Effect of Confinement in Coaxial Swirling Jets: Numerical Study

The confinement effect on two recirculation zones (RZ) observed in the coaxial swirling jets is investigated by employing the numerical unsteady Reynolds-averaged Navier–Stokes (URANS) approach. The RZs are classified based on modified Rossby number ( \({\text{Ro}}_{{\text{m}}}\) ). A \({\text{Ro}}_{{\text{m}}}\)  > 1 case and a \({\text{Ro}}_{{\text{m}}}\)  ≅ 0 are considered. The 3D simulations are carried out in ANSYS Fluent 19.2. In particular \({\text{SST}}\, k - \omega\) , the turbulent model is employed to capture the turbulent flow field. Two confinement ratios CR = 1.81 and 2.7 are used to study the confinement effect. It is observed that the CR = 1.81 produces a significant wall/confinement effect compared to CR = 2.7 evidenced by the enrichment/enhancement of time-mean vorticity, Reynolds stress, and turbulent kinetic energy contour plots. The CR = 2.7 effect is similar to that of unconfined conditions.