Application of similarity laws to the blade passage sound of centrifugal fans

This paper is concerned with similarity laws governing the harmonic components of the sound radiated from centrifugal fans. Measurements are made with two precisely similar fans having impellers of 140 mm and 280 mm diameter. The experimental apparatus used is in accordance with the in-duct method suggested in a recent ISO-proposal 1]. The present experimental results verify Weidemann's 2] formulation of similarity laws, which describes the radiated sound pressure as a product of non-dimensional terms. The experiments also prove that it is possible to extrapolate data from a model fan to other geometrically similar fans of different size.