SEARCH · Engineering Papers

Results for “Pressure Core”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 613 records · Page 34

All sources NASA NTRS DOE OSTI

NASA NTRS2000

An Interconnected Network of Core-Forming Melts Produced by Shear Deformation

The formation mechanism of terrestrial planetary is still poorly understood, and has been the subject of numerous experimental studies. Several mechanisms have been proposed by which metal-mainly iron with some nickel-could have been extracted from a silicate mantle to form the core. Most recent models involve gravitational sinking of molten metal or metal sulphide through a partially or fully molten mantle that is often referred to as a'magma ocean. Alternative models invoke percolation of molten metal along an interconnected network (that is, porous flow) through a solid silicate matrix. But experimental studies performed at high pressures have shown that, under hydrostatic conditions, these melts do not form an interconnected network, leading to the widespread assumption that formation of metallic cores requires a magma ocean. In contrast, here we present experiments which demonstrate that shear deformation to large strains can interconnect a significant fraction of initially isolated pockets of metal and metal sulphide melts in a solid matrix of polycrystalline olivine. Therefore, in a dynamic (nonhydrostatic) environment, percolation remains a viable mechanism for the segregation and migration of core-forming melts in a solid silicate mantle.

Bruhn, D.↗

NASA NTRS1977

Measurement of vortex velocities over a wide range of vortex age, downstream distance and free stream velocity

A wind tunnel test was conducted to obtain vortex velocity signatures over a wide parameter range encompassing the data conditions of several previous researchers while maintaining a common instrumentation and test facility. The generating wing panel was configured with both a revolved airfoil tip shape and a square tip shape and had a semispan aspect of 4.05/1.0 with a 121.9 cm span. Free stream velocity was varied from 6.1 m/sec to 76.2 m/sec and the vortex core velocities were measured at locations 3, 6, 12, 24 and 48 chordlengths downstream of the wing trailing edge, yielding vortex ages up to 2.0 seconds. Wing pitch angles of 6, 8, 9 and 12 deg were investigated. Detailed surface pressure distributions and wing force measurements were obtained for each wing tip configuration. Correlation with vortex velocity data taken in previous experiments is good. During the rollup process, vortex core parameters appear to be dependent primarily on vortex age. Trending in the plateau and decay regions is more complex and the machanisms appear to be more unstable.

Rorke, J. B.↗

NASA NTRS2006

Aeroacoustic Improvements to Fluidic Chevron Nozzles

Fluidic chevrons use injected air near the trailing edge of a nozzle to emulate mixing and jet noise reduction characteristics of mechanical chevrons. While previous investigations of "first generation" fluidic chevron nozzles showed only marginal improvements in effective perceived noise levels when compared to nozzles without injection, significant improvements in noise reduction characteristics were achieved through redesigned "second generation" nozzles on a bypass ratio 5 model system. The second-generation core nozzles had improved injection passage contours, external nozzle contour lines, and nozzle trailing edges. The new fluidic chevrons resulted in reduced overall sound pressure levels over that of the baseline nozzle for all observation angles. Injection ports with steep injection angles produced lower overall sound pressure levels than those produced by shallow injection angles. The reductions in overall sound pressure levels were the result of noise reductions at low frequencies. In contrast to the first-generation nozzles, only marginal increases in high frequency noise over that of the baseline nozzle were observed for the second-generation nozzles. The effective perceived noise levels of the new fluidic chevrons are shown to approach those of the core mechanical chevrons.

Henderson, Brenda↗

NASA NTRS1993

Development of hypersonic engine seals: Flow effects of preload and engine pressures

A new type of engine seal is being developed to meet the needs of advanced hypersonic engines. A seal braided of emerging high temperature ceramic fibers comprised of a sheath-core construction was selected for study based on its low leakage rates. Flexible, low-leakage, high temperature seals are required to seal the movable engine panels of advanced ramjet-scramjet engines either preventing potentially dangerous leakage into backside engine cavities or limiting the purge coolant flow rates through the seals. To predict the leakage through these flexible, porous seal structures as a function of preload and engine pressures, new analytical flow models are required. An empirical leakage resistance/preload model is proposed to characterize the observed decrease in leakage with increasing preload. Empirically determined compression modulus and preload factor are used to correlate experimental leakage data for a wide range of seal architectures. Good agreement between measured and predicted values are observed over a range of engine pressures and seal preloads.

Cai, Zhong↗

NASA NTRSDate not supplied

Overview of the SLS Core Stage Thrust Vector Control System Design

The Space Launch System (SLS) Core Stage (CS) Thrust Vector Control (TVC) consists of four independent hydraulic systems. The SLS CS TVC system is comprised of 8 mechanical feedback Shuttle heritage Type III TVC actuators and four RS-25 engines, each attached to a Shuttle heritage gimbal block/bearing. Each hydraulic system nominally provides hydraulic power to one RS-25 engine and two actuators. Additionally, each system provides redundant control capability to one actuator on each of its neighboring systems. The RS-25 uses hydraulic power to control propellant valves, and the TVC actuators are used to move the engine in the pitch and yaw gimbal planes. The TVC system design leverages hardware from the Space Shuttle program as well as new hardware designed specifically for the Core Stage. The Space Shuttle heritage hardware directly reused on SLS includes the Orbiter TVC hydraulic servo-actuators (with two slight design modifications), the Orbiter hydraulic circulation pumps, the Orbiter gimbal block/bearing, and the Solid Rocket Booster hydraulic pumps. The Solid Rocket Booster APU turbines are powered by hot gas produced by a catalyzed hydrazine decomposition. The SLS Core Auxiliary Power Unit (CAPU) is derived from the Space Shuttle Orbiter Auxiliary Power Unit (APU); on the SLS Core Stage, the CAPU turbine is spun using cold gas tapped-off from the RS-25 to CS liquid hydrogen autogenous pressurization line. The remaining hardware in the TVC system (hydraulic Filter Manifold (FM), hydraulic Supply Accumulator (SA), hydraulic Return Accumulator (RA), Hydraulic Reservoir, Exhaust Gas Heat Exchanger (EGHE)) as well as the avionics providing control and telemetry (TVC Actuator Controller (TAC) and CAPU Controller (CAPUC) are new components developed for SLS. This paper is the first installment in a seven-paper series surveying the design, engineering, test validation, and flight performance of the Core Stage Thrust Vector Control system. In this paper, the overall design architecture of the CS TVC is presented, with a focus on the interfaces between the TVC actuators, the engines, their hydraulic power systems, and the avionics that provide commands from the SLS Vehicle Management (VM) software to effect stable and robust flight control for the integrated SLS launch vehicle.

Thrust Vector Control↗

NASA NTRSDate not supplied

Overview of the SLS Core Stage Thrust Vector Control System Design

Thrust Vector Control↗

NASA NTRS1974

Geostrophic current investigations with Seasat

The measurement of sea surface topology by SEASAT satellite allows for the detection of baroclinic or barotropic geostrophic flows, as well as the tracking of cyclonic cold core rings generated by currents. It is stipulated that SEASAT is the only system capable of measuring pressure and motion fields of a sea surface reliably, synoptically, and at an affordable cost.

Byrne, H. M.↗

NASA NTRS1980

Design and cold-air test of single-stage uncooled turbine with high work output

A solid version of a 50.8 cm single stage core turbine designed for high temperature was tested in cold air over a range of speed and pressure ratio. Design equivalent specific work was 76.84 J/g at an engine turbine tip speed of 579.1 m/sec. At design speed and pressure ratio, the total efficiency of the turbine was 88.6 percent, which is 0.6 point lower than the design value of 89.2 percent. The corresponding mass flow was 4.0 percent greater than design.

Moffitt, T. P.↗

NASA NTRS1984

Theoretical approach to labyrinth seal forces - cross-coupled stiffness of a straight-through labyrinth seal

Two kinds of three dimensional flows in a labyrinth seal, a jet flow and a core flow, are considered and theoretical equations are set up concerning the motion of each flow. The pressure distribution within the labyrinth is calculated, when the rotor shaft makes a small displacement from the center line of the casing, keeping parallel with it. The theoretical values of cross coupled stiffness obtained by integrating the pressure under different labyrinth geometries and operating conditions through these formulas are compared with the experimental data.

Kameoka, T.↗

NASA NTRS1986

A spectroscopic study of the cataclysmic binary star SU Ursae Majoris

Spectroscopic observations of SU UMa, the prototype of a class of short-period cataclysmic binaries, are reported. The orbital period is found to be 0.076351 + or - 4.3 x 10 to the -5th days. The velocity amplitude of the emission line source is 58 + or - 4 km/s, leading to a mass function of about 0.0015 solar mass and implying a moderately low inclination. The line cores in H-alpha and H-beta lead the wings slightly in orbital phase, contrary to the predictions of simple hot spot models of the line core. The velocity widths of the Balmer series increase toward higher members of the series, suggesting that pressure broadening may contribute nonnegligibly to the emission line widths.

Thorstensen, John R.↗

NASA NTRS1990

The radio properties of cD galaxies in Abell clusters. I - An X-ray selected sample

The radio and X-ray properties of a sample of 27 cD galaxies in rich clusters are presented. The radio data consist of 6 cm VLA maps at a resolution of 1-2 arcsec. The X-ray data consist of images and surface-brightness profiles from the Einstein IPC and derived quantities such as cooling times, mass-accretion rates, and thermal pressures from Arnaud (1988). These data are used to explore the relationship between X-ray cooling cores, and the power and morphology of the radio emission. It is found that 71 percent of the cD's with X-ray cooling cores are radio loud, whereas a smaller but still significant 23 percent of cD's without cooling cores are detected at 6 cm above 0.2 mJy. Among the radio galaxies in noncooling core clusters are luminous and extended wide-angle tails. There is a weak correlation between the mass-accretion rate and the radio power for cD's. There is also an interesting class of cooling core cluster (e.g., A2052) with small diameter, amorphous radio emission that may be the result of diffusion along radial magnetic fields set up in cooling inflows. Finally, the relationships between optical emission-line luminosity with radio power and mass-accretion rate are examined.

Burns, Jack O.↗

NASA NTRS1990

Numerical simulations of three-dimensional rotor blade-vortex interactions

A numerical procedure which has been developed (Hassan and Charles, 1989) for the prediction of helicopter blade loads during self-generated blade-vortex interactions (BVI) is described. These BVIs result in significant and frequent impulsive changes in the rotor blade aerodynamic loads and moments that are known to lead to vibrations and severe noise problems. Potential BVIs are identified and tracked in time at even increments of rotor azimuth employing the lifting line helicopter/rotor trim code CAMRAD. The accuracy of the predicted leading edge pressures for self-generated interactions is shown to rely heavily on the user-specified vortex core radius, and more significantly on the CAMRAD-predicted geometry of the interaction vortex elements and their relative orientation with respect to the blade. Thus, the robustness of the surface transpiration approach for modeling subcritical-type BVIs is proven.

Hassan, A. A.↗

NASA NTRS1991

Wing tip vortex calculations with an unstructured adaptive-grid Euler solver

A solution-adaptive grid method has been developed for computing tip-vortex flowfields around rectangular wings. This method uses subdivision in order to locally refine the grid in regions with high vorticity. Two different flow solvers are used. Each solves the three-dimensional Euler equations on unstructured grids. Computed results are compared to experimentally measured surface pressures and vortex velocities on a NACA 0015 rectangular wing. Predicted results for surface pressures and integrated lift agree well with the experimental data. The predicted size of the rotational vortex core is larger than the experimentally-measured value and the peak velocities are less. This discrepancy appears to be caused by deficiencies in the inviscid Euler-equation model. This model cannot capture the complex viscous effects at the tip that determine the detailed structure of the resulting vortex. In spite of this limitation, the present Euler unstructured adaptive-grid method demonstrates the ability to convert vortical flows with low numerical diffusion. Applications for modeling helicopter rotor wake systems are discussed.

Strawn, Roger C.↗

NASA NTRS1993

Melt infiltration of silicon carbide compacts. II - Evaluation of solidification microstructures

Microstructural aspects of alloy solidification within the interstices of porous compacts of platelet-shaped single crystals of alpha-SiC, when the latter are infiltrated with a hot metal under pressure, have been described. Microstructural evidence is presented of selective reorientation of platelets and nonhomogeneous solute distribution under shear of pressurized melt, of constrained growth of primary solid within finite width zones, and of the modulation of coring due to microsegregation as a result of variations in the pore size of compacts.

Asthana, Rajiv↗

NASA NTRS1998

Superconductor-Mediated Modification of Gravity? AC Motor Experiments with Bulk YBCO Disks in Rotating Magnetic Fields

We have previously reported results using a high precision gravimeter to probe local gravity changes in the neighborhood of large bulk-processed high-temperature superconductors. Podkietnov, et al (Podkietnov, E. and Nieminen, R. (1992) A Possibility of Gravitational Force Shielding by Bulk YBa2 Cu3 O7-x Superconductor, Physica C, C203:441-444.) have indicated that rotating AC fields play an essential role in their observed distortion of combined gravity and barometric pressure readings. We report experiments on large (15 cm diameter) bulk YBCO ceramic superconductors placed in the core of a three-phase, AC motor stator. The applied rotating field produces up to a 12,000 revolutions per minute magnetic field. The field intensity decays rapidly from the maximum at the outer diameter of the superconducting disk (less than 60 Gauss) to the center (less than 10 Gauss). This configuration was applied with and without a permanent DC magnetic field levitating the superconducting disk, with corresponding gravity readings indicating an apparent increase in observed gravity of less than 1 x 10(exp -6)/sq cm, measured above the superconductor. No effect of the rotating magnetic field or thermal environment on the gravimeter readings or on rotating the superconducting disk was noted within the high precision of the observation. Implications for propulsion initiatives and power storage flywheel technologies for high temperature superconductors will be discussed for various spacecraft and satellite applications.

Noever, David A.↗

NASA NTRS2006

Multiphysics Thrust Chamber Modeling for Nuclear Thermal Propulsion

The objective of this effort is to develop an efficient and accurate thermo-fluid computational methodology to predict environments for a solid-core, nuclear thermal engine thrust chamber. The computational methodology is based on an unstructured-grid, pressure-based computational fluid dynamics formulation. A two-pronged approach is employed in this effort: A detailed thermo-fluid analysis on a multi-channel flow element for mid-section corrosion investigation; and a global modeling of the thrust chamber to understand the effect of heat transfer on thrust performance. Preliminary results on both aspects are presented.

Wang, Ten-See↗

NASA NTRS2006

Multiphysics Analysis of a Solid-Core Nuclear Thermal Engine Thrust Chamber

The objective of this effort is to develop an efficient and accurate thermo-fluid computational methodology to predict environments for a hypothetical solid-core, nuclear thermal engine thrust chamber. The computational methodology is based on an unstructured-grid, pressure-based computational fluid dynamics methodology. Formulations for heat transfer in solids and porous media were implemented and anchored. A two-pronged approach was employed in this effort: A detailed thermo-fluid analysis on a multi-channel flow element for mid-section corrosion investigation; and a global modeling of the thrust chamber to understand the effect of hydrogen dissociation and recombination on heat transfer and thrust performance. The formulations and preliminary results on both aspects are presented.

Wang, Ten-See↗

NASA NTRS2008

The CME Flare Arcade and the Width of the CME in the Outer Corona

Moore, Sterling, & Suess (2007, ApJ, 668, 1221) present evidence that (1) a CME is typically a magnetic bubble, a low-beta gplasmoid with legs h having roughly the 3D shape of a light bulb, and (2) in the outer corona the CME plasmoid is in lateral pressure equilibrium with the ambient magnetic field. They present three CMEs observed by SOHO/LASCO, each from a very different source located near the limb. One of these CMEs came from a compact ejective eruption from a small part of a sunspot active region, another came from a large quiet-region filament eruption, and the third CME, an extremely large and fast one, was produced in tandem with an X20 flare arcade that was centered on a huge delta sunspot. Each of these CMEs had more or less the classic lightbulb silhouette and attained a constant heliocentric angular width in the outer corona. This indicates that the CME plasmoid attained lateral magnetic pressure balance with the ambient radial magnetic field in the outer corona. This lateral pressure balance, together with the standard scenario for CME production by the eruption of a sheared-core magnetic arcade, yields the following simple estimate of the strength B(sub Flare) of the magnetic field in the flare arcade produced together with the CME: B(sub Flare) 1.4(theta CME/theta Flare)sup 2 G, where theta (sub CME) is the heliocentric angular width of the CME plasmoid in the outer corona and theta (sub Flare) is the heliocentric angular width of the full-grown flare arcade. Conversely, theta (sub CME) approximately equal to (R(sub Sun)sup -1(phi(sub Flare)/1.4)sup 1/2 radians, where Flare is the magnetic flux covered by the full-grown flare arcade. In addition to presenting the three CMEs of Moore, Sterling, & Suess (2007) and their agreement with this relation between CME and Flare, we present a further empirical test of this relation. For CMEs that erupt from active regions, the co-produced flare arcade seldom if ever covers the entire active region: if AR is the total magnetic flux of the active region, Flare . AR, and we predict that CME. (R(sub Sun))sup -1(theta AR/1.4)sup 1/2 radians. For a random sample of 31 CMEs that erupted from active regions within 30 of the limb, for each CME we have measured CME from LASCO/C3 and have measured AR from a SOHO/MDI magnetogram of the source active region when it was within 30 of disk center. We find that each CME obeys the above predicted inequality, none having width greater than half of the upper bound given by theta(sub AR). Thus, an active region's magnetic flux content, together with its location on the solar disk, largely determines whether the active region can possibly produce a CME that is wide enough to intercept the Earth.

Moore, Ron↗