Forced Response Analysis of a Counter-Rotating Fan using the Energy Method

Abstract

The forced response for each rotor of a two stage counter-rotating fan was investigated applying the energy method. The analysis focuses on the rotor-rotor interaction, which means, the effects that the unsteady total pressure distribution of a blade row will produce in the adjacent row. The forced Response of the system can be calculated from the values of the forcing work and the damping work by energy balance. The eigenfrequencies of each rotor stage were calculated in a modal analysis with the Finite Element Software NASTRAN and the resonance points were identified in a Campbell Diagramm. Time-linearized flutter and forced response analyses were performed with the in-house tool TRACE in order to obtain the damping and forcing work values at the resonance points. Finally, the forced response results obtained by this method were evaluated with respect to the high cycle fatigue limits of the blade material to determine if the rotor-rotor interaction can affect the integrity of the subject fan.