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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16

All sources NASA NTRS DOE OSTI

NASA NTRS1973

Development of mainshaft seals for advanced air breathing propulsion systems

A gas-film face seal design incorporating shrouded Rayleigh step lift pads at the primary sealing face was analyzed for performance over a wide range of gas turbine engine conditions. Acceptable leakage rates and operation without rubbing contact was predicted for engine conditions that included sealed pressures to 500 psi, sliding speeds to 600 ft/sec, and sealed gas temperatures to 1200 F. In the experimental evaluation, measured gas leakage rates were, in general, close to that predicted and sometimes lower. Satisfactory performance of the gas-film seal was demonstrated at the maximum seal seat axial runout expected in present positive contact face seal applications. Stable operation was shown when testing was performed with air-entrained dirt.

Dobek, L. J.↗

NASA NTRS1973

Space shuttle seal material and design development for earth storable propellant systems

The results of a program to investigate and characterize seal materials suitable for space shuttle storable propellant systems are given. Two new elastomeric materials were identified as being potentially superior to existing state-of-the art materials for specific sealing applications. These materials were AF-E-124D and AF-E-411. AF-E-124D is a cured perfluorinated polymer suitable for use with dinitrogen tetroxide oxidizer, and hydrazine base fuels. AF-E-411 is an ethylene propylene terpolymer material for hydrazine base fuel service. Data are presented relative to low and high temperature characteristics as well as propellant exposure effects. Types of data included are: mechanical properties, stress strain curves, friction and wear characteristics, compression set and permeability. Sealing tests with a flat poppet-seal valve were conducted for verification of sealing capability. A bibliography includes over 200 references relating to seal design or materials and presents a concise tabulation of the more useful seal design data sources.

Source record↗

NASA NTRS1972

Steady-state and dynamic performance of a gas-lubricated seal

Steady-state and dynamic performance of a gas-lubricated, self-acting face seal was determined using numerical methods based on a variable grid, finite-difference, time-transient procedure. Results were obtained for a gas turbine main shaft seal operating at 206.9 newton per square centimeter (300 psi) sealed air pressure and 152.4 meters per second (500 ft/sec) sliding velocity. Analysis of the seal dynamics revealed that the response of the seal nosepiece to runout of the seat face is markedly affected by secondary seal friction and by nosepiece inertia. The nosepiece response was determined for various levels of secondary seal friction and seat face runout magnitudes.

Colsher, R.↗

NASA NTRS1976

Hydrostatic lift-off seal

Interpropellant turbopump oxidizer seal consists of smooth flat surface on back of second-stage oxidizer impeller, floating seal ring, semistatic piston ring secondary seal, and low pressure flexible-bellows static secondary seal. Seal performs static sealing at rest and controlled leakage sealing in operation.

Buckmann, P. S.↗

NASA NTRS1976

Face-seal lubrication: 1: Proposed and published models

The numerous published theories on the mechanism of hydrodynamic lubrication of face seals were reviewed. These theories employ either an inclined-slider-bearing macrogeometry or an inclined-slider-bearing microgeometry to produce hydrodynamic pressure that separates the surfaces of the primary seal. Secondary seal friction and primary ring inertia effects are not considered. Hypothetical seal operating models were devised to include secondary seal friction and primary ring inertia effects. It was hypothesized that these effects induce relative angular misalinement of the primary seal faces and that this misalinement is, in effect, an inclined slider macrogeometry. Stable running was postulated for some of these hypothetical operating models. In others, periodic loss of hydrodynamic lubrication was postulated to be possible with certain combinations of waviness and angular misalinement. Application of restrictions that apply to seal operation led to a hydrodynamic governing equation for the new model that is a two-dimensional, time-dependent Reynolds equation with the short-bearing approximation.

Ludwig, L. P.↗

NASA NTRS1977

Testing of polyimide second-stage rod seals for single-state applications in advanced aircraft hydraulic systems

Machined polyimide second-stage rod seals were evaluated to determine their suitability for single-stage applications where full system pressure acts on the upstream side of the seal. The 6.35-cm (2.5-in.) K-section seal was tested in impulse screening tests where peak pressure was increased in 3.448-MPa (500-psi) increments each 20,000 cycles. Seal failure occurred at 37.92 MPa (5,500 psi), indicating a potential for acceptability in a 27.58-MPa (4,000-psi) system. Static pressurization for 600 sec at pressures in excess of 10.34 MPa (1,500 psi) revealed structural inadequacy of the seal cross section to resist fracture and extrusion. Endurance testing showed the seals capable of at least 65,000 1.27-cm (0.5-in.) cycles at 450 K (350 F) without leakage. It was concluded that the second-stage seals were proven to be exceptional in the 1.379-MPa (200-psi) applications for which they were designed, but polyimide material properties are not adequate for use in this design at pressure loading equivalent to that present in single-stage applications.

Waterman, A. W.↗

NASA NTRS1977

Development of a plasma sprayed ceramic gas path seal for high pressure turbine applications

The plasma sprayed graded layered yittria stabilized zirconia (ZrO2)/metal(CoCrAlY) seal system for gas turbine blade tip applications up to 1589 K (2400 F) seal temperatures was studied. Abradability, erosion, and thermal fatigue characteristics of the graded layered system were evaluated by rig tests. Satisfactory abradability and erosion resistance was demonstrated. Encouraging thermal fatigue tolerance was shown. Initial properties for the plasma sprayed materials in the graded, layered seal system was obtained, and thermal stress analyses were performed. Sprayed residual stresses were determined. Thermal stability of the sprayed layer materials was evaluated at estimated maximum operating temperatures in each layer. Anisotropic behavior in the layer thickness direction was demonstrated by all layers. Residual stresses and thermal stability effects were not included in the analyses. Analytical results correlated reasonably well with results of the thermal fatigue tests. Analytical application of the seal system to a typical gas turbine engine application predicted performance similar to rig specimen thermal fatigue performance. A model for predicting crack propagation in the sprayed ZrO2/CoCrAlY seal system was proposed, and recommendations for improving thermal fatigue resistance were made. Seal system layer thicknesses were analytically optimized to minimize thermal stresses in the abradability specimen during thermal fatigue testing. Rig tests on the optimized seal configuration demonstrated some improvement in thermal fatigue characteristics.

Shiembob, L. T.↗

NASA NTRS1977

High-pressure cryogenic seals for pressure vessels

This investigation of the problems associated with reliably containing gaseous helium pressurized to 1530 bars (22 500 psi) between 4.2 K and 150 K led to the following conclusions: (1) common seal designs used in existing elevated-temperature pressure vessels are unsuitable for high-pressure cryogenic operation, (2) extrusion seal-ring materials such as Teflon, tin, and lead are not good seal materials for cryogenic high-pressure operation; and (3) several high-pressure cryogenic seal systems suitable for large-pressure vessel applications were developed; two seals required prepressurization, and one seal functioned repeatedly without any prepressurization. These designs used indium seal rings, brass or 304 stainless-steel anvil rings, and two O-rings of silicone rubber or Kel-F.

Buggele, A. E.↗

NASA NTRS1977

Small High-Speed Self-Acting Shaft Seals for Liquid Rocket Engines

Design analysis, fabrication, and experimental evaluation were performed on three self-acting facetype LOX seal designs and one circumferential-type helium deal design. The LOX seals featured Rayleigh step lift pad and spiral groove geometry for lift augmentation. Machined metal bellows and piston ring secondary seal designs were tested. The helium purge seal featured floating rings with Rayleigh step lift pads. The Rayleigh step pad piston ring and the spiral groove LOX seals were successfully tested for approximately 10 hours in liquid oxygen. The helium seal was successfully tested for 24 hours. The shrouded Rayleigh step hydrodynamic lift pad LOX seal is feasible for advanced, small, high-speed oxygen turbopumps.

Burcham, R. E.↗

NASA NTRS1977

High-pressure cryogenic seals for pressure vessels

Problems associated with maintaining high pressures at cryogenic temperatures in pressure vessels are investigated. The goals were to identify the appropriate materials and design for a seal intended for cryogenic applications at pressures up to 4,080 bars (60,000 psi), and to examine the factors affecting the seal performance. The method employed and the apparatus used in a series of experimental seal system tests, and the test results are described in detail. It is concluded that the common seal designs and extrusion seal-ring materials such as Teflon, tin, and lead are not suitable. However, new seal systems developed using indium seal rings, brass or 304 stainless steel anvil rings, and two 0-rings of silicone rubber or Kel-F did prove suitable.

Buggle, A. E.↗

NASA NTRS1977

Development of spiral-groove self-acting face seals

An experimental evaluation and a 100-hour endurance test were performed on a spiral groove geometry, self-acting face seal. The seal was tested and operated successfully at maximum conditions of 243.8 m/s surface speed, 199.9 N/sq cm air pressure, and 645.4K (702 F) air temperature. The maximum speed condition of 243.8 m/s was obtained at a shaft speed of 72,500 rpm. Seal wear, gas leakage, and sealing element temperature were monitored during the test. Condition of the seal at the completion of the test was documented and found acceptable for further use. The spiral groove wear rate measured during the endurance test indicates a minimum potential seal life of over 2700 hours. Seal air leakage measured during the test program is within the range considered acceptable for consideration for use in a small gas turbine engine.

Obrien, M.↗

NASA NTRS1978

Self-acting shaft seals

Self-acting seals are described in detail. The mathematical models for obtaining a seal force balance and the equilibrium operating film thickness are outlined. Particular attention is given to primary ring response (seal vibration) to rotating seat face runout. This response analysis reveals three different vibration models with secondary seal friction being an important parameter. Leakage flow inlet pressure drop and affects of axisymmetric sealing face deformations are discussed. Experimental data on self-acting face seals operating under simulated gas turbine conditions are given. Also a spiral groove seal design operated to 244 m/sec (800 ft/sec) is described.

Ludwig, L. P.↗

NASA NTRS1978

Wear of seal materials used in aircraft propulsion systems

The various types of seal locations in a gas turbine engine are described, and the significance of wear to each type is reviewed. Starting with positive contact shaft seals, existing material selection guidelines are reviewed, and the existing PV (contact pressure X sliding velocity) criteria for selecting seal materials are discussed, along with the theoretical background for these criteria. Examples of wear mechanisms observed to operate in positive contact seals are shown. Design features that can extend the operating capabilities of positive contact seals, including pressure balancing and incorporation of hydrodynamic lift are briefly discussed. It is concluded that, despite the benefits arising from these design features, improved positive contact seal materials from the standpoint of wear, erosion and oxidation resistance will be necessary for further improvements in seal performance and durability, and to meet stringent future challenges.

Bill, R. C.↗

NASA NTRS1966

Fluid pressure balanced seal

A seal which increases in effectiveness with increasing pressure is presented. The seal's functional capability throughout both static and dynamic operation makes it particularly useful for sealing ball valve ports. Other features of the seal include the ability to seal two opposed surfaces simultaneously, tolerance of small misalignments, tolerance of wide temperature ranges, ability to maintain positive sealing contact under conditions of internal or external pressurization, and ability to conform to slight irregularities in seal or surface contours.

Marsh, H. W.↗

NASA NTRS1981

Measurement of oil film thickness for application to elastomeric Stirling engine rod seals

The rod seal in the Stirling engine has the function of separating high pressure gas from low or ambient pressure oil. An experimental apparatus was designed to measure the oil film thickness distribution for an elastomeric seal in a reciprocating application. Tests were conducted on commercial elastomeric seals having a 76 mm rod and a 3.8 mm axial width. Test conditions included 70 and 90 seal durometers, a sliding velocity of 0.8 m/sec, and a zero pressure gradient across the seal. An acrylic cylinder and a typical synthetic base automotive lubricant were used. The experimental results showed that the effect of seal hardness on the oil film thickness is considerable. A comparison between analytical and experimental oil film profiles for an elastomeric seal during relatively high speed reciprocating motion showed an overall qualitative agreement.

Krauter, A. I.↗

NASA NTRS1982

Flow induced force of labyrinth seal

Flow induced instability force due to a labyrinth seal is analyzed. An approximate solution is given for the partial differential equation representing the flow in labyrinth seal and it is compared with the finite difference method in order to verify the accuracy of both methods. The effects of difference of inlet and outlet pressures of the seal, deflection of pressure and mass flow from the steady state, rotor diameter, seal clearance, seal interval and seal number on the flow induced force of the seal are investigated and it is known that some of these factors are very influential on the flow induced force.

Iwatsubo, T.↗

NASA NTRS1983

Labyrinth seal forces on a whirling rotor

An experimental investigation of air labyrinth seal forces on a subsynchronously whirling model rotor is described and test results are given for diverging, converging, and straight two-strip seals. The effects of pressure drop, provide basic experimental data needed in the development of design methods for predicting and preventing self-excited whirl of turbine rotors and other machines having labyrinth seals. The total dynamic seal forces on the whirling model rotor are measured accurately by means of an active damping and stiffness system that is adjusted to obtain neutral whirl stability of the model rotor system. In addition, the whirling pressure pattern in the seal annulus is measured for a few test conditions and the corresponding pressure forces on the rotor are compared with the total measured forces. This comparison shows that either radial and axial pressure gradients in the seal annulus or drag forces on the rotor are significant. Comparisons made between the measured seal forces and theoretical results show that present theory is inadequate.

Wright, D. V.↗

NASA NTRS1983

Design analysis of a self-acting spiral-groove ring seal for counter-rotating shafts

A self-acting spiral groove inter-shaft ring seal of nominal 16.33 cm (6.43 in.) diameter for sealing fan bleed air between counter rotating shafts in advanced turbofan engines was analyzed. The analysis focused on the lift force characteristics of the spiral grooves. A NASA Lewis developed computer program for predicting the performance of gas lubricated face seals was used to optimize the spiral groove geometry to produce maximum lift force. Load capacity curves (lift force as function of film thickness) were generated for four advanced turbofan engine operating conditions at relative seal speeds ranging from 17,850 to 29,800 rpm, sealed air pressures from 6 to 42 N/sq cm (9 to 60 psi) absolute and temperatures from 95 to 327 C (203 to 620 F). The relative seal sliding speed range was 152 to 255 m/sec (500 to 836 ft/sec). The analysis showed that the spiral grooves are capable of producing sufficient lift force such that the ring seal will operate in a noncontacting mode over the operating range of typical advanced turbofan engines.

Dirusso, E.↗