Structural analysis of the back plate and finding its optimum thickness in a backward inclined centrifugal fan

Centrifugal fans are classified as industrial fans which have a flow direction change of 90°. This action is done through the revolution of a part called Impeller which consists of a back plate, a number of blades and a shroud. Among these parts, the optimum thickness of the back plate is of central importance, regarding the fact that the back plate should withstand the pressure loads caused by fluid flow, as well as structural stresses ensued from rotation, while having the least possible weight which could result in less moment of inertia.To find the optimum thickness of the back plate of a selected centrifugal fan, we use the commercial finite element (FE) package ANSYS. The pressure contours on impeller components are adopted from a previously solved computational fluid dynamics (CFD) simulation on the 3-D model. Next, we conduct our structural analyses on different thicknesses of the back plate, considering the loads caused by air pressure, rotation and inertia. The independency of results from the generated mesh is also investigated. The most critical stress point is found to be located on the blade’s leading edge, at the connecting point with shroud and back plate. According to this analysis, when the thickness of back plate increases, the maximum shear stress of the Tresca failure criterion goes down, while the weight grows significantly. Therefore, a compromise needs to be reached between weight and stress to find an optimum design. Finally, it is concluded that a thickness of 8 mm with a safety factor of 1.5 may be chosen as the best thickness for the back plate, which is also approved by the industry.

Keywords:

Centrifugal fan , impeller , back plate , static structural analysis , optimum thickness