Numerical Investigation of Pressure Recovery for an Induced Draught Fan Arrangement

Abstract

This study investigates the potential gain in operating volume flow rate and static efficiency for an induced draught fan arrangement by reducing the outlet kinetic energy loss. The reduction is achieved through pressure recovery, which is the conversion of dynamic pressure into static pressure. Downstream diffusers, stator blade rows, or a combination of these can recover pressure. Six different discharge configurations are tested for a fan. An annular diffuser with equiangular walls at an angle of 22° from the axial direction and a length equal to the fan diameter recovers the most pressure over a range of volume flow rates. The diffuser causes the operating volume flow rate and static efficiency to increase by 6.3 % (relative) and 20 % (absolute), respectively, compared to the initial design point of the particular fan.

Performance Enhancement of an Induced Draught Axial Flow Fan Through Pressure Recovery

“…The effects of turbulence on the mean flow were modelled using the k-ω model of Wilcox [23]. Bekker et al [14] found that this model predicted swirling flow in a conical diffuser with reasonable accuracy.…”

“…Bekker et al [14] aimed to find a discharge configuration for the M-fan that produces high pressure recovery coefficients over a range of operating volume flow rates. They considered stator blade rows, conical and annular diffusers, as well as stator-diffuser combinations.…”

“…The same procedure as followed by Bekker et al [14] was thus repeated for two shorter diffuser lengths: Firstly, a length equal to 40 % of the fan diameter, which Kröger [1] terms "practical". Secondly, an even shorter length of 20 % the fan diameter.…”

“…Bekker et al [14] tested for grid dependence by refining the mesh and for sensitivity to boundary distances by increasing the size of the dump used to represent the open atmosphere. For each sensitivity test, they compared the measured pressure difference between the outlet and the inlet of the domain and they compared velocity profiles inside the diffuser.…”

“…Bekker et al [14] investigated pressure recovery for an induced draught axial flow fan. They tested various discharge configurations which included a downstream stator blade row, conical and annular diffusers with and without stators at their inlets, and an annular diffuser with a stator row at its outlet.…”