Impact of free-stream orientation and thermal buoyancy on aerodynamic and heat transfer characteristics in mixed convective flow past an elliptical cylinder

Abstract

This study conducts a thorough numerical investigation into the aerodynamic and heat transfer characteristics of mixed convective flow past an elliptical cylinder. Analysis is carried out for a constant Reynolds number (Re = 100), a Prandtl number (Pr = 0.71), and an angle of attack (λ=0°), utilizing the Oberbeck–Boussinesq approximation to solve mass, momentum, and energy equations via an in-house numerical solver. It explores a wide range of free-stream orientations, from 0° (upward flow aligned with gravity) to 90° (cross-flow). Additionally, Richardson number (Ri) is varied from forced convection (Ri = 0) to mixed convection regimes, up to Ri = 1.25. Two aspect ratios (AR=Major axis length/Minor axis length), specifically 2 and 4, are examined to assess their impact on flow behavior. The paper elucidates variations of lift coefficient, drag coefficient, and Nusselt number with Ri at different free-stream orientations. Furthermore, it investigates dynamics of both steady and unsteady flow regimes, correlating flow behavior with observed aerodynamic and heat transfer characteristics. Steady and unsteady periodic flow regimes are identified in the parametric space of (α, Ri) for AR = 2 and 4. The mean heat transfer rate increases with Ri in both steady and unsteady flow regimes at (α=0°, 30°, and 60°) for AR = 2 and 4, except at α=90°, where it decreases. These findings provide insights for designing compact heat exchangers utilizing elliptic tube cross-sections.