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Author(s): Vera Maria Machado Ribeiro
Hugo Ferreira
Patrícia Catarina Saraiva de Sousa
Paulo José da Silva Martins Coelho
Fernando Manuel Coutinho Tavares de Pinho
Manuel António Moreira Alves
Title: Three-dimensional effects in low Reynolds number flow around confined cylinders
Issue Date: 2008
Abstract: An experimental and numerical study is carried out to investigate three-dimensional effects in theflow of Newtonian fluids around confined cylinders, for Reynolds numbers below 40 and aspect ratiosbetween 1 and 16. Experiments rely on flow visualizations and detailed velocity measurements by PIV,while predictions were carried out using a finite volume method. Velocity peaks near the side walls werefound to occur at all Reynolds numbers and for AR > 3. At low Reynolds numbers these velocity peaks aredue to the excessive braking role of the side wall, which forces a local fluid acceleration for massconservation that the very small diffusive spanwise-streamwise momentum flux x (xz) is unable to smooth out.This disappears when the aspect ratio is reduced and by implication the xz stress increases strongly. Inertiacounteracts the role of this diffusive momentum flux so much that at AR = 1 there are still velocity peakswhen Re = 40. When inertia is strong there is flow separation in the wake of the cylinder, but this separatedflow region is open. The fluid particles near the side wall, but not too near, are better able to sustain theadverse streamwise pressure gradient and recover better the pressure as they flow across the cylinder.Consequently, the separated flow region is shorter and the pressure is higher in that region leading to asecondary spiraling spanwise flow from the side wall to the centre plane. The fluid exits the recirculationregion at the centre plane and enters it at the velocity peak region near the wall, which is being fed by fluidcoming from the neighbour region located to the inner side of the duct. This has a positive feedbackenhancing the velocity peaks. At the wall itself friction extracts so much energy from the fluid particles thatthese are less able to sustain the adverse streamwise pressure gradient and the separated flow lengthincreases significantly.
Subject: Engenharia mecânica, Engenharia mecânica
Mechanical engineering, Mechanical engineering
Source: 14th International Symposium on Applications of Laser Techniques to Fluid Mechanics
Document Type: Artigo em Livro de Atas de Conferência Internacional
Rights: restrictedAccess
Appears in Collections:FEUP - Artigo em Livro de Atas de Conferência Internacional

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