Estimation of Scale Effects in Axial Flow Fans: A Simple Method of Analysis Which Compares the Losses in the Rotor, Guide Vanes and Diffuser of a Model and a Prototype

The losses in a fan unit consisting of rotor, guide vanes and tail fairing have been studied and the average losses are expressed in terms of non‐dimensional similarity parameters, frequently referred to as ‘fan laws’. It was found that for a specified duty and fan geometry the losses depend on: (a) The magnitude of the lift‐drag ratio of the rotor blades. (b) The drag coefficient of the guide vanes. (c) The loss over the tail faring. Since for complete similarity the parameters for model and prototype are considered to be equal, the discrepancy in losses between model and prototype, that is, scale effect, is mainly due to the variations of the aerodynamic characteristics of the blade and guide‐vane profile with the Reynolds number.