A new approach to the calculation of Euler work for centrifugal fan impellers

Abstract

In a conventional one-dimensional scheme design of centrifugal fans and compressors, it is assumed that there is no flow prewhirl at the impeller inlet when the inlet guide vane is absent. However, many experiments have proved that the flow prewhirl does exist at the inlet of centrifugal impellers. This results in an error in the design of centrifugal fans and compressors. In this study a new method is presented to calculate the Euler work of centrifugal impellers considering the presence of an inlet flow prewhirl in the case without the inlet guide vane. Stodola's approach dealing with the slip velocity at the impeller outlet is applied to the impeller inlet. A new formula for Euler work calculation is deduced to evaluate the effect of the inlet prewhirl. The new formula has been applied to 33 industrial centrifugal fans and the calculated results have been compared with the experimental data of these fans. The comparison shows that the new formula is more accurate in most cases than the original formula without consideration of the inlet flow prewhirl, and the accuracy has been improved by more than 10 per cent on average. The aim of this study is to improve the accuracy of the one-dimensional scheme design of centrifugal fans and to provide a reference for a similar research.