Prediction of Flow Behavior and Performance of Squirrel-Cage Centrifugal Fans Operating at Medium and High Flow Rates

This paper describes a method for predicting flow behavior and performance for centrifugal fans of the squirrel-cage type. The work is directed at improving under standing of the factors affecting performance of these fans. A simulation approach has been adopted. That is, the fan is subdivided into a number of zones (inlet zone, blading zone, volute zone) and the zones are divided into elements. Flow behavior in the zones and elements and interactions between them are modeled using appropriate equations and correlations. The blading correlations make use of new experimental data for high-solidity cascades of bent sheet metal blades, typical of squirrel-cage fans. Predicted fan performance characteristics are in reasonable agreement with experimental results for flow rates at and above the best-efficiency operating point. Although relatively simple, the method recognizes the main flow phenomena and interactions that occur in squirrel-cage fans and it thus represents a substantial advance over what is currently available in the literature. Together with earlier experimental work, development of the method has provided considerable insight into the relative importance of various aspects of flow behavior. The ability to deal with extensive reverse flow through the rotor blading has not yet been incorporated and it is evident that this ability is essential for realistic prediction of flow behavior and performance at below-design flow rates.