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Journal articles on the topic 'Favourable pressure gradient'

Author: Grafiati

Published: 4 June 2021

Last updated: 4 February 2022

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1

CHERNYSHENKO, S. I., B. GALLETTI, A. IOLLO, and LUCA ZANNETTI. "Trapped vortices and a favourable pressure gradient." Journal of Fluid Mechanics 482 (May 10, 2003): 235–55. http://dx.doi.org/10.1017/s0022112003004026.

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2

Volchkov, E. P., M. S. Makarov, and A. Yu Sakhnov. "Boundary layer with asymptotic favourable pressure gradient." International Journal of Heat and Mass Transfer 53, no. 13-14 (2010): 2837–43. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2010.02.014.

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3

CAL, RAÚL BAYOÁN, BRIAN BRZEK, T. GUNNAR JOHANSSON, and LUCIANO CASTILLO. "The rough favourable pressure gradient turbulent boundary layer." Journal of Fluid Mechanics 641 (November 25, 2009): 129–55. http://dx.doi.org/10.1017/s0022112009991352.

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Laser Doppler anemometry measurements of the mean velocity and Reynolds stresses are carried out for a rough-surface favourable pressure gradient turbulent boundary layer. The experimental data is compared with smooth favourable pressure gradient and rough zero-pressure gradient data. The velocity and Reynolds stress profiles are normalized using various scalings such as the friction velocity and free stream velocity. In the velocity profiles, the effects of roughness are removed when using the friction velocity. The effects of pressure gradient are not absorbed. When using the free stream vel

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4

Cohen, Elie, and Xavier Gloerfelt. "Influence of pressure gradients on wall pressure beneath a turbulent boundary layer." Journal of Fluid Mechanics 838 (January 22, 2018): 715–58. http://dx.doi.org/10.1017/jfm.2017.898.

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This study investigates the effects of a pressure gradient on the wall pressure beneath equilibrium turbulent boundary layers. Excitation of the walls of a vehicle by turbulent boundary layers indeed constitutes a major source of interior noise and it is necessary to take into account the presence of a pressure gradient to represent the effect of the curvature of the walls. With this aim, large-eddy simulations of turbulent boundary layers in the presence of both mild adverse and mild favourable pressure gradients are carried out by solving the compressible Navier–Stokes equations. This method

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5

Tichenor, N. R., R. A. Humble, and R. D. W. Bowersox. "Response of a hypersonic turbulent boundary layer to favourable pressure gradients." Journal of Fluid Mechanics 722 (March 28, 2013): 187–213. http://dx.doi.org/10.1017/jfm.2013.89.

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AbstractThe role of streamline curvature-driven favourable pressure gradients in modifying the turbulence structure of a Mach 4.9, high-Reynolds-number (${\mathit{Re}}_{\theta } = 43\hspace{0.167em} 000$) boundary layer is examined. Three pressure gradient cases ($\beta = (\mathrm{d} p/ \mathrm{d} x)({\delta }^{\ast } / {\tau }_{w} )= 0. 07, - 0. 3$ and $- 1. 0$) are characterized via particle image velocimetry. The expected stabilizing trends in the Reynolds stresses are observed, with a sign reversal in the Reynolds shear stress in the outer part of the boundary layer for the strongest favou

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6

VEYNANTE, DENIS, and THIERRY POINSOT. "Effects of pressure gradients on turbulent premixed flames." Journal of Fluid Mechanics 353 (December 25, 1997): 83–114. http://dx.doi.org/10.1017/s0022112097007556.

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In most practical situations, turbulent premixed flames are ducted and, accordingly, subjected to externally imposed pressure gradients. These pressure gradients may induce strong modifications of the turbulent flame structure because of buoyancy effects between heavy cold fresh and light hot burnt gases. In the present work, the influence of a constant acceleration, inducing large pressure gradients, on a premixed turbulent flame is studied using direct numerical simulations.A favourable pressure gradient, i.e. a pressure decrease from unburnt to burnt gases, is found to decrease the flame wr

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7

METZGER, M., A. LYONS, and P. FIFE. "Mean momentum balance in moderately favourable pressure gradient turbulent boundary layers." Journal of Fluid Mechanics 617 (December 25, 2008): 107–40. http://dx.doi.org/10.1017/s0022112008003637.

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Moderately favourable pressure gradient turbulent boundary layers are investigated within a theoretical framework based on the unintegrated two-dimensional mean momentum equation. The present theory stems from an observed exchange of balance between terms in the mean momentum equation across different regions of the boundary layer. This exchange of balance leads to the identification of distinct physical layers, unambiguously defined by the predominant mean dynamics active in each layer. Scaling domains congruent with the physical layers are obtained from a multi-scale analysis of the mean mom

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8

Escudier, M. P., A. Ramadan, and M. W. Johnson. "Response of a skewed turbulent boundary layer to favourable pressure gradient." Experiments in Fluids 30, no. 6 (2001): 657–71. http://dx.doi.org/10.1007/s003480000247.

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9

PRALITS, JAN O., A. HANIFI, and D. S. HENNINGSON. "Adjoint-based optimization of steady suction for disturbance control in incompressible flows." Journal of Fluid Mechanics 467 (September 24, 2002): 129–61. http://dx.doi.org/10.1017/s0022112002001301.

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The optimal distribution of steady suction needed to control the growth of single or multiple disturbances in quasi-three-dimensional incompressible boundary layers on a flat plate is investigated. The evolution of disturbances is analysed in the framework of the parabolized stability equations (PSE). A gradient-based optimization procedure is used and the gradients are evaluated using the adjoint of the parabolized stability equations (APSE) and the adjoint of the boundary layer equations (ABLE). The accuracy of the gradient is increased by introducing a stabilization procedure for the PSE. R

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10

Harun, Zambri, Jason P. Monty, Romain Mathis, and Ivan Marusic. "Pressure gradient effects on the large-scale structure of turbulent boundary layers." Journal of Fluid Mechanics 715 (January 9, 2013): 477–98. http://dx.doi.org/10.1017/jfm.2012.531.

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AbstractResearch into high-Reynolds-number turbulent boundary layers in recent years has brought about a renewed interest in the larger-scale structures. It is now known that these structures emerge more prominently in the outer region not only due to increased Reynolds number (Metzger & Klewicki, Phys. Fluids, vol. 13(3), 2001, pp. 692–701; Hutchins & Marusic, J. Fluid Mech., vol. 579, 2007, pp. 1–28), but also when a boundary layer is exposed to an adverse pressure gradient (Bradshaw, J. Fluid Mech., vol. 29, 1967, pp. 625–645; Lee & Sung, J. Fluid Mech., vol. 639, 2009, pp. 101–

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11

MIMURA, Ryota, Hiroki SUZUKI, Takatsugu KAMEDA, and Shinsuke MOCHIZUKI. "Turbulent Structure in Flat Plate Boundary Layer Subjected to Favourable Pressure Gradient." Proceedings of the Fluids engineering conference 2016 (2016): 0215. http://dx.doi.org/10.1299/jsmefed.2016.0215.

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12

Wu, H., S. Moreau, and R. D. Sandberg. "Effects of pressure gradient on the evolution of velocity-gradient tensor invariant dynamics on a controlled-diffusion aerofoil at." Journal of Fluid Mechanics 868 (April 17, 2019): 584–610. http://dx.doi.org/10.1017/jfm.2019.129.

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A weakly compressible flow direct numerical simulation of a controlled-diffusion aerofoil at $8^{\circ }$ geometrical angle of attack, a chord-based Reynolds number of $Re_{c}=150\,000$ and a Mach number of $M=0.25$ based on the free-stream velocity relevant to many industrial applications was conducted to improve the understanding of the impact of the pressure gradient on the development of turbulent structures. The evolution equations for the two invariants $Q$ and $R$ of the velocity-gradient tensor have been studied at various locations along the aerofoil chord on its suction side. The sha

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13

Joshi, Pranav, Xiaofeng Liu, and Joseph Katz. "Effect of mean and fluctuating pressure gradients on boundary layer turbulence." Journal of Fluid Mechanics 748 (April 28, 2014): 36–84. http://dx.doi.org/10.1017/jfm.2014.147.

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AbstractThis study focuses on the effects of mean (favourable) and large-scale fluctuating pressure gradients on boundary layer turbulence. Two-dimensional (2D) particle image velocimetry (PIV) measurements, some of which are time-resolved, have been performed upstream of and within a sink flow for two inlet Reynolds numbers, ${Re}_{\theta }(x_{1})=3360$ and 5285. The corresponding acceleration parameters, $K$, are ${1.3\times 10^{-6}}$ and ${0.6\times 10^{-6}}$. The time-resolved data at ${Re}_{\theta }(x_{1})=3360$ enables us to calculate the instantaneous pressure distributions by integrati

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14

HOLLOWAY, A. G. L., D. C. ROACH, and H. AKBARY. "Combined effects of favourable pressure gradient and streamline curvature on uniformly sheared turbulence." Journal of Fluid Mechanics 526 (March 10, 2005): 303–36. http://dx.doi.org/10.1017/s0022112004003088.

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15

Williams, A. J., and R. E. Hewitt. "Micro-slot injection into a boundary layer driven by a favourable pressure gradient." Journal of Engineering Mathematics 107, no. 1 (2017): 19–35. http://dx.doi.org/10.1007/s10665-017-9933-7.

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16

JOHNSTONE, RODERICK, GARY N. COLEMAN, and PHILIPPE R. SPALART. "The resilience of the logarithmic law to pressure gradients: evidence from direct numerical simulation." Journal of Fluid Mechanics 643 (December 1, 2009): 163–75. http://dx.doi.org/10.1017/s0022112009992333.

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Wall-bounded turbulence in pressure gradients is studied using direct numerical simulation (DNS) of a Couette–Poiseuille flow. The motivation is to include adverse pressure gradients, to complement the favourable ones present in the well-studied Poiseuille flow, and the central question is how the scaling laws react to a gradient in the total shear stress or equivalently to a pressure gradient. In the case considered here, the ratio of local stress to wall stress, namely τ+, ranges from roughly 2/3 to 3/2 in the ‘wall region’. By this we mean the layer believed not to be influenced by the oppo

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17

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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18

Abe, Hiroyuki. "Reynolds-number dependence of wall-pressure fluctuations in a pressure-induced turbulent separation bubble." Journal of Fluid Mechanics 833 (November 7, 2017): 563–98. http://dx.doi.org/10.1017/jfm.2017.694.

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Direct numerical simulations are used to examine the behaviour of wall-pressure fluctuations $p_{w}$ in a flat-plate turbulent boundary layer with large adverse and favourable pressure gradients, involving separation and reattachment. The Reynolds number $Re_{\unicode[STIX]{x1D703}}$ based on momentum thickness is equal to 300, 600 and 900. Particular attention is given to effects of Reynolds number on root-mean-square (r.m.s.) values, frequency/power spectra and instantaneous fields. The possible scaling laws are also examined as compared with the existing direct numerical simulation and expe

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19

HIKITA, Yudai, Hiroki SUZUKI, Takatsugu KAMEDA, and Shinsuke MOCHIZUKI. "An experimental study on the equilibrium boundary layer subjected to favourable pressure gradient (Effect of pressure gradient on law of the wall)." Transactions of the JSME (in Japanese) 87, no. 894 (2021): 20–00394. http://dx.doi.org/10.1299/transjsme.20-00394.

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20

Escudier, M. P., A. Abdel-Hameed, M. W. Johnson, and C. J. Sutcliffe. "Laminarisation and re-transition of a turbulent boundary layer subjected to favourable pressure gradient." Experiments in Fluids 25, no. 5-6 (1998): 491–502. http://dx.doi.org/10.1007/s003480050255.

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21

DIXIT, SHIVSAI AJIT, and O. N. RAMESH. "Large-scale structures in turbulent and reverse-transitional sink flow boundary layers." Journal of Fluid Mechanics 649 (April 13, 2010): 233–73. http://dx.doi.org/10.1017/s0022112009993430.

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Aspects of large-scale organized structures in sink flow turbulent and reverse-transitional boundary layers are studied experimentally using hot-wire anemometry. Each of the present sink flow boundary layers is in a state of ‘perfect equilibrium’ or ‘exact self-preservation’ in the sense of Townsend (The Structure of Turbulent Shear Flow, 1st and 2nd edns, 1956, 1976, Cambridge University Press) and Rotta (Progr. Aeronaut. Sci., vol. 2, 1962, pp. 1–220) and conforms to the notion of ‘pure wall-flow’ (Coles,J. Aerosp. Sci., vol. 24, 1957, pp. 495–506), at least for the turbulent cases. It is fo

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22

Womack, Kristofer M., Charles Meneveau, and Michael P. Schultz. "Comprehensive shear stress analysis of turbulent boundary layer profiles." Journal of Fluid Mechanics 879 (September 27, 2019): 360–89. http://dx.doi.org/10.1017/jfm.2019.673.

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Motivated by the need for accurate determination of wall shear stress from profile measurements in turbulent boundary layer flows, the total shear stress balance is analysed and reformulated using several well-established semi-empirical relations. The analysis highlights the significant effect that small pressure gradients can have on parameters deduced from data even in nominally zero pressure gradient boundary layers. Using the comprehensive shear stress balance together with the log-law equation, it is shown that friction velocity, roughness length and zero-plane displacement can be determi

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23

Matai, Racheet, and Paul Durbin. "Large-eddy simulation of turbulent flow over a parametric set of bumps." Journal of Fluid Mechanics 866 (March 13, 2019): 503–25. http://dx.doi.org/10.1017/jfm.2019.80.

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Turbulent flow over a series of increasingly high, two-dimensional bumps is studied by well-resolved large-eddy simulation. The mean flow and Reynolds stresses for the lowest bump are in good agreement with experimental data. The flow encounters a favourable pressure gradient over the windward side of the bump, but does not relaminarize, as is evident from near-wall fluctuations. A patch of high turbulent kinetic energy forms in the lee of the bump and extends into the wake. It originates near the surface, before flow separation, and has a significant influence on flow development. The highest

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24

Katz, Y., A. Seifert, and I. Wygnanski. "On the evolution of the turbulent spot in a laminar boundary layer with a favourable pressure gradient." Journal of Fluid Mechanics 221 (December 1990): 1–22. http://dx.doi.org/10.1017/s0022112090003469.

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The evolution of a turbulent spot in an accelerating laminar boundary-layer flow was investigated. The type of boundary layer chosen for this experiment resembles in every respect the flow in the vicinity of a stagnation point theoretically described by Falkner and Skan. The rate of growth of the spot was significantly inhibited by the favourable pressure gradient in all three directions. It became much shorter and narrower in comparison with a similar spot generated in a Blasius boundary layer at comparable distances from its origin and comparable Reynolds numbers. The celerities of its bound

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25

Marxen, Olaf, Matthias Lang, and Ulrich Rist. "Discrete linear local eigenmodes in a separating laminar boundary layer." Journal of Fluid Mechanics 711 (September 27, 2012): 1–26. http://dx.doi.org/10.1017/jfm.2012.263.

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AbstractThe evolution of two- and three-dimensional small-amplitude disturbances in the laminar part of a laminar separation bubble is investigated in detail. We apply a combination of local linear stability theory, results from different experimental measurement campaigns and direct numerical simulations to identify two different discrete eigenmodes in the laminar part of the bubble. A stable eigenmode, the outer mode, governs unsteady oscillations in the upstream part of the bubble. However, this perturbation is quickly overtaken by an unstable eigenmode, the inner mode, which eventually lea

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26

Lutum, E., J. von Wolfersdorf, K. Semmler, J. Dittmar, and B. Weigand. "An experimental investigation of film cooling on a convex surface subjected to favourable pressure gradient flow." International Journal of Heat and Mass Transfer 44, no. 5 (2001): 939–51. http://dx.doi.org/10.1016/s0017-9310(00)00158-7.

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27

Zedan, M. F., and Charles Dalton. "The inverse method applied to a body of revolution with an extended favourable pressure gradient forebody." Communications in Applied Numerical Methods 2, no. 1 (1986): 113–19. http://dx.doi.org/10.1002/cnm.1630020115.

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28

ARAYA, GUILLERMO, LUCIANO CASTILLO, CHARLES MENEVEAU, and KENNETH JANSEN. "A dynamic multi-scale approach for turbulent inflow boundary conditions in spatially developing flows." Journal of Fluid Mechanics 670 (February 22, 2011): 581–605. http://dx.doi.org/10.1017/s0022112010005616.

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A dynamic method for prescribing realistic inflow boundary conditions is presented for simulations of spatially developing turbulent boundary layers. The approach is based on the rescaling–recycling method proposed by Lund, Wu & Squires (J. Comput. Phys, vol. 140, 1998, pp. 233–258) and the multi-scale method developed by Araya, Jansen & Castillo (J. Turbul., vol. 10, no. 36, 2009, pp. 1–33). The rescaling process requires prior knowledge about how the velocity and length scales are related between the inlet and recycle stations. Here a dynamic approach is proposed in which such inform

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29

Zuo, Feng-Yuan, Antonio Memmolo, Guo-ping Huang, and Sergio Pirozzoli. "Direct numerical simulation of conical shock wave–turbulent boundary layer interaction." Journal of Fluid Mechanics 877 (August 19, 2019): 167–95. http://dx.doi.org/10.1017/jfm.2019.558.

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Direct numerical simulation of the Navier–Stokes equations is carried out to investigate the interaction of a conical shock wave with a turbulent boundary layer developing over a flat plate at free-stream Mach number $M_{\infty }=2.05$ and Reynolds number $Re_{\unicode[STIX]{x1D703}}\approx 630$, based on the upstream boundary layer momentum thickness. The shock is generated by a circular cone with half opening angle $\unicode[STIX]{x1D703}_{c}=25^{\circ }$. As found in experiments, the wall pressure exhibits a distinctive N-wave signature, with a sharp peak right past the precursor shock gene

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30

Umur, H., R. I. Crane, and J. H. Whitelaw. "Acceleration and Injection Effects on Longitudinal Vortices in Concave Wall Boundary Layers." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 209, no. 1 (1995): 1–10. http://dx.doi.org/10.1243/pime_proc_1995_209_116_02.

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Measurements of longitudinal velocity and wall temperature have been obtained in a wind tunnel with a concave wall, with momentum thickness Görtler numbers from 5 to 10 at the initial station. Vortex generators were used to enhance the vortex structure in flow with zero streamwise pressure gradient. Spanwise variations existed over a limited range which is quantified. It is shown that mild acceleration amplified the vortices and enhanced the regularity of the spanwise variation; strong acceleration, with velocity gradient parameter K near 2 times 10−6, suppressed them and limited the growth in

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31

Bowles, Robert I. "Upstream influence and the form of standing hydraulic jumps in liquid-layer flows on favourable slopes." Journal of Fluid Mechanics 284 (February 10, 1995): 63–96. http://dx.doi.org/10.1017/s0022112095000279.

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Steady planar flow of a liquid layer over an obstacle is studied for favourable slopes. First, half-plane Poiseuille flow is found to be a non-unique solution on a uniformly sloping surface since eigensolutions exist which are initially exponentially small far upstream. These have their origin in a viscous–inviscid interaction between the retarding action of viscosity and the hydrostatic pressure from the free surface. The cross-stream pressure gradient caused by the curvature of the streamlines also comes into play as the slope increases. As the interaction becomes nonlinear, separation of th

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32

Pandey, Sanjay Kumar, and Jagdish Prasad Maurya. "Exploration of Characteristics Governing Dynamics of Whirlwinds: Application to Dust Devils." Zeitschrift für Naturforschung A 72, no. 8 (2017): 763–78. http://dx.doi.org/10.1515/zna-2017-0163.

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AbstractIt is intended to model mathematically an ideal whirlwind which characterises this geo-physical phenomenon and eventually helps us decode the inherent dynamics. A dense cylindrical aerial mass is taken into consideration surrounding a rarer aerial region in order to keep a radial favourable gradient of pressure to sustain a rotational motion. It has been concluded that the whirlwind will survive as long as the low pressure region exists. The vertical pressure gradient also plays an equally important role. Since it is not connected to any cloud and the axial velocity is in the verticall

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33

Maqbool, Khadija, Naeema Manzoor, Sebastien Poncet, and Abdul Majeed Siddiqui. "Inertial Flow of Viscoelastic Second-Grade Fluid in a Ciliated Channel under a Magnetic Field and Darcy’s Resistance." Applied Sciences 11, no. 9 (2021): 3819. http://dx.doi.org/10.3390/app11093819.

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This paper proposes a mathematical analysis of the inertial flow of an MHD second-grade non-Newtonian fluid in a ciliated channel. The two-dimensional flow is modelled under the effect of inertial forces, magnetic field and Darcy’s resistance, which make the system of partial differential equations highly non-linear. To solve the complex system of partial differential equations, the Homotopy Perturbation Method (HPM) is preferred. The HPM solutions for the velocity profile, stream function and pressure gradient are obtained using the software MATHEMATICA. The significances of the Reynolds numb

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34

Booty, M. R., and B. J. Matkowsky. "Slowly varying filtration combustion waves." European Journal of Applied Mathematics 4, no. 2 (1993): 205–24. http://dx.doi.org/10.1017/s0956792500001078.

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We describe the slow evolution of the wave speed and reaction temperature in a model of filtration combustion. In the counterflow configuration of the process, a porous solid matrix is converted to a porous solid product by injecting an oxidizing gas at high pressure into one end of a fresh sample of the solid while igniting it at the other end. The solid and gas react exothermically at high activation energy and, under favourable conditions, a self-sustaining combustion wave travels along the sample, converting reactants to product. Since the reaction rate depends on the gas pressure p in the

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35

OWEIS, GHANEM F., ERIC S. WINKEL, JAMES M. CUTBRITH, STEVEN L. CECCIO, MARC PERLIN, and DAVID R. DOWLING. "The mean velocity profile of a smooth-flat-plate turbulent boundary layer at high Reynolds number." Journal of Fluid Mechanics 665 (December 6, 2010): 357–81. http://dx.doi.org/10.1017/s0022112010003952.

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Smooth flat-plate turbulent boundary layers (TBLs) have been studied for nearly a century. However, there is a relative dearth of measurements at Reynolds numbers typical of full-scale marine and aerospace transportation systems (Reθ = Ueθ/ν > 105, where Ue = free-stream speed, θ = TBL momentum thickness and ν = kinematic viscosity). This paper presents new experimental results for the TBL that forms on a smooth flat plate at nominal Reθ values of 0.5 × 105, 1.0 × 105 and 1.5 × 105. Nominal boundary layer thicknesses (δ) were 80–90mm, and Karman numbers (δ+) were 17000, 32000 and 47000, res

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36

FERNHOLZ, H. H., and D. WARNACK. "The effects of a favourable pressure gradient and of the Reynolds number on an incompressible axisymmetric turbulent boundary layer. Part 1. The turbulent boundary layer." Journal of Fluid Mechanics 359 (March 25, 1998): 329–56. http://dx.doi.org/10.1017/s0022112097008513.

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The effects of a favourable pressure gradient (K[les ]4×10−6) and of the Reynolds number (862[les ]Reδ2[les ]5800) on the mean and fluctuating quantities of four turbulent boundary layers were studied experimentally and are presented in this paper and a companion paper (Part 2). The measurements consist of extensive hot-wire and skin-friction data. The former comprise mean and fluctuating velocities, their correlations and spectra, the latter wall-shear stress measurements obtained by four different techniques which allow testing of calibrations in both laminar-like and turbulent flows for the

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37

Stefes, B., and H. H. Fernholz. "The influence of high free-stream turbulence and a favourable pressure gradient on an incompressible axisymmetric turbulent boundary layer." European Journal of Mechanics - B/Fluids 24, no. 2 (2005): 167–87. http://dx.doi.org/10.1016/j.euromechflu.2004.06.004.

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38

SCHWARZ, A. C., M. W. PLESNIAK, and S. N. B. MURTHY. "Response of turbulent boundary layers to multiple strain rates." Journal of Fluid Mechanics 458 (May 10, 2002): 333–77. http://dx.doi.org/10.1017/s0022112002007863.

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Many practical applications, such as in blade cascades and turbomachinery, involve inhomogeneous turbulent shear flows subjected simultaneously to multiple strains. In principle, the applied strain can be combined to yield an effective strain. However, no simple stress–strain relation is capable of establishing turbulent stress or energy balance in the mean or on an instantaneous basis. In the current investigation, a turbulent boundary layer is examined in the presence of convex curvatures of different strengths combined with streamwise (favourable and adverse) pressure gradients, with variou

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39

Barnes, C. J., M. R. Visbal, and P. G. Huang. "On the effects of vertical offset and core structure in streamwise-oriented vortex–wing interactions." Journal of Fluid Mechanics 799 (June 21, 2016): 128–58. http://dx.doi.org/10.1017/jfm.2016.320.

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This article explores the three-dimensional flow structure of a streamwise-oriented vortex incident on a finite aspect-ratio wing. The vertical positioning of the incident vortex relative to the wing is shown to have a significant impact on the unsteady flow structure. A direct impingement of the streamwise vortex produces a spiralling instability in the vortex just upstream of the leading edge, reminiscent of the helical instability modes of a Batchelor vortex. A small negative vertical offset develops a more pronounced instability while a positive vertical offset removes the instability alto

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40

Araya, Guillermo, Luciano Castillo, and Fazle Hussain. "The log behaviour of the Reynolds shear stress in accelerating turbulent boundary layers." Journal of Fluid Mechanics 775 (June 19, 2015): 189–200. http://dx.doi.org/10.1017/jfm.2015.296.

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Direct numerical simulation of highly accelerated turbulent boundary layers (TBLs) reveals that the Reynolds shear stress,$\overline{u^{\prime }v^{\prime }}^{+}$, monotonically decreases downstream and exhibits a logarithmic behaviour (e.g. $-\overline{u^{\prime }v^{\prime }}^{+}=-(1/A_{uv})\ln y^{+}+B_{uv}$) in the mesolayer region (e.g. $50\leqslant y^{+}\leqslant 170$). The thickness of the log layer of$\overline{u^{\prime }v^{\prime }}^{+}$increases with the streamwise distance and with the pressure gradient strength, extending over a large portion of the TBL thickness (up to 55 %). Simula

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41

Tolkachev, Stepan, Victor Kozlov, and Valeriya Kaprilevskaya. "Influence of two-dimensional roughness element on boundary layer structure in the favourable pressure gradient region of the swept wing." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 234, no. 1 (2019): 20–27. http://dx.doi.org/10.1177/0954410019841776.

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In this article, the results of research about stationary and secondary disturbances development behind the localized and two-dimensional roughness elements are presented. It is shown that the two-dimensional roughness element has a destabilizing effect on the disturbances induced by the three-dimensional roughness element lying upstream. In this case, the two-dimensional roughness element causes the appearance of stationary structures, and then secondary perturbations, whose frequency range lies lower than in the case of the stationary vortices excited by a three-dimensional roughness element

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Fink, A. H., T. Brücher, V. Ermert, A. Krüger, and J. G. Pinto. "The European storm Kyrill in January 2007: synoptic evolution, meteorological impacts and some considerations with respect to climate change." Natural Hazards and Earth System Sciences 9, no. 2 (2009): 405–23. http://dx.doi.org/10.5194/nhess-9-405-2009.

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Abstract. The synoptic evolution and some meteorological impacts of the European winter storm Kyrill that swept across Western, Central, and Eastern Europe between 17 and 19 January 2007 are investigated. The intensity and large storm damage associated with Kyrill is explained based on synoptic and mesoscale environmental storm features, as well as on comparisons to previous storms. Kyrill appeared on weather maps over the US state of Arkansas about four days before it hit Europe. It underwent an explosive intensification over the Western North Atlantic Ocean while crossing a very intense zona

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Shamsoddin, Sina, and Fernando Porté-Agel. "Wind turbine wakes over hills." Journal of Fluid Mechanics 855 (September 19, 2018): 671–702. http://dx.doi.org/10.1017/jfm.2018.653.

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Understanding and predicting the behaviour of wind turbine wake flows over hills is important for optimal design of wind-farm configurations on topography. In this study, we present an analytical modelling framework together with large-eddy simulation (LES) results to investigate turbine wakes over two-dimensional hills. The analytical model consists of two steps. In the first step, we deal with the effect of the pressure gradient on the wake evolution; and in the second step, we consider the effect of the hill-induced streamline distortion on the wake. This model enables us to obtain the wake

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P., Arun Kumar, and E. Rathakrishnan. "Triangular tabs for supersonic jet mixing enhancement." Aeronautical Journal 118, no. 1209 (2014): 1245–78. http://dx.doi.org/10.1017/s0001924000009969.

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AbstractThe mixing promoting capability of right-angled triangular tab with sharp and truncated vertex has been investigated by placing two identical tabs at the exit of a Mach 2 axi-symmetric nozzle. The mixing promoting efficiency of these tabs have been quantified in the presence of adverse and marginally favourable pressure gradients at the nozzle exit. It was found that, at all levels of expansion of the present study though the core length reduction caused by both the tabs are appreciable, but the mixing caused by the truncated tab is superior. The mixing promoting efficiency of the trun

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Perry, A. E., and Ivan Marušić. "A wall-wake model for the turbulence structure of boundary layers. Part 1. Extension of the attached eddy hypothesis." Journal of Fluid Mechanics 298 (September 10, 1995): 361–88. http://dx.doi.org/10.1017/s0022112095003351.

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The attached eddy hypothesis developed for zero pressure gradient boundary layers and for pipe flow is extended here to boundary layers with arbitrary streamwise pressure gradients, both favourable and adverse. It is found that in order to obtain the correct quantitative results for all components of the Reynolds stresses, two basic types of eddy structure geometries are required. The first type, called type-A, is interpreted to give a ‘wall structure’ and the second, referred to as type-B, gives a ‘wake structure’. This is in analogy with the conventional mean velocity formulation of Coles wh

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Wu, Wen, and Ugo Piomelli. "Effects of surface roughness on a separating turbulent boundary layer." Journal of Fluid Mechanics 841 (February 26, 2018): 552–80. http://dx.doi.org/10.1017/jfm.2018.101.

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Separating turbulent boundary layers over smooth and rough flat plates are studied by large-eddy simulations. A suction–blowing velocity distribution imposed at the top boundary of the computation domain produces an adverse-to-favourable pressure gradient and creates a closed separation bubble. The Reynolds number based on the momentum thickness and the free-stream velocity before the pressure gradient begins is 2500. Virtual sand grain roughness in the fully rough regime is modelled by an immersed boundary method. Compared with a smooth-wall case, streamline detachment occurs earlier and the

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HAYNES, TIM S., and HELEN L. REED. "Simulation of swept-wing vortices using nonlinear parabolized stability equations." Journal of Fluid Mechanics 405 (February 25, 2000): 325–49. http://dx.doi.org/10.1017/s0022112099007260.

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The nonlinear development of stationary crossflow vortices over a 45° swept NLF(2)-0415 airfoil is studied. Previous investigations indicate that the linear stability theory (LST) is unable to accurately describe the unstable flow over crossflow-dominated configurations. In recent years the development of nonlinear parabolized stability equations (NPSE) has opened new pathways toward understanding unstable boundary-layer flows. This is because the elegant inclusion of nonlinear and non-parallel effects in the NPSE allows accurate stability analyses to be performed without the difficulties and

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Recek. "Venous pressure gradients in the lower extremity and the hemodynamic consequences." Vasa 39, no. 4 (2010): 292–97. http://dx.doi.org/10.1024/0301-1526/a000052.

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Pressure differences play an important role in the hemodynamics of both arterial and venous circulation. Venous ambulatory pressure gradient of about 35 mm Hg arises during the activity of the calf muscle venous pump between the veins in the thigh and the lower leg; this is the initiator launching venous reflux in varicose vein patients. The hemodynamic consequence of venous reflux is interference with the physiological decrease in venous pressure in the lower leg and foot and the occurrence of ambulatory venous hypertension, the degree of which depends on the magnitude of refluxing blood. Pre

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Provost, Alden M., and W. H. Schwarz. "A theoretical study of viscous effects in peristaltic pumping." Journal of Fluid Mechanics 279 (November 25, 1994): 177–95. http://dx.doi.org/10.1017/s0022112094003873.

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Intuition and previous results suggest that a peristaltic wave tends to drive the mean flow in the direction of wave propagation. New theoretical results indicate that, when the viscosity of the transported fluid is shear-dependent, the direction of mean flow can oppose the direction of wave propagation even in the presence of a zero or favourable mean pressure gradient. The theory is based on an analysis of lubrication-type flow through an infinitely long, axisymmetric tube subjected to a periodic train of transverse waves. Sample calculations for a shear-thinning fluid illustrate that, for a

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Bicknell, G. V. "Turbulent jets and the energy budget in Fanaroff–Riley class-I radio sources." Canadian Journal of Physics 64, no. 4 (1986): 495–500. http://dx.doi.org/10.1139/p86-093.

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There are good reasons, based upon laboratory data and jet morphology, for believing that the jets in Fanaroff–Riley class-I radio sources are turbulently expanding and decelerating owing to the related entrainment. This provides a simple explanation for the usual slow decline of jet-surface brightness in class-I radio sources. A turbulent jet model in which the velocity variation is inferred from the spreading rate is presented and applied to the main jet in NGC 315. Besides providing a reasonable fit to the surface-brightness variation, the model provides the following simple explanation for

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