Designing a Centrifugal Fan of Carbon Fiber Laminate for High Circumferential Speed

A2 - Fan Mechanical Design

Centrifugal fans made of plastic are commonly used in systems where the transported fluids containing acid materials. Nonmetallic materials have, additionally to their persistence against corrosion, the advantage of a low noise level. Conversely the low strength of plastic limits the load to the structure and hence the maximum circumferential velocity.
Within the scope of this project a given impeller design of plastic is optimized with the goal of higher efficiency and the ability of higher circumferential speed.
As material for the new fan carbon fiber laminate is chosen, due to its resistance against high stresses and persistence to acid materials. Because carbon fibers must be positioned without any sharp bends to avoid tension cracks, the use of such fiber materials restricts the design options of the fan. These requirements lead to a non-standard geometry especially at the intersections blade to shroud and blade to hub.
This paper presents the approach of designing an impeller geometry which fulfills all required restrictions. With the goal to construct a high efficient fan, 3D steady and unsteady CFD calculations of the impeller and the complete fan are carried out. They are based on a block structured mesh of 1.3 million cells for the impeller and inlet nozzle resp. 2.8 million cells for the complete fan.
21 different fan geometries were calculated, successively optimizing the impeller geometry. The calculations of the final impeller show higher efficiency rates at all given operation points, additionally the geometry fulfills all restrictions given by the material.