ICMCTF2005 Session A4: Clearance Control

Wednesday, May 4, 2005 1:30 PM in Room Sunrise

Wednesday Afternoon

Time Period WeA Sessions | Abstract Timeline | Topic A Sessions | Time Periods | Topics | ICMCTF2005 Schedule

Start Invited? Item
1:30 PM A4-1 Turbomachine Interface Sealing
R.C. Hendricks (NASA Glenn Research Center); R.E. Chupp (General Electric Global Research); S.B. Lattime, B.M. Steinetz (NASA Glenn Research Center)
Clearance control becomes a major issue in power systems turbomachine design and operational life. Insufficient clearances limit coolant flows, cause interface rubbing, and engender turbomachine instabilities and system failures. Excessive clearances lead to losses in cycle efficiency, flow instabilities, hot gas ingestion into disk cavities, bearing and materials failures and potential compressor stall. Yet clearance control though effective sealing becomes the most cost effective way to enhance system performance. Coatings, films and combined use of materials both metals and ceramics play a major role in maintaining interface clearances in turbomachine sealing. In our paper, we will focus on conventional and innovative materials and design practices for shroud sealing, yet include internal flow sealing interfaces and some effects of controlling seal rubs for both static and dynamic seals.
2:10 PM A4-3 Thermal and Mechanical Testing and Analysis of Abradable Coating Materials
N.P. Hopkins (Rolls-Royce, United Kingdom)

The difficulties associated with generating material property data for thermally sprayed coatings are well known. This is especially an issue for abradable coatings, due to their inherently low mechanical strength and often complex thermal behaviour. In addition, a lack of globally recognised testing standards has lead to a range of company specific in-house test methods, which often provide data that is difficult or impossible to cross-reference. These factors have highlighted the need for robust industry standard methods for the testing and analysis of abradable coating materials.

Material property data, which can be linked to abradability performance and thermal behaviour, is an important element in developing a robust fundamental understanding of abradable coatings. This data will not only assist with the coating manufacture and source control of current abradable systems, but also provide an essential component in the development of new abradable coatings.

This paper highlights the key aspects of a two-phase process, aimed at the development of a suite of internationally recognised test standards for abradable coating materials. These will facilitate a greater fundamental understanding abradable materials and support future coating developments.

Phase one of the process involved evaluating the test methodologies that are currently available, and defined where possible, the standardised parameters and process conditions. This work initially focused on the increasing number of abradability test facilities and the testing of abradable materials over a range of parameters and test conditions. The capability of each facility was assessed against specific testing objectives and analytical requirements. Generic abradability parameters, which are independent of facility specific variables, such as disc size and specimen geometer were defined. These will provide the building block of a test standard for future abradability testing.

Phase two highlights strategic areas, where there is a requirement for robust test methods or analysis techniques. These encompass fundamental mechanical test methods as well as the latest non-destructive evaluation (NDE) techniques, which have potentially far reaching applications from source control at manufacture to 'on-wing' inspection.

As part of this study, a process has been developed by Rolls-Royce (patent pending) for the mechanical testing of freestanding thermally sprayed coating materials. This enables abradable material test pieces to a range of geometries, to be tested using standard mechanical testing equipment in a reproducible manor.

NDE techniques could potentially offer significant quality control and cost saving benefits to coating suppliers and engine manufacturers alike. Recent developments in capability and equipment mean that robust techniques, can be carried out on an industrial scale often using potable or even hand held equipment with extremely high precision.

This study covers the aspects of abradable material testing and analysis discussed above and highlights future requirements of abradable testing, which would benefit from standardisation and globally recognised procedures.

2:30 PM A4-4 Abradable Coating Development for Industrial Gas Turbines
D.B. Allen (Siemens Westinghouse Power Corporation)
Abradable coatings have been used in aero turbines for the past 30 years but until recently have not found widespread use in industrial gas turbines. With ever increasing performance, efficiency and emissions requirements, however, these coatings are becoming more important to the IGT designers. Siemens Westinghouse is actively pursuing sealing developments in both the compressor and turbine sections of their large engines, with the majority of our work focused on Rows 1 and 2 of the turbine. This talk will cover the clearance design methodology of our engines and some of our recent results.
2:50 PM A4-6 High Temperature Abradables for Gas Turbine Applications
F. Ghasripoor, R.E. Chupp, Y.C. Lau (General Electric Global Research)
Improving dynamic sealing between rotating and stationary parts in industrial turbines can significantly increase unit performance. One type of improved sealing being incorporated into turbines is abradable seals to reduce the blade-tip clearances. An abradable material is placed on the stationary shroud or casing opposite the rotating blade tips to reduce clearances with minimum risk to the turbine components during rubs. Also, applying an abradable material further reduces effective clearances for often-encountered casing out of roundness and rotor lateral movement. A thermally sprayed coating is applied to higher temperature, stage 1 gas turbine shrouds to reduce tip clearances and improve turbine performances up to 0.8%. Efforts are in progress to develop abradable materials for these turbine locations with increased service life.
3:10 PM A4-7 Future Abradable Requirements Needed by Aerospace OEM's and their Material and Equipment Suppliers
M.R. Dorfman (Sulzer Metco (US) Inc.); K. Hajmrle, P. Fiala (Sulzer Metco Inc., Canada); C. Britton (Sulzer Metco Ltd., United Kingdom); M.M. Nonni (Sulzer Metco (US) Inc.)
There is a high cost associated with re-spraying turbine components due to process inconsistency, as well as, in-service clearance control coating failure analysis. Understanding these problems can be labor intensive and time consuming to the aerospace OEM. It is for these reasons that OEM's will be requiring vendors of materials and equipment to have: 1) greater in-process controls on spray process equipment, 2) greater statistical process control (SPC) documentation of key powder manufacturing process variables, 3) increased documentation of cause and effect of process variables and a better understanding of the influence of these variables on overall performance and 4) more detailed coating/powder specifications. This paper will discuss the future needs of aerospace OEM's in these four areas and specifically discuss how vendors are addressing these needs.
3:30 PM A4-8 Abradable Testing Capabilities at Sulzer Innotec
S. Wilson (Sulzer Innotec, Sulzer Markets & Technology AG, Switzerland)

The abradable testing facility at Sulzer Innotec consists of a rotor, movable specimen stage and heating device; the infrastructure being that of a large turbine balancing facility with a 2 MW electric rotor drive. A wide range of aero, power and steam turbine OEMs have used the rig over the past ten years, usually in partnership with abradable coating developers.

The special features of the rig are its capacity for abradable evaluation at temperatures up to 1200°C, blade tip speeds from 30 to 410 m/s and blade incursion rates into abradable shrouds from 2 to 2000 µm/s. The broad range of test conditions available cover the entire in-situ conditions experienced by fan, compressor and turbine clearance control systems.

In recent years, the facility has diversified into elevated temperature testing of labyrinth seal systems using a dedicated rotor with removable seal strip capability. Also available are testing of instrumented blades, with measurement and evaluation of blade foil and root vibration modes during incursion at temperature into shroud materials. An overview of the rig features will be provided together with a brief look at the evolution of some general abradable technology trends over the past ten years.

3:50 PM A4-9 Rub Test Rig at Praxair Surface Technologies
T.A. Taylor (Praxair Surface Technologies)
The test machine recently designed and built by PST is undergoing checkout and testing. The capabilities for testing abradable seal coatings snd wear-resistant or abrasive tip coatings are described, including certain design features. Trial testing and data acquired are described.
Time Period WeA Sessions | Abstract Timeline | Topic A Sessions | Time Periods | Topics | ICMCTF2005 Schedule