SEARCH · Search NASA

Results for “Particle Drag”

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 217 records · Page 12

All sources NASA NTRS DOE OSTI

NASA NTRS1992

Particle simulation of rarefied aeropass maneuvers of the Magellan spacecraft

Rarefied and free molecular flowfields corresponding to proposed aeropass maneuvers through the atmosphere of Venus by the Magellan spacecraft are computed with a vectorized particle simulation method. The significance of rarefaction and reaction effects are assessed and surface heat flux, drag coefficients, and flowfield properties are computed. A simple surface heat transfer model is coupled directly to the simulation and assumes that each surface element is in radiative equilibrium with deep space. This allows direct computation of surface temperature distributions rather than requiring prescribed isothermal boundary conditions. Uncoupled dual-node heat transfer models, which account for heat capacity and thermal conductivity within each structural component, permit more accurate determination of surface temperatures. Such temperatures restrict the allowable altitudes and entry speeds of the aeropass maneuvers, and must therefore be estimated accurately. Simulations with an entry velocity of 8600 m/s at altitudes between 125 and 140 km reveal that allowable surface temperatures occur only at the highest altitudes where the flowfield is appropriately modeled as free-molecular. Excessive surface heat flux occurs at lower altitudes where molecular collisions are significant.

Haas, Brian L.↗

NASA NTRS1993

Diffusive redistribution of water vapor in the solar nebula revisited

Stevenson and Lunine presented a model for enhancing the abundance of solid material in the region of the solar nebula at the water condensation point. This was used to provide a means to produce a much more rapid formation of Jupiter than the standard solar nebula models. However, they underestimated the drag induced sun-ward radial drift of the planetesimals of interest. Reanalysis reveals that these particles would spread over the inner solar system and might influence the formation of the asteroids.

Sears, William D.↗

NASA NTRS2003

Numerical Simulation of One- and Two-Phase Flows in Propulsion Systems

Four subprojects were conducted using analytical methods, numerical simulation and experimental tests: (A) Shock wave mitigation by spike-shaped blunt bodies with application for the purpose of drag, lift and longitudinal momentum optimization. The main result in this subproject is: application of a single needle against a supersonic flow provides higher benefits for blunt body drag reduction and heat transfer to the body than the application of multiple needles. (B) Solid particles, liquid and air jet injection through the front of a blunt body against a supersonic flow. In this case, the research conducted and analysis of multiple previous investigations in this area have shown essential benefits and preferable application of solid particle injection. (C) Comparison of different methods of fuel injection into supersonic duct flows. Preliminary numerical simulations and theoretical analysis show promising results for Telescope-shaped inlet applications in SCRAMJET; and (D) Development of an acoustic source location method for different applications including propulsion systems.

Gilinsky, Mikhail↗

NASA NTRS1993

Formation of planetesimals in the solar nebula

The evolution of solid particles in the solar nebula (or other circumstellar disk) is described. Motions of bodies less than about 1 km in size were dominated by gas drag rather than gravity. An original population of microscopic grains had to produce greater than km-sized planetesimals before gravitational accretion of planets could begin. Planetesimals probably formed by coagulation of grain aggregates that collided due to differential settling, turbulence, and drag-induced orbital decay. Growth of such aggregates depended on sticking mechanisms and their mechanical properties, which are poorly understood. Their growth was aided by concentration of larger bodies toward the central plane of the disk. The nebula could remain optically thick during this process. It is unlikely that a particle layer formed by settling would undergo gravitational instability, as a small amount of turbulence would keep the particle layer from reaching the critical density. This conclusion is independent of the particle size, as even large bodies do not effectively decouple from the gas. Even in a laminar disk, shear in the particle layer would generate enough turbulence to keep it stirred up.

Weidenschilling, S. J.↗

NASA NTRS1994

Physics of interplanetary dust capture via impact into organic polymer foams

The physics of hypervelocity impacts into foams is of interest because of the possible application to interplanetary dust particle (IDP) capture by spacecraft. We present a model for the phenomena occurring in such impacts into low-density organic polymer foams. Particles smaller than foam cells behave as if the foam is a series of solid slabs and are fragmented and, at higher velocities, thermally altered. Particles much larger than the foam cells behave as if the foam were a continuum, allowing the use of a continuum mechanics model to describe the effects of drag and ablation. Fragmentation is expected to be a major process, especially for aggregates of small grains. Calculations based on these arguments accurately predict experimental data and, for hypothetical IDPs, indicate that recovery of organic materials will be low for encounter velocities greater than 5 km/s. For an organic particle 100 micrometers in diameter, approx. 35% of the original mass would be collected in an impact at 5 km/s, dropping to approx. 10% at 10 km/s and approx. 0% at 15 km/s. For the same velocities the recovery ratios for troilite (FeS) are approx. 95%, 65%, and 50%, and for olivine (Mg2SiO4) they are approx. 98%, 80%, and 65%, demonstrating that inorganic materials are much more easily collected. The density of the collector material has only a second-order effect, changing the recovered mass by less than 10% of the original mass.

Anderson, William W.↗

NASA NTRS1972

Particle trackability considerations for laser Doppler velocimetry

The technique for calculating single particle trackability in a fluid flow in terms of rms velocities is discussed. The general equation for the motion of a single particle as a response to a fluid flow driving force is presented, and a criterion for greatly simplifying the governing equation is developed. It is shown that in the case of large particle- to fluid-density ratio and low frequency fluid motion compared to the natural time constant of the particle response, the governing equation can be reduced to a simple balance of inertia force and linear viscous drag (i.e., Stokes drag).

Karchmer, A. M.↗

NASA NTRSDate not supplied

Sensitivity Study of Dust-Induced Surface Erosion during Martian Planetary Entry

Large, global dust storms that periodically form in the Martian atmosphere pose a threat to NASA missions due to a lack of understanding of how they will affect the heat loading and mass loss of the entry vehicle’s thermal protection system (TPS). Previous studies have laid out viable methodologies for estimating the amount of surface recession from a significant dust storm, but rely on underlying modeling assumptions that are difficult to validate. The current work utilizes the DUST library, which is a Lagrangian particle solver under development at NASA Ames Research Center. DUST includes variable-fidelity fluid-particle coupling and has been tested for a wide range of problem types. The DUST library is used in conjunction with the US3D Naiver-Stokes solver. Using these tools, a sensitivity study is performed to determine the influence of the underlying dust modeling (drag coefficient, Nusselt number, and size distribution) on the surface erosion through a hypersonic Martian entry trajectory. The surface erosion was found to be insensitive to the drag and heating models, but was affected significantly by the size distributions parameters. The total recession was comparable to the thermochemical ablation predicted by material response codes, but the lack of a particle erosion model for PICA limits the predictive capability of the current work.

Thermal Protection Systems↗

NASA NTRS2017

A Comparison of Damaging Meteoroid and Orbital Debris Fluxes in Earth Orbit

Low Earth orbit is populated with a substantial amount of orbital debris, and it is usually assumed that the flux from these objects contributes to most of the hypervelocity particle risk to spacecraft in this region. The meteoroid flux is known to be dominant at very low altitudes (<300 km), where atmospheric drag rapidly removes debris, and at very high altitudes beyond GEO (geostationary), where debris is practically non-existent. The vagueness of these boundaries has prompted this work, in which we compare the fluxes of meteoroids and orbital debris capable of penetrating a millimeter thick aluminum plate for circular orbits with altitudes ranging from the top of the atmosphere to 100,000 km. The outputs from the latest NASA debris and meteoroid models, ORDEM 3.0 and MEMR2, are combined with the modified Cour-Palais ballistic limit equation to make a realistic evaluation of the damage-capable particle fluxes, thereby establishing the relative contributions of hazardous debris and meteoroids in near Earth space.

Cooke, William↗

NASA NTRS1991

Dust particles from comets and asteroids collected at the Earth's orbit: Parent-daughter relationships

The relative contributions of comets and asteroids to the reservoir of dust in the interplanetary medium is not well known. There are direct observations of dust released from comets and there is evidence to associate the IRAS dust bands with possible collisions of Asteroids in the main belt. It is believed that one may combine lab analysis of the physics and chemistry of captured particles with orbital data in order to identify comet and asteroid parent bodies. It is possible to use the collected orbits of the dust to connect with its source in two ways. One is to consider the long time orbit evolution of the dust under Poynting-Robertson drag. The other is to look at the prompt orbit change of dust from comets onto trajectories that intersect the earth's orbit. In order to characterize the orbits of dust particles evolved over a long period of time, a study of its orbital evolution was undertaken. Various parameters associated with these dust orbits as they cross the Earth's orbit were considered in order to see if one may discriminate between particles evolved from comets and asteroids. The method was to calculate by a numerical procedure the orbits of dust particles after they left their parent bodies. It appears that as the particles pass the Earth's orbit, asteroidal grains and cometary grains can be differentiated on the basis of their measured orbital eccentricities even after much planetary perturbation. Broad parent daughter associations can be made on this basis from measurement of their trajectories intercepted in earth orbit.

Jackson, A. A.↗

NASA NTRS1972

Ice crystal terminal velocities

Terminal velocities of different ice crystal forms were calculated using the most recent ice crystal drag coefficients, aspect ratios, and densities. The equations derived were primarily for use in calculating precipitation rates by sampling particles with an aircraft in cirrus clouds, and determining particle size in cirrus clouds by Doppler radar. However, the equations are sufficiently general for determining particle terminal velocity at any altitude, and most any crystal type. Two sets of equations were derived. The general equations provide a good estimate of terminal velocities at any altitude. The specific equations are a set of equations for ice crystal terminal velocities at 1000 mb. The calculations are in good agreement with terminal velocity measurements. The results from the present study were also compared to prior calculations by others and seem to give more reasonable results, particularly at higher altitudes.

Heymsfield, A.↗

NASA NTRS1972

Ice crystal terminal velocities.

Terminal velocities of different ice crystal forms were calculated, using the most recent ice crystal drag coefficients, aspect ratios, and densities. The equations derived were primarily for use in calculating precipitation rates by sampling particles with an aircraft in cirrus clouds, and determining particle size in cirrus clouds by Doppler radar. However, the equations are sufficiently general for determining particle terminal velocity at any altitude, and almost any crystal type. Two sets of equations were derived. The 'general' equations provide a good estimate of terminal velocities at any altitude. The 'specific' equations are a set of equations for ice crystal terminal velocities at 1000 mb. The calculations are in good agreement with terminal velocity measurements. The results from the present study were also compared to prior calculations by others and seem to give more reasonable results, particularly at higher altitudes.

Heymsfield, A.↗

NASA NTRS2017

A Comparison of Damaging Meteoroid and Orbital Debris Fluxes in Earth Orbit

Low Earth orbit is populated with a substantial amount of orbital debris, and it is usually assumed that the flux from these objects contributes to most of the hypervelocity particle risk to spacecraft in this region. The meteoroid flux is known to be dominant at very low altitudes (less than 300 km), where atmospheric drag rapidly removes debris, and at very high altitudes (beyond geostationary), where debris is practically non-existent. The vagueness of these boundaries and repeated questions from spacecraft projects have prompted this work, in which we compare the fluxes of meteoroids and orbital debris capable of producing a millimeter-deep crater in aluminum for circular orbits with altitudes ranging from the top of the atmosphere to 100,000 km. The outputs from the latest NASA debris and meteoroid models, ORDEM 3.0 and MEMR2, are combined with the modified Cour-Palais ballistic limit equation to make a realistic evaluation of the damage-capable particle fluxes, thereby establishing the relative contributions of hazardous debris and meteoroids throughout near-Earth space.

Cooke, William↗

NASA NTRS1983

Cloud particle effects on laminar flow and instrumentation for their measurement aboard a NASA LFC aircraft

Fuel costs account now for approximately 60 percent of the direct operating costs of airlines and future commercial transport will utilize advanced technologies for saving fuel on the basis of drag reduction. Laminar flow control (LFC) represents such an advanced technology. A new laminar flow wing on a reconfigured WB-66 aircraft was tested in the X-21 flight program. The tests confirmed that extensive laminar flow could be achieved at subsonic transport cruise conditions. Factors affecting adversely the maintenance of laminar flow were found to be related to ice particles encountered during the penetration of cirrus clouds or haze. The present investigation is concerned with the effect of ice particles on LFC, taking into account the results obtained in the Leading Edge Flight Test (LEFT) being conducted by NASA. Attention is given to ice particle measurements in the LEFT program.

Davis, R. E.↗

NASA NTRS1992

Hypervelocity impact facility for simulating materials exposure to impact by space debris

The Space Power Institute at Auburn University has constructed an electromagnetically driven particle accelerator for simulating the effects of space debris on the materials for use in advanced spacecraft. The facility consists of a capacitively driven accelerator section, a drift tube and a specimen impact chamber. The drift tube is sufficiently long that all electrical activity has ceased prior to impact in the specimen chamber. The impact chamber is large enough to allow a wide range of specimen geometries, ranging from small coupons to active portions of advanced spacecraft. The electric drive for the accelerator consists of a 67 kJ, 50 k capacitor bank arranged in a low inductance configuration. The bank is discharged through an aluminum armature/plastic ablator plate/projectile load in roughly 1.2 microsec. The evaporation of the ablaitor plate produces an expanding gas slug, mostly H2, traveling at a velocity of some 60 km/sec. Because of the pressure and local density, the expanding gas cloud accelerates projectiles due to plasma drag. To date, we have utilized projectiles consisting of 100 micron SiC, 100 and 400 micron Al2O3, 100 and 145 micron olivines. Since many particles are accelerated in a given experiment, there is a range of velocities for each shot as well as some particle breakup. Advanced diagnostics techniques allow determination of impact coordinates, velocity, and approximate size for as many as 50 individual impacts in a given experiment. We routinely measure velocities in the range 1-15 km/sec. We have used this facility to study a variety of impact generated phenomena on coated surfaces, both paint and plastic, thermal blanket material, solar cell arrays, and optical materials such as glass and quartz lenses. The operating characteristics of the gun, the advanced diagnostic scheme, and the results of studies of crater morphology are described in detail. Projectile residue analysis, as a function of impact velocity for the materials listed above, is also discussed. Wherever possible, these results are compared to those obtained by LDEF investigators and future experiments suggested which could help to explain unique features associated with LDEF impacts.

Rose, M. Frank↗

NASA NTRS1984

A method for measuring skin friction drag on a flat plate in contaminated gas flows

A technique for measuring friction drag in turbulent gas and gas/particle flows over flat plates is presented, and preliminary results are reported. A 0.25-in.-thick 72 x 6-in. Al plate is suspended by six horizontal support air bearings and four vertical alignment air bearings between fixed dummy plates and leading-edge and trailing-edge fairings in the 32-in.-high 48-in.-wide 11-ft-long test section of a closed-circuit atmospheric wind tunnel operating at 50-150 ft/sec. Particles of Fe and Al oxides of diameter 20-150 microns and density up to 0.3 lb particles per lb air are injected via a 6 x 0.167-in. nozzle; turbulence is induced by a roughened section of the leading-edge fairing; and friction drag is measured using a load-cell pressure transducer. Sample results are shown in a graph, demonstrating good agreement with theoretical drag calculations.

Oetting, R. B.↗

NASA NTRS1980

Volcanic explosion clouds - Density, temperature, and particle content estimates from cloud motion

Photographic records of 10 vulcanian eruption clouds produced during the 1978 eruption of Fuego Volcano in Guatemala have been analyzed to determine cloud velocity and acceleration at successive stages of expansion. Cloud motion is controlled by air drag (dominant during early, high-speed motion) and buoyancy (dominant during late motion when the cloud is convecting slowly). Cloud densities in the range 0.6 to 1.2 times that of the surrounding atmosphere were obtained by fitting equations of motion for two common cloud shapes (spheres and vertical cylinders) to the observed motions. Analysis of the heat budget of a cloud permits an estimate of cloud temperature and particle weight fraction to be made from the density. Model results suggest that clouds generally reached temperatures within 10 K of that of the surrounding air within 10 seconds of formation and that dense particle weight fractions were less than 2% by this time. The maximum sizes of dense particles supported by motion in the convecting clouds range from 140 to 1700 microns.

Wilson, L.↗

NASA NTRS1984

Solar array: Plasma interactions

Interactions between space systems and their orbital particle and field environments have significant impact on the system's operation and life. Interactions such as radiation damage and aerodynamic drag are considered in designing space systems. There are, however, a number of orbital environmental interactions which become important design considerations only for large or high power systems. Their impact is assessed to ensure successful design. Interactions between higher voltage solar arrays and the space plasma which are of critical concern in designing large orbital photovoltaic power systems are outlined.

Purvis, C. K.↗

NASA NTRS1991

Collision probabilities in the presence of nebular gas drag

We are developing a model to determine what fraction of the planetesimals would have hit a protoplanet on their sunward journey as opposed to having a close approach and passing into an inferior orbit. The model involves direct numerical integration of restricted-three-body orbits using a predictor-corrector integrator. A simple gas drag law with a v(exp 2) dependence was also included in the equations of motion. Runs of 100 to 500 particles were already performed, while some future runs may require several times this number in order to get good impact statistics. All planetesimals start in superior orbits with semi-major axes 5 to 10 R(sub H) from the protoplanets, where R(sub H) is the protoplanet's Hill Sphere radius. The orbit is followed until the planetesimal passed into an inferior orbit at least 10 R(sub H) from the protoplanet. This process typically requires 10(exp 4) to 10(exp 5) orbits.

Kary, David M.↗