Vortex induced vibration for mixed convective flow past a square cylinder

Abstract

In this work, a comprehensive numerical investigation of the combined effect of buoyancy and flow approach angle (α) on vortex-induced vibration of an elastically mounted square cylinder at a fixed Reynolds number, Re = 100, Prandtl number (Pr = 7.1) and mass ratio (Mred) of 2 is conducted. Extensive numerical experiments were carried out for different flow approach angles (α = 0°-90°) and for various reduced velocities (Ured = 3–25) at Richardson number, Ri = 0, 0.25 and 0.50. The Arbitrary Lagrangian-Euler (ALE) approach models the solid-fluid interaction. The coupled fluid-structure interaction problem in two-degree-of-freedom (2-DOF) was solved using a high-fidelity finite difference-based solver. The Lock-in regime was found to be fixed, between Ured = 5 and 6, for all flow approach angles irrespective of Ri. For all flows other than transverse flow, the reduced frequency is found to be equal in both directions (fx=fy) but in the transverse situation, (α=90°), reduced frequency in the x-direction is twice that of the y-direction for all reduced velocities (Ured). Different vortex shedding modes 2S, 2S*, P + S and 2P are also observed in the study. The average coefficient of drag (C¯D) and Nusselt number (N¯u) was found to peak at α = 45° for all Ured. It was also found that as α is increased, C¯DandN¯u increases due to larger heated surface area exposure to the fluid particles. When Ri increases, C¯DandN¯u increases at a α due to the higher heat transfer rate. Highest value of N¯u is observed for Ured = 6, α = 45° at Ri = 0.5.