Aeroelastic Stability Assessment of an Industrial Compressor Blade Including Mistuning Effects

Abstract

This paper presents a comprehensive investigation into the aeroelastic stability behavior of a transonic front blade in an industrial compressor when operating outside its normal range of service parameters. The evolution of the airfoil’s aeroelastic stability in the first flexural mode is studied as the front blade operation progresses towards choked flow conditions. First, linearized 3D flutter computations representing today’s industry standard are performed. The linearized calculations indicate a significant, shock-driven flutter risk at these off-design flow conditions. To further explore the aeroelastic behavior of the rotor and to find a viable solution toward flutter risk elimination, two parallel investigations are undertaken: (i) flow perturbation nonlinearity effects and potential presence of limit-cycle oscillation; and (ii) effects of blade mistuning and flutter mitigation potential of intentional mistuning, including its impact on forced response behavior. The nonlinear harmonic analyses show that the minimum aerodynamic damping increases rapidly and essentially linearly with blade oscillation amplitude beyond the linear regime. Thus, a state of safe limit-cycle oscillation is predicted for the fully tuned blade. Additionally, it is found that intentional, realizable blade frequency offsets in an alternating pattern efficiently stabilize the blade. Finally, it is verified that alternating mistuning has a beneficial effect versus the inevitable random mistuning also in the forced response.

Aerodynamic Investigation of a Composite Low-Speed Fan for UHBR Application

“…While the fundamental understanding of the causes for flutter has been improved throughout the past decades and allowed to develop efficient countermeasures like intentional mistuning (i.a. [4]), the causes for NSV are still under discussion in the literature. Concerning typical fan flutter (part speed flutter bite), the dominant mechanism is an acoustic resonance between a structural vibration pattern and acoustic modes, which are reflected in the intake [5].…”

Forced Response Excitation due to Stagger Angle Variation in a Multi-Stage Axial Turbine

“…In the present study a stagger angle variation of λ = 1.5 deg is implemented in the fourth stage and compared with the reference case where all vanes are identical. The alternating distribution of the geometric variation is typical after the regeneration of turbine blades because the mistuning results in a positive effect of the flutter stability ( [13] and [14]). This study is performed for two part-loaded operating points (OP1 and OP2) and the design point (OP3) listed in Tab.1.…”