Computation of jet engine dynamics including nonlinearities by squeeze film damper and ball bearing models,utilizing an enhanced harmonic balance method with integrated dynamic condensation

Abstract

A common approach in jet engine modeling is the use of linear supports in order to reduce simulation times and facilitate design procedures, thus neglecting the nonlinear complexities arising from squeeze film dampers (SFD) and rolling element bearings (REB). In order to address the nonlinear nature of the system while maintaining low simulation times, this study employs the Harmonic Balance method with a mathematical manipulation to segregate linear and nonlinear degrees of freedom, thus reducing the number of equations to be solved. In conjunction with this method, analytical and numerical models for the calculation of the nonlinear forces are incorporated and thus a realistic dual-spool, mechanical whole engine model (WEM) is presented and simulated. Using this approach, the study delves into the design aspect by examining the influence of various geometrical and operational SFD parameters on the engine’s dynamic behavior. Furthermore, oscillations due to unbalance on both of the shafts are examined by exploiting their commensurable speed ratio to effectively choose the sampling period for the FFT on the forces. The results presented are compared with transient analysis simulations, affirming the method’s effectiveness in simulating realistic engine models without simulation time hindering the design process.