On the flow topology and mean flow characteristics of the swirl jet upon impingement

Jet impingement enhances heat transfer and is characterized by the complex flow patterns formed when a jet impacts a plate aligned normal to it. While traditional round jet impingement has been extensively studied to comprehend flow and associated heat transfer, there is still room for research when it comes to the investigation of flow structures in swirl jet impingement. This paper focuses on the flow topology of swirl jets generated by a 45° axial vane swirler, impinging on a flat plate studied at dimensionless jet-plate distances (H/D = 1–4) and Reynolds numbers (Re = 16 600 and 23 000). The flow structures, the mean velocity components, and the turbulence characteristics using two-dimensional particle image velocimetry (PIV) experiments at the front (r-z) and top (r-θ) planes of impingement are presented. Furthermore, results from the three-dimensional numerical simulations are presented to support the results in studying impingement cases where the PIV study had experimental limitations. The effect of impingement distance or jet-plate distance (H/D) on the mean flow properties and turbulence parameters is discussed. A proper orthogonal decomposition analysis has been performed to understand the dominant coherent structures at different cases of impingement distance (H/D). We show that the turbulence parameters are more pronounced at smaller jet-plate distances (H/D ≤ 2), which could explain the enhancement of heat transfer with these jets at smaller H/D.