0000000000389874

AUTHOR

Flavio Giannetti

showing 3 related works from this author

Global Linear Stability Analysis of the Flow Around a Superhydrophobic Circular Cylinder

2016

International audience; Over the last few years, superhydrophobic (SH) surfaces have been receiving an increasing attention in many scientific areas by virtue of their ability to enhance flow slip past solid walls and reduce the skin-friction drag. In the present study, a global linear-stability analysis is employed to investigate the influence of the SH-induced slip velocity on the primary instability of the 2D flow past a circular cylinder. The flow regions playing the role of 'wavemaker' are identified by considering the structural sensitivity of the unstable mode, thus highlighting the effect of slip on the global instability of the considered flow. In addition, a sensitivity analysis t…

Hopf BifurcationFlow (psychology)Direct numerical simulationSlip SurfaceSlip (materials science)01 natural sciencesInstability010305 fluids & plasmasPhysics and Astronomy (all)symbols.namesakeTheoretical physics0103 physical sciencesCylinder[PHYS.MECA.MEFL]Physics [physics]/Mechanics [physics]/Fluid mechanics [physics.class-ph]010303 astronomy & astrophysicsHopf bifurcationPhysicsDirect Numerical SimulationStrouhal NumberMechanicsbody regionsDragsymbolsStrouhal numberSlip Length[MATH.MATH-OC]Mathematics [math]/Optimization and Control [math.OC]
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Towards a quantitative comparison between global and local stability analysis

2017

A methodology is proposed here to estimate the stability characteristics of bluff-body wakes using local analysis under the assumption of weakly non-parallel flows. In this connection, a generalisation of the classic spatio-temporal stability analysis for fully three-dimensional flows is first described. Secondly, an additional higher-order correction term with respect to the common saddle-point global frequency estimation is included in the analysis. The proposed method is first validated for the case of the flow past a circular cylinder and then applied to two fully three-dimensional flows: the boundary layer flow over a wall-mounted hemispherical body and the wake flow past a fixed spher…

PhysicsMechanical Engineeringabsolute/convective instabilityMechanicsinstability; Key words absolute/convective instability; wakes; Condensed Matter Physics; Mechanics of Materials; Mechanical EngineeringKey words absolute/convective instabilityCondensed Matter Physics01 natural sciencesStability (probability)Instabilitywakes010305 fluids & plasmasTerm (time)Boundary layerinstabilityFlow (mathematics)Local analysisMechanics of Materials0103 physical sciencesApplied mathematics010306 general physicsabsolute/convective instability; instability; wakesEigenvalues and eigenvectorsSaddle
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Boundary-layer Flows Past an Hemispherical Roughness Element: DNS, Global Stability and Sensitivity Analysis

2015

Abstract We investigate the full three-dimensional instability mechanism arising in the wake of an hemispherical roughness element immersed in a laminar Blasius boundary layer. The inherent three-dimensional flow pattern beyond the critical Reynolds number is characterized by coherent vortical structures called hairpin vortices. Direct numerical simulation is used to analyze the formation and the shedding of hairpin packets inside the shear layer. The first bifurcation characteristics are investigated by global stability tools. We show the spatial structure of the linear direct and adjoint global eigenmodes of the linearized Navier-Stokes operator and use structural sensitivity analysis to …

TriGlobal Linear StabilityDirect numerical simulation02 engineering and technologyWake01 natural sciencesInstability010305 fluids & plasmasPhysics::Fluid Dynamicssymbols.namesake0203 mechanical engineeringHairpin vortices0103 physical sciencesPhysics020301 aerospace & aeronauticsRoughness ElementHairpin vortices; Roughness Element; TriGlobal Linear Stability; Mechanical EngineeringMechanical EngineeringReynolds numberLaminar flowGeneral MedicineMechanicsVortexBoundary layerClassical mechanicsBlasius boundary layersymbolsProcedia IUTAM
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