Development of integral bladed rotor using linear optimisation technique

Abstract

Bladed disks are the most flexible elements in high speed rotating machinery. Stress analysis of these elements present some challenges. These challenges stem from high stress gradients due to contact faces, the non-linearities attending conforming contact with friction. Thermal gradients are also encountered across the disc bore and rim due to uneven temperature distribution. The rim of the disc is made heavier to resist the centrifugal pull of the blade, thus making the assembly heavier. Investigations have been carried out to develop and improve ‘blisks’ which are integrated version of blades and disc, offering significant weight saving. The present paper describes the possible development process of upgrading a general purpose conventional bladed disc of a single stage compressor into blisk, using linear programme, a finite element analysis tool for linear optimisation, as a dedicated ‘design-tool’ keeping the same operating conditions and the allowable design limits through numerical models. Design methodology, burst-failure criteria of blisk and bladed disc are discussed in full length. This tool developed exploits the quick convergence ability of a linear system for handling large iterations and overcomes the limitation imposed by material non-linearity, over-speed and burst margin for all decision points based on stress, strain and displacement, in the design-flow process.