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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Brush seal leakage performance with gaseous working fluids at static and low rotor speed conditions

The leakage performance of a brush seal with gaseous working fluids at static and low rotor speed conditions was studied. The leakage results included for air, helium, and carbon dioxide at several bristle/rotor interferences. Also, the effects of packing a lubricant into the bristles and also of reversing the pressure drop across the seal were studied. Results were compared to that of an annular seal at similar operating conditions. In order to generalize the results, they were correlated using corresponding state theory. The brush seal tested had a bore diameter of 3.792 cm (1.4930 in.), a fence height of 0.0635 cm (0.025 in.), and 1800 bristles/cm circumference (4500 bristles/in. circumference). Various bristle/rotor radial interferences were achieved by using a tapered rotor. The brush seal reduced the leakage in comparison to the annular seal, up to 9.5 times. Reversing the pressure drop across the brush seal produced leakage rates approximately the same as that of the annular seal. Addition of a lubricant reduced the leakage by 2.5 times. The air and carbon dioxide data were successfully correlated using corresponding state theory. However, the helium data followed a different curve than the air and carbon dioxide data.

Carlile, Julie A.↗
NASA NTRS2012

Investigation of Turbulent Tip Leakage Vortex in an Axial Water Jet Pump with Large Eddy Simulation

Detailed steady and unsteady numerical studies were performed to investigate tip clearance flow in an axial water jet pump. The primary objective is to understand physics of unsteady tip clearance flow, unsteady tip leakage vortex, and cavitation inception in an axial water jet pump. Steady pressure field and resulting steady tip leakage vortex from a steady flow analysis do not seem to explain measured cavitation inception correctly. The measured flow field near the tip is unsteady and measured cavitation inception is highly transient. Flow visualization with cavitation bubbles shows that the leakage vortex is oscillating significantly and many intermittent vortex ropes are present between the suction side of the blade and the tip leakage core vortex. Although the flow field is highly transient, the overall flow structure is stable and a characteristic frequency seems to exist. To capture relevant flow physics as much as possible, a Reynolds-averaged Navier-Stokes (RANS) calculation and a Large Eddy Simulation (LES) were applied for the current investigation. The present study reveals that several vortices from the tip leakage vortex system cross the tip gap of the adjacent blade periodically. Sudden changes in local pressure field inside tip gap due to these vortices create vortex ropes. The instantaneous pressure filed inside the tip gap is drastically different from that of the steady flow simulation. Unsteady flow simulation which can calculate unsteady vortex motion is necessary to calculate cavitation inception accurately even at design flow condition in such a water jet pump.

Hah, Chunill↗
NASA NTRS1973

Measurements of the atmospheric neutron leakage rate

The atmospheric neutron leakage rate in the energy range from 0.01 to 10,000,000 eV has been measured as a function of latitude, altitude, and time with a neutron detector on board the Ogo 6 satellite. The latitude dependence of the neutron leakage is in reasonable agreement with that predicted by Lingenfelter (1963) and Light et al. (1973) if the neutron energy spectrum has the shape calculated by Newkirk (1963). The change in the neutron latitude dependence with the cosmic ray modulation agrees with the predictions of Lingenfelter and Light et al. For several solar proton events enhancements were observed in the neutron counting rates at lambda greater than or equal to 70 deg. Such events, however, provide an insignificant injection of protons at E less than or equal to 20 MeV into the radiation belts. An isotropic angular distribution of the neutron leakage in the energy range from 0.1 keV to 10 MeV best fits the observed altitude dependence of the neutron leakage flux.

Lockwood, J. A.↗
NASA NTRS1985

Effects of leakage through clearance seals on the performance of a 10 K Stirling-cycle refrigerator

The use of clearance seals is essential to achieve long life, wear free operation of Stirling cycle cryogenic refrigerators. The effect of leakage through clearance seals on the performance of such a refrigerator operating at temperatures ranging from 20 K down to 10 K was determined. The ability of a Stirling cycle refrigerator to achieve 10 K with clearance seals was successfully demonstrated. It is indicated that the leakage flow undergoes gap regeneration before reaching the cold expansion volume. A simple model of gap regeneration was used to estimate the regeneration loss due to the leakage flow. This regeneration process minimizes the loss in refrigerator performance caused by the clearance seal leakage. It is found that clearance seals remain effective down to a refrigeration temperature of 10 K.

Keung, C. S.↗
NASA NTRS1986

Leakage-current properties of encapsulants

A theoretical modeling of leakage current in ethylene vinyl acetate (EVA) and polyvinyl butyral (PVB) modules is being developed and is described. The modeling effort derives mathematical relationships for the bulk and surface conductivites of EVA and PVB, the surface conductivities of glass and polymeric films, and the EVA and PVB pottants, all as functions of environmental parameters. Results from the modeling indicate that for glass/EVA, the glass surface controls the interfacial conductivity, although EVA bulk conductivity controls total leakage current. For PVB/glass, the interface conductivity controls leakage currents for relative humidity (RH) less than 40 to 50%, but PVB bulk conductivity controls leakage current above 50% RH.

Wen, L. C.↗
NASA NTRS1991

Atmospheric leakage and condensate production in NASA's biomass production chamber. Effect of diurnal temperature cycles

A series of tests were conducted to monitor atmospheric leakage rate and condensate production in NASA's Biomass Production Chamber (BPC). Water was circulated through the 64 plant culture trays inside the chamber during the tests but no plants were present. Environmental conditions were set to a 12-hr photoperiod with either a matching 26 C (light)/20 C (dark) thermoperiod, or a constant 23 C temperature. Leakage, as determined by carbon dioxide decay rates, averaged about 9.8 percent for the 26 C/20 C regime and 7.3 percent for the constant 23 C regime. Increasing the temperature from 20 C to 26 C caused a temporary increase in pressure (up to 0.5 kPa) relative to ambient, while decreasing the temperature caused a temporary decrease in pressure of similar magnitude. Little pressure change was observed during transition between 23 C (light) and 23 C (dark). The lack of large pressure events under isothermal conditions may explain the lower leakage rate observed. When only the plant support inserts were placed in the culture trays, condensate production averaged about 37 liters per day. Placing acrylic germination covers over the tops of culture trays reduced condensate production to about 7 liters per day. During both tests, condensate production from the lower air handling system was 60 to 70 percent greater than from the upper system, suggesting imbalances exist in chilled and hot water flows for the two air handling systems. Results indicate that atmospheric leakage rates are sufficiently low to measure CO2 exchange rates by plants and the accumulation of certain volatile contaminants (e.g., ethylene). Control system changes are recommended in order to balance operational differences (e.g., humidity and temperature) between the two halves of the chamber.

Wheeler, Raymond M.↗
NASA NTRS1935

Effect of Viscosity on Fuel Leakage Between Lapped Plungers and Sleeves and on the Discharge from a Pump-Injection System

Test data and analysis show that the rate of fuel leakage between a lapped plunger and sleeve varies directly with the density of the fuel, the diameter of the plunger, the pressure producing the leakage, and the cube of the mean clearance between the plunger and sleeve. The rate varies inversely as the length of the lapped fit and the viscosity of the fuel. With a mean clearance between the plunger and sleeve of 0.0001 inch the leakage amounts to approximately 0.2 percent of the fuel injected with gasoline and as low as 0.01 percent with diesel fuel oils. With this mean clearance an effective seal is obtained when the length of the lap is three times the diameter of the lap. The deformation of the sleeve and plunger under pressure is sufficient to change the rate of leakage appreciably from that which would be obtained if the clearance was constant under pressure.

Rothrock, A M↗
NASA NTRS1993

Compressibility effects on rotor forces in the leakage path between a shrouded pump impeller and its housing

A modified approach to Childs' previous work on fluid-structure interaction forces in the leakage path between an impeller shroud and its housing is presented in this paper. Three governing equations consisting of continuity, path-momentum, and circumferential-momentum equations were developed to describe the leakage path inside a pump impeller. Radial displacement perturbations were used to solve for radial and circumferential force coefficients. In addition, impeller-discharge pressure disturbances were used to obtain pressure oscillation responses due to precessing impeller pressure wave pattern. Childs' model was modified from an incompressible model to a compressible barotropic-fluid model (the density of the working fluid is a function of the pressure and a constant temperature only). Results obtained from this model yielded interaction forces for radial and circumferential force coefficients. Radial and circumferential forces define reaction forces within the impeller leakage path. An acoustic model for the same leakage path was also developed. The convective, Coriolis, and centrifugal acceleration terms are removed from the compressible model to obtain the acoustics model. A solution due to impeller discharge pressure disturbances model was also developed for the compressible and acoustics models. The results from these modifications are used to determine what effects additional perturbation terms in the compressible model have on the acoustic model. The results show that the additional fluid mechanics terms in the compressible model cause resonances (peaks) in the force coefficient response curves. However, these peaks only occurred at high values of inlet circumferential velocity ratios greater than 0.7. The peak pressure oscillation was shown to occur at the wearing ring seal. Introduction of impeller discharge disturbances with n = 11 diametral nodes showed that maximum peak pressure oscillations occurred at nondimensional precession frequencies of f = 6.4 and f = 7.8 for this particular pump. Bolleter's results suggest that for peak pressure oscillations to occur at the wearing ring seal, the nondimensional excitation frequency should be on the order of f = 2.182 for n = 11. The resonances found in this research do not match the excitation frequencies predicted by Bolleter. At the predicted peak excitation frequencies given by Bolleter, the compressible model shows an attenuation of the pressure oscillations at the seal exit. The compressibility of the fluid does not have a significant influence on the model at low values of nondimensional excitation frequency. At high values of nondimensional frequency, the effects of compressibility become more significant. For the acoustic analysis, the convective, Coriolis, and centrifugal acceleration terms do affect the results to a limited extent for precession excitation and to a large extent for a pressure excitation when the fluid operates at relatively high Mach numbers.

Cao, Nhai The↗
NASA NTRS1999

Analytical Assessment of a Gross Leakage Event Within the International Space Station (ISS) Node 2 Internal Active Thermal Control System (IATCS)

Results of the International Space Station (ISS) Node 2 Internal Active Thermal Control System (IATCS) gross leakage analysis are presented for evaluating total leakage flowrates and volume discharge caused by a gross leakage event (i.e. open boundary condition). A Systems Improved Numerical Differencing Analyzer and Fluid Integrator (SINDA/FLUINT) thermal hydraulic mathematical model (THMM) representing the Node 2 IATCS was developed to simulate system performance under steady-state nominal conditions as well as the transient flow effects resulting from an open line exposed to ambient. The objective of the analysis was to determine the adequacy of the leak detection software in limiting the quantity of fluid lost during a gross leakage event to within an acceptable level.

Holt, James M.↗
NASA NTRS2001

Analytical Assessment of a Gross Leakage Event Within the International Space Station (ISS) Node 2 Internal Active Thermal Control System (IATCS)

Results of the International Space Station (ISS) Node 2 Internal Active Thermal Control System (IATCS) gross leakage analysis are presented for evaluating total leakage flow rates and volume discharge caused by a gross leakage event (i.e. open boundary condition). A Systems Improved Numerical Differencing Analyzer and Fluid Integrator (SINDA85/FLUINT) thermal hydraulic mathematical model (THMM) representing the Node 2 IATCS was developed to simulate system performance under steady-state nominal conditions as well as the transient flow effect resulting from an open line exposed to ambient. The objective of the analysis was to determine the adequacy of the leak detection software in limiting the quantity of fluid lost during a gross leakage event to within an acceptable level.

Holt, James M.↗
NASA NTRS2006

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.

Delgado, Irebert R.↗
NASA NTRS2007

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

Seal leakage decreases with increasing surface speed due to reduced clearances from disk centrifugal growth. Annular and labyrinth seal leakage are 2-3 times greater than brush and finger seal leakage. Seal leakage rates increase with increasing temperature because of seal clearance growth due to different coefficients of thermal expansion between the seal and test disk. Seal power loss is not strongly affected by inlet temperature. Seal power loss increases with increasing surface speed, seal pressure differential, mass flow rate or flow factor, and radial clearance. The brush and finger seals had nearly the same power loss. Annular and labyrinth seal power loss were higher than finger or brush seal power loss. The brush seal power loss was the lowest and 15-30% lower than annular and labyrinth seal power loss.

Delgado, Irebert R.↗
NASA NTRS2011

Trending of Overboard Leakage of ISS Cabin Atmosphere

The International Space Station (ISS) overboard leakage of cabin atmosphere is continually tracked to identify new or aggravated leaks and to provide information for planning of nitrogen supply to the ISS. The overboard leakage is difficult to trend with various atmosphere constituents being added and removed. Changes to nitrogen partial pressure is the nominal means of trending the overboard leakage. This paper summarizes the method of the overboard leakage trending and presents findings from the trending.

Schaezler, Ryan N.↗
NASA NTRS2014

Computational Investigation of Novel Tip Leakage Mitigation Methods for High Pressure Turbine Blades

This paper presents preliminary findings on a possible approach to reducing tip leakage losses. In this paper a computational study was conducted on the Energy Efficient Engine (EEE) High Pressure Turbine (HPT) rotor tip geometry using the commercial numerical solver ANSYS FLUENT. The flow solver was validated against aerodynamic data acquired in the NASA Transonic Turbine Blade Cascade facility. The scope of the ongoing study is to computationally investigate how the tip leakage and overall blade losses are affected by (1) injection from the tip near the pressure side, (2) injection from the tip surface at the camber line, and (3) injection from the tip surface into the tip separation bubble. The objective is to identify the locations on the tip surface at which to place appropriately configured blowing keeping in mind the film cooling application of tip blowing holes. The validation was conducted at Reynolds numbers of 85,000, 343,000, and 685,000 and at engine realistic flow conditions. The coolant injection simulations were conducted at a Reynolds number of 343,000 based on blade chord and inlet velocity and utilized the SST turbulence model in FLUENT. The key parameters examined are the number of jets, jet angle and jet location. A coolant to inlet pressure ratio of 1.0 was studied for angles of +30 deg, -30 deg, and 90 deg to the local free stream on the tip. For the 3 hole configuration, 3 holes spaced 3 hole diameters apart with length to diameter ratio of 1.5 were used. A simulation including 11 holes along the entire mean camber line is also presented (30 deg toward suction side). In addition, the effect of a single hole is also compared to a flat tip with no injection. The results provide insight into tip flow control methods and can be used to guide further investigation into tip flow control. As noted in past research it is concluded that reducing leakage flow is not necessarily synonymous with reducing losses due to leakage.

Ibrahim, Mounir↗
NASA NTRS2014

Computational Investigation of Novel Tip Leakage Mitigation Methods for High Pressure Turbine Blades

This paper presents preliminary findings on a possible approach to reducing tip leakage losses. In this paper a computational study was conducted on the EEE (Energy Efficient Engine) HPT (High Pressure Turbine) rotor tip geometry using the commercial numerical solver ANSYS FLUENT. The flow solver was validated against aerodynamic data acquired in the NASA Transonic Turbine Blade Cascade facility. The scope of the ongoing study is to computationally investigate how the tip leakage and overall blade losses are affected by 1. injection from the tip near the pressure side, 2. injection from the tip surface at the camber line, and 3. injection from the tip surface into the tip separation bubble. The objective is to identify the locations on the tip surface at which to place appropriately configured blowing keeping in mind the film cooling application of tip blowing holes. The validation was conducted at Reynolds numbers of 85,000, 343,000 and 685,000 and at engine realistic flow conditions. The coolant injection simulations were conducted at a Reynolds number of 343,000 based on blade chord and inlet velocity and utilized the SST turbulence model in FLUENT. The key parameters examined are the number of jets, jet angle and jet location. A coolant to inlet pressure ratio of 1.0 was studied for angles of +30 deg., -30 deg. and 90 deg. to the local free stream on the tip. For the 3 hole configuration, 3 holes spaced 3 hole diameters apart with length to diameter ratio of 1.5 were used. A simulation including 11 holes along the entire mean camber line is also presented (30 degrees toward suction side). In addition, the effect of a single hole is also compared to a flat tip with no injection. The results provide insight into tip flow control methods and can be used to guide further investigation into tip flow control. As noted in past research it is concluded that reducing leakage flow is not necessarily synonymous with reducing losses due to leakage.

Ibrahim, Mounir↗
NASA NTRS2015

Leakage Currents and Gas Generation in Advanced Wet Tantalum Capacitors

Currently, military grade, established reliability wet tantalum capacitors are among the most reliable parts used for space applications. This has been achieved over the years by extensive testing and improvements in design and materials. However, a rapid insertion of new types of advanced, high volumetric efficiency capacitors in space systems without proper testing and analysis of degradation mechanisms might increase risks of failures. The specifics of leakage currents in wet electrolytic capacitors is that the conduction process is associated with electrolysis of electrolyte and gas generation resulting in building up of internal gas pressure in the parts. The risk associated with excessive leakage currents and increased pressure is greater for high value advanced wet tantalum capacitors, but it has not been properly evaluated yet. In this work, in Part I, leakages currents in various types of tantalum capacitors have been analyzed in a wide range of voltages, temperatures, and time under bias. Gas generation and the level of internal pressure have been calculated in Part II for different case sizes and different hermeticity leak rates to assess maximal allowable leakage currents. Effects related to electrolyte penetration to the glass seal area have been studied and the possibility of failures analyzed in Part III. Recommendations for screening and qualification to reduce risks of failures have been suggested.

degradation mechanisms↗
NASA NTRS2019

Leakage Correlation

The allowable leakage rate for space hardware is typically specified as scc/sec of helium. It is important to be able to use the measured helium leakage rate to calculate the expected leakage rate of the working fluid. In this U.S. Spacesuit Knowledge Capture seminar, Dr. Eugene Ungar will explore the physical configuration of typical leak paths, discuss the physics of molecular, transition, and continuum flow, and present the accepted method of conservatively calculating the expected leakage rate of the working fluid.

Ungar, Eugene↗
NASA NTRS1969

Leakage measuring method

Technique measures leakages of high pressure test specimens occurring on the input rather than the output side of a test specimen. Technique involves paralleling-off the pressure supply line and duplicating and measuring the leakage flowing into a specimen rather than attempting to measure the leakage flowing out of it.

Clausen, H. J.↗