Consequences of Borescope Blending Repairs on Modern High Pressure Compressor Blisk Aeroelasticity

Abstract

Objective of this paper is to analyze the consequences of borescope blending repairs on the aeroelastic behavior of a modern high pressure compressor (HPC) blisk. To investigate the blending consequences in terms of aerodynamic damping and forcing changes, a generic blending of a rotor blade is modeled. Steady-state flow parameters like total pressure ratio, polytropic efficiency, and the loss coefficient are compared. Furthermore, aerodynamic damping is computed utilizing the aerodynamic influence coefficient (AIC) approach for both geometries. Results are confirmed by single passage flutter (SPF) simulations for specific interblade phase angles (IBPA) of interest. Finally, a unidirectional forced response analysis for the nominal and the blended rotor is conducted to determine the aerodynamic force exciting the blade motion. The frequency content as well as the forcing amplitudes is obtained from Fourier transformation of the forcing signal. As a result of the present analysis, the change of the blade vibration amplitude is computed.

A novel model reduction approach for blisks with blend repairs and small mistuning

“…In this section, the SMART approach will be tested in two case studies: (1) an academic blisk FE model with a single/multiple blend repairs and small stiffness mistuning; (2) an academic blisk FE model with a single blend repair and small geometric mistuning. The SMART ROMs will be constructed to compute both the natural frequencies/modes and forced responses of the blisks under typical engine order excitations.…”

“…For this reason, the mistuning induced by blend repairs raises some concern. This relies on the observation that small-sized blends may notably alter both the blade frequencies and mode shapes [2], adding further mistuning to a blisk already mistuned by blade geometry variances due to manufacturing tolerance and wear, etc [3]. Recent researches therefore are focused on building high-fidelity models for blended blisks through precise geometry measurements by 3D optical scanning systems [4,5].…”

Blisk With Small Geometry Mistuning and Blend Repair: As-Measured Finite Element Model and Experimental Verification

“…Functional evaluation of the blended blisks is an indispensable step in the repair process in order to ensure its structural integrity and avoid failures not foreseen at the repair stage. Recently, there are increasing research interests that address the aerodynamic performance [2][3][4], aeroelastic behavior [5], fatigue strength [6], and "single" blade vibration frequencies [7] of blended blisks. However, there is still a limited understanding of the blending effect on the global dynamics of blisks.…”