Effect of Flow Confinement on the Hydrodynamics and Heat Transfer Characteristics of Swirling Impinging Jets

Although confined swirling jets are typically used in many practical applications, a detailed investigation in the literature is, however, very limited. As such, this paper investigates the fundamental thermofluidic behaviors of swirling impinging jets due to flow confinements at small impingement distance. In this regard, turbulent flow simulations with an ambient air jet are carried out using RANS approach, whereby turbulence is governed by SST k-omega model. Inlet boundary conditions are applied from the CTA anemometer derived experimental data for the same nozzle geometry in order for a realistic analysis. The flow dynamics and heat transfer between a swirling jet and the impingement plate are studied for a Reynolds number (Re) equals to 11,600 and Swirl numbers (S) from 0 to 0.74 for an impingement distance equals to 0.5 nozzle diameter. The results show that a strong flow recirculation zone appears between the nozzle and the surface, even for non-swirling jets. For highly swirling jets, another secondary recirculation zone exists around the central axis near the stagnation point. The surface static pressure distribution is found to be negative due to flow confinement for all swirl conditions. The degree of swirl intensity and the associated flow recirculation also largely affect heat transfer behaviors on the impingement surface.