Raymond Edward Chupp

Sealing in Turbomachinery

Clearance control is of paramount importance to turbomachinery designers and is required to meet todays aggressive power output, efficiency, and operational life goals. Excessive clearances lead to losses in cycle efficiency, flow instabilities, and hot gas ingestion into disk cavities. Insufficient clearances limit coolant flows and cause interface rubbing, overheating downstream components and damaging interfaces, thus limiting component life. Designers have put renewed attention on clearance control, as it is often the most cost effective method to enhance system performance. Advanced concepts and proper material selection continue to play important roles in maintaining interface clearances to enable the system to meet design goals. This work presents an overview of turbomachinery sealing to control clearances. Areas covered include: characteristics of gas and steam turbine sealing applications and environments, benefits of sealing, types of standard static and dynamics seals, advanced seal designs, as well as life and limitations issues.

Evaluation of brush seals for limited-life engines

Brush seals are a relatively new concept for replacing labyrinth seals in gas turbine engines. An evaluation was performed to assess the potential of brush seals for limited-life gas turbine engines. A rotating rig was designed and built to test labyrinth and brush seals over a range of simulated engine conditions. An initial set of brush seals was rig-tested to determine leakage and wear performance and identify potential optimum configurations. The measured results showed that brush seals offer significant improvements over labyrinth seals with a factor of three or more reduction in leakage flow. Brush seals exhibit an initial wear-in period but retain significantly reduced leakage over labyrinth seals for times exceeding most limited-life engine applications. Consequently, brush seals offer the potential to precisely meter cooling/leakage air, thereby decreasing parasitic leakage and improving fuel consumption and thrust. Thus, brush seals are a definite candidate for replacing labyrinth seals in gas turbine engines.

Advanced Seals for Industrial Turbine Applications: Dynamic Seal Development

The ongoing need for higher performance industrial turbines has lead to extensive efforts to improve various components of gas turbines, steam turbines, compressors, and generators. One area being addressed is improved seals to reduce parasitic leakage flows. Major progress has been made to implement advanced dynamic seals into industrial turbines with resulting performance gains. Brush seals have significantly decreased labyrinth seal leakages in gas-turbine compressors and turbine interstages, steam-turbine interstage and end packings, industrial compressor shaft seals, and generator seals. Abradable seals are being developed for blade-tip locations in various turbine locations. The development and implementation of advanced seals in industrial turbines is summarized and with a focus on dynamic seals.

Advanced Seals for Industrial Turbine Applications: Design Approach and Static Seal Development

Changes in the market place are imposing increasing demands to improve efficiency (decreasing heat rate) and power output for both existing and new industrial turbines. The improvement is to be done while maintaining or decreasing emission levels. This demand has led to extensive efforts to improve the performance of the various components in industrial gas turbines, steam turbines, compressors, and generators. One of the critical areas being addressed is reducing the parasitic leakage flows through the various static and dynamic seals. Implementing advanced seals into industrial turbines has progressed well over the last several years, with significant operating performance gains achieved. Advanced static seals have been placed in gas-turbine hot gas-path junctions and steam-turbine packing ring segment end gaps. The status of efforts to develop and implement advanced static seals in industrial turbines is summarized. The design approach following design-for-six-sigma methodology is summarized, and the development efforts for each static seal type are presented.

Development of Higher Temperature Abradable Seals for Gas Turbine Applications

Improving sealing between rotating and stationary parts in industrial turbines can significantly increase unit performance. Abradable seals are being developed to reduce blade-tip clearances where 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. A newly developed metallic abradable material is a thermally sprayed coating on the first stage of gas turbine shrouds to reduce tip clearances; thereby, improving turbine power and efficiency by about 1/2 percent. This material is an improvement over currently available metallic abradables increasing the maximum operating temperature from 750°C to about 950°C with no special treatments required on the rotating blade tips. Initial engine field tests have shown the new material to be abradable and on target to meet life requirements.Copyright