Experimental Investigation of Modified Cast-cored Blades Having Hollow Tip Sections
Explore the source record for details and available documents.
Oldrieve, Robert E↗
SEARCH · Search NASA
Results for “hollow tip”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Multiscale water drop contact angles at selected silica surfaces
In this paper, multiscale advancing contact angles for glycerol/water drops at silica surfaces are reported for millidrops, submicron-drops, and nanodrops. Selected silica surfaces were muscovite, silicon, and talc. The contact angles for millidrops (1–2 mm) were determined by the traditional sessile drop technique. For submicron-drops (0.1–1.0 μm), a hollow tip Atomic Force Microscope (AFM) procedure was used. The contact angles for nanodrops (~7 nm) were examined from Molecular Dynamics (MD) simulation. The results were compared to evaluate the effect of drop size on the contact angle. In the case of the hydrophobic talc surface, the 75° advancing contact angle did not vary significantly with drop size. For the hydrophilic muscovite surface, the water drop wet the surface and an advancing contact angle of about 10° was found for the millidrops and submicron-drops. However, for the MD simulated nanodrops, attachment and spreading of the ~7 nm drop created a 2D film of molecular dimensions, the contact angle of which was difficult to define and varied from 0° to 17°. Perhaps of equal interest from the MD simulation results was that the spreading of the glycerol/water nanodrop at the muscovite surface resulted in crystallographic directional transport of water molecules to the extremities of the 2D film. Such separation and segregation left the center of the film with an increased concentration of glycerol. Based on these results, the line tension, which has been found in other investigations to account for contact angle decrease with a decrease in drop size, does not seem to be a significant factor in this study.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Inert gas thrusters
Inert gases, particularly argon and xenon, are of interest as possible alternatives to the usual electric thruster propellants of mercury and cesium. Hollow cathode data were obtained for a wide range of operating conditions. Some test conditions gave plasma coupling voltages at or below the sputtering threshold, hence should permit long operating lifetimes. All observations of hollow cathode operation were consistent with a single theory of operation, in which a significant amount of the total electron emission is from localized areas within the orifice. This mode of emission is also supported by scanning electron microscope photographs that indicate local temperatures at or near the melting temperature of the tungsten tip. Experimental hollow cathode performance was correlated for two orifice diameters, three inert gas propellants, and a range of flow rates for each propellant. The basic theory for the production of doubly ionized argon and xenon was completed. Experimental measurements of the doubly ionized fraction agree with theory within about plus or minus 20 percent. High voltage isolators were studied for the propellant feed line. The breakdown voltage per segment ranged from 300 to over 500 V with argon.
Kaufman, H. R.↗
Flight Tests of a Man Standing on a Platform Supported by a Teetering Rotor
Because previous flight tests of a man standing on a jet-supported platform were very successful, a series of flight tests were made to determine the flying qualities of a man standing on a platform supported by a teetering rotor. The rotor was 7 feet in diameter and was driven by air jets at the rotor tips fed by hollow blades and air hoses connected to an external air supply. The machine was tested with a free-teetering rotor and with a spring-restrained rotor, and, as an alternate arrangement, with the rotor and foot platform isolated from the framework by rubber connections to reduce the inertia of the moving parts. The machine was tested indoors in hovering and in limited translational flight and outdoors in light and in strong gusty winds. The stability and controllability with the spring-restrained rotor were uniformly good. The stability with the free-teetering rotor was marginal, but, when an experienced flyer placed his hands on a hand rail, the stability and controllability were good. The stability and controllability with the rubber-isolated frame and spring-restrained teetering rotor were very good and quite like the jet-supported platform.
Paul R Hill↗
Preliminary investigation of hollow-bladed turbines having closed and open blade tips
Explore the source record for details and available documents.
Smith, Gordon T↗
Hollow cathodes with BaO impregnated, porous tungsten inserts and tips
The technology of impregnated materials is described and some inherently advantageous characteristics of impregnated cathodes are discussed. Thermionic emission measurements are presented for oxide coated and impregnated cathodes. Five cathode configurations with barium oxide impregnated porous tungsten inserts and/or tips have been fabricated and tested. Reliability, durability, and stability of operation are characterized. One of the cathodes has accumulated over 9000 operational hours, another has been cycled on and off more than 800 times.
Hudson, W. R.↗
Hollow cathodes with BaO impregnated, porous tungsten inserts and tips
The technology of impregnated materials is described and some inherently advantageous characteristics of impregnated cathodes are discussed. Thermionic emission measurements are presented for oxide coated and impregnated cathodes. Five cathode configurations with barium oxide impregnated porous tungsten inserts and/or tips have been fabricated and tested. Reliability, durability, and stability of operation are characterized. One of the cathodes has accumulated over 9000 operational hours, another has been cycled on and off more than 900 times.
Hudson, W. R.↗
A preliminary study of a propeller powered by gas jets issuing from the blade tips
Computations are made of the performance of a propeller designed to develop 56 thrust horsepower at 100 miles per hour. The fuel consumption of the jet-operated propeller would be considerably higher than that of a reciprocating engine and a propeller. The lighter weight of the jet-operated propeller will result in a lighter weight of engine plus fuel for short-range flights. A theoretical analysis is made of a propeller powered by gas jets issuing from the blade tips. In the propeller considered, the air is drawn through the hub and passes through the hollow propeller blades to the tips, where propellers heat the air and expel it through the nozzles in the blade tips. The reaction of the tips rotates the propeller. For long range flights, the weight of the jet-operated propeller with its fuel would be greater than the weight of a reciprocating engine with its propeller and fuel.
Sanders, J C↗
Operating characteristics of a hollow-cathode neutralizer for 5 and 8 centimeter-diameter electron bombardment mercury ion thrusters
Thin-tip 0.3-cm-outside-diameter hollow-cathode neutralizers were used to investigate causes of neutralizer tip erosion experienced in thruster endurance tests. Bell-jar tests indicated that neutralizers with new rolled tantalum foil inserts coated with an emissive mixture eroded very little over the neutral flow rates investigated (3 to 10 mA) for simulated 5- and 8-cm-diameter thruster neutralizer conditions. Tip erosion rates of neutralizers operated with no insert or emissive mixture increased by two orders of magnitude for both configurations as the neutral flow rate decreased. Spectroscopic analysis of the discharge plasma from neutralizers operated with inserts coated with the emissive mixture detected tungsten at all neutral flow rates for both thruster neutralizer conditions. The only source of tungsten was the tip. Therefore, detection of tungsten indicated neutralizer tip erosion. Barium, an element of the emissive mixture, was detected at low neutral flow rates for the 5-cm-diameter thruster neutralizer operating condition only.
Weigand, A. J.↗
Hypervelocity Impact Testing of International Space Station Meteoroid/Orbital Debris Shielding Using an Inhibited Shaped Charge Launcher
Engineers at the NASA Johnson Space Center have conducted hypervelocity impact (HVI) performance evaluations of spacecraft meteoroid and orbital debris (M/OD) shields at velocities in excess of 7 km/s. The inhibited shaped charge launcher (ISCL), developed by the Southwest Research Institute, launches hollow, circular, cylindrical jet tips to approximately 11 km/s. Since traditional M/OD shield ballistic limit performance is defined as the diameter of sphere required to just perforate or spall a spacecraft pressure wall, engineers must decide how to compare ISCL derived data with those of the spherical impactor data set. Knowing the mass of the ISCL impactor, an equivalent sphere diameter may be calculated. This approach is conservative since ISCL jet tips are more damaging than equal mass spheres. A total of 12 tests were recently conducted at the Southwest Research Institute (SWRI) on International Space Station M/OD shields. Results of these tests are presented and compared to existing ballistic limit equations. Modification of these equations is suggested based on the results.
Kerr, Justin H.↗
Miniaturized double latching solenoid valve
A valve includes a generally elongate pintle; a spacer having a rounded surface that bears against the pintle; a bulbous tip fixed to the spacer; and a hollow, generally cylindrical collar fixed to the pintle, the collar enclosing the spacer and the tip and including an opening through which a portion of the tip extends, the opening in the collar and interior of the collar being of a size such that the tip floats therein.
Smith, James T.↗
Integration issues of a plasma contactor Power Electronics Unit
A hollow cathode-based plasma contactor is baselined on International Space Station Alpha (ISSA) for spacecraft charge control. The plasma contactor system consists of a hollow cathode assembly (HCA), a power electronics unit (PEU), and an expellant management unit (EMU). The plasma contactor has recently been required to operate in a cyclic mode to conserve xenon expellant and extend system life. Originally, a DC cathode heater converter was baselined for a continuous operation mode because only a few ignitions of the hollow cathode were expected. However, for cyclic operation, a DC heater supply can potentially result in hollow cathode heater component failure due to the DC electrostatic field. This can prevent the heater from attaining the proper cathode tip temperature for reliable ignition of the hollow cathode. To mitigate this problem, an AC cathode heater supply was therefore designed, fabricated, and installed into a modified PEU. The PEU was tested using resistive loads and then integrated with an engineering model hollow cathode to demonstrate stable steady-state operation. Integration issues such as the effect of line and load impedance on the output of the AC cathode heater supply and the characterization of the temperature profile of the heater under AC excitation were investigated.
Pinero, Luis R.↗
Experimental investigation of a 2.5 centimeter diameter Kaufman microthruster
A 2.5-centimeter-diameter Kaufman electron bombardment microthruster was fabricated and tested. The microthruster design was based on the 15-centimeter-diameter SERT 2 and 5-centimeter-diameter Lewis experimental thruster designs. The microthruster with a two-grid system, operating at a net accelerating potential of 600 volts and an accelerator potential of 500 volts, produced a calculated 445 micronewton thrust when it was run with a 9-milliampere beam current. A glass grid was initially used in testing. Later a two-grid system was successfully incorporated. Both the propellant utilization efficiency and the total power efficiency were lower than for large-size advanced thrusters, as expected; but they were sufficiently high that 2.5-centimeter thrusters show promise for future space applications. Total power of the microthruster with an assumed 7-watt hollow-cathode neutralizer was less than 30 watts at a thrust level of 445 micronewton (100 Nu LBf). The hollow cathode was operated at zero tip heater power for power requirement tests.
Cohen, A. J.↗
On the emission mechanism in high current hollow cathode arcs
Large hollow cathodes have been operated in a magnetoplasmadynamic arc over wide ranges of current and mass flow, with orifice current densities and mass fluxes encompassing those encountered in low current steady state hollow cathode arcs. Detailed cathode interior measurements of current and potential distributions show that maximum current penetration into the cathode is about one diameter axially upstream from the tip, with peak inner surface current attachment up to one cathode diameter upstream of the tip. The spontaneous attachment of peak current upstream of the cathode tip is suggested as a criterion for characteristic hollow cathode operation. This empirical criterion was verified by experiment.
Krishnan, M.↗
Visualization of Rotor Tip Secondary Flows with Blade Tip Air Discharge and Suction in a Low-speed Turbine
Smoke was used to visualize outer-wall secondary flows in a low-speed turbine utilizing rotor tip air discharge and suction. Photographs as well as visual observations of the effect of tip air discharge and suction were made by independently varying the direction and quantity of the tip air discharge and suction, and varying tip clearance, and main-stream air speed. In addition, the cross-sectional area of the hollow blade discharge opening was varied for the case of tip air discharge.
Kofskey, Milton G↗
Subspace Iteration Method for Complex Eigenvalue Problems with Nonsymmetric Matrices in Aeroelastic System
Modern airplane design is a multidisciplinary task which combines several disciplines such as structures, aerodynamics, flight controls, and sometimes heat transfer. Historically, analytical and experimental investigations concerning the interaction of the elastic airframe with aerodynamic and in retia loads have been conducted during the design phase to determine the existence of aeroelastic instabilities, so called flutter .With the advent and increased usage of flight control systems, there is also a likelihood of instabilities caused by the interaction of the flight control system and the aeroelastic response of the airplane, known as aeroservoelastic instabilities. An in -house code MPASES (Ref. 1), modified from PASES (Ref. 2), is a general purpose digital computer program for the analysis of the closed-loop stability problem. This program used subroutines given in the International Mathematical and Statistical Library (IMSL) (Ref. 3) to compute all of the real and/or complex conjugate pairs of eigenvalues of the Hessenberg matrix. For high fidelity configuration, these aeroelastic system matrices are large and compute all eigenvalues will be time consuming. A subspace iteration method (Ref. 4) for complex eigenvalues problems with nonsymmetric matrices has been formulated and incorporated into the modified program for aeroservoelastic stability (MPASES code). Subspace iteration method only solve for the lowest p eigenvalues and corresponding eigenvectors for aeroelastic and aeroservoelastic analysis. In general, the selection of p is ranging from 10 for wing flutter analysis to 50 for an entire aircraft flutter analysis. The application of this newly incorporated code is an experiment known as the Aerostructures Test Wing (ATW) which was designed by the National Aeronautic and Space Administration (NASA) Dryden Flight Research Center, Edwards, California to research aeroelastic instabilities. Specifically, this experiment was used to study an instability known as flutter. ATW was a small-scale airplane wing comprised of an airfoil and wing tip boom. This wing was formulated based on a NACA-65A004 airfoil shape with a 3.28 aspect ratio. The wing had a span of 18 inch with root chord length of 13.2 inch and tip chord length of 8.7 inch. The total area of this wing was 197 square inch. The wing tip boom was a 1 inch diameter hollow tube of length 21.5 inch. The total weight of the wing was 2.66 lbs.
Pak, Chan-gi↗
Use of Nucleating Agent NA11 in the Preparation of Polyvinylidene Fluoride Dual-Layer Hollow Fiber Membranes
Polyvinylidene fluoride (PVDF) dual-layer hollow fiber membranes were simultaneously fabricated by thermally induced phase separation (TIPS) and non-solvent induced phase separation (NIPS) methods using a triple orifice spinneret (TOS) for water treatment application. The support layer was prepared from a TIPS dope solution, which was composed of PVDF, gamma-butyrolactone (GBL), and N-methyl-2-pyrrolidone (NMP). The coating layer was prepared from a NIPS dope solution, which was composed of PVDF, N,N-dimethylacetamide (DMAc), and polyvinylpyrrolidone (PVP). In order to improve the mechanical strength of the dual-layer hollow fiber, a nucleating agent, sodium 2,2'-methylene bis-(4,6-di-tert-butylphenyl) phosphate (NA11), was added to the TIPS dope solution. The performance of the membrane was evaluated by surface and cross-sectional morphology, water flux, mechanical strength, and thermal property. Our results demonstrate that NA11 improved the mechanical strength of the PVDF dual-layer hollow fiber membranes by up to 42%. In addition, the thickness of the coating layer affected the porosity of the membrane and mechanical performance to have high durability in enduring harsh processing conditions.
36 MATERIALS SCIENCE↗
Development and Testing of High Current Hollow Cathodes for High Power Hall Thrusters
NASA's Office of the Chief Technologist In-Space Propulsion project is sponsoring the testing and development of high power Hall thrusters for implementation in NASA missions. As part of the project, NASA Glenn Research Center is developing and testing new high current hollow cathode assemblies that can meet and exceed the required discharge current and life-time requirements of high power Hall thrusters. This paper presents test results of three high current hollow cathode configurations. Test results indicated that two novel emitter configurations were able to attain lower peak emitter temperatures compared to state-of-the-art emitter configurations. One hollow cathode configuration attained a cathode orifice plate tip temperature of 1132 degC at a discharge current of 100 A. More specifically, test and analysis results indicated that a novel emitter configuration had minimal temperature gradient along its length. Future work will include cathode wear tests, and internal emitter temperature and plasma properties measurements along with detailed physics based modeling.
Kamhawi, Hani↗