Optimal Vortex Designs of Rotor-Only Axial Fans for Improved Static Pressure Recovery

In the discharge flow of rotor-only axial fans installed in a free discharge configuration (ISO 5801 types A and C), a static pressure recovery occurs. This pressure recovery is part of the energy conversion process of the machine and is therefore included in the ISO 5801 definition of the static fan efficiency. Current fan design methods typically neglect this pressure recovery. In this paper, theoretically optimal vortex designs for improved static pressure recoveries over the full range of the relevant design space are presented. Compared to the state-of-the-art vortex designs for this type of machine that typically minimize the kinetic energy in the fan discharge, the newly presented vortex designs exhibit a higher kinetic energy, which is then overcompensated by an improved static pressure recovery resulting in an overall higher theoretical fan efficiency.