THE NUMERICAL AND EXPERIMENTAL EVALUATION OF A COUPLED BLADE DYNAMIC LIMIT RESPONSE WITH FRICTION CONTACTS

Increasing demand on turbine power and efficiency requires larger and higher loaded turbine blades, which in turn requires the consideration of aeromechanical interactions. Whilst CFD tools can reliably predict stability using aerodynamic damping as an indicator, the component of mechanical damping also needs consideration. An understanding of the mechanical damping in the system becomes key to a robust blade design. Mechanical damping for such a part comes predominantly from friction occurring at the coupling contact faces. It is well established and published that such contact forces are nonlinear in relation to the relative movement at the contact interface. Moreover, contact area, the rigidity in the contact, friction coefficient, and normal contact force must also be considered and included as parameters that influence the result. Consequently, the level of system damping is not a constant, and depends highly on the system response itself, as well as the other forementioned parameters. In the case of self-excited vibration such as flutter, the evaluation of the damped limit response is a part of the blade design process. A tool has been developed to numerically simulate contact friction forces with the intention of parametrically evaluating the limit response and relating this to the mechanical integrity of the part. This paper presents the modelling of a coupled blade system with friction contact forces, results coming from this evaluation, and a comparison with test data.