Aerodynamic shape optimization of axial flow fans

Abstract

The purpose of this work is to improve the efficiency of large scale axial flow fans through the introduction of a more uniform velocity distribution over the fan blades. This improved velocity di tribution being realized through the use of an aerodynamically optimized inlet cone. The procedure for optimization the inlet cone uses existing aerodynamic optimization methods programmed into a completely self contained FORTRAN program. The type of optimization algorithm used here is the use of design optimization to solve an inverse design problem. The different modules of the program include a surface vorticity panel method flow solver, a Bezier curve surface definition routine and a minimization method. Three different minimization methods were tested to determine the most appropriate one, this being the downhill simplex method in multidimensions. Many different sized fans and inlet cones were tested, with two different types of optimized inlet cones being discovered. Short inlet cones typically make use of avery blunt inlet cone with a slight hump or rise above the hub radius. Longer inlet cones make use of a more curved inlet cone with no hump. It was also shown that the hub-to-tip ratio of the fan has a significant impact on the velocity distribution and therefore the efficiency of the fan unit. As well, it was shown that only a small change in the length of the inlet cone could affect the velocity istribution. It was also found from this work that the relatively simple methods used can provide an adequate modeling of the problem and a easonable solution.