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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Mechanical Testing of PMCs under Simulated Rapid Heat-Up Propulsion Environments: In-Plane Compressive Behavior - II

Carbon fiber thermoset polymer matrix composites (PMC) with high temperature polyimide based in-situ polymerized monomer reactant (PMR) resin has been used for some time in applications which can see temperatures up to 550 F. Currently, graphite fiber PMR based composites are used in several aircraft engine components including the outer bypass duct for the GE F-404, exit flaps for the P&W F-100-229, and the core cowl for the GE/Snecma CF6-80A3. Newer formulations, including PMR-II-50 are being investigated as potential weight reduction replacements of various metallic components in next generation high performance propulsion rocket engines that can see temperatures which exceed 550 F. Extensive FEM thermal modeling indicates that these components are exposed to rapid heat-up rates (up to -200 F/sec) and to a maximum temperature of around 600 F. Even though the predicted maximum part temperatures were within the capability of PW-II-50, the rapid heat-up causes significant through-thickness thermal gradients in the composite part and even more unstable states when combined with moisture. Designing composite parts for such extreme service environments will require accurate measurement of intrinsic and transient mechanical properties and the hygrothermal performance of these materials under more realistic use conditions. The mechanical properties of polymers degrade when exposed to elevated temperatures even in the absence of gaseous oxygen. Accurate mechanical characterization of the material is necessary in order to reduce system weight while providing sufficient factors of safety. Historically, the testing of PMCs at elevated temperatures has been plagued by the antagonism between two factors. First, moisture has been shown to profoundly affect the mechanical response of these materials at temperatures above their glass transition temperature while concurrently lowering the material's Tg. Moisture phenomena is due to one or a combination of three effects, i.e., plastization of polymeric material by water, the internal pressure generated by the volatilization of water at elevated temperatures, and hydrolytic chemical decomposition. However, moisture is lost from the material at increasing rates as temperature increases. Second, because PMCs are good thermal insulators, when they are externally heated at even mild rates large thermal gradients can develop within the material. At temperatures where a material property changes rapidly with temperature the presence of a large thermal gradient is unacceptable for intrinsic property characterization purposes. Therefore, long hold times are required to establish isothermal conditions. However, in the service environments high-heating-rates, high temperatures, high-loading rates are simultaneous present along with residual moisture. In order to capture the effects of moisture on the material, holding at- temperature until isothermal conditions are reached is unacceptable particularly in materials with small physical dimensions. Thus, the effects due to moisture on the composite's mechanical characteristics, ie., their so-called analog response, may be instructive. One approach employed in this program was rapid heat-up (approx. 200 F/sec.) and loading of both dry and wet in-plane compressive specimens to examine the effects of moisture on this resin dominated mechanical property of the material.

Stokes, Eric H.↗
NASA NTRS2011

Use of Heated Helium to Simulate Surface Pressure Fluctuations on the Launch Abort Vehicle During Abort Motor Firing

The solid-rocket plumes from the Abort motor of the Multi-Purpose Crew Vehicle (MPCV, also know as Orion) were simulated using hot, high pressure, Helium gas to determine the surface pressure fluctuations on the vehicle in the event of an abort. About 80 different abort situations over a wide Mach number range, (0.3< or =M< or =1.2) and vehicle attitudes (+/-15deg) were simulated inside the NASA Ames Unitary Plan, 11-Foot Transonic Wind Tunnel. For each abort case, typically two different Helium plume and wind tunnel conditions were used to bracket different flow matching critera. This unique, yet cost-effective test used a custom-built hot Helium delivery system, and a 6% scale model of a part of the MPCV, known as the Launch Abort Vehicle. The test confirmed the very high level of pressure fluctuations on the surface of the vehicle expected during an abort. In general, the fluctuations were found to be dominated by the very near-field hydrodynamic fluctuations present in the plume shear-layer. The plumes were found to grow in size for aborts occurring at higher flight Mach number and altitude conditions. This led to an increase in the extent of impingement on the vehicle surfaces; however, unlike some initial expectations, the general trend was a decrease in the level of pressure fluctuations with increasing impingement. In general, the highest levels of fluctuations were found when the outer edges of the plume shear layers grazed the vehicle surface. At non-zero vehicle attitudes the surface pressure distributions were found to become very asymmetric. The data from these wind-tunnel simulations were compared against data collected from the recent Pad Abort 1 flight test. In spite of various differences between the transient flight situation and the steady-state wind tunnel simulations, the hot-Helium data were found to replicate the PA1 data fairly reasonably. The data gathered from this one-of-a-kind wind-tunnel test fills a gap in the manned-space programs, and will be used to establish the acoustic environment for vibro-acoustic qualification testing of the MPCV.

Panda, Jayanta↗
NASA NTRS1977

Instrumentation, control and data management for the MIST (Modular Integrated Utility System) Facility

An appendix providing the technical data required for computerized control and/or monitoring of selected MIST subsystems is presented. Specific computerized functions to be performed are as follows: (1) Control of the MIST heating load simulator and monitoring of the diesel engine generators' cooling system; (2) Control of the MIST heating load simulator and MIST heating subsystem including the heating load simulator; and (3) Control of the MIST air conditioning load simulator subsystem and the MIST air conditioning subsystem, including cold thermal storage and condenser water flows.

Celino, V. A.↗
NASA NTRS2007

Simulation of Stagnation Region Heating in Hypersonic Flow on Tetrahedral Grids

Hypersonic flow simulations using the node based, unstructured grid code FUN3D are presented. Applications include simple (cylinder) and complex (towed ballute) configurations. Emphasis throughout is on computation of stagnation region heating in hypersonic flow on tetrahedral grids. Hypersonic flow over a cylinder provides a simple test problem for exposing any flaws in a simulation algorithm with regard to its ability to compute accurate heating on such grids. Such flaws predominantly derive from the quality of the captured shock. The importance of pure tetrahedral formulations are discussed. Algorithm adjustments for the baseline Roe / Symmetric, Total-Variation-Diminishing (STVD) formulation to deal with simulation accuracy are presented. Formulations of surface normal gradients to compute heating and diffusion to the surface as needed for a radiative equilibrium wall boundary condition and finite catalytic wall boundary in the node-based unstructured environment are developed. A satisfactory resolution of the heating problem on tetrahedral grids is not realized here; however, a definition of a test problem, and discussion of observed algorithm behaviors to date are presented in order to promote further research on this important problem.

Gnoffo, Peter A.↗
NASA NTRS2011

High Temperature Microwave Dielectric Properties of JSC-1AC Lunar Simulant

Microwave heating has many potential lunar applications including sintering regolith for lunar surface stabilization and heating regolith for various oxygen production reactors. The microwave properties of lunar simulants must be understood so this technology can be applied to lunar operations. Dielectric properties at microwave frequencies for a common lunar simulant, JSC-1AC, were measured up to 1100 C, which is approximately the melting point. The experimentally determined dielectric properties included real and imaginary permittivity (epsilon', epsilon"), loss tangent (tan delta), and half-power depth, the di stance at which a material absorbs 50% of incident microwave energy. Measurements at 2.45 GHz revealed tan delta of JSC-1A increases from 0.02 at 25 C to 0.31 at 110 C. The corresponding half-power depth decreases from a peak of 286 mm at 110 C, to 13 mm at 1100 C. These data indicate that JSC-1AC becomes more absorbing, and thus a better microwave heater as temperature increases. A half-power depth maximum at 100-200 C presents a barrier to direct microwave heating at low temperatures. Microwave heating experiments confirm the sluggish heating effect of weak absorption below 200 C, and increasingly strong absorption above 200 C, leading to rapid heating and melting of JSC-1AC.

Allan, Shawn M.↗
NASA NTRS1958

Free-Flight Investigation of Aerodynamic Heat Transfer to a Simulated Glide-Rocket Shape at Mach Numbers up to 10

Heat-transfer measurements were made on a simulated glide-rocket shape in free flight at Mach numbers up to 10 and free-stream Reynolds numbers of 2 x 10 based on distance along surface from apex and 3 x 10 based on nominal leading-edge diameter. The model simulated the bottom of a 75 deg delta wing at 8O deg angle of attack. The data indicated that for the test conditions a modified three-dimensional stagnation-point theory will predict to reasonable engineering accuracy the heating on a highly swept wing leading edge, the heating being reduced by sweep by the 3/2 power of the cosine of the sweep angle. The data also indicate that laminar heating rates over the windward surface of a highly swept flat glider wing at moderate angles of attack can be predicted with reasonable engineering accuracy by flat-plate theory using wedge local flow conditions and basing Reynolds numbers on lengths from the wing leading edge parallel to the surface center line.

FREE FLIGHT↗
NASA NTRS1989

Simulations and observations of heating of auroral ion beams

Two-dimensional three-velocity electrostatic particle simulations were used to determine the nonlinear evolution of the distributions of auroral ion beams and thereby to determine quantitatively signatures in the ion distributions produced by the ion-ion instability for a variety of plasma conditions in the auroral zone. The signatures determined from these simulations were compared with observations from DE 1, making it possible to characterize semiquantitatively the heating of the ionospheric ions, and to investigate the causes of variability seen in the observations of Reiff et al. (1988). A comparison of the simulation with observations showed features consistent with heating via the ion-ion instability including perpendicular heating in the supersonic regime and parallel heating in the subsonic regime, and a change in the heating between these regimes as the ratio of the H(+) beam speed to the local sound speed decreases.

Winglee, R. M.↗
NASA NTRS2018

The Laser Enhanced Arc-Jet Facility (LEAF-Lite): Simulating Convective and Radiative Heating with Arc-Jets and Multiple 50-KW CW Lasers

LEAF-Lite (Laser Enhanced Arc-Jet Facility) is a radiative laser heating facility that has been added to the 60 MW Interaction Heating Facility (IHF) convective plasma arc-jet located at NASA Ames Research Center. Together, these two systems can simulate both convective and radiative heating at heat fluxes reaching 551 W/cm2 by simultaneously combining a highest measured heat flux of 160 W/cm2 convective and 391 W/cm2 radiative heating on a 152-mm x 152-mm wedge model configuration. Adding radiant heating to an existing convective facility better simulates Earth atmospheric entry from hyperbolic lunarreturn speeds. The radiative heat is provided by multiple 50-kW CW IR lasers, which is nearly uniform across the illuminated surface with a total variation less than 6%, while the convective heat is provided by a high enthalpy plasma arc-jet. In a later phase, the facility will expand to test panel test articles of 432-mm x 432-mm and provide 100 W/cm2 of radiative heating in a plasma convective flow environment. The paper describes this new combined heating capability, its current testing conditions, and the unique application of the laser system with respect to the Orion test flight lunar orbits.

Cushman, Geoff↗
NASA NTRS1985

Heating of thermal helium in the equatorial magnetosphere - A simulation study

The heating of He(+) ions observed by the GEOS satellite at L of about seven starting from an initial anisotropic proton distribution is studied. A simulation of electromagnetic ion cyclotron waves in a plasma consisting of hot anisotropic protons, a dominant thermal hydrogen plasma, and a minority species of helium ions is utilized. It is shown that the thermal ions are heated to 100 times their initial temperature due to the growth of large-amplitude ion cyclotron waves. He(+) ions are heated mainly in the perpendicular direction, and they are heated more than cold H(+) ions. The He(+) ions are heated in a two-step process. First, they are set into oscillations by the growing wave until some of the ions reach a parallel velocity on the order of the resonant velocity; then, strong heating occurs.

Omura, Y.↗
NASA NTRS1992

Numerical simulations of inductive-heated float-zone growth

The present work provides an improved fluid flow and heat-transfer modeling of float-zone growth by introducing a RF heating model so that an ad hoc heating temperature profile is not necessary. Numerical simulations were carried out to study the high-temperature float-zone growth of titanium carbide single crystal. The numerical results showed that the thermocapillary convection occurring inside the molten zone tends to increase the convexity of the melt-crystal interface and decrease the maximum temperature of the molten zone, while the natural convection tends to reduce the stability of the molten zone by increasing its height. It was found that the increase of induced heating due to the increase of applied RF voltage is reduced by the decrease of zone diameter. Surface tension plays an important role in controlling the amount of induced heating. Finally, a comparison of the computed shape of the free surface with a digital image obtained during a growth run showed adequate agreement.

Chan, Y. T.↗