How the distance between the fan outlet and the surrounding walls affects the fan efficiency. An Investigation of the Influence of Outlet-Wall Distance on Fan Efficiency using Computational Fluid Dynamics

Abstract

This thesis investigates the influence of the outlet-wall distance on the aerodynamic performance of centrifugal fans used in Air Handling Units (AHUs). The study was conducted using steady-state Computational Fluid Dynamics (CFD) simulations with a realizable k–ε turbulence model and Moving Reference Frame (MRF) methodology. The aim was to identify how variations in the height, width, and depth of the outlet enclosure affect fan efficiency and static pressure rise. A mesh independence study was first carried out to ensure result validity, followed by a systematic variation of outlet geometry. Results showed that increasing the outlet enclosure dimensions led to improved flow uniformity, reduced turbulence, and enhanced fan efficiency. However, the improvements diminished beyond a certain geometric threshold, indicating an optimal enclosure size for performance. Additional modifications such as cone extensions, cylindrical blockages, and rounded corners were also tested and showed further performance gains. The results offer design guidance for optimizing outlet-wall distances in spaceconstrained AHU systems. While the findings are based on numerical simulations, they lay the groundwork for future experimental validation and further CFD studies using transient solvers.