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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Eccentricity effects on leakage of a brush seal at low speeds

The effects of eccentricity on brush seal leakage at low rotational speeds were investigated. Included are the leakage results for ambient temperature air and nearly saturated streams at three different rotor eccentricities at both 0 and 400 rpm. A brush seal with a nominal bore diameter of 13.647 cm. (5.3730 in.) was used. It had a radial concentric interference of 0.071 cm (0.0028 in.) and a fence height of 0.0927 cm (0.0365 in.). There were 1060 bristles per centimeter of circumference (2690 bristles per inch of circumference). Rotor eccentricities of 0.003, 0.010, 0.038, and 0.043 cm (0.001, 0.004, 0.015, and 0.017 in.) were achieved by using bushings with different offsets. The results were compared with an annular seal model (FLOWCAL) for air and to a standard labyrinth seal model for steam. The annular seal model was also compared with a bulk flow model of a concentric brush seal in air. Large eccentricities did not damage the brush seals or their Haynes 25 bristles. However, the 304 stainless steel rotor did not show wear, indicating a harder surface is needed. Only the stream data showed hysteresis and were affected by shaft rotation. The brush seal had lower leakage rates than those predicted for comparable annular and labyrinth seals (conventional) because of the large clearances those seals require to accommodate large shaft excursions.

Schlumberger, Julie A.↗
NASA NTRS1991

Flow visualization and quantitative velocity and pressure measurements in simulated single and double brush seals

A method to visualize and characterize the complex flow fields in simulated single and double brush seals is presented. The brush seal configuration was tested in a gravity fed water tunnel and a pump driven pressurized oil tunnel. Visualization of the flow field revealed regions that are characteristically river jetting, vortical, crossflow and exist upstream, downstream or within the seal. Such flows are especially engendered by variations in fiber void that are spatial and temporal and affect changes in seal leakage and stability. While the effects of interface motion and cylindrical configuration have not been considered herein, it is believed that the observed flow fields and pressure drop patterns characterize flow phenomenology in brush seals. The axial pressure profiles upstream, across and downstream of the brush have been measured under a variety of inlet pressure conditions and the ensuing pressure maps are presented and discussed. Through the application of the Full Flow Field Tracking method developed by the authors, the flow patterns and the accompanying fluid velocities inside the brush were non-intrusively determined and graphically reconstructed.

Braun, M. J.↗
NASA NTRS1994

Turbine-Driven Pipe-Cleaning Brush

Simple pipe-cleaning device includes small turbine wheel axially connected, by standoff, to circular brush. Turbine wheel turns on hub bearing attached to end of upstream cable. Turbine-and-brush assembly inserted in pipe with cable trailing upstream and brush facing downstream. Water or cleaning solution pumped through pipe. Cable held at upstream end, so it holds turbine and brush in pipe at location to be cleaned. Flow in pipe turns turbine, which turns wheel, producing desired cleaning action. In addition to brushing action, device provides even mixing of cleaning solution in pipe.

Werlink, Rudy J.↗
NASA NTRS1995

Design optimization of a brush turbine with a cleaner/water based solution

Recently, a turbine-brush was analyzed based on the energy conservation and the force momentum equation with an empirical relationship of the drag coefficient. An equation was derived to predict the rotational speed of the turbine-brush in terms of the blade angle, number of blades, rest of geometries of the turbine-brush and the incoming velocity. Using the observed flow conditions, drag coefficients were determined. Based on the experimental values as boundary conditions, the turbine-brush flows were numerically simulated to understand first the nature of the flows, and to extend the observed drag coefficient to a flow without holding the turbine-brush.

Kim, Rhyn H.↗
NASA NTRS1997

Bidirectional Brush Seals: Post-Test Analysis

A post-test analysis of a set of inside-diameter/outside-diameter (ID/OD) bidirectional brush seals used in three-port wave rotor tests was undertaken to determine brush bristle and configuration wear, pullout, and rotor coating wear. The results suggest that sharp changes in the pressure profiles were not well reflected in bristle tip configuration patterns or wear. Also, positive-to-negative changes in axial pressure gradients appeared to have little effect on the backing plates. Although the brushes had similar porosities, they had very different unpacked arrays. This difference could explain the departure of experimental data from computational fluid dynamics flow predictions for well-packed arrays at higher pressure drops. The rotor wear led to "car-track" scars (upper and lower wear bands) with a whipped surface between the bands. Those bands may have resulted from bristle stiffening at the fence and gap plates during alternate portions of the rotor cycle. Within the bristle response range the wear surface reflected the pressure distribution effect on bristle motion. No sacrificial metallurgical data were taken. The bristles did wear, with correspondingly more wear on the ID brush configurations than on the OD configurations; the complexity in constructing the ID brush was a factor.

Hendricks, Robert C.↗
NASA NTRS1999

Motor Brush Testing for Mars and Vacuum

Brush motors have been qualified and flown successfully on Mars missions, but upcoming missions require longer life and higher power. A test program was therefore undertaken to identify the best brush material for operation in the Mars atmosphere. Six different brush materials were used in 18 identical motors and operated under various load conditions for a period of four weeks in low-pressure CO2. All motors performed acceptably, with accumulated motor revolutions between 98 and 144 million revolutions, depending on load. A proprietary silver-graphite material from Superior Carbon (SG54-27) appears to be the best choice for long life, but even the stock copper-graphite brushes performed reliably with acceptable wear. The motors from the CO2 test were then cleaned and run in vacuum for 2 weeks. The difference in results was dramatic, with 5 motors failing catastrophically and wear rates increasing by orders of magnitude for the SG54-27 material. Three brush materials survived the test with no failures: SG54-27 with a proprietary Ball Aerospace impregnation, a silver-graphite-molybdenum disulfide material from Superior Carbon (SG59), and a copper sulfide-graphite material also from Superior Carbon (BG91).

Noon, Don E.↗
NASA NTRS1972

Friction, wear and noise of slip ring and brush contacts for synchronous satellite use.

A program is being conducted for testing of slip rings for synchronous orbit application. Instrumentation systems necessary for monitoring electrical noise, friction, and brush wear at atmospheric pressure and at less than 50 ntorr have been developed. A multiplex scheme necessary for the simultaneous recording of brush displacement, friction, and electrical noise has also been developed. Composite brushes consisting of silver-molybdenum disulfide-graphite and silver-niobium diselenide-graphite have been employed on rings of coin silver and rhodium plate. Four contact combinations have been tested during an ambient condition run-in at 150 rpm and a humidity sequence at 0.1 rpm. The first six months of the two year vacuum test at 0.1 rpm have been completed. Electrical noise, friction and brush wear data recorded during these periods have been analyzed.

Lewis, N. E.↗
NASA NTRS1973

Friction, wear, and noise of slip ring and brush contacts for synchronous satellite use.

A program is being conducted for testing of slip rings for synchronous orbit application. Instrumentation systems necessary for monitoring electrical noise, friction, and brush wear at atmospheric pressure and at less than 50 nanotorr have been developed. A multiplex scheme necessary for the simultaneous recording of brush displacement, friction, and electrical noise has also been developed. Composite brushes consisting of silver-molybdenum disulfide-graphite and silver-niobium diselenide-graphite have been employed on rings of coin silver and rhodium plate. Brush property measurements made included measurement of density, electrical resistivity, shear strength, and microstructure.

Lewis, N. E.↗
NASA NTRS1991

Effects of brush seal morphology on leakage and pressure drops

Research on brush seals which was undertaken earlier by Braun et al. (1990) is continued. Particular attention is given to the effects of brush positioning, design, and morphology on sealing surfaces, fluid leakage, and associated pressure drops. It is found that both the structure and the design of the brush are important to its performance. High resistance to the flow of the brush/fence combination can result in catastrophic failure of the brush, while at lower flow resistances, the failure is more gradual.

Braun, M. J.↗
NASA NTRS1990

Flow visualization in a simulated brush seal

A method to visualize and characterize the complex flow fields in simulated brush seals is presented. The brush seal configuration was tested in a water and then in an oil tunnel. The visualization procedure revealed typical regions that are rivering, jetting, vortical or lateral flows and exist upstream, downstream or within the seal. Such flows are engendered by variations in fiber void that are spatial and temporal and affect changes in seal leakage and stability. While the effects of interface motion for linear or cylindrical configurations have not been considered herein, it is believed that the observed flow fields characterize flow phenomenology in both circular and linear brush seals. The axial pressure profiles upstream, across and downstream of the brush in the oil tunnel have been measured under a variety of inlet pressure conditions and the ensuing pressure maps are presented and discussed.

Braun, M. J.↗
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 are 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 approx. 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 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 NTRS1993

Modeling bristle lift-off in idealized brush seal configurations

We attempt in this paper to develop a model for the flow through brush seals and determine their elastic behavior in order to predict the dependence of brush/journal clearance on geometry and operating conditions. Several idealizations regarding brush seal configuration, flow conditions, and elastic behavior are made in the analysis in order to determine closed form parametric dependence. This formulation assumes that there is no initial interference between the bristle tip and the rotor. Also, interbristle, bristle-backing plate, and bristle-rotor friction is neglected. The bristle bundle or the brush seal as it is alternately called is assumed homogeneous and isotropic on a macroscopic scale so that a physical property like permeability is uniform. The fluid is assumed to be homogeneous, incompressible, viscous, and flowing under steady conditions. A schematic of a brush seal is shown. If the nominal bristle-shaft interference is absent then under static conditions the bristles may deflect axially due to the imposed pressure differential. This axial deflection may create a clearance permitting leakage flow in excess of that which occurs through the porous matrix formed by the bristle bundles. Under dynamic conditions the Couette flow created by shaft motion could be strong enough to cause bristle deflection and once again a clearance may develop. The paper proposes a means to determine this clearance (or at least describe its parametric dependence on geometry and operating conditions) under static as well as dynamic conditions.

Modi, Vijay↗
NASA NTRS1994

Brush Seal Performance and Durability Issues Based on T-700 Engine Test Results

The integrity and performance of brush seals have been established. Severe bench and engine tests have shown high initial wear or run-in rates, material smearing at the interface, and bristle and rub-runner wear, but the brush seals did not fail. Short-duration (46 hr) experimental T-700 engine testing of the compressor discharge seal established over 1-percent engine performance gain (brush versus labyrinth). Long-term gains were established only as leakage comparisons, with the brush at least 20 percent better at controlling leakage. Long-term materials issues, such as wear and ultimately seal life, remain to be resolved. Future needs are cited for materials and analysis tools that account for heat generation, thermomechanical behavior, and tribological pairing to enable original equipment manufacturers to design high-temperature, high-surface-speed seals with confidence.

Hendricks, R. C.↗
NASA NTRS1994

Brush seals for turbine engine fuel conservation

The program objective is to demonstrate brush seals for replacing labyrinth seals in turboprop engines. The approach taken was to design and procure brush seals with assistance from Sealol, modify and instrument an existing T407 low pressure turbine test rig, replace inner balance piston and outer balance piston labyrinth seals with brush seals, conduct cyclic tests to evaluate seal leakage at operating pressures and temperatures, and evaluate effect of seal pack width and rotor eccentricity. Results are presented in viewgraph format and show that brush seals offer performance advantages over labyrinth seals.

Sousa, Mike↗
NASA NTRS1995

Relative performance comparison between baseline labyrinth and dual-brush compressor discharge seals in a T-700 engine test

In separate series of YT-700 engine tests, direct comparisons were made between the forward-facing labyrinth and dual brush compressor discharge seals. Compressor speeds to 43 000 rpm, surface speeds to 160 m/s (530 ft/s), pressures to 1 MPa (145 psi), and temperatures to 680 K (765 F) characterized these tests. The wear estimate for 46 hr of engine operations was less than 0.025 mm (0.001 in.) of the Haynes 25 alloy bristles running against a chromium-carbide-coated rub runner. The pressure drops were higher for the dual-brush seal than for the forward-facing labyrinth seal and leakage was lower-with the labyrinth seal leakage being 2-1/2 times greater-implying better seal characteristics, better secondary airflow distribution, and better engine performance (3 percent at high pressure to 5 percent at lower pressure) for the brush seal. (However, as brush seals wear down (after 500 to 1000 hr of engine operation), their leakage rates will increase.) Modification of the secondary flow path requires that changes in cooling air and engine dynamics be accounted for.

Hendricks, Robert C.↗
NASA NTRS2010

Three-Wheel Brush-Wheel Sampler

A new sampler is similar to a common snow blower, but is robust and effective in sample collection. The brush wheels are arranged in a triangle shape, each driven by a brushless DC motor and planetary gearhead embedded in the wheel shaft. Its speed can be varied from 800 - 2,000 rpm, depending on the surface regolith resistance. The sample-collecting flow path, and internal features, are designed based on flow dynamics, and the sample-collecting rates have consistently exceeded the requirement under various conditions that span the range of expected surface properties. The brush-wheel sampler (BWS) is designed so that the flow channel is the main body of the apparatus, and links the brush-wheel assembly to the sample canister. The combination of the three brush wheels, the sample flow path, and the canister location make sample collection, storage, and transfer an easier task.

Duckworth, Geoffrey A.↗
NASA NTRS1970

Motor brush wear measured with strain gages

Balanced bridge circuit, supplied with low-voltage direct current and connected to a readout device, measures remaining brush material, rate of brush wear, armature runout, and brush signature.

Farrell, W. T.↗