Integrative Simulation Method for the Prediction of Anisotropic and Time-Dependent Mechanical Behavior of Injection Molded Fiber-Reinforced Fan Impellers – Numerical and Experimental Approach

Fan Design & Materials

Currently installed fans are responsible for more than 10% of the total European energy consumption. Therefore, minimum efficiencies have been defined to ensure that future developments aim for the lowest energy consumption. Nowadays, fans are increasingly produced using fiber reinforced plastic materials as it contributes to energy and resource savings and reduces weight. Injection molding offers great flexibility in the design of innovative, noise reduced and energy efficient fans, as blade add-ons like winglets, gurney flaps or vortex generators as well as special shaped leading or trailing edges can be incorporated.
In the current effort an integrative simulation method is developed to combine injection molding, aerodynamic and structural mechanic simulations. For this purpose, fiber orientation, material properties and pressure distribution are mapped onto a related structural mechanical model. Thereby, the influence of anisotropic material properties towards the time- and load-dependent displacements of axial and radial fan made of short glass-fiber reinforced plastics can be investigated. The influences of aerodynamic and centrifugal loads were compared to each other in order determine their relevance in the structural design process.
The stress and strain distribution strongly depends on the local fiber orientation of the glass fiber reinforced injection molded material. In order to validate the numerical strain results two strain measurement systems will be presented. First, an optical system based on a three-dimensional and high-resolution digital image correlation was developed to investigate the strain distribution on the surface of an impeller. Second, a strain gauge system was designed, which is capable to measure the local strain within the rotating frame. The second system was specially designed without slip ring contacts for under-water applications and was tested for local strain measurements at a rotor blade under operational conditions. The application of these measurements techniques to axial and radial fans with diameters less than 900 mm is new and allows to obtain up to ten strain voltage signals with a maximum sampling frequency of 1 kHz. Due to its compact design it can be applied to most fans with a hub diameters greater than 110 mm.