Forced response in a multi-stage aeroderivative axial compressor with acoustic excitations: Method validation with field data

This paper presents the application of a forced response prediction process to an industrial aeroderivative axial compressor and its validation against experimental data. The forced response process is based on a dedicated strategy to decompose the overall unsteady aerodynamic forcing coming from URANS analyses, and an improved use of the interference diagram to detect additional acoustic forcing in the entire operating range. The identification of potential resonance conditions, or crossings, in the interference diagram is based on the assumptions of a cyclic symmetry tuned structure and a forcing function having an aliased engine order driven only by the airfoil count of the rotor/stator interactions of interest. Despite this, it is not rare that unexpected resonances appear during compressor validation tests, often calling for painful and time-consuming redesigns. This is witnessed by the unsteady analysis of an 11-stage axial compressor in which the spatial content of engine order forcing is influenced also by further rotor/stator interactions by means of Tyler-Sofrin acoustic modes that cause the onset of additional crossing conditions.

The theory based on time and space decomposition is validated with full 3D unsteady forced response simulations of the entire multistage compressor. Numerical results, obtained by an in-house modal work approach, are compared with experimental data focusing on two resonances, the first of which can be detected by the classical interference diagram, while the second one is justified only by the improved use that considers the acoustic excitations. In both cases, the predicted blade responses are in good agreement with measurements.

The theory associated with the generation mechanism of the additional nodal diameters is further explained using the results of dedicated numerical experiments conducted by changing the relative stator and rotor airfoil count on a reduced compressor domain.