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Tip Rubs

Blade tip rubs have been explored at the GTL in a vacuum at room temperature in both the Compressor Spin Pit Facility (CSPF) and the Large Spin Pit Facility (LSPF). The previous work in this area has been published in a variety of journals and conferences.

Size comparison between casing segments for CSPF (small) and LSPF (large)Among the many phenomena that can be investigated in the CSPF and LSPF are asymmetric and full rotor clearance closure for actual engine stages. In single blade asymmetric clearance closure investigations, a rapid contact of the bladed rotor with its housing is simulated as would occur in an abrupt flight maneuver. In full rotor clearance closure, an extended contact of the bladed rotor with its housing is simulated as could be experienced in some flight phases due to temporary thermal imbalances in different parts of the engine.

CSPF incursion mechanism and rub-shoe.

Blade-to-case rub can degrade the performance of jet engines through the introduction of high amplitude shaft vibration and severe blade/seal wear. It can even lead to catastrophic failure of the whole engine in the worst occurrence. Aerodynamic requirements dictate that engines operate with the minimum blade tip clearances that are mechanically practical. However, the smaller the blade tip clearances, the higher the possibility for blade-to-case rubbing during operation. Complex blade-casing rub-in-systems are used to improve the tip clearance and maintain greater gap uniformity over the life of the engine. Typically a rub-in-system in the compressor section of the engine may consist of a specific circumferential area of the metal alloy case shaped to accept coatings of materials selected for in-service wear and, when required, fire shielding interactions. In the experiments at the GTL, single blade rubs have obtained the same wear pattern in the facility as observed in field occurrences. Detailed measurements of blade stresses and casing forces have been obtained and modeling is in progress to improve predictions of the structural modal response.