Papers

ICMCTF2007 Session A4: Clearance Control

Friday, April 27, 2007 8:00 AM in Room Sunrise

Friday Morning

Start	Invited?	Item
8:00 AM		A4-1 Clearance Control Systems in Gas Turbines D. Sporer (Sulzer Metco, Germany) Gas turbine engines hav many seal locations: along the main shaft, over rotor blade tips and between stages. A large engine may have over 50 seal positions which are all significant with respect to safe and efficient engine operation. By reducing the clearance between rotating and stationary parts at these seal locations, the efficiency and stall margin is increased. Clearance control systems are designed to minimize gaps by allowing the rotating hardware to cut into stationary components during transient engine conditions, manoeuvre loads or as a result of thermal growth, casing distortion or surge events. This paper will give a survey of designs, methods of manufacturing and material solutions of clearance control systems in compressor and turbine modules of gas turbine engines. Typical compressor seal systems will be presented and discussed. A focus will be placed on thermally sprayed abradables. Various material concepts and their performance will be reviewed. Improvements in application techniques and processing control will be highlighted. Turbine-side seals are often low density, robust metal structures fabricated from heat resistant, mainly Ni based alloys. A short overview of these will be given. With the appearance of thermal fatigue resistant ceramics, new high temperature turbine sealing concepts could be developed. Making use of ceramic clearance control surfaces frequently involves thermal spraying. Established and novel high temperature ceramic seals and competeing metallic systems will be presented. The paper will include a short survey of blade hard tipping solutions for compressor and turbine blades for enhanced cutting performance. Finally, a short excursion into steam turbine sealing technology will be undertaken.
8:40 AM		A4-3 A Proposal for Numerical Simulations of Abradability Tests J.-L. Seichepine, H.I. Faraoun, F. Peyraut, C. Coddet (University of Technology of Belfort-Montbeliard, France); C. Sellars (Rolls-Royce plc., United Kingdom); D. Sporer (Sulzer Metco, Germany); M. Hertter (MTU Aero Engines, Germany) The newly designed abradable coatings are usually validated by rig tests, simulating actual working conditions in an aircraft engine. The aim of this work was to develop a numerical model of these rig tests, allowing extensive studies on the influence of coating properties and test conditions. The proposed model includes several steps: image analysis on micrographs of deposits cross sections, structural description of their microgeometry, estimation of the parameters of an anisotropic elastic-plastic law of behavior by FE simulations of mechanical tests, FE simulation of a single blade-to-coating rubbing hit, and finally a global approach of the complete abradability test.
9:00 AM		A4-4 High Speed Rub Wear Mechanism in IN-718 vs. NiCrAl-Bentonite Coating T.A. Taylor (Praxair Surface Technologies) A matrix of rub tests with blade tip speeds and infeed rates as variables gave rub force and tip wear results. Here, the rubbed tip material (bare IN-718, Rc=42) and the abradable coating NiCrAl-Bentonite (HR15Y=50) were examined in the SEM and polished cross section to gain insight into the wear mechanisms involved.
9:40 AM		A4-7 Freestanding Abradable Coating Manufacture and Tensile Test Development R.E. Johnston (University of Wales Swansea, United Kingdom); W.J. Evans (University of Walse Swansea, United Kingdom) Abradable coatings are used extensively within gas turbines. Abradable material is applied to the inside surface of the compressor and turbine shroud sections using thermal spray methods, coating the periphery of the blade rotation path. The function of an abradable seal is to wear preferentially when rotating blades come into contact with it, while minimising the over-tip clearance, and improving the overall efficiency of the engine. There is a distinct lack of established materials property data for all abradable materials, due to the difficulty of testing this very unique class of materials. Abradables understanding is historically limited, with the field often described as a ‘black art’, and component/material improvements habitually being ‘firefighting’ actions. This work is part of a wider programme in partnership with Rolls-Royce plc. to gain a greater understanding of abradable materials, how the perform, and ultimately how to improve their performance in-service. This paper describes a novel method, devised in tandem with Rolls-Royce plc, of producing free-standing abradable tensile test specimens via thermal spray. Abradables are thermally sprayed onto the engine shroud when manufacturing engine parts, therefore the specimen manufacture mimics the processes used in practice. The specimen mould is composed of a dissolvable polymer composite which maintains its integrity during spraying and cooling, and is then ‘washed’ away in an ultrasonic water bath. This results in near-net shape specimens, which are then machined to a specific geometry. This paper details the iterative testing development that contributed to a final working design and testing methodology for a previously untested class of materials.