Structural Analysis and Optimization of a Propfan Blade by Use of the Finite Element Method.

Structural analysis of advanced propellers (propfans) is only possible by use of numerical methods because, due to the geometry and the loading, a geometrically non-linear calculation is required. Algorithms applicable to the finite-element-method are presented and employed in the calculation of a propfan-blade. This blade is discretized as a shallow shell. The constitutive equations for isotropic and for layered material are implemented into the formulation of the finite elements. The quasistatic deformations resulting from centrifugal forces as well as the eigenmodes and eigenfrequencies (as a function rotational speed) are presented. For a propfan-blade of composite material with 6 layers of equal thickness the methods of mathematical optimization are used to minimize the displacement at the tip of the balde, using the fiber orientation as design variables. In a second calculation, the twisting of the blade is minimized. It is shown that the deformation behaviour can greatly be influenced by the fiber orientation