Finite element simulation of transient laminar flow past a circular cylinder and two cylinders in tandem - Influence of buoyancy

Flow Past an isolated circular cylinder and two cylinders in tandem is nume rically simulated under the influence of buoyancy aiding and opposing the f low. A modified velocity correction method is employed which has second ord er accuracy in both space and time. The influence of buoyancy on the tempor al fluid flow patterns is investigated, with respect to streamlines, isothe rms and streaklines. Comparisons are made with respect to mean centre line velocities, drag coefficients, Strouhal number and streakline patterns. Deg eneration of naturally occurring Karman vortex street into a twin eddy patt ern is noticed in the Reynolds number (Re) range of 41-200, under buoyancy aided convection. On the contrary, buoyancy opposed convection could trigge r vortex shedding even at a lore Re range of 20-40, where only twin eddies are found in the natural wake. Temporal evolution of unsteady eddy patterns is visualized by means of numerical particle release (NPR). Zones of vorte x shedding and twin vortices are demarcated on a plot of Richardson number against Strouhal number. Root mean square (RMS) lift coefficients (C-L,C-MR S) and average drag coefficient (<(C-d)over bar>) are obtained as a functio n of Richardson number (Ri).