Optimum Design of Inhomogeneous Rotating Disks for Minimum Creep Induced Radial Displacement

Abstract

Gas turbine disks are subject to mechanical stresses due to centrifugal forces exerted by the blades, as well as thermal stresses due to high temperature gradient. High stresses in the presence of elevated temperatures cause the rotating disk material to undergo considerable creep. This phenomenon is significant particularly in cases of turbine blades for power generators, which run almost continuously. Creep strains, in time, lead to deformations resulting in increase of the disk diameter, causing the clearance between blade tips and the turbine’s outer shell to reduce in time. As the above clearance gap is usually limited, this matter is of concern in the design of such equipment for long life. In this investigation, an optimization method is formulated, which is capable of proportioning the thickness distribution of inhomogeneous rotating disks under temperature gradient, so that their long term radii increase due to creep would be minimum. An example is given, which shows the viability of the method.