Bharat S. Bagepalli

Design and Testing of CFCC Shroud and Combustor Components

This paper presents initial results in the development and testing of SiC-based Continuous Fiber Ceramic Composites (CFCC) materials for combustor and stage 1 shroud components of large utility-class gas turbines. Use of CFCC’s for these components has the potential for increasing output power and thermal efficiency and reducing emissions.First stage turbine shroud components were fabricated using five material systems including three SiC/SiC-Si systems made by silicon melt infiltration (MI), chemical vapor infiltrated (CVI) enhanced SiC-SiC and directed metal oxidation (DIMOX) Al2O3-SiC composite. A combustor liner was made of MI CFCC. Before and after testing the components were inspected by several NDE techniques including IR thermography, resonance testing and visual examination.A novel, high pressure test rig was used to test four shroud components and a combustor liner simultaneously. Components were exposed to hot gas temperature of 1200°C at 12.5 bar in cyclic and steady-state tests. Cyclic testing simulated engine trip conditions with 200 flame-on, flame-off cycles. Steady state testing involved 100 hours of exposure at high temperature and pressure with hot combustion gases. At the conclusion of the first phase of testing there was visible damage to two pieces of one of the material systems. Destructive testing of the components following rig exposure showed little degradation to the MI composite materials. In summary, high pressure combustion rig testing of these components demonstrated excellent performance with little degradation among the material systems.Copyright

High Performance Combustor Cloth Seals

Design of combustor seals poses a real challenge to designers who seek to achieve extended service life. In gas turbines with can-annular combustion systems, the combustor seals are used to seal the gap between the cans (transition duct) and the first stage nozzles. Combination of concentrated contact loads caused by thermal distortions and combustor dynamics limit the part service life. The introduction of flexible cloth seals has demonstrated the promise to extend the service life by 50% or more. However, to provide more air for combustion, and to satisfy decreasing NOx emissions limits, leakage reduction beyond existing levels is also required in addition to extending the service life. This paper describes the new combustor cloth seals designed to minimize leakage while extending the service life. Flexibility introduced by composite cloth assembly extends seal life by reducing contact load severity. Uniform slot contact minimizes leakage. To achieve maximum part life with minimum leakage rate, seal design has been optimized using statistical analysis tools. The systematic life improvement started with optimization of the metallic cloth. Once the process capability has been defined, the best vendor, weave and orientation were identified. Critical design areas have been identified through field inspections of prototypes. To minimize cloth wear in transition duct aft frame slots, seal slot engagements have been optimized using the tolerances on design parameters. The parameter values were assumed to be normally distributed within the tolerance bands. Inner-outer and side seal junctions have been redesigned to reduce contact load severity. Two separate Design of Experiments (DOE) series were conducted to develop load distribution transfer functions for both in-plane and out-of-plane cases representing the observed offset between neighboring * Copyright

Rotary compressor with vane positioned to reduce noise

The noise of a rotary compressor is reduced by orienting the sliding vane. In particular, the vane is oriented such that the force component which is perpendicular to the vane motion and which tends to jam the vane and create high frictional effects is minimized. The vane is tilted towards the high pressure chamber so as to result in a smaller force component perpendicular to the direction of vane motion, which direction corresponds to the direction of the vane slot itself. The vane may be shifted laterally from its previously known position in order to achieve the same lower friction and lower noise effects.

Parasitic Corner Leakage Reduction in Gas Turbine Nozzle-Shroud Inter-Segment Locations

Multi-segment nozzle and shroud construction is commonly used in large industrial gas turbines. Such a breakdown into subsystems is essential for ease of assembly and to accommodate misalignments and thermal growth. The gaps between nozzle and shroud segments constitute a parasitic leakage path. Due to the complex interface geometry involved, most of these junctions require multiple seal segments. This work describes efforts to minimize corner leakage occurring at the gaps between the seal segments. Use of flexible cloth seals eliminates the need to segment seals at some corners. To achieve the best leakage performance, optimum turn radius has been investigated. To compare sealing performance at various curvature levels a high pressure static seal test setup has been developed. Backto-back leakage tests were performed using both segmented rigid seals and curved cloth seals. Variation in leakage with changing direction of pressure application has also been investigated. Flow rates for each test configuration were normalized with baseline leakage of rigid seal strips. Leakage test results indicated that corner leakage flow decreases with increased turn radius. Overall, cloth seals provided up to 75% corner leakage flow reduction over segmented rigid seals.