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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Turbulent atmospheric flow over a backward-facing step

The phenomenon of atmospheric shear layer separation over a man-made structure such as a building (modeled as a backward-facing step) has been analyzed theoretically by (1) solving the two-dimensional equations of motion in the two variables, stream function and vorticity, and by (2) employing an approximate integral technique. Boundary conditions for the undisturbed flow are that of the turbulent atmospheric shear flow over a rough terrain. In the first approach a two-equation model of turbulence was used. In the second approach an approximate technique was utilized in an attempt to describe the details of the flow in the recirculation zone behind the step. The results predict velocity profiles in sufficient detail that the presence of the corner eddy in the region of negative surface pressure gradient is evident. The magnitude of the reversed flow velocity in the recirculation eddy has been found to agree with that found from experiments. Also, a surface eddy viscosity distribution has been an outgrowth of the method which realistically follows the magnitude of the surface pressure gradient distribution as found experimentally.

Kaul, U. K.↗
NASA NTRS1977

Simplified computer program for the analysis of phase change in liquid face seals

A simplified computer program is presented which allows for the prediction of boiling (phase change) in liquid face seals. The program determines if and when boiling occurs and then calculates the location of the boiling interface, pressure and temperature profiles, and load. The main assumption which allows for a simplified analysis is the assumption of an isothermal gas phase.

Birchak, M.↗
NASA NTRS1977

Design considerations in mechanical face seals for improved performance. 2: Lubrication

The importance of sealing technology in our industrial, chemical-oriented society in regard to maintenance and environmental contamination is pointed out. It is stated that seal performance (leakage, life) is directly related to seal lubrication. Current thinking in regard to seal lubrication is reviewed; the effect of energy dissipation in the thin lubricating film separating the sealing faces is pointed out, and the results of vaporization due to heating are illustrated. Also, hydrodynamic lubrication is reviewed, and an inherent tendency for the seal to operate with angular misalignment is shown. Recent work on hydrostatic effects is summarized and the conditions for seal instability are discussed. Four different modes of seal lubrication are postulated with the mode type being a strong function of speed and pressure.

Ludwig, L. P.↗
NASA NTRS1977

Effects of grazing flow on the steady-state flow resistance and acoustic impedance of thin porous-faced liners

The results of an investigation of the effects of grazing flow on the steady-state flow resistance and acoustic impedance of seven Feltmetal and three Rigimesh thin porous-faced liners are presented. The acoustic impedance was measured using the two-microphone method. The principal findings of the study are (1) the effects of grazing flow were measured and found to be negligible, (2) negligible differences were measured between steady-state and acoustic resistance, (3) a semi-empirical model was derived that correlated both the steady-state resistance data and the acoustic impedance data of the seven Feltmetal liners. These findings suggest that nongrazing flow steady-state flow resistance tests could provide considerable insight into the acoustic behavior of porous liners in a grazing flow environment.

Hersh, A. D.↗
NASA NTRS1977

Design considerations in mechanical face seals for improved performance. 1: Basic configurations

Basic assembly configurations of the mechanical face seal are described and some advantages associated with each are listed. The various forms of seal components are illustrated, and functions pointed out. The technique of seal pressure balancing and its application are described; and the concept of the PV factor, its different forms and limitations are discussed. Brief attention is given to seal lubrication since it is covered in detail in a companion paper. Finally, the operating conditions for various applications of low pressure seals (aircraft transmissions) are listed, and the seal failure mode of a particular application is discussed.

Ludwig, L. P.↗
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

Flight-measured pressure characteristics of aft-facing steps in high Reynolds number flow at Mach numbers of 2.20, 2.50, and 2.80 and comparison with other data

The YF-12 airplane was studied to determine the pressure characteristics associated with an aft-facing step in high Reynolds number flow for nominal Mach numbers of 2.20, 2.50, and 2.80. Base pressure coefficients were obtained for three step heights. The surface static pressures ahead of and behind the step were measured for the no-step condition and for each of the step heights. A boundary layer rake was used to determine the local boundary layer conditions. The Reynolds number based on the length of flow ahead of the step was approximately 10 to the 8th power and the ratios of momentum thickness to step height ranged from 0.2 to 1.0. Base pressure coefficients were compared with other available data at similar Mach numbers and at ratios of momentum thickness to step height near 1.0. In addition, the data were compared with base pressure coefficients calculated by a semiempirical prediction method. The base pressure ratios are shown to be a function of Reynolds number based on momentum thickness. Profiles of the surface pressures ahead of and behind the step and the local boundary layer conditions are also presented.

Powers, S. G.↗
NASA NTRS1977

Radial forces in a misaligned radial face seal

Radial forces on the primary seal ring of a flat misaligned seal are analyzed, taking into account the radial variation in seal clearance. An analytical solution for both hydrostatic and hydrodynamic effects is presented that covers the whole range from zero to full angular misalignment. The net radial force on the primary seal ring is always directed so as to produce a radial eccentricity which generates inward pumping. Although the radial force is usually very small, in some cases it may be one of the reasons for excessive leakage through both the primary and secondary seals of a radial face seal.

Etsion, I.↗
NASA NTRS1977

Design considerations in mechanical face seals for improved performance. I - Basic configurations

Basic assembly configurations of the mechanical face seal are described and some advantages associated with each are listed. The various forms of seal components (the primary seal, secondary seal, etc.) are illustrated, and functions pointed out. The technique of seal pressure balancing and its application is described; and the concept of the PV factor, its different forms and limitations are discussed. Brief attention is given to seal lubrication since it is covered in detail in a companion paper. Finally, the operating conditions for various applications of low pressure seals (aircraft transmissions) are listed, and the seal failure mode of a particular application is discussed.

Ludwig, L. P.↗
NASA NTRS1977

Design considerations in mechanical face seals for improved performance. II - Lubrication

The importance of sealing technology in the U.S. industrial chemical-orientated society in regard to maintenance and environmental contamination is pointed out. It is stated that seal performance (leakage, life) is directly related to seal lubrication, which is a mechanism not well understood. Current thinking in regard to seal lubrication is reviewed, the effect of energy dissipation in the thin lubricating film separating the sealing faces is pointed out, and the results of vaporization due to heating are illustrated. Also, hydrodynamic lubrication is reviewed, and an inherent tendency for the seal to operate with angular misalignment is pointed out. Recent work on hydrostatic effects is summarized and the conditions for seal instability are discussed. Four different modes of seal lubrication are postulated with the mode type being a strong function of speed and pressure.

Ludwig, L. P.↗
NASA NTRS1980

Phase changes in liquid face seals

Computer program predicts boiling (phase change) in liquid face seals. Program determines if and when boiling occurs, and calculates location of boiling interface, pressure and temperature profiles, and load.

Hughes, W. F.↗
NASA NTRS1978

Compressible flow across narrow passages: Comparison of theory and experiment for face seals

Computer calculation for determining compressible flow across radial face seals were compared with measured results obtained in a seal simulator rig at pressure ratios to 0.9 (ambient pressure/sealed pressure). In general, the measured and calculated leakages across the seal dam agreed within 3 percent. The resultant loss coefficient, dependent upon the pressure ratio, ranged from 0.47 to 0.68. The calculated pressures were within 2.5 N/cu um of the measured values.

Allen, G. P.↗
NASA NTRS1979

Effect of number of probes and their orientation on the calculation of several compressor face distortion descriptors

A study was performed to determine the effects of the number and position of total pressure probes on the calculation of five compressor face distortion descriptors. This study used three sets of 320 steady state total pressure measurements that were obtained with a special rotating rake apparatus in wind tunnel tests of a mixed-compression inlet. The inlet was a one third scale model of the inlet on a YF-12 airplane, and it was tested in the wind tunnel at representative flight conditions at Mach numbers above 2.0. The study shows that large errors resulted in the calculation of the distortion descriptors even with a number of probes that were considered adequate in the past. There were errors as large as 30 and -50 percent in several distortion descriptors for a configuration consisting of eight rakes with five equal-area-weighted probes on each rake.

Stoll, F.↗
NASA NTRS1978

Radial forces in a misaligned radial face seal

Radial forces on the primary seal ring of a flat misaligned seal are analyzed, taking into account the radial variation in seal clearance. An analytical solution for both hydrostatic and hydrodynamic effects is presented that covers the whole range from zero to full angular misalignment. The net radial force on the primary seal ring is always directed so as to produce a radial eccentricity which generates inward pumping. Although the radial force is usually very small, in some cases it may be one of the reasons for excessive leakage through both the primary and secondary seals of a radial face seal.

Etsion, I.↗
NASA NTRS1978

The accuracy of the narrow seal approximation in analyzing radial face seals

The accuracy of the narrow seal approximation which enables closed form analytical solutions for radial face seals is examined in this paper. Both hydrostatic and hydrodynamic effects in a flat, misaligned seal are considered. Analytical results obtained from a simplified Reynolds equation, based on the neglect of circumferential pressure gradient and seal curvature, are compared with accurate results from numerical solution of the complete Reynolds equation. The agreement between the approximate and accurate solutions is quite reasonable over a wide range of a seal's inner-to-outer radius ratio. For radius ratios greater than 0.8, the accuracy of the narrow seal approximation is better than 1 percent over most of the range of angular misalignment.

Etsion, I.↗
NASA NTRS1980

Design considerations for mechanical face seals

Two companion reports deal with design considerations for improving performance of mechanical face seals, one of family of devices used in general area of fluid sealing of rotating shafts. One report deals with basic seal configuration and other with lubrication of seal.

Ludwig, L. P.↗
NASA NTRS1980

Dynamic response to rotating-seat runout in non-contacting face seals

The dynamic response of a flexibly mounted ring to runout of the rotating seat in mechanical face seals is analyzed assuming small perturbations. It is found that tracking ability of the stator depends only on its dynamic characteristics and operating conditions and is not affected by the amount of runout. Three different modes of dynamic response are shown and the condition for parallel tracking is presented.

Etsion, I.↗
NASA NTRS1979

The structural behavior of a graphite-polymide honeycomb sandwich panel with quasi-isotropic face sheets and an orthotropic core

The results of a series of tests of graphite-polyimide honeycomb sandwich panels are presented. The panels were 1.22 m long, 0.508 m wide, and approximately 13.3 m thick. The face sheets were a T-300/PMR-15 fabric in a quasi-isotropic layup and were 0.279 mm thick. The core was Hexcel HRH 327-3/16 - 4.0 glass reinforced polyimide honeycomb, 12.7 mm thick. Three panels were used in the test: one was cut into smaller pieces for testing as beam, compression, and shear specimens; a second panel was used for plate bending tests; the third panel was used for in-plane stability tests. Presented are the experimental results of four point bending tests, short block compression tests, core transverse shear modulus, three point bending tests, vibration tests, plate bending tests, and panel stability tests. The results of the first three tests are used to predict the results of some of the other tests. The predictions and experimental results are compared, and the agreement is quite good.

Hyer, M. W.↗