An Analytic Study of the Energy Dissipation of Turbomachinery Bladed-Disk Assemblies Due to Inter-Shroud Segment Rubbing

A novel computational method is presented for analytically studying the energy dissipative characteristics of turbomachinery bladed-disk assemblies due to inter-shroud segment rubbing. Coulomb friction, as the dissipative mechanism, is utilized in this method with broader generality than that in other similar studies heretofore. The immediate objectives of this study were 1) to obtain an understanding of the general slippage characteristics of the shroud segment interfaces in the presence of both steady normal (to the shroud segment interfaces) lock-up stresses and stresses due to modal vibration, and 2) to incorporate these characteristics in a calculation of the minimum modal deflection required for incipient slipping as well as an estimation of the energy dissipation (damping) due to subsequent rubbing. The utlimate applications of this knowledge are for more accurate calculations of flutter stability margins and dynamic magnifications of stresses, and for a more rigorous formulation of the shroud boundary conditions used in the calculation of natural frequencies and mode shapes. As a result of this preliminary investigation it is concluded that the energy dissipation due to inter-shroud segment rubbing tends to an amplitude squared dependency and is thus similar to classic structural damping.