Leveraging virtues of circular and oval shapes in multi-orifice synthetic jet flow and heat transfer characteristics

Abstract

An experimental investigation is carried out using particle image velocimetry (PIV) and infrared thermography to study the flow dynamics and heat transfer behavior. The orifice configurations studied are single-circular, single-oval, multi-circular, multi-oval, and mixed (circular + oval). The single-oval has higher vorticity levels in the near-field region (Z/D<2) compared to the single-circular due to axis-switching phenomena. While the reduction in the vorticity level is gradual in single-orifice configurations, multi-orifice configurations retain it up to Z/D~8, and a sudden decrease is observed. Oval-shaped orifices produced more turbulence near-field region (Z/D~2), this results in a superior heat transfer performance in oval-shaped orifices at Z/D=2. In comparison to single-orifice configuration, the multi-orifice configurations show a greater rate of entrainment in the near-field of the orifice exit (Z/D<2). The normal stress contours of multi-orifice jets near the orifice exit are thicker and wider, indicating higher turbulence than single-orifice jets, though this turbulence cannot be sustained over longer axial distances. Notably, multi-oval orifices exhibit higher centerline velocities, while single-circular and single-oval orifices demonstrate lower centerline velocities. The single-circular spreads more after Z/D=7, while the multi-orifice spread is larger in the near-field region (Z/D~2). A ~29 % increment in average Nusselt number is observed in multi-oval configuration than in single-circular. The mixed-orifice configuration shows similar characteristics to that of oval-shaped at lower Z/D, while at higher Z/D to that of circular. These findings contribute to a comprehensive understanding of the flow dynamics in synthetic jets with various orifice configurations, offering valuable insights for applications in enhanced mixing and thermal management applications. Keywords: Synthetic jet, Heat Transfer, PIV, Nusselt Number, Turbulence.