The transient evolution of infinitesimal flow disturbances which optimally induce algebraic growth in the Lamb–Oseen (Gaussian) vortex is studied using a direct-adjoint technique. This optimal perturbation analysis reveals that allows for intense amplification kinetic energy two-dimensional and three-dimensional perturbations azimuthal wavenumber m=1. In both cases, experiencing most initially take form concentrated spirals at outer periphery rapidly excite bending waves within core. limit...

In this paper, a numerical investigation of three-dimensional round jets subjected to streamwise and azimuthal perturbations is reported. The main objective the study give consistent scenario for breaking rotational symmetry in such flows which may ultimately lead production intense side jets. particular it shown that development Widnall instability on primary vortex rings evolution Bernal Roshko [J. Fluid Mech. 170, 499 (1986)] vortices generated by braid could be deeply intertwined. A...

Stable columnar vortices subject to hydrodynamic noise (e.g. turbulence) present recurrent behaviours, such as the systematic development of vortex rings at periphery core. This phenomenon lacks a comprehensive explanation, partly because it is not associated with an instability stricto sensu . The aim paper identify physical mechanism triggering this intrinsic feature using optimal perturbation analysis tool investigation. We find that generation linked intense and rapid amplification...

This paper investigates the three-dimensional stability of Lamb–Chaplygin vortex pair. Short-wavelength instabilities, both symmetric and antisymmetric, are found. The antisymmetric mode possesses largest growth rate is indeed one reported in a recent experimental study [J. Fluid Mech. 360, 85 (1998)]. rates, wave numbers maximum amplification, spatial eigenmodes these short-wavelength instabilities good agreement with predictions from elliptic instability theory. A long-wavelength similar...

The aim of the present paper is to analyse dynamics Lamb–Oseen vortex when continuously forced by a random excitation. Stochastic forcing classically used mimic external perturbations in realistic configurations, such as variations atmospheric conditions, weak compressibility effects, wing-generated turbulence injected into aircraft wakes, or free-stream wind tunnel experiments. linear response stochastic can be decomposed relation azimuthal symmetry perturbation given wavenumber m . In...

The generic problem of the spatiotemporal instability a periodic basic flow (Stuart vortices) is considered in order to interpret sequence bifurcations observed open shear flows. Using novel numerical technique, we show that more concentrated vortices, smaller backflow needed trigger absolute instability. These results allow us propose an alternative interpretation for subharmonic resonance forced flows, which classically attributed acoustic feedback.

The present work investigates experimentally the dynamics of vortex rings in shear-thinning fluids at low generalized Reynolds numbers, with a focus on range from 300 down to 30. experimental apparatus consists vertical cylinder-piston system lower part immersed tank filled liquid. Particle image velocimetry is used analyze influence non-Newtonian nature fluid generation, propagation, and eventual dissipation rings. results show that controls generation phase, whereas ring subsequent...

We present a linear optimal perturbation analysis of streamwise invariant disturbances evolving in parallel round jets. The potential for transient energy growth perturbations with azimuthal wavenumber m≥1 is analyzed different values Reynolds number Re. Two families steady (frozen) and unsteady (diffusing) base flow velocity profiles have been used, aspect ratios α = R/θ, where R the jet radius θ shear layer momentum thickness. Optimal initial conditions correspond to infinitesimal...

The present work investigates the local modal and non-modal stability of round jets for varying aspect ratios α = R/θ, where R is jet radius θ shear layer momentum thickness, Reynolds numbers ranging from 10 to 000. competition between axisymmetric (azimuthal wavenumber m 0) helical (m 1) perturbations depending on ratio, α, quantified at different time horizons. Three techniques have been used, namely, a classical temporal analysis in order characterize unstable modes jet; an optimal...

A computational study is reported of the close interaction nominally anti-parallel vortex tubes with unequal strengths, Γ 1 and − 2 , where / [les ] 1. The computations are performed using a spectral method, periodic boundary conditions Reynolds number Re ≡ v = 1500, vortices perturbed by wavelength for which pair unstable because their mutual interaction. numerical method tested case equal-strength vortices, exhibits classic reconnection phenomenon typified bridging between cores formation...

The topology and dynamics of the flow bypassing an automobile A-pillar modeled by a 30° dihedron are investigated experimentally. various components identified means low high frequency particle image velocimetry. For each component, time evolution position, displacement, vorticity magnitude, circulation, fluctuating kinetic energy analyzed along A-pillar. More precisely, is composed two vortex structures with different behaviors. major structure grows in size, circulation total amount...

The present work investigates the existence and evolution of a spanwise vortex at front shallow dipolar vortices. dipoles are experimentally generated using double flap apparatus. Particle image velocimetry measurements performed in horizontal plane vertical symmetry flow. dynamics such vortical structures is investigated through parametric study which both Reynolds number Re=U0D0/ν∈[90,470] aspect ratio α=h/D0∈[0.075,0.7], associated with shallowness flow, varied, where U0 initial velocity...

Several families of two-dimensional instabilities exhibiting maximal growth rates at low Reynolds numbers are observed in a frozen Lamb-Oseen vortex dipole. Despite their damping due to base-flow unsteadiness, these unstable modes able grow the time-evolving aircraft wake by taking advantage transient based on Orr mechanism.

The A-pillar vortex is a three-dimensional coherent structure that appears on vehicles in motion such as cars, trucks, trains and even delta wings. has conical shape evolves along the vehicle or upper surface of Such phenomenon complex dynamics strong interaction with its environment (fluid solid) generating aerodynamic noise vibrations. significant aspect project not only to understand topology flow but also what part it directly responsible for wall pressure fluctuations structure. A...

Vortex rings are self-propagating structures that can transport mass and momentum to locations remote from the ring creation. We focus on reorganization of a light vortex impinging, at given angle vertical, layer fluid stably stratified in density, as many environmental applications. also examine response with regard baroclinic vorticity internal gravity wave generation. The symmetry both flow field is preserved over time for normal impacts. For inclined impacts, reorganizes into vertically...

Afin d'améliorer la compréhension de mise en suspension vase au fond des estuaires, une étude paramétrique stabilité d’un écoulement bidimensionnel cisaillé modélisant deux couches fluides miscibles masse volumique et viscosité dynamique différentes. Le code simulation numérique directe JADIM l'IMFT (Institut Mécanique Fluides Toulouse) est utilisé pour calculer l’évolution temporelle ces écoulements. modèle initialisé à l'aide profils verticaux continus type erf(z) toutes les grandeurs...

Abstract A computational code EZ‐vortex is developed for the motion of slender vortex filaments closed or open shape. The integro‐differential equations governing centre lines are either Callegari and Ting equations, which leading order solution a matched asymptotic analysis, equivalent forms these equations. They include large axial velocity nonsimilar profiles in vortical cores. fluid may be viscous inviscid. This validated both against known solutions results from linear stability...