Choke flutter instability sources tracking with linearized calculations

Abstract

Purpose The choke flutter is a fluid-structure interaction that can lead to the failure of fan or compressor blade in turbojet engines. In ultra high bypass ratio (UHBR) fans, the choke flutter appears at part-speed regimes and at low or negative incidence when a strong shock-wave chokes the blade to blade channel. The purpose of this study is to locate the main excitation sources and improving the understanding of the different work exchange mechanisms. This work contributes to avoiding deficient and dangerous fan design. Design/methodology/approach In this paper, an UHBR fan is analyzed using a time-linearized Reynolds-averaged Navier–Stokes equation solver to investigate the choke flutter. The steady-state and the imposed vibration (inter blade phase angle, reduced frequency and mode shape) are selected to be in choke flutter situation. Superposition principle induced by the linearization allow to decompose the blade in numerous small subsections to track the contribution of each local vibration to the global damping. All simulations have been performed on a two-dimensional blade to blade extraction. Findings Result analysis points to a restricted number of excitation sources at the trailing edge which induce a large part of the work exchange in a limited region of the airfoil. Main phenomena suspected are the shock-wave motion and the shock-wave/boundary layer interaction. Originality/value An original excitation source tracking methodology allowed by the linearized calculation is addressed and applied to a UHBR fan test case.

UHBR Open-test-case fan ECL5/Catana, Part 2: Mechanical and aeroelastic stability analysis

“…In this context, a new open-test-case fan stage named ECL5 has been developed at Ecole Centrale de Lyon (Brandstetter et al, 2021). In parallel, the preliminary design has been used to develop flutter investigation methods (Duquesne et al (2019b) and Rendu et al (2020)). This open-test-case is provided to the turbomachinery community within the European CleanSky-2 project CATANA (Composite Aeroelastics and Aeroacoustics).…”

Analysis of a Linear Model for Non-Synchronous Vibrations Near Stall

“…For quantitative predictions of blade amplitudes and stresses during flutter, non-linearities must be taken into account. For a more detailed discussion of flutter the reader is referred to, for example, the work of Sisto [1], Carter and Kilpatrick [6], Corral [7] or Duquesne et al [8].…”