Numerical analysis of the coupling mechanisms between blade/disk friction and blade-tip/casing contacts on the state-of-the-art ECL5/Catana fan stage

Abstract

For the first time, the interaction between two contact nonlinearities, blade-tip/casing contact and blade/disk friction, is investigated simultaneously. This contribution addresses the associated complex coupling mechanisms on the state-of-the-art industrial fan stage ECL5/Catana open test case. Both contact interfaces are accounted for in nonlinear calculations using the harmonic balance method. First, a static analysis is performed to investigate the coupling mechanism between the friction coefficient and the static blade-tip gap. Then, the dynamics response of the blade is analyzed in forced response for two reference configurations: (1) with blade-tip/casing contacts only and (2) with blade/disk friction only. Particular attention is paid to the contact kinematics of both interfaces and the vibrational motion of the blade. The forced responses are analyzed using different local indicators of the contact interfaces. As the friction coefficient is usually uncertain, the robustness of the numerical strategy is then demonstrated by performing a large number of simulations on different root friction coefficients. In the end, even more computations are performed, as a part of sensitivity studies on first order parameters, in order to map out the different relevant quantities of both interfaces: number of contacting nodes at the tip, tip contact resultant force, energy dissipation. These large scale mappings allow to identify trends and inter-dependences between the kinematics of each interface. The originality of this paper lies in the thorough analysis of this seldom studied nonlinear interaction, that is crucially important for the design of safe and efficient aircraft engines. This work demonstrates that accounting for the blade/disk friction interface in numerical simulations strongly mitigates the dynamics of the blade-tip/casing contacts and can even prevent it for a specific range of friction coefficients.