Identification of blade operational mode shapes during wear of abradable coating

Abstract

Abradable liner materials are often used in turbine engines between the compressor blade tips and the casing. The abradable liner serves as a partially sacrificial material to improve the overall engine efficiency by creating a tight seal, minimising gas flow leakage. During operation, the rubbing interaction between the blade tips and abradable lined casing induces vibrations in the blades. These vibrations not only can have a significant influence on the wear mechanism and wear efficiency of the blade tips, but also the early fatigue failure of the blades, and therefore are of interest. In this paper, a newly developed approach is presented that can be used to identify the operational blade vibration modes. A non-contact single point laser sensor is used to measure the vibrational displacements during the wear process. A mathematical transform is introduced to correct for blade position due to its rotating frame of reference. After applying the transform, the vibrational energy is calculated at various positions throughout the blade. The continuous wavelet-based modal identification is then introduced to identify the blade mode shape. The Modal Assurance Criterion (MAC) is used to demonstrate the similarity of the mode shapes as a function of wear time illustrating that the blade mode shapes change slightly with the level of wear.

Galvanic Corrosion Performance of an Al–BN Abradable Seal Coating System in Chloride Solution

“…However, as the last immersion, the hydrolysis of anodic reaction products Al 3+ produces H + in the pits. Due to the consumption of O 2 and accumulation of H + in the pits, the predominant cathodic reaction may change to Equation (6).…”

“…where I a presents the anodic current of the reaction as Equation ( 1), while I c presents the cathodic current of reaction as Equation ( 5) or (6).…”

“…Similarly, the total cathodic current density for the tested couple is essentially that for oxygen consumption or hydrogen evolution reaction on Ni5Al/substrate cathode. Thus, the corrosion potential for the Al-BN ACS and the corresponding corrosion current for the Al-BN layer are given by the intersection of the polarization curves for reactions shown in Equations ( 1), ( 5) and (6). A simplified schematic diagram (Figure 13) was drawn to elucidate the features of long-term galvanic corrosion of Al-BN coating system mentioned above, which is particularly the reason why the galvanic potential shifted to more negative values with the increase in immersion time.…”

“…Abradable seal coatings have achieved great success in this regard by preventing unnecessary gas leakage through clearance control and are now been used extensively in aero-engines [2]. During operation, abradable seal coating wears preferentially to the blade, and the gas path clearance is maintained at the smallest scale without blade wear, so that to improve the efficiency of the engine by reducing SFC [3][4][5][6]. Abradable seal materials often operate in highly demanding environments, and the seal coatings are designed to have excellent environmental resistance (i.e., abrasion resistance, corrosion and oxidation resistance and particles erosion resistance).…”

Smart Active Vibration Control System of a Rotary Structure Using Piezoelectric Materials

“…Mokhtar et al [ 42 ] investigated the rotor–stator interaction phenomenon in the FE framework using Lagrange multiplier based on contact mechanics. Tang et al [ 43 ] presented a developed approach for the identification of the operational blade vibration modes by measuring the vibrational displacements with a non-contact single-point laser sensor during the wear process. Liu et al [ 44 ] studied structural vibration by establishing a dynamic equilibrium equation of a coupled system comprising a five-leaf blade.…”