Scott B. Lattime

Turbine Engine Clearance Control Systems: Current Practices and Future Directions

Improved blade tip sealing in the high pressure compressor (HPC) and high pressure turbine (HPT) can provide dramatic reductions in specific fuel consumption (SFC), time-on-wing, compressor stall margin, and engine efficiency as well as increased payload and mission range capabilities. Maintenance costs to overhaul large commercial gas turbine engines can easily exceed

Preliminary Evaluation of an Active Clearance Control System Concept

1M. Engine removal from service is primarily due to spent exhaust gas temperature (EGT) margin caused mainly by the deterioration of HPT components. Increased blade tip clearance is a major factor in hot section component degradation. As engine designs continue to push the performance envelope with fewer parts and the market drives manufacturers to increase service life, the need for advanced sealing continues to grow. A review of aero gas turbine engine HPT performance degradation and the mechanisms that promote these losses are discussed. Benefits to the HPT due to improved clearance management are identified. Past and present sealing technologies are presented along with specifications for next generation engine clearance control systems.

Design Considerations towards the Construction of Hybrid Floating Brush Seal (HFBS)

*† ‡ § ¶ §§ Reducing blade tip clearances through active tip clearance control in the high pressure turbine can lead to significant reductions in emissions and specific fuel consumption as well as dramatic improvements in operating efficiency and increased service life. Current engines employ scheduled cooling of the outer case flanges to reduce high pressure turbine tip clearances during cruise conditions. These systems have relatively slow response and do not use clearance measurement, thereby forcing cold build clearances to set the minimum clearances at extreme operating conditions (e.g., takeoff, reburst) and not allowing cruise clearances to be minimized due to the possibility of throttle transients (e.g., step change in altitude). In an effort to improve upon current thermal methods, a first generation mechanically-actuated active clearance control (ACC) system has been designed and fabricated. The system utilizes independent actuators, a segmented shroud structure, and clearance measurement feedback to provide fast and precise active clearance control throughout engine operation. Ambient temperature performance tests of this first generation ACC system assessed individual seal component leakage rates and both static and dynamic overall system leakage rates. The ability of the nine electric stepper motors to control the position of the seal carriers in both open- and closed-loop control modes for single and multiple cycles was investigated. The ability of the system to follow simulated engine clearance transients in closed-loop mode showed the system was able to track clearances to within a tight tolerance (≤ 0.001 in. error).

CONTINUED EVALUATION OF THE HYBRID FLOATING BRUSH SEAL (HFBS)

The hybrid floating brush seal (HFBS) represents an advance in brush seal technology by combining brush seal and film riding face seal technologies to create a hybrid seal that allows both axial and radial excursions of the sealed shaft without damage to seal integrity. At the same time, it eliminates interface surface speeds between the rotor and the brush bristles. This accomplishment is possible because the brush seal, which forms the primary seal, rotates with the shaft, while floating against a hydrodynamic face seal surface, which makes up the secondary seal. The present paper presents continuation work (Int J of Rotating Machinery, 7, 2002) and will concentrate on the methodology of (i) designing and choosing brush characteristics, and (ii) the design of the face seal that allows the floating of the brush plates against it. The brush simplified analytical model predicts the effects of centrifugal force on the bristles and allows implementation of a methodology for choosing and optimizing bristle geometry. The face seal design concentrates on ensuring seal integrity and dynamic stability of the entire assembly.

Qualitative and quantitative nonintrusive study of flow patterns, velocities and pressure effects in banks of cylindrical tubes in a rectangular tunnel

The objective of this presentation is to increase thrust to weight ratio, decrease specific fuel consumption, and to eliminate wear of sealing components.

Turbomachine Interface Sealing

The recent years have seen an ever increasing amount of work in the field of brush seals. Fundamental and prototypal industrial research have attested to the improved fluidic and dynamic performance of such seals when compared to other classes of seals. This paper presents a continuation of the basic research performed by Braun et al. and further explores the nature of the flow and pressure patterns in configurations of dense array of cylinders simulating brush seal behavior. The investigation follows through the method of Full Field Flow Tracking (FFFT). The images supplied by the FFFT system are processed by means of a computer-integrated image quantification method (CIIQ) into quantitative information for flow trajectories and velocities. The tracking method permits identification and tracking of the same particle in a lagrangian frame of reference.