Numerical investigation on flow mechanisms of a squirrel cage fan

Squirrel cage fan has found wide applications in heating, ventilation and air-conditioning as well as other cooling systems. Although many studies have been conducted to investigate the performance of the squirrel cage fan, the complex flows and the associated flow mechanisms have not been fully elucidated. In this paper, computational fluid dynamics simulations are performed for a comprehensive analysis of the flow throughout a whole squirrel cage fan. A novel representation technique is proposed for a vivid and quantitative description of the flow velocity distributions at the impeller inlet and outlet to aid a heuristic analysis of the complex flows in squirrel cage fan. The pressure gradient distributions, together with the pressure itself, along the volute wall are also extracted and analyzed to explore the local flow conditions of the volute profile with four segmental arcs. The results show that the proposed representation technique is capable of effectively measuring the circumferentially nonuniform flow conditions at both the impeller inlet and outlet. The strong interaction between the impeller and the volute tongue induces reversed flows at both the impeller inlet and outlet, which further aggravates the circumferential nonuniformity of inactive zone and the upstream impeller flow field. Despite the first-order continuity of the volute profile itself, there are strong variations of tangential pressure gradients and sudden diffusion-expansion effects at the junctions of adjacent arcs. These findings benefit a deep understanding of the complex flow mechanisms within the squirrel cage fan.