Computational investigation of effect of Reynolds number on centrifugal fan performance at design flow condition

A steady state computational study has been carried out to analyze the performance of a centrifugal fan with a vaneless diffuser at five different Reynolds numbers viz. 0.30, 0.41, 0.55, 0.69 and 0.80 × 105 based on the impeller tip speed, impeller blade exit height and kinematic viscosity at design flow coefficient of 0.34. The present study is carried out by solving RANS equations using commercial software ANSYS CFX. SST based γ-θ transition turbulence model is used to compute the turbulent nature of the flow. Computational method is validated with experimental results at a Reynolds number of 0.80 × 105 comparing mass averaged total and static pressure coefficients in the diffuser. Results show performance of the fan deteriorates at low Reynolds numbers chosen in the present study. Total pressure losses are dominant in both the impeller and diffuser of the fan at low Reynolds number and they are function of Reynolds number. Wake formation at the impeller exit is spread all over the shroud suction side corner and reverse flow is found to occur at low Reynolds numbers.