perturbations grow exponentially rather than algebraically with axial distan

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20

Sivasubramanian, Jayahar, and Hermann F. Fasel. "Direct numerical simulation of transition in a sharp cone boundary layer at Mach 6: fundamental breakdown." Journal of Fluid Mechanics 768 (March 10, 2015): 175–218. http://dx.doi.org/10.1017/jfm.2014.678.

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Direct numerical simulations (DNS) were performed to investigate the laminar–turbulent transition in a boundary layer on a sharp cone with an isothermal wall at Mach 6 and at zero angle of attack. The motivation for this research is to make a contribution towards understanding the nonlinear stages of transition and the final breakdown to turbulence in hypersonic boundary layers. In particular, the role of second-mode fundamental resonance, or (K-type) breakdown, is investigated using high-resolution ‘controlled’ transition simulations. The simulations were carried out for the laboratory condit

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21

LUO, Jisheng. "Inherent mechanism of breakdown in laminar-turbulent transition of plane channel flows." Science in China Series G 48, no. 2 (2005): 228. http://dx.doi.org/10.1360/04yw0168.

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22

Tian, Zhaohua, Meirong Dong, Shishi Li, and Jidong Lu. "Spatially resolved laser-induced breakdown spectroscopy in laminar premixed methane–air flames." Spectrochimica Acta Part B: Atomic Spectroscopy 136 (October 2017): 8–15. http://dx.doi.org/10.1016/j.sab.2017.08.001.

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23

Salas, M. D., and G. Kuruvila. "Vortex breakdown simulation: A circumspect study of the steady, laminar, axisymmetric model." Computers & Fluids 17, no. 1 (1989): 247–62. http://dx.doi.org/10.1016/0045-7930(89)90020-0.

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24

Pruett, C. D., and T. A. Zang. "Direct numerical simulation of laminar breakdown in high-speed, axisymmetric boundary layers." Theoretical and Computational Fluid Dynamics 3, no. 6 (1992): 345–67. http://dx.doi.org/10.1007/bf00417933.

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25

Jovanovic´, J., and M. Pashtrapanska. "On the Criterion for the Determination Transition Onset and Breakdown to Turbulence in Wall-Bounded Flows1." Journal of Fluids Engineering 126, no. 4 (2004): 626–33. http://dx.doi.org/10.1115/1.1779663.

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Starting from the basic conservation laws of fluid flow, we investigated transition and breakdown to turbulence of a laminar flat plate boundary layer exposed to small, statistically stationary, two-component, three-dimensional disturbances. The derived equations for the statistical properties of the disturbances are closed using the two-point correlation technique and invariant theory. By considering the equilibrium solutions of the modeled equations, the transition criterion is formulated in terms of a Reynolds number based on the intensity and the length scale of the disturbances. The deduc

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26

Gumowski, K., and S. Kubacki. "Experimental study of laminar-to-turbulent transition in an adverse pressure gradient flow." Journal of Physics: Conference Series 2367, no. 1 (2022): 012018. http://dx.doi.org/10.1088/1742-6596/2367/1/012018.

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Abstract Experimental results on laminar-to-turbulent transition in a separated laminar boundary layer formed over a flat plate in an adverse pressure gradient are provided. Experiments have been performed for a range of Reynolds numbers (1.4 − 2.4 · 105) and for two freestream turbulence levels (Tu =3.6 and 5.3%). The measurements of mean and fluctuating velocity profiles have been carried out at inlet to the test section using Constant Temperature Anemometry (CTA). The data might be useful for validation and development of transition models. In order to characterize the dynamics leading to t

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27

Thomson, K. D. "Some comments on the later stages of transition from laminar to turbulent flow in the flat plate boundary layer." Aeronautical Journal 92, no. 918 (1988): 309–14. http://dx.doi.org/10.1017/s0001924000016341.

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Pseudo-streamwise vortices develop during the transition of a boundary layer from the laminar to the turbulent state. It is suggested that the induced velocities associated with these vortices cause a gross change in the flow, and that the initial uniform flow is no longer tenable. The character of the flow in the boundary layer must change suddenly, and it is believed that this change provides the trigger for flow breakdown to turbulence.

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28

Watmuff, Jonathan H. "Effects of Weak Free Stream Nonuniformity on Boundary Layer Transition." Journal of Fluids Engineering 128, no. 2 (2005): 247–57. http://dx.doi.org/10.1115/1.2169813.

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Experiments are described in which well-defined weak Free Stream Nonuniformity (FSN) is introduced by placing fine wires upstream of the leading edge of a flat plate. Large amplitude spanwise thickness variations form in the boundary layer as a result of the interaction between the steady laminar wakes from the wires and the leading edge. The centerline of a region of elevated layer thickness is aligned with the centerline of the wake in the freestream and the response is shown to be remarkably sensitive to the spanwise length-scale of the wakes. The region of elevated thickness is equivalent

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29

Zuikov, Andrey L., and Elena V. Bazhina. "Viscous stress tensor and stability of laminar contravortical flows." Vestnik MGSU, no. 7 (July 2019): 870–84. http://dx.doi.org/10.22227/1997-0935.2019.7.870-884.

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Introduction: coaxial layers in contravortical flows rotate in the opposite directions. This determines their complicated spatial structure. The relevance of the subject is in the uniquely effective mixing of the moving medium. This property has a great potential of application from microbiology and missile building for obtaining highly dispersed mixtures to heat engineering for increasing the intensity of heat transfer. However, contravortical flows have a high degree of hydrodynamic instability. This hinders effective development of these technologies. Contravortical flows are observed behin

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30

Chew, J. W. "Computation of Forced Laminar Convection in Rotating Cavities." Journal of Heat Transfer 107, no. 2 (1985): 277–82. http://dx.doi.org/10.1115/1.3247411.

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Finite difference solutions are presented for forced laminar convection in a rotating cylindrical cavity with radial outflow. This forms a simple model of the cooling flow between two compressor disks in a gas turbine engine. If the fluid enters the cavity from a uniform radial source, it is shown that the local Nusselt number changes from that of a “free disk” near the center of the cavity to that for Ekman layer flow at larger radii. With an axial inlet, the flow, and consequently, the heat transfer, is more complex. If vortex breakdown occurs, then the results are very similar to those for

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31

Kro¨ner, M., J. Fritz, and T. Sattelmayer. "Flashback Limits for Combustion Induced Vortex Breakdown in a Swirl Burner." Journal of Engineering for Gas Turbines and Power 125, no. 3 (2003): 693–700. http://dx.doi.org/10.1115/1.1582498.

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Flame flashback from the combustion chamber into the mixing zone limits the reliability of swirl stabilized lean premixed combustion in gas turbines. In a former study, the combustion induced vortex breakdown (CIVB) has been identified as a prevailing flashback mechanism of swirl burners. The present study has been performed to determine the flashback limits of a swirl burner with cylindrical premixing tube without centerbody at atmospheric conditions. The flashback limits, herein defined as the upstream flame propagation through the entire mixing tube, have been detected by a special optical

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32

Wang, Meng, Sanjiva K. Lele, and Parviz Moin. "Sound radiation during local laminar breakdown in a low-Mach-number boundary layer." Journal of Fluid Mechanics 319, no. -1 (1996): 197. http://dx.doi.org/10.1017/s0022112096007318.

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Xu, Guoliang, and Song Fu. "A Four-Equation Eddy-Viscosity Approach for Modeling Bypass Transition." Advances in Applied Mathematics and Mechanics 6, no. 4 (2014): 523–38. http://dx.doi.org/10.4208/aamm.2013.m266.

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AbstractIt is very important to predict the bypass transition in the simulation of flows through turbomachinery. This paper presents a four-equation eddy-viscosity turbulence transition model for prediction of bypass transition. It is based on the SST turbulence model and the laminar kinetic energy concept. A transport equation for the non-turbulent viscosity is proposed to predict the development of the laminar kinetic energy in the pre-transitional boundary layer flow which has been observed in experiments. The turbulence breakdown process is then captured with an intermittency transport equ

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34

Skripkin, S. G. "Parametric study of cone angle influence on bubble vortex breakdown onset in laminar conical flow at various swirl numbers." Journal of Physics: Conference Series 2119, no. 1 (2021): 012019. http://dx.doi.org/10.1088/1742-6596/2119/1/012019.

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Abstract The current work studies a swirling laminar viscous pipe flow with a controllable swirl number and varying pipe divergence cone angle. Such flows are widely used in various engineering applications. When a certain level of flow swirl is reached, a phenomenon called vortex breakdown occurs, the characteristics of which depend on the intensity of swirling of the flow and the Reynolds number. However, in addition to these two parameters, an important influence is exerted by the pipe opening angle, which often does not allow generalizing the results obtained in the pipe flow with even sli

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35

YU, PENG, T. S. LEE, Y. ZENG, and H. T. LOW. "EFFECT OF VORTEX BREAKDOWN ON MASS TRANSFER IN A CELL CULTURE BIOREACTOR." Modern Physics Letters B 19, no. 28n29 (2005): 1543–46. http://dx.doi.org/10.1142/s0217984905009869.

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The present work shows that vortex breakdown may also occur in a bioreactor for animal cell or tissue culture. The aim is to study the effect of vortex breakdown on the fluid environment for cell growth, particularly hydrodynamic stress and mass transfer. A numerical simulation of the fluid flow and oxygen transfer in a cylindrical bioreactor is presented, in which a rotating base wall is used to generate the medium flow and mixing. The steady and laminar, axisymmetric Navier-Stokes and species equations are solved by the numerical model based on finite volume method. The hydrodynamic stress a

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36

WILLIAMSON, N., N. SRINARAYANA, S. W. ARMFIELD, G. D. McBAIN, and W. LIN. "Low-Reynolds-number fountain behaviour." Journal of Fluid Mechanics 608 (July 11, 2008): 297–317. http://dx.doi.org/10.1017/s0022112008002310.

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Experimental evidence for previously unreported fountain behaviour is presented. It has been found that the first unstable mode of a three-dimensional round fountain is a laminar flapping motion that can grow to a circling or multimodal flapping motion. With increasing Froude and Reynolds numbers, fountain behaviour becomes more disorderly, exhibiting a laminar bobbing motion. The transition between steady behaviour, the initial flapping modes and the laminar bobbing flow can be approximately described by a function FrRe2/3=C. The transition to turbulence occurs at Re > 120, independent of

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37

Kumar, Vivaswat, Federico Pizzi, André Giesecke, et al. "The effect of nutation angle on the flow inside a precessing cylinder and its dynamo action." Physics of Fluids 35, no. 1 (2023): 014114. http://dx.doi.org/10.1063/5.0134562.

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The effect of the nutation angle on the flow inside a precessing cylinder is experimentally explored and compared with numerical simulations. The focus is laid on the typical breakdown of the directly forced m = 1 Kelvin mode for increasing precession ratio (Poincaré number) and the accompanying transition between laminar and turbulent flows. Compared to the reference case with a 90° nutation angle, prograde rotation leads to an earlier breakdown, while in the retrograde case, the forced mode continues to exist also for higher Poincaré numbers. Depending largely on the occurrence and intensity

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38

Cheng, K. C., and Y. W. Kim. "Flow Visualization Studies on Vortex Instability of Natural Convection Flow Over Horizontal and Slightly Inclined Constant-Temperature Plates." Journal of Heat Transfer 110, no. 3 (1988): 608–15. http://dx.doi.org/10.1115/1.3250536.

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Flow visualization experiments were performed in a low-speed wind tunnel to study vortex instability of laminar natural convection flow along inclined isothermally heated plates having inclination angles from the horizontal of θ = 0, 5, 10, 15 and 20 deg. The temperature difference between plate surface and ambient air ranged from ΔT = 15.5 to 37.5°C and the local Grashof number range was Grx = 1.02×106 to 2.13×108. Three characteristic flow regimes were identified as follows: a two-dimensional laminar flow, a transition regime for developing longitudinal vortices, and a turbulent regime after

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39

Walker, G. J., and J. P. Gostelow. "Effects of Adverse Pressure Gradients on the Nature and Length of Boundary Layer Transition." Journal of Turbomachinery 112, no. 2 (1990): 196–205. http://dx.doi.org/10.1115/1.2927633.

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Existing transition models are surveyed and deficiencies in previous predictions, which seriously overestimate transition length under an adverse pressure gradient, are discussed. A new model for transition in an adverse pressure gradient situation is proposed and experimental results are provided that confirm its validity. A correlation for transition length is advanced that incorporates both Reynolds number and pressure gradient effects. Under low free-stream turbulence conditions the basic mechanism of transition is laminar instability. There are, however, physical differences between zero

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Moise, Pradeep, and Joseph Mathew. "Bubble and conical forms of vortex breakdown in swirling jets." Journal of Fluid Mechanics 873 (June 24, 2019): 322–57. http://dx.doi.org/10.1017/jfm.2019.401.

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Experimental investigations of laminar swirling jets had revealed a new form of vortex breakdown, named conical vortex breakdown, in addition to the commonly observed bubble form. The present study explores these breakdown states that develop for the Maxworthy profile (a model of swirling jets) at inflow, from streamwise-invariant initial conditions, with direct numerical simulations. For a constant Reynolds number based on jet radius and a centreline velocity of 200, various flow states were observed as the inflow profile’s swirl parameter $S$ (scaled centreline radial derivative of azimuthal

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HAIN, R., C. J. KÄHLER, and R. RADESPIEL. "Dynamics of laminar separation bubbles at low-Reynolds-number aerofoils." Journal of Fluid Mechanics 630 (July 10, 2009): 129–53. http://dx.doi.org/10.1017/s0022112009006661.

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The laminar separation bubble on an SD7003 aerofoil at a Reynolds numberRe= 66000 was investigated to determine the dominant frequencies of the transition process and the flapping of the bubble. The measurements were performed with a high-resolution time-resolved particle image velocimetry (TR-PIV) system. Contrary to typical measurements performed through conventional PIV, the different modes can be identified by applying TR-PIV. The interaction between the shed vortices is analysed, and their significance for the production of turbulence is presented. In the shear layer above the bubble the

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ASAI, MASAHITO, MASAYUKI MINAGAWA, and MICHIO NISHIOKA. "The instability and breakdown of a near-wall low-speed streak." Journal of Fluid Mechanics 455 (March 25, 2002): 289–314. http://dx.doi.org/10.1017/s0022112001007431.

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The instability of the three-dimensional high-shear layer associated with a near-wall low-speed streak is investigated experimentally. A single low-speed streak, not unlike the near-wall low-speed streaks in transitional and turbulent flows, is produced in a laminar boundary layer by using a small piece of screen set normal to the wall. In order to excite symmetric and anti-symmetric modes separately, well-controlled external disturbances are introduced into the laminar low-speed streak through small holes drilled behind the screen. The growth of the excited symmetric varicose mode is essentia

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Di Giovanni, Antonio, and Christian Stemmer. "Cross-flow-type breakdown induced by distributed roughness in the boundary layer of a hypersonic capsule configuration." Journal of Fluid Mechanics 856 (October 5, 2018): 470–503. http://dx.doi.org/10.1017/jfm.2018.706.

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Direct numerical simulations are undertaken to investigate the nature of instability mechanisms induced by singular and distributed roughnesses on a blunt-capsule configuration. On the base of a capsule-like hemispherical forebody at wind-tunnel conditions ($M=5.9$), we analyse the development of unsteady disturbances behind a patch of two different roughness geometries. First, spanwise periodic roughness elements are considered and cross-validation with other methods of the stability analysis is achieved. Two main unstable modes are found in the roughness wake, corresponding to the symmetric

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Brinkerhoff, Joshua R., and Metin I. Yaras. "Numerical investigation of transition in a boundary layer subjected to favourable and adverse streamwise pressure gradients and elevated free stream turbulence." Journal of Fluid Mechanics 781 (September 16, 2015): 52–86. http://dx.doi.org/10.1017/jfm.2015.457.

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Laminar-to-turbulent transition of a boundary layer subjected to streamwise pressure gradients and elevated free stream turbulence is computed through direct numerical simulation. The streamwise pressure distribution and elevated free stream turbulence levels mimic the conditions present on the suction side of highly-cambered airfoils. Longitudinal streamwise streaks form in the laminar boundary layer through the selective inclusion of low-frequency disturbances from the free stream turbulence. The spanwise spacing normalized by local inner variables indicates stabilization of the streaks occu

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Nering, Konrad, and Kazimierz Rup. "Modified algebraic model of laminar-turbulent transition for internal flows." International Journal of Numerical Methods for Heat & Fluid Flow 30, no. 4 (2019): 1743–53. http://dx.doi.org/10.1108/hff-10-2018-0597.

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Purpose For internal flows with small values of the Reynolds number, there is often at a considerable distance from the pipe inlet cross-section a change of the flow form from laminar to turbulent. To describe this phenomenon of laminar-turbulent transition in the pipe, also parallel-plate channel flow, a modified algebraic intermittency model was used. The original model for bypass transition developed by S. Kubacki and E. Dick was designed for simulating bypass transition in turbomachinery. Design/methodology/approach A modification of mentioned model was proposed. Modified model is suitable

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MATTNER, T. W., P. N. JOUBERT, and M. S. CHONG. "Vortical flow. Part 1. Flow through a constant-diameter pipe." Journal of Fluid Mechanics 463 (July 25, 2002): 259–91. http://dx.doi.org/10.1017/s0022112002008741.

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This paper describes an exploration of the behaviour and properties of swirling flow through a constant-diameter pipe. The experiments reveal a complicated transition process as the swirl intensity Ω is increased at fixed pipe Reynolds number Re ≈ 4900. For Ω [les ] 1.09, the vortex was steady, laminar, axisymmetric, and developed slowly with streamwise distance. The upstream velocity profiles were similar to those commonly appearing in the literature in similar apparatus. Spiral vortex breakdown appeared in the test section for 1.09 [les ] Ω [les ] 1.31 and was associated with a localized tra

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Valencia, Alvaro. "Pulsating Flow in a Channel With a Backward-Facing Step." Applied Mechanics Reviews 50, no. 11S (1997): S232—S236. http://dx.doi.org/10.1115/1.3101841.

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The incompressible laminar flow in a channel with a backward-facing step is studied for steady cases and for pulsating inlet flow conditions. For steady flows, the influrnce of the inlet velocity profile, the height of the step, and the Reynolds number on the reattachment length is investigated. A parabolic entrance profile was used for pulsating flow. It was found with amplitude of oscillation of one by Re = 100 that the primary vortex breakdown through one pulsatile cycle and the wall shear stress in the separation zone varied markedly with pulsating inlet flow.

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Zuikov, Andrey, and Genrikh Orekhov. "Hydrodynamic structure of laminar flows with oppositely-swirled coaxial layers." MATEC Web of Conferences 265 (2019): 02022. http://dx.doi.org/10.1051/matecconf/201926502022.

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The article is devoted to the theoretical study of hydrodynamics of laminar flows with coaxial layers swirled in opposite directions and moving along the pipe. Such flows in a turbulent range have a wide practical application potential in technologies of dissipation of mechanical energy and mixing multiphase and heterogeneous media in microbiology, chemistry, ecology, heat engineering, power engineering, engine and rocket engineering. The article describes the tensor of viscous tangents (τii) and normal (σii) stresses. The questions of stability of flow according to the Rayleigh (Ra) and Richa

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Mishra, Pratima, Rohit Kumar, and Awadhesh Kumar Rai. "Development and optimization of experimental parameters for the detection of trace of heavy metal (Cr) in liquid samples using laser-induced breakdown spectroscopy technique." Journal of Laser Applications 35, no. 2 (2023): 022021. http://dx.doi.org/10.2351/7.0000959.

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Detection of traces of impurities/elements present in liquid samples using laser-induced breakdown spectroscopy (LIBS) is challenging because the signal intensity is weaker than in the case of solid samples. The present paper deals with the optimization of experimental parameters for different phases of a liquid sample and the improvement of the limit of detection (LOD) in these LIBS experimental setups. LIBS spectra of chromium in the liquid sample have been recorded in three different configurations [laminar flow, i.e., liquid flowing through a small jet, frozen liquid (ice), and liquid depo

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Kamiyo, Ola, and Abimbola Dada. "Laminar Natural Convection in Attics of Rooftops with Depressed Walls." FUOYE Journal of Engineering and Technology 9, no. 2 (2024): 258–64. http://dx.doi.org/10.4314/fuoyejet.v9i2.15.

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Laminar natural convection in the attics of rooftops with depressed upper walls and heated base wall has been investigated numerically using a finite volume CFD package. Selected roofs referred to as Combination, Clerestory and Butterfly roofs are compared with standard isosceles triangular roof having the same pitch and base length. The results obtained show that the depressed wall distorts the multicellular air movement pattern within the attics. It compressed the cells, thereby reducing their sizes and damping their rotation. The depression brings the upper walls closer to the base wall res

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