Wall effects on the performance of ceiling fans: a two-dimensional model

Abstract

The distance between the rotor and the ceiling wall is known to have a significant effect on the performance of ceiling fans, especially at a close proximity. A simplified ideal fluid flow model is developed to analyse this problem and predict the effect of the wall. A plane version of the classical actuator-disk model is modified by inclusion of an artificial vertical boundary downstream of the rotor to make it aerodynamically self-consistent The conformal mapping technique is then used to obtain the flow field induced by the rotor. The effects of ceiling gap on the flow rate and the aerodynamic power generated by the fan are presented. The shapes of the jet boundary for different ceiling gaps are also given. The upstream flow is diverted due to the presence of the ceiling, which results in reductions in the jet area and the flow rate and a higher loading on the rotor owing to the suction pressure at the ceiling. For an example when the ceiling gap is half of the rotor radius the reduction on the flow rate (at the same induced power) is 30% and the increase in the induced power (which produces the same flow rate) is 200%.