Margaret P. Proctor

Leakage and Power Loss Test Results for Competing Turbine Engine Seals

ABSTRACT Advanced brush and finger seal technologies offer reduced leakage rates over conventional labyrinth seals used in gas turbine engines. To address engine manufacturers’ concerns about the heat generation and power loss from these contacting seals, brush, finger, and labyrinth seals were tested in the NASA High Speed, High Temperature Turbine Seal Test Rig. Leakage and power loss test results are compared for these competing seals for operating conditions up to 922 K (1200 °F) inlet air temperature, 517 KPa (75 psid) across the seal, and surface velocities up to 366 m/s (1200 ft/s). INTRODUCTION Reducing secondary air leakage within jet engines enables higher engine performance in terms of decreased specific fuel consumption and increased available thrust [1]. These reductions are made possible by the use of current and advanced engine seals, such as labyrinth, brush, or finger seals, which are used to control leakage across a stationary/rotating interface within a jet engine. Studies have shown that small investments in sealing technology have shown a greater increase in engine performance than investments made to improve component technologies such as compressors or turbines [1]. Heat generation and power loss effects through seal use are necessary considerations that can negatively impact engine performance. Changes in engine air temperatures from stage to stage can negatively affect engine efficiencies. For example, heat generation may cause unaccounted rotor or casing growth resulting in increased clearances, higher leakage rates, and reduced engine efficiencies [1]. Moreover, friction generated from contacting seals increases the amount of torque the rotating machinery needs to overcome to produce thrust thereby reducing the efficiency of the engine. Advanced engines operate at very high temperatures; and significant heat generation at the seals could expose downstream components to temperatures that exceed material capabilities. Baseline labyrinth and brush seals were tested in NASA Glenn Research Center’s High-Speed, High-Temperature Turbine Seal Test Rig. Static, performance, and endurance tests were conducted. The results of these baseline tests are compared to each other and to finger seal leakage and power loss performance data obtained in the same test rig. Brush and finger seal wear results are presented along with an assessment of the rotor coating performance.

Pressure Balanced, Low Hysteresis, Finger Seal Test Results

Abstract : The finger seal is a revolutionary new technology in air to air sealing for secondary flow control and gas path sealing in gas turbine engines. Though the seal has been developed for gas turbines, it can be easily used in any machinery where a high pressure air cavity has to be sealed from a low pressure air cavity, for both static and rotating applications. This seal has demonstrated air leakage considerably less than a conventional labyrinth seal and costs considerably less than a brush seal. A low hysteresis finger seal design was successfully developed and tested in a seal rig at NASA Glenn Research Center. A total of thirteen configurations were tested to achieve the low hysteresis design. The best design is a pressure balanced finger seal with higher stiffness fingers. The low hysteresis seal design has undergone extensive rig testing to assess its hysteresis, leakage performance and life capabilities. The hysteresis, performance and endurance test results are presented. Based on this extensive testing, it is determined that the finger seal is ready for testing in an engine.

Continued Investigation of Leakage and Power Loss Test Results for Competing Turbine Engine Seals

Secondary seal leakage in jet engine applications results in power losses to the engine cycle. Likewise, seal power loss in jet engines not only result in efficiency loss but also increase the heat input into the engine resulting in reduced component lives. Experimental work on labyrinth and annular seals was performed at NASA Glenn Research Center to quantify seal leakage and power loss at various temperatures, seal pressure differentials, and surface speeds. Data from annular and labyrinth seals are compared with previous brush and finger seal test results. Data are also compared to literature. Annular and labyrinth seal leakage rates are 2 to 3 times greater than brush and finger seal rates. Seal leakage decreases with increasing speed but increases with increasing test temperature due to thermal expansion mismatch. Also seal power loss increases with surface speed, seal pressure differential, mass flow rate, and radial clearance. Annular and labyrinth seal power losses were higher than those of brush or finger seal data. The brush seal power loss was 15 to 30 percent lower than annular and labyrinth seal power loss.

Preliminary Test Results of a Non-Contacting Finger Seal on a Herringbone-Grooved Rotor

Low leakage, non-contacting finger seals have potential to reduce gas turbine engine specific fuel consumption by 2 to 3 percent and to reduce direct operating costs by increasing the time between engine overhauls. A non-contacting finger seal with concentric lift-pads operating adjacent to a test rotor with herringbone grooves was statically tested at 300, 533, and 700 K inlet air temperatures at pressure differentials up to 576 kPa. Leakage flow factors were approximately 70 percent less than state-of-the-art labyrinth seals. Leakage rates are compared to first order predictions. Initial spin tests at 5000 rpm, 300 K inlet air temperature and pressure differentials to 241 kPa produced no measurable wear.