Comparison of Linear and Nonlinear Frequency Domain Methods for Flutter Analysis

Abstract

Both linear and nonlinear frequency domain methods have been applied successfully to the investigation of time-periodic phenomena in turbomachinery. Linear methods allow to perform flutter analysis of turbomachinery blade rows very efficiently. Nonlinear frequency domain method can be applied to flutter analysis as well. If a pseudo-time solution algorithm is employed as a solver the nonlinear frequency domain method takes advantage of the stabilizing effect of the nonlinear coupling of the harmonics. Additionally, it allows studying the influence of nonlinear effects on the flutter stability. A linear GMRes based method and a harmonic balance method using a pseudo-time solution approach are compared with respect to computational efficiency when applied to the flutter analysis of blades of a stationary gas turbine and a low pressure turbine of a jet engine. It is shown that both methods have their merits and limitation depending on the type of problem at hand.

Experimental and Numerical Assessment of a Last Stage St Blade Damping at Low Load Operation

“…Numerical methods for blade damping estimation require the computation of the unsteady pressure response caused by the row vibration. They are usually classified in time-linearized, harmonic balance and non-linear approach both in frequency and time domain [4,6,7]. The validation of all these methods firstly started in the branch of low pressure turbines for aviation [3,8] and has been gradually extended to compressor blades and steam turbine rows [9].…”