Effect of the computational domain selection on the calculation of axial fan performance

In this study, the aerodynamic performance of a jet fan (considered as a free-inlet free-outlet axial fan which does not contain any duct at the upstream or downstream) is obtained by using CFD (Computational Fluid Dynamics) method. The numerical calculations are performed by using the commercial software ANSYS CFX. Three different inlet and outlet computational domain shapes that are widely used for simulations of axial flow fans are evaluated. In the first method, the fan is modeled inside a circular pipe. The second approach does not contain the domain of a pipe at the inlet and the outlet but large inlet and outlet domains connected instead directly to the fan casing. The third method is similar to the second approach except a bellmouth located at the inlet of the fan that is not present in the second approach. The aerodynamic performance of the fan at atmospheric conditions is obtained by three approaches and the results are compared to each other and to the ones obtained experimentally. The results show that the simulation of a jetfan as if it works in a pipe brings an error of 45 % in flowrate which can be decreased to 25 % by placing a bellmouth at the intake of the fan casing.