Thermal fluid dynamics interaction between dual cylinders: Numerical analysis of groove effects and rotational speed

Abstract

This paper numerically analyses the thermal characteristics of tandem cylinders, considering different grooves and non-dimensional rotation speeds (Ω). Two cylinders have the same diameter, D, with a spacing of 4D. The upstream cylinder features grooves on its leading surface, whereas the downstream smooth cylinder is subjected to different rotational speeds. Investigations are conducted at a constant Reynolds number (Re = 200) for three different types of grooves (rectangle, triangle and dimple) at various angular positions (θ = 0°, 45° and 90°) and six dimensionless rotational speeds (Ω = 0–5). This study focuses on how the Ω, groove type and angular position affect the wake dynamics and thermal characteristics. The results indicate that triangular and dimpled grooves demonstrate a similar anti-phase trend in lift coefficient under static conditions with Ω = 1 once θ is set to 90°. The variation in the Strouhal number is closely associated with groove type, significantly altering the energy of the dominant vortices. This effect is particularly remarkable at θ = 45°, where different groove types substantially impact vortex energy. On the other hand, dimpled grooves notably strengthen the activity of negative vortices in the wake. Moreover, groove patterns alter flow separation, resulting in a pea-shaped wake vortex on one side at θ = 90°. Subsequently, at the highest speed of Ω = 5, the thermal boundary layer tilts and distributes evenly, forming two asymmetric independent thermal plumes. Further investigation revealed that the groove’s shape significantly impacts the time-averaged surface Nusselt number (<N¯u1>) value; notably, a rectangular groove decreases the <N¯u1> value by approximately 6.7 %. Besides, at low speed (Ω = 1) and θ = 0°, the tandem triangular groove configuration provides the best drag reduction. When θ increases to 90°, the pressure drop remains below 1 in all cases except when Ω = 5. However, at Ω = 5, the TPI of triangular grooves surpasses other cases, indicating optimal thermal performance at high speeds (Ω ≥ 5) and θ = 45°. Although the TPI for triangular and dimpled grooves slightly decreases at θ = 90° compared to θ = 45° (0 ≤ Ω ≤ 2), all groove types still positively impact thermal behavior.