Towards structural topology optimization of rotor blisks

The current trend in turbomachinery is pushing forward more and more efficient machines, increasing speeds, reducing components mass and improving their vibrational behaviour. Structural topology optimization is a challenging and promising approach to satisfy all these demands, with a very remarkable economic impact. Topology optimization allows the definition of objective functions and specific constraints to manage the structure topology, significantly improving material distribution within a given design space for a given set of boundary conditions and loads. This approach enables the creation of free-form continuous structures, which are usually difficult or impossible to be produced using traditional manufacturing processes. However, thanks to innovative technologies, as new additive manufacturing techniques for high-resistance alloys, it is now possible to effectively exploit topology optimization to develop innovative components characterized by complex three-dimensional geometries. The aim of this work is to demonstrate the applicability of structural topology optimization techniques in the turbomachinery field, to improve the dynamic performances of critical components in terms of weights, stresses, displacements and vibrational behaviour (natural frequencies). To do this, a 3D mock-up blade geometry based on T106 profile has been designed to reproduce a typical rotor blade in design conditions. The blade has been mounted on a rough disk model, to obtain a rotor blisk in order to ensure a wide design space for the optimization. During the structural optimization process, the aerodynamic blade surface has been maintained unchanged, while the design space, where the optimization procedure may alter the mass distribution, are the blade interior and the whole disk geometry. The optimization has been carried out by applying mean and fluctuating loads coming from a 3D unsteady computation of 1.5stage (stator-rotor-stator) together with the centrifugal stresses. The unsteady loads acting on the rotor skin are due to the wake of the upstream stator and the potential field generated by the downstream stator. Through this new optimization technique, a new concept design for the blisk has been developed and the optimized geometry has been compared to the original one to highlight the improvements in terms of blade mass reduction and, at the same time, improved dynamic behaviour. This paper will confirm the suitability of this approach to turbomachinery components (blades, disk, etc…) and a prototype of optimized geometry will be ready to be manufactured through innovative additive manufacturing techniques for high resistance alloys.