Influence of the Steady Deformation on Numerical Flutter Prediction for Highly Loaded and Flexible Fan Blades

Abstract

Deflections at off-design conditions can change the aeroelastic behavior of turbomachinery blades significantly. Therefore, steady-state deformations at each operating point cannot be neglected and need to be captured by CFD-CSM coupling.

The implementation of an automated toolchain for the generation of a compressor map is presented. It includes steady FSC and is preceded by a flutter analysis. The CFD mesh is adapted to steady surface deflections via a mesh deformation using radial basis functions interpolation. Mode shape vibrations are computed at each operating point. Aerodynamic damping for each mode and IBPA is than assessed by unsteady RANS computations with time-linearization around the steady flow field.

A detailed compressor map of a highly flexible CFRP fan, that was optimized within a multidisciplinary toolchain, is generated based on the geometry for design conditions. Elastic deformations affect a shift of the speedlines especially in near-choked conditions. At the surge line, some cases did not reach a steady-state deformation, oscillating between two deflections and indicating possible stall flutter.

The impact of the steady deformation on predicting flutter boundaries for very elastic blades is pointed out by the comparison to a rigid setup. Significant differences are identified in the region of near-surged and stalled conditions and are due to large deformations, especially torsional deflections. The results of the underlying work of this paper will assist in identifying critical designs during optimization runs more quickly.