Endless Fibre-reinforced Composite-Metal-Impeller: Investigation and Comparison of the Damping Behaviour

The performance and efficiency of future and existing blowers can be improved by using new types of high-performance impellers made of fibre composite materials. Composites have excellent density related mechanical properties allowing to significantly increasing the rotational speed. Reduced mass of the impellers, especially the lower inertia, allows faster reactions to variable speeds and uses less energy. Composites enable variable designs of the blades, which leads to flow-optimised cross-sections improving the efficiency and may reduce noise. Furthermore, the layered structure of such impellers for the integration of sensors provides a basis for component monitoring and data generation. Due to the large number of adjustable parameters, the special knowledge required for their design as well as the high expenses and risks for the development and production of integral rotors, these are currently only niche products. Therefore, in cooperation with the German Forschungsvereinigung für Luft- und Trocknungstechnik (FLT), a modular design of a high-performance impeller was developed at the TU Dresden, whose functionality was presented in a first FAN paper 1. Compared to the integral solutions, the manufacturing effort of this modular design is significantly reduced, allowing higher availability and variability in production. In addition to the developed design, a numerically based methodology for the mechanical construction was elaborated and presented and allows to consider the material specific damage and failure behaviour. Using this virtual development, speeds of approx. 7,500 rpm were achieved in the first test, corresponding to a circumferential speed of approx. 400 m/s and increasing the speed by approx. 30{%} compared to the metallic model. Using the developed and manufactured fans, this paper shows the potential of such modular fibre composite-metal hybrid structures for vibration-damped fans. In a first step, numerical and experimental modal analyses for the determination of natural frequencies, vibration modes and modal loss factors on disc rotors made of steel and fibre composite material were performed and compared. Subsequently, a fibre composite impeller was manufactured and also subjected to an experimental modal analysis. The determined loss factors impressively confirm the high potential of fibre composite materials for vibration damping of impellers. The fibre-composite metal hybrid construction method mentioned above also enables a further improvement in vibration damping through additional joining zones. References 1 Spitzer S., Pohl M., Grothe R., Langkamp A., Hermerath P., Gude M.: Endless fibre-reinforced composite-metal-impeller: material related design and dimensioning process for hybrid radial-fans. FAN 2018, Darmstadt, 18-23. April 2018 Keywords: Composite Material, Radial Fan, Hybrid Design, Steel, Damping