Effect of axial gap between inlet nozzle and impeller on efficiency and flow pattern in centrifugal fans, numerical and experimental analysis

Inlet is one of the basic elements of squirrel cage fan that can have great effect on performance and losses, especially between inlet nozzle exit and first section of impeller width. But, enough research has not been done on its parameters. In this paper the effect of axial gap between inlet nozzle and impeller on performance and flow pattern is considered. Four inlet nozzle sizes with respect to impeller size (two smaller, nearly same and bigger than inner impeller diameter) and three axial gaps within the physical dimensions of the casing and impeller were chosen. Numerical simulations with different turbulence models, special geometry and mesh pattern were performed to find the effect of this axial gap on flow pattern, performance and efficiency. For the validation of numerical results, some experiments were done and all the performance parameters were compared with that of numerical simulations. These results show good matching between experimental and numerical results. From the simulation of each case study, flow pattern and its mechanism and the causes affecting the efficiency and performance due to axial gap are analyzed and presented.