Application of Finite Element Analysis to Rotating Fan Impellers

Abstract

The aim of this work was to investigate the computer aided stress analysis of centrifugal fan impellers fabricated from thin plate. The finite element method has been chosen as a tool to solve this problem, since it has gained considerable attention, wide spread popularity, and proved to be a powerful tool for the designer engineer. The semiloof shell element was adopted, in view of its demonstrated ability to deal with thin branching shells having sharp corners and multiple junction regions such as are found in fan structures. The objectives of this research were achieved by establishing: (i) A general purpose finite element package for plates and shells using the semiloof shell element for stresses and displacements. (ii) A 'tailor made' finite element package for the impellers themselves where rotational stresses are significant for stresses and displacements. This package was developed further to cater for the sectorial symmetry of rotating fan impellers: by these means, data preparation, memory requirements and computing time are greatly reduced. An experimental study was conducted, using the strain gauge technique, to evaluate the displacements and stresses predicted numerically. This was carried out for a simplified and an actual fan impeller as well as special Simple test structures. Numerical results for the thin plate and shell structures showed excellent agreement with those obtained by other methods. A satisfactory correlation was obtained between the experimental and the numerical predictions for the simplified and actual fan impellers. A desk top computer HP9845B was used since it is a ‘user friendly', low cost machine with interactive graphics and other powerful facilities. Other topics which may be investigated as an extension for this work have been pointed out.