Irebert R. Delgado

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.

Baseline Experimental Results on the Effect of Oil Temperature on Shrouded Meshed Spur Gear Windage Power Loss

Rotorcraft gearbox efficiencies are reduced at increased surface speeds due to viscous and impingement drag on the gear teeth. This windage power loss can affect overall mission range, payload, and frequency of transmission maintenance. Experimental and analytical studies on shrouding for single gears have shown it to be potentially effective in mitigating windage power loss. Efficiency studies on unshrouded meshed gears have shown the effect of speed, oil viscosity, temperature, load, lubrication scheme, etc. on gear windage power loss. The open literature does not contain experimental test data on shrouded meshed spur gears. Gear windage power loss test results are presented on shrouded meshed spur gears at elevated oil inlet temperatures and constant oil pressure both with and without shrouding. Shroud effectiveness is compared at four oil inlet temperatures. The results are compared to the available literature and follow-up work is outlined. INTRODUCTION Rotorcraft gearboxes are critical in efficiently transferring power from the turboshaft jet engine to the main and tail rotors for a conventional helicopter. Efficiencies of 95 to 97 percent are common [1] as they are used in fixed wing aircraft such as geared turbofans and the VTOL (Vertical Take-Off and Landing) V-22 Osprey. With ever increasing fuel costs for air transportation, research is focused on demonstrating and maturing alternative and more efficient means of propulsion while minimizing aircraft weight [2]. This includes gearbox materials that improve overall life, alternative power transmission concepts that increase power density, reductions in gearbox form factor, as well as innovative lubrication methods that reduce the amount of required lubricant or means of cooling. One area of active research is in minimizing gearbox windage for rotorcraft transmissions. Gear windage power loss reduces the efficiency of the transmission due to drag on the gear teeth at high surface speeds. Not only is windage drag detrimental to gearbox efficiency, but the increased friction generates additional heating in the gearbox thereby placing more demand on cooling requirements. CFD analyses by Hill and others [3] show that this phenomenon is due to the air/oil environment impinging on the gear tooth face as well as on the sides of the gear. The resulting reduced transmission efficiency, negatively impacts rotorcraft performance [4]. Research has shown the potential for shrouding to reduce windage power loss for gears at high surface speeds. Dawson [5] studied the effect of clearance and percent shroud enclosure on a single spur gear in air and noted significant reductions in windage power loss using smooth circumferential shrouds with side plates at close clearances. Lord [6] also showed reductions in windage power loss for a shrouded single spur gear in air compared to the unshrouded case. In an air and oil environment for a single enclosed spur gear at 1 mm axial and radial clearance, he observed that power loss was higher than in an air only environment at the same clearance. By increasing the peripheral shrouding clearance, he observed a reduction in windage power loss but not to the levels shown for the same test in air only. The CFD analyses of Hill and others [3] compared well with experimental data taken from the NASA Glenn windage rig for a single shrouded spur gear. In contrast to Lord’s [6] results, the smallest axial and radial shroud clearances minimized windage power loss. A number of studies exist in the literature on unshrouded meshed spur gear windage power loss. Lord [6] provides power loss data on unshrouded meshed spur gears but not in the shrouded configuration. Ariura [7] presents torque loss data on unshrouded meshed spur gears with jet lubrication at various fluid viscosities. Experimental power loss data by Mizutani [8] for unshrouded meshed spur gears shows increasing values with increased loads and oil pressures. Petry-Johnson [9] shows the effect of oil viscosity of unshrouded meshed spur gears on spin https://ntrs.nasa.gov/search.jsp?R=20170006031 2019-12-02T04:00:11+00:00Z

Fatigue Crack Growth Behavior Evaluation of Grainex Mar-M 247 for NASA's High Temperature High Speed Turbine Seal Test Rig

The fatigue crack growth behavior of Grainex Mar-M 247 is evaluated for NASA s Turbine Seal Test Facility. The facility is used to test air-to-air seals primarily for use in advanced jet engine applications. Because of extreme seal test conditions of temperature, pressure, and surface speeds, surface cracks may develop over time in the disk bolt holes. An inspection interval is developed to preclude catastrophic disk failure by using experimental fatigue crack growth data. By combining current fatigue crack growth results with previous fatigue strain-life experimental work, an inspection interval is determined for the test disk. The fatigue crack growth life of the NASA disk bolt holes is found to be 367 cycles at a crack depth of 0.501 mm using a factor of 2 on life at maximum operating conditions. Combining this result with previous fatigue strain-life experimental work gives a total fatigue life of 1032 cycles at a crack depth of 0.501 mm. Eddy-current inspections are suggested starting at 665 cycles since eddy current detection thresholds are currently at 0.381 mm. Inspection intervals are recommended every 50 cycles when operated at maximum operating conditions.

Strain-Life Assessment of Grainex Mar-M 247 for NASA's Turbine Seal Test Facility

Abstract : NASAs Turbine Seal Test Facility is used to test air-to-air seals for use primarily in advanced jet engine applications. Combinations of high temperature, high speed, and high pressure limit the disk life, due to the concern of crack initiation in the bolt holes of the Grainex Mar-M 247 disk. The primary purpose of this current work is to determine an inspection interval to ensure safe operation. The current work presents high temperature fatigue strain-life data for test specimens cut from an actual Grainex Mar-M 247 disk. Several different strain-life models were compared to the experimental data including the Manson-Hirschberg Method of Universal Slopes, the Halford-Nachtigall Mean Stress Method, and the Modified Morrow Method. The Halford-Nachtigall Method resulted in only an 18 percent difference between predicted and experimental results. Using the experimental data at a -99.95 percent prediction level and the presence of 6 bolt holes it was found that the disk should be inspected after 665 cycles based on a total strain of 0.5 percent at 649 degrees C.

Fatigue Crack Growth Behavior Evaluation of Grainex Mar-M 247 for NASA’s High Temperature, High Speed Turbine Seal Test Rig

The fatigue crack growth behavior of Grainex Mar-M 247 is evaluated for NASA’s Turbine Seal Test Facility. The facility is used to test air-to-air seals for use primarily in advanced jet engine applications. Because of extreme seal test conditions of temperature, pressure, and surface speeds, surface cracks may develop over time in the disk bolt holes. An inspection interval is developed to preclude catastrophic disk failure by using experimental fatigue crack growth data. By combining current fatigue crack growth results with previous fatigue strain-life experimental work an inspection interval is determined for the test disk. The fatigue crack growth life of the NASA disk bolt holes is found to be 367 cycles at a crack depth of 0.501 mm using a factor of 2 on life at maximum operating conditions. Combining this result with previous fatigue strain-life experimental work gives a total fatigue life of 1032 cycles at a crack depth of 0.501 mm. Eddy-current inspections are suggested starting at 665 cycles since eddy current thresholds are currently at 0.381 mm. Inspection intervals are recommended every 50 cycles at maximum operating conditions.

Strain-Life Assessment of Grainex Mar-M 247 for NASA’s Turbine Seal Test Facility

NASA’s Turbine Seal Test Facility is used to test air-to-air seals for use primarily in advanced jet engine applications. Combinations of high temperature, high speed, and high pressure limit the disk life, due to the concern of crack initiation in the bolt holes of the Grainex Mar-M 247 disk. The primary purpose of this current work is to determine an inspection interval to ensure safe operation. The current work presents high temperature fatigue strain-life data for test specimens cut from an actual Grainex Mar-M 247 disk. Several different strain-life models were compared to the experimental data including the Manson-Hirschberg Method of Universal Slopes, the Halford-Nachtigall Mean Stress Method, and the Modified Morrow Method. The Halford-Nachtigall Method resulted in only an 18% difference between predicted and experimental results. Using the experimental data at a −99.95% prediction level and the presence of 6 bolt holes it was found that the disk should be inspected after 665 cycles based on a total strain of 0.5% at 649°C.Copyright