Binayak Roy

Decoupled temperature and strain measurements using fiber Bragg grating sensors

Temperature and strain sensing of critical aircraft engine components is a critical health and prognostics tool for future engine programs. Real-time feedback of key temperature and strain measurements can be used to provide better estimates to ground crews of engine component life, thus minimizing engine downtime and maximizing the effectiveness of planned inspections. One method for monitoring distributed stress and temperature throughout an engine is through the use of Fiber Bragg Grating (FBG) sensors. With just a single sensor line, both temperature and strain can be monitored simultaneously and in a distributed fashion. Unfortunately, FBG sensors bonded to a host structure are susceptible to both thermal strains and mechanically-loaded strains simultaneously, and without intelligent sensor design, the two signals are indistinguishable from each other. In the present work, a sensing array design is proposed and demonstrated to provide a means for separating thermal and mechanically-loaded strain signals by using two FBG sensors in close proximity to each other. Experimental results are provided using a structural beam element to demonstrate the feasibility of the proposed approach for decoupling the temperature and strain effect from fiber Bragg grating sensors.

Active Retractable Seals for High-efficiency Steam Turbines

*† ‡ § ** Rotor end leakage at the high-pressure section accounts for about 20% of the total leakage loss in a steam turbine. Advanced sealing technology at end packing locations can bring about significant improvement in overall turbine efficiency. In this paper, we propose an active seal, which can be retracted during rotor transients. As a result, tighter clearances can be designed and preserved during the life of the turbine. The concept is an extension of commonly used Variable Clearance Positive Pressure Packing technology, where the seal opens and closes depending on the pressure differential across it. The proposed extension involves the addition of a bypassing mechanism across the seal, which can actively control the pressure differential and hence the opening and closure of the seal. The design concept was initially demonstrated in a subscale test rig. Operational validation was performed through extensive testing on a full-scale rig.

Experimental Characterization of Variable Bristle Diameter Brush Seal Leakage, Stiffness and Wear

Brush seals are used in a wide variety of turbomachinery for sealing rotor-stator and stator-stator clearances. Application of traditional brush seals is limited by their life and performance at high differential pressures. GE’s patent-pending Variable Bristle Diameter (VBD) brush seal overcomes the limitations of the traditional brush seal by sandwiching a layer of fine bristles, with better sealing capability, between adjacent rows of stiffer bristles capable of withstanding larger differential pressure and flow disturbance. The General Electric VBD design uses thick bristles both in front and back rows. In addition to leakage performance, for successful design it is important to understand the force interactions between a brush seal bristle pack and the rotor. The important failure mechanisms to avoid include overheating and rotor dynamic instabilities caused by excessive brush seal forces. Brush seal stiffness, defined as brush seal force per unit circumferential length per unit incursion of the rotor, depends on the complex interaction of the pressure-dependent inter-bristle forces, the blow-down forces and the friction forces between the backplate and the bristle pack. Furthermore, brush seals exhibit different hysteresis and wear behavior under different pressure loading conditions. In this article, we present experimentally measured leakage, stiffness and wear characteristics of three different VBD brush seal designs subjected to a wide range of pressure loading.© 2013 ASME

Progressive Clearance Labyrinth Seal for Turbo-Machinery Applications

Turbomachinery sealing is a challenging problem due to the varying clearances caused by thermal transients, vibrations, bearing lift-off etc. Leakage reduction has significant benefits in improving engine efficiency and reducing emissions. Conventional labyrinth seals have to be assembled with large clearances to avoid rubbing during large rotor transients. This results in large leakage and lower efficiency. In this paper, we propose a novel Progressive Clearance Labyrinth Seal that is capable of providing passive fluidic feedback forces that balance at a small tip-clearance. A modified packing ring is supported on flexures and employs progressively tighter teeth from the upstream to the downstream direction. When the tip-clearance reduces below the equilibrium clearance, fluidic feedback forces cause the packing ring to open. Conversely, when the tip-clearance increases above the equilibrium clearance, the fluidic feedback forces cause the packing ring to close. Due to this self-correcting behavior, the seal provides high differential pressure capability, low leakage and non-contact operation even in the presence of large rotor transients. Theoretical models for the feedback phenomenon have been developed and validated by experimental results.Copyright