POF: Instability and Transition http://scitation.aip.org/ POF: Instability and Transition Secondary instability in the near-wake past two tandem square cylinders http://link.aip.org/link/?PHF/24/024102/1&agg=rss Choon-Bum Choi, Yong-Jun Jang, and Kyung-Soo Yang<br/> Floquet stability analysis has been carried out to detect the onset of the secondary instability in the laminar flow past two identical square cylinders in tandem. Presence of a neighbouring cylinder alters flow topology, leading to change of stability characteristics. A parametric study has been pe ... [Phys. Fluids 24, 024102 (2012)] published Wed Feb 8, 2012. Study of instabilities and transitions for a family of quasi-two-dimensional magnetohydrodynamic flows based on a parametrical model http://link.aip.org/link/?PHF/24/024101/1&agg=rss S. Smolentsev, N. Vetcha, and R. Moreau<br/> In this study, flow phenomena associated with inflectional and boundary-layer instabilities, as well as a mixed instability mode in quasi-two-dimensional magnetohydrodynamic flows in a rectangular duct are accessed with the help of a parametrical model, where the basic velocity profile with near-wal ... [Phys. Fluids 24, 024101 (2012)] published Tue Feb 7, 2012. Low-dimensional model of spatial shear layers http://link.aip.org/link/?PHF/24/014108/1&agg=rss Mingjun Wei, Bashar R. Qawasmeh, Matthew Barone, Bart G. van Bloemen Waanders, and Lin Zhou<br/> The aim of this work is to develop nonlinear low-dimensional models to describe vortex dynamics in spatially developing shear layers with periodicity in time. By allowing a free variable g(x) to dynamically describe downstream thickness spreading, we are able to obtain basis functions in a scaled re ... [Phys. Fluids 24, 014108 (2012)] published Tue Jan 31, 2012. Cavitation inception during the interaction of a pair of counter-rotating vortices http://link.aip.org/link/?PHF/24/014107/1&agg=rss Natasha A. Chang, Jaehyug Choi, Ryo Yakushiji, and Steven L. Ceccio<br/> Pairs of unequal strength, counter-rotating vortices were produced to examine the inception and dynamics of vortex cavitation as the vortices undergo a long-wavelength instability. The instability causes the weaker, secondary vortex to be turned and stretched by the stronger primary vortex. Folding ... [Phys. Fluids 24, 014107 (2012)] published Thu Jan 19, 2012. The linear stability of oscillating pipe flow http://link.aip.org/link/?PHF/24/014106/1&agg=rss C. Thomas, A. P. Bassom, and P. J. Blennerhassett<br/> An investigation is made of the three-dimensional linear stability of the Stokes layer generated within a fluid contained inside a long oscillating cylinder. Both longitudinal and torsional vibrations are examined and the system of disturbance equations derived using Floquet theory are solved using ... [Phys. Fluids 24, 014106 (2012)] published Wed Jan 11, 2012. Experimental evidence of a triadic resonance of plane inertial waves in a rotating fluid http://link.aip.org/link/?PHF/24/014105/1&agg=rss Guilhem Bordes, Frederic Moisy, Thierry Dauxois, and Pierre-Philippe Cortet<br/> Plane inertial waves are generated using a wavemaker, made of oscillating stacked plates, in a rotating water tank. Using particle image velocimetry, we observe that, after a transient, the primary plane wave is subject to a subharmonic instability and excites two secondary plane waves. The measured ... [Phys. Fluids 24, 014105 (2012)] published Wed Jan 11, 2012. Falling liquid films on longitudinal grooved geometries: Integral boundary layer approach http://link.aip.org/link/?PHF/24/014104/1&agg=rss I. Mohammed Rizwan Sadiq, Tatiana Gambaryan-Roisman, and Peter Stephan<br/> Falling thin liquid film on a substrate with complex topography is modeled using a three equation integral boundary layer system. Linear stability and nonlinear dynamics of the film in the framework of this model are studied on a topography with sinusoidal longitudinal grooves aligned parallel in th ... [Phys. Fluids 24, 014104 (2012)] published Mon Jan 9, 2012. An experimental study of transitional pulsatile pipe flow http://link.aip.org/link/?PHF/24/014103/1&agg=rss R. Trip, D. J. Kuik, J. Westerweel, and C. Poelma<br/> The transitional regime of a sinusoidal pulsatile flow in a straight, rigid pipe is investigated using particle image velocimetry. The main aim is to investigate how the critical Reynolds number is affected by different pulsatile conditions, expressed as the Womersley number and the oscillatory Reyn ... [Phys. Fluids 24, 014103 (2012)] published Fri Jan 6, 2012. Negative Magnus lift on a rotating sphere at around the critical Reynolds number http://link.aip.org/link/?PHF/24/014102/1&agg=rss Masaya Muto, Makoto Tsubokura, and Nobuyuki Oshima<br/> Negative Magnus lift acting on a sphere rotating about the axis perpendicular to an incoming flow was investigated using large-eddy simulation at three Reynolds numbers of 1.0 x 10, 2.0 x 10, and 1.14 x 10. The numerical methods used were first validated on a non-rotating sphere, and the spati ... [Phys. Fluids 24, 014102 (2012)] published Thu Jan 5, 2012. Three-dimensional swirling flows in a tall cylinder driven by a rotating endwall http://link.aip.org/link/?PHF/24/014101/1&agg=rss J. M. Lopez<br/> The onset and nonlinear dynamics of swirling flows in relatively tall cylinders driven by the rotation of an endwall are studied numerically. These flows are distinguished from the more widely studied swirling flows in shorter cylinders; the instability in the taller cylinders is direct to three-dim ... [Phys. Fluids 24, 014101 (2012)] published Wed Jan 4, 2012. Measurements of axial instability waves in the near exit region of a high speed liquid jet http://link.aip.org/link/?PHF/23/124105/1&agg=rss J. E. Portillo, S. H. Collicott, and G. A. Blaisdell<br/> This work presents wavelength measurements of axial instability waves along the surface of a liquid jet operated within the atomization regime. The surface waves appear in the near exit region of the initially laminar jet. The measurements show that the waves stretch as they are convected downstream ... [Phys. Fluids 23, 124105 (2011)] published Fri Dec 30, 2011. Three-dimensional evolution of flow structures in transitional circular and chevron jets http://link.aip.org/link/?PHF/23/124104/1&agg=rss Daniele Violato and Fulvio Scarano<br/> The three-dimensional behavior of flow transition in circular and 6-chevron jets at Re = 5000 is investigated with experiments conducted on a free water jet by time-resolved tomographic particle image velocimetry. The emphasis is on the unsteady organization of coherent flow structures, which play a ... [Phys. Fluids 23, 124104 (2011)] published Tue Dec 27, 2011. Holmboe instability in non-Boussinesq fluids http://link.aip.org/link/?PHF/23/124103/1&agg=rss Ricardo Barros and Wooyoung Choi<br/> We perform the stability analysis for stratified shear flows whose density transition layer is much thinner than, and possibly, displaced with respect to, the velocity shear layer for which Holmboe instability along with the well-known Kelvin-Helmholtz (KH) instability is known to be present. Here, ... [Phys. Fluids 23, 124103 (2011)] published Thu Dec 22, 2011. Interaction of viscous and inviscid instability modes in separationbubble transition http://link.aip.org/link/?PHF/23/124102/1&agg=rss Joshua R. Brinkerhoff and Metin I. Yaras<br/> This paper describes numerical simulations that are used to examine the interaction of viscous and inviscid instability modes in laminar-to-turbulent transition in a separation bubble. The results of a direct numerical simulation are presented in which separation of a laminar boundary-layer occurs i ... [Phys. Fluids 23, 124102 (2011)] published Wed Dec 14, 2011. A simple analytic approximation to the Rayleigh-Benard stability threshold http://link.aip.org/link/?PHF/23/124101/1&agg=rss Andrea Prosperetti<br/> The Rayleigh-Benard linear stability problem is solved by means of a Fourier series expansion. It is found that truncating the series to just the first term gives an excellent explicit approximation to the marginal stability relation between the Rayleigh number and the wave number of the perturbatio ... [Phys. Fluids 23, 124101 (2011)] published Wed Dec 7, 2011. The instability of the boundary layer over a disk rotating in an enforced axial flow http://link.aip.org/link/?PHF/23/114108/1&agg=rss Z. Hussain, S. J. Garrett, and S. O. Stephen<br/> We consider the convective instability of stationary and traveling modes within the boundary layer over a disk rotating in a uniform axial flow. Complementary numerical and high Reynolds number asymptotic analyses are presented. Stationary and traveling modes of type I (crossflow) and type II (strea ... [Phys. Fluids 23, 114108 (2011)] published Wed Nov 30, 2011. Transient growth of secondary instabilities in parallel wakes: Anti lift-up mechanism and hyperbolic instability http://link.aip.org/link/?PHF/23/114106/1&agg=rss Sabine Ortiz and Jean-Marc Chomaz<br/> This paper investigates the three-dimensional temporal instabilities and the transient growth of perturbations on a Von Karman vortex street, issuing from the development of the primary instability of a parallel Bickley velocity profile typical of a wake forming behind a thin flat plate. By solving ... [Phys. Fluids 23, 114106 (2011)] published Mon Nov 28, 2011. Nonlinear effects in the combined Rayleigh-Taylor/Kelvin-Helmholtz instability http://link.aip.org/link/?PHF/23/114107/1&agg=rss Britton J. Olson, Johan Larsson, Sanjiva K. Lele, and Andrew W. Cook<br/> The combined Rayleigh-Taylor/Kelvin-Helmholtz (RT/KH) instability is studied in the early nonlinear regime. Specifically, the effect of adding shear to a gravitationally unstable configuration is investigated. While linear stability theory predicts that any amount of shear would increase the growth ... [Phys. Fluids 23, 114107 (2011)] published Mon Nov 28, 2011. Resonant phenomenon of elliptical cylinder flows in a subcritical regime http://link.aip.org/link/?PHF/23/114105/1&agg=rss Shih-Sheng Chen and Ruey-Hor Yen<br/> The resonant phenomena in the wake behind a transversely vibrating elliptical cylinder with different axis ratios from Ar = 0.01 to Ar = 2.0 in the subcritical regime is numerically investigated. Navier-Stokes equations are solved by a spectral element code with a triangular mesh. Reynolds numbers r ... [Phys. Fluids 23, 114105 (2011)] published Tue Nov 22, 2011. On the early evolution in the transient BenardMarangoni problem http://link.aip.org/link/?PHF/23/114104/1&agg=rss M. Weidenfeld and I. Frankel<br/> We focus on the early evolution of small (linear) perturbations following the sudden (step-function) exposure of a liquid layer to a cold adjacent atmosphere. On a time scale short relative to that characterizing thermal relaxation across the liquid layer, the temperature distribution is nonlinear a ... [Phys. Fluids 23, 114104 (2011)] published Tue Nov 22, 2011. Effect of base cavities on the stability of the wake behind slender blunt-based axisymmetric bodies http://link.aip.org/link/?PHF/23/114103/1&agg=rss E. Sanmiguel-Rojas, J. I. Jimenez-Gonzalez, P. Bohorquez, G. Pawlak, and C. Martinez-Bazan<br/> We extend our previous research on the instability properties of the laminar incompressible flow of density rho and viscosity [mu], which develops behind a cylindrical body with a rounded nose and length-to-diameter ratio L/D = 2, aligned with a free-stream of velocity w [E. Sanmiguel-Rojas et al., ... [Phys. Fluids 23, 114103 (2011)] published Fri Nov 18, 2011.