Controlled Fan Blade Tip/Shroud Rubs at Engine Conditions

Abstract

The purpose of this paper is to describe the new facility design and operation improvements, and to demonstrate utility by providing typical results obtained as part of a typical measurement program. Since 2002 a number of experiments have been conducted to generate a broad database for tip rubs using two unique experimental facilities at the Gas Turbine Laboratory of The Ohio State University. Development of an in-ground spin-pit facility specifically designed to investigate rub-in-systems for jet engine components using real hardware rotating at representative engine speeds was reported several years ago. While the original smaller facility is still in use, more recently a much larger in-ground spin-pit facility for which the basic design and operation of the blade tip/shroud incursion technique is very different from the original facility design has been commissioned, and the results of a measurement program completed using a full-scale titanium-alloy fan blade rubbing an abradable casing are presented. The Large Spin-Pit Facility [LSPF] is designed to allow rotating engine hardware from low RPM [typically a few thousands] to 18,000 rpm, using two interchangeable spindle arrangements mounted above ground onto an in-ground containment tank. The LSPF is also designed to allow the progressive insertion of a casing segment into the path of a single-bladed or multiple-bladed disk. Segments extending 90 or 120 degrees are in use for different applications. For the configuration discussed in this paper, a 90-degree segment of a representative fan casing is forced to rub the tip of a titanium-alloy fan blade at a rotational speed in the vicinity of 6000 rpm.

Rotor to stator contacts in turbomachines. Review and application

“…Two types of test bench are used to study blade-casing contacts. The first are generally limited to a section of rigid and instrumented casing [68][69][70][71][72]. They use rotors with a single blade to facilitate the control of the contact process.…”

“…The localization and extent of contacts are evaluated by analyzing the parts after testing and by using blue ink coating on the casing and the blade [70]. Two optical sensors detect blade passage and an electric circuit allows determining the number of contacts between the two parts [71]. Fig.…”

“…The combination of axial, radial and circumferential blade deformations tends toward contact at the trailing edge. Padova [70,71] showed that the presence of abradable coatings on the casing considerably reduces contact forces and stresses in the blade.…”

Identification of blade operational mode shapes during wear of abradable coating

“…As a result, the entire life of the blades can be shortened from its intended design life. Several scaled test rigs [4][5][6][7] have been developed to represent the inservice conditions for the blade tip to abradable rubbing. Wear tests using these scaled rigs have been conducted to investigate the correlations of some important factors (including abradable incursion feed rates [8,9], contact force history [10][11][12], blade tip treatment [13] and abradable materials and structures [14][15][16]) to the wear mechanisms [17] present using in-situ measurement techniques.…”