Minimising Clearance Consumption: A Key Factor for the Design of Blades Robust to Rotor/Stator Interactions?

Abstract

The recent development of a numerical strategy dedicated to the simulation of rotor/stator interactions stemming from structural contacts in modern aircraft engines led to the first optimization of a high-pressure compressor blade profile accounting for criteria related to non-linear contact simulations. This optimization procedure revealed very significant improvements in terms of amplitudes of vibration but failed to identify key design parameters. Satisfying numerical results were obtained by a minor modification of a combination of many design parameters. Based on this observation, this contribution intends to shed a new light on this previous redesign operation focusing on one key quantity: the clearance consumption. This quantity is presented in the first section. In the second section, results of the redesign operation are recalled before the presentation of original results, featuring detailed interaction maps in the frequency domain, on which focuses the third section of the article. Finally, the blade profiles are extensively compared based on their specific clearance consumption and presented results suggest that this quantity may be key in discriminating acceptable from unacceptable blade profiles with respect to their vibratory behaviour when structural contacts occur.

Blade/casing rubbing interactions in aircraft engines: Numerical benchmark and design guidelines based on NASA rotor 37

“…22), blades L 50 and L 100 also lead to a slightly smaller dynamic clearance than the reference blade, S 50 and S 100 lead to a dramatic reduction in dynamic clearance, and CS 50 and CS 100 exhibit the same dynamic clearance as the reference blade. These observations are consistent with previous studies showing that smaller dynamic clearance is related to lower blade's responses to contact events [59], as S 50 and S 100 exhibit the largest decrease in dynamic clearance as well as the lowest radial and tangential displacements. It is important to note, however, that the reduction is particularly striking for the first torsion mode, while interactions seem to occur mainly with the first bending mode.…”

“…Previous works have shown a relationship between a blade's robustness to contact events and its dynamic clearance, studied in details in [56] and investigated previously as the "clearance consumption" in [59]. The dynamic clearance quantifies the variation of the radial position of a given point on the blade tip as the blade vibrates along one of its free-vibration modes: large dynamic clearance means that vibration along the mode modifies significantly the blade/casing clearance.…”

Towards the Structural Optimization of Bladed Components Featuring Contact Interfaces

“…Thus, the stacking line, whose parameters are defined in Fig. 6, controls the blade tilt with the lean angle (15) and the sweep angle (16) and the blade curvature with the bowed distance (17). The hub radius (18) and the blade height (19) give the radial positions of the root profile and the tip profile.…”

“…All other profile parameters are bound within a ±20% variation range. Finally, all extrusion parameters are constant but (17) the bowed distance that may vary within a ±20% variation range.…”

“…But, to the best of the authors' knowledge, only one publication [16] focuses on a redesign operation following structural contact events. The aftermath of this redesign operation was later on investigated in [17]. It was evidenced that the redesigned blade profile essentially differs from the original blade design with respect to its ability to maintain an almost constant blade/casing clearance as it vibrates along its first bending mode.…”