Performance Optimization Method for Radial Fans With Combined Vaneless Circular and Volute Diffusers Applied to an Industrial Fan

The use of high speed radial impellers is very common for industrial fans and blowers. The aerodynamic design of these machines can be made through direct or inverse means. The design process is almost always direct, based on the existing impeller series and available experimental data [1]. This paper presents the design results and optimization of high speed radial impellers with combined vaneless radial and volute diffusers used for industrial fans, through a combined analytical–numerical method validated by measurements of prototypes at the test rig. The reduction of the velocity from the outlet of the impeller to the outlet of the vaneless diffuser and hence the velocity at the inlet of the volute has a significant influence on the turbulence intensity and hence on the noise and therefore was a major parameter in determining the outer diameter of the circular vaneless diffuser. The designs where then validated by means of CFD computation, and following the numerical results, prototypes for both the volute and the impeller were built and experimentally investigated. The experimental results confirmed the numerical ones and it was shown that the optimized impeller had an absolute increase in efficiency with 70% at the operating point. One has to mention, that in this design, because of the special medical application, the operating point has to be unusually chosen shifted from the maximum efficiency. The results presented show the potential and advantages of the combined analytical and numerical method suited to perform a coupled design of high efficiency radial impellers and spiral casings. It shows also that new designs and improvement of existing designs are possible without the need of a previous impeller series or knowledge of experimental data.