Session: 24-01 Compressor aerodynamic damping

Paper Number: 82160

82160 - On the Effect of Frequency Separation, Mass Ratio, Solidity and Aerodynamic Resonances in Coupled Mode Flutter of a Linear Compressor Cascade 

With the current trend for more aggressive engine design yielding higher blade loading, thinner profiles and general weight reduction, the blade mass ratio to air is significantly reduced. As a consequence, coupled or multi mode flutter is likely as the structural motions are not decoupled from the aerodynamic forces anymore. Decoupled analyses like the work-per-cycle approach, also known as the energy method, lead to a non-conservative result in these cases. The absence of friction dampers significantly reduces the blade structural damping and almost all vibrational damping has to be aerodynamic, thus the blades are prone to self-induced aerodynamic excitations.

 

The p-k method can be utilized to solve the coupled aeroelastic eigenvalue problem for frequency and damping respectively excitation of the multi-mode vibration. Assuming small perturbations in the vicinity of flutter onset, vibrations can be treated by a linearized approach. The aerodynamic responses are independent of the amplitude and the structural vibration can be expressed as a superposition of linear mode shapes. This paper is a follow-up to the previous publication GT2020-14105 which verified and validated the p-k method against time-marching simulations.

 

In this paper, the effects of different structural aspects are investigated for a two-dimensional compressor cascade. The key nondimensional parameters are frequency separation, mass ratio and solidity. Each influence is evaluated for a subsonic and a transonic operating condition. It is confirmed that a sufficiently low frequency separation or mass ratio will ultimately lead to coupled mode flutter. The influence of the solidity is discussed by varying the blade-to-blade distance for the linear cascade.

 

Furthermore, the effect of a high frequency dependency of the aerodynamic forces is investigated. Such phenomena can happen in case of aerodynamic or acoustic resonances. If the resonance peaks are close to the aeroelastic frequency, a discontinuous behavior of the frequency or damping solution can lead to a rapid destabilization of the system, once the aeroelastic frequency is pushed from one side to the other of the peak. In these regimes, it is crucial to have a high resolution of the frequency-dependent generalized aerodynamic forces for an accurate prediction of the flutter onset.

Presenting Author: Matthias Schuff German Aerospace Center

Presenting Author Biography: -Studied aerospace engineering at the University of Stuttgart<br/>-Research associate at German Aerospace Center since 2015<br/>-PhD candidate at the Technical University of Berlin

Authors:

Matthias Schuff German Aerospace Center
Virginie Anne Chenaux German Aerospace Center