Numerical Investigation of Scaling Effects on the Performance Characteristics of Large-Scale Axial-Flow Fans

Large-diameter axial-flow fans are predominantly used for cooling purposes, such as in air-cooled heat exchangers. Since it is difficult to experimentally test large-scale fans in the controlled environments provided by fan test facilities, smaller scaled-down versions of the fans are tested instead. Scaling laws, also called affinity laws, are then used to determine the performance characteristics of the large-scale fan. The size difference between the two scaled fans means that it is not possible to match their Reynolds numbers when testing with the same test fluid. A comparison is conducted using experimental results and four numerical models for two different fans, which are scaled to different fan sizes: 0.63 m, 1.542 m, 3.658 m and 7.315 m, to determine the effect of Reynolds number on the performance characteristics of an axial-flow fan. The numerical geometries are based on the M- and B2a-fans, and are tested in the A-type experimental setup fan test facility at Stellenbosch University, which is used to obtain the experimental results. It was found that the numerical approach discussed within this paper, namely a Reynolds-Averaged Navier–Stokes (RANS) approach, can predict the performance of multiple fan sizes without relying on turbomachinery or blade-specific empirical correlations. This approach accelerates the evaluation of fan performance while enabling the parameterization of fan configurations.