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NASA NTRS1973

Interaction of gases with lunar materials - Apollo 12, 14, and 16 samples

Surface properties of lunar fines samples from the Apollo 12, 14, and 16 missions have been investigated by studying the adsorption of nitrogen, argon, oxygen, carbon monoxide (all at 77 K), and water vapor (at 20 or 22 C) on the samples. Initially the samples were all nonporous and had a uniformly low specific surface area (0.3 to 0.6 sq m/g). Water interacts strongly with the surface of lunar fines, chemisorbing at low pressures followed by a massive adsorption at high pressures. Nitrogen adsorption measurements after the interaction with water showed that the surface properties had undergone a severe alteration as a result of the attack by water vapor. This alteration consisted of a marked increase in the specific surface area and the creation of a pore system. The results are interpreted on the basis of a penetration of water into the damage tracks.

Holmes, H. F.↗

NASA NTRS1986

The calculation of supersonic viscous flows using the parabolized Navier-Stokes equations

Solution of the parabolic Navier-Stokes (PNS) equations for supersonic flows is discussed, and compatibility of the PNS method with the triple-deck theory of Stewartson (1974) is demonstrated. Characteristic and stability analyses show that use of an appropriate filter on the pressure term in the x-momentum equation can suppress the departure solutions, giving the usual desired weak interaction solution. An Alternating Direction Explicit procedure, with minimal computer storage requirements compared to the full Navier-Stokes solvers, is proposed to calculate strongly interacting flows using a global iteration procedure for the PNS equations. The PNS equations are used to solve the hypersonic viscous interaction problem, and good agreement is found with experimental results.

Davis, R. T.↗

NASA NTRS1987

Numerical simulations of unsteady airfoil-vortex interactions

Numerical methods based on the thin layer Navier-Stokes, Euler and transonic small disturbance equations, all three of which use the perturbation form of an implicit numerical algorithm, are used to formulate the unsteady interactions of a moving vortex with a stationary airfoil. Results are presented for both transonic and subsonic flows, as well as for weak and strong interactions. In general, the results exhibit an overwhelming influence of the vortex on the flow field around the airfoil, especially when the convecting vortex is within one chord of the airfoil. It is noted that even the ostensibly weak interactions produced vortex/shock-induced boundary layer separation.

Srinivasan, G. R.↗

NASA NTRS1992

Stopping powers and cross sections due to two-photon processes in relativistic nucleus-nucleus collision

The radiation dose received from high energy galactic cosmic rays (GCR) is a limiting factor in the design of long duration space flights and the building of lunar and martian habitats. It is of vital importance to have an accurate understanding of the interactions of GCR in order to assess the radiation environment that the astronauts will be exposed to. Although previous studies have concentrated on the strong interaction process in GCR, there are also very large effects due to electromagnetic (EM) interactions. In this report we describe our first efforts at understanding these EM production processes due to two-photon collisions. More specifically, we shall consider particle production processes in relativistic heavy ion collisions (RHICs) through two-photon exchange.

Cheung, Wang K.↗

NASA NTRS1996

Lack of Evidence for Prenucleation Aggregate Formation in Lysozyme Crystal Growth Solutions

There have been numerous claims of large concentrations of prenucleation aggregates in supersaturated as well as undersaturated lysozyme solutions at high salt concentrations. The presence of these aggregates was derived from measurements of the light or neutron scattering intensity, ultracentrifugation and dialysis behavior, as well as over-simplified crystal growth kinetics considerations. In all these interpretations it has been assumed that lysozyme solutions are either ideal or that protein interactions are independent of salt concentration. Contrary to these presumptions, our static and dynamic light scattering experiments provide evidence that lysozyme forms highly non-ideal, strongly interacting solutions. At low salt concentrations, the scattering intensities fall well below the values expected for an ideal, monomeric solution at the same protein concentration, while diffusivities increase with increasing protein concentration. Upon increase in salt concentration, these trends are eventually reversed. This enhancement in scattering intensity and decrease in diffusivity was widely interpreted as sign of aggregate formation. Yet, a quantitative interpretation of the scattering behavior over the whole salt concentration range can only be given in terms of a transition from net repulsion to net attraction between lysozyme monomers. Increased salt screening of the electrostatic repulsion among the protein macro-ions, together with attractive protein interactions, such as van der Waals, hydrophobic and hydration forces, provide an unambiguous mechanism for the observed transition and a more physical interpretation of the various observations.

Muschol, Martin↗

NASA NTRS1988

Transient aerodynamic forces on a fighter model during simulated approach and landing with thrust reversers

Previous wind tunnel tests of fighter configurations have shown that thrust reverser jets can induce large, unsteady aerodynamic forces and moments during operation in ground proximity. This is a concern for STOL configurations using partial reversing to spoil the thrust while keeping the engine output near military (MIL) power during landing approach. A novel test technique to simulate approach and landing was developed under a cooperative Northrop/NASA/USAF program. The NASA LaRC Vortex Research Facility was used for the experiments in which a 7-percent F-18 model was moved horizontally at speeds of up to 100 feet per second over a ramp simulating an aircraft to ground rate of closure similar to a no-flare STOL approach and landing. This paper presents an analysis of data showing the effect of reverser jet orientation and jet dynamic pressure ratio on the transient forces for different angles of attack, and flap and horizontal tail deflection. It was found, for reverser jets acting parallel to the plane of symmetry, that the jets interacted strongly with the ground, starting approximately half a span above the ground board. Unsteady rolling moment transients, large enough to cause the probable upset of an aircraft, and strong normal force and pitching moment transients were measured. For jets directed 40 degrees outboard, the transients were similar to the jet-off case, implying only minor interaction.

Humphreys, A. P.↗

NASA NTRS1977

Interacting turbulent boundary layer over a wavy wall

The two dimensional supersonic flow of a thick turbulent boundary layer over a train of relatively small wave-like protuberances is considered. The flow conditions and the geometry are such that there exists a strong interaction between the viscous and inviscid flow. The problem cannot be solved without inclusion of interaction effects due to the occurrence of the separation singularity in classical boundary layer methods. The interacting boundary layer equations are solved numerically using a time-like relaxation method with turbulence effects represented by the inclusion of the eddy viscosity model. Results are presented for flow over a train of up to six waves for Mach numbers of 10 and 32 million/meter, and wall temperature rations (T sub w/T sub 0) of 0.4 and 0.8. Limited comparisons with independent experimental and analytical results are also given. Detailed results on the influence of small protuberances on surface heating by boundary layers are presented.

Polak, A.↗

NASA NTRS1985

Disturbance-wave interactions in flows with crossflow

The leading-edge region of swept wings is dominated by the crossflow instability, resulting in vortices that all rotate in the same sense. The effect of these possibly unsteady vortices on the behavior of other disturbances is examined, and a strong interaction between these and disturbances of half the dominating crossflow wavelength is predicted. According to theory, the interaction is of crossflow-crossflow type. The effect explains the anomalies found in the experimental observations of Saric and Yeates. Visually, they observe vortices at the wavelength predicted by linear theory; however, in their hot-wire measurements they find that the superharmonic dominates disturbance growth, eventually having three times the amplitude of the primary wave. In this case, the usual transition prediction methods would fail, clearly indicating the importance of studying interactions of this sort.

Reed, H. L.↗

NASA NTRS1977

Interacting turbulent boundary layer over a wavy wall

This paper is concerned with the two-dimensional supersonic flow of a thick turbulent boundary layer over a train of relatively small wave-like protuberances. The flow conditions and the geometry are such that there exists a strong interaction between the viscous and inviscid flow. The problem cannot be solved without inclusion of interaction effects due to the occurrence of the separation singularity in classical boundary layer methods. Here the interacting boundary layer equations are solved numerically using a time-like relaxation method with turbulence effects represented by the inclusion of the eddy viscosity model of Cebeci and Smith. Results are presented for flow over a train of up to six waves for Mach numbers of 2.5 and 3.5, Reynolds numbers of 10,000,000/m and 32,000,000/m, and wall temperature ratios of 0.4 and 0.8. Limited comparisons with independent experimental and analytical results are also given.

Polak, A.↗

NASA NTRS1983

A multi-grid method for the computation of viscid/inviscid interactions on airfoils

An improved version of the 'GRUMFOIL' code has been developed for the computation of airfoil flows. The method employs a conservative difference scheme for the potential equation, integral methods for the boundary layer, and viscous coupling conditions that fully account for the wake and strong interaction effects at trailing edges. The improved version uses Jameson's 'MAD' scheme to accelerate convergence of the inviscid solution, an improved 2nd order artificial viscosity and far field 'TARE' correction to reduce spatial truncation errors and Carter's semi-inverse method for the viscous solution. Results are presented which demonstrate a factor of ten reduction in computing cost.

Melnik, R. E.↗

NASA NTRS1985

Magnetotails of the terrestrial planets: A comparative study

Spacecraft observations have established that all of the terrestrial planets interact strongly with the solar wind and possess well developed magnetic tails. At Mercury, Earth, and possibly Mars the tail forms as a result of the solar wind dragging back field lines intrinsic to the planet. Venus differs dramatically from the other planets in that its magnetotail is composed of interplanetary field lines draped about the ionopause. Accordingly, the observations made at the terrestrial planets provide an opportunity to compare not only induced (Venus) magnetic tail properties with those of intrinsic field tails, but also the variation among intrinsic field tails ion the limits of no ionosphere (Mercury), weak intrinsic magnetic field (Mars), and strong magnetic field and ionosphere (Earth). A comparative investigation is made of terrestrial planet magnetotail structure and dynamics. The results are discussed in terms of the physical properties of these planets and their interactions with the solar wind.

Slavin, J. A.↗

NASA NTRS2015

Open-Source Conceptual Sizing Models for the Hyperloop Passenger Pod

Hyperloop is a new mode of transportation proposed as an alternative to California's high speed rail project, with the intended benefits of higher performance at lower overall costs. It consists of a passenger pod traveling through a tube under a light vacuum and suspended on air bearings. The pod travels up to transonic speeds resulting in a 35 minute travel time between the intended route from Los Angeles and San Francisco. Of the two variants outlined, the smaller system includes a 1.1 meter tall passenger capsule traveling through a 2.2 meter tube at 700 miles per hour. The passenger pod features water-based heat exchangers as well as an on-board compression system that reduces the aerodynamic drag as it moves through the tube. Although the original proposal looks very promising, it assumes that tube and pod dimensions are independently sizable without fully acknowledging the constraints of the compressor system on the pod geometry. This work focuses on the aerodynamic and thermodynamic interactions between the two largest systems; the tube and the pod. Using open-source toolsets, a new sizing method is developed based on one-dimensional thermodynamic relationships that accounts for the strong interactions between these sub-systems. These additional considerations require a tube nearly twice the size originally considered and limit the maximum pod travel speed to about 620 miles per hour. Although the results indicate that Hyperloop will need to be larger and slightly slower than originally intended, the estimated travel time only increases by approximately five minutes, so the overall performance is not dramatically affected. In addition, the proposed on-board heat exchanger is not an ideal solution to achieve reasonable equilibrium air temperatures within the tube. Removal of this subsystem represents a potential reduction in weight, energy requirements and complexity of the pod. In light of these finding, the core concept still remains a compelling possibility, although additional engineering and economic analyses are markedly necessary before a more complete design can be developed.

design analysis↗

NASA NTRSDate not supplied

Emergence of Complex Modes in Lightly Damped Structural Systems

In this short presentation format, we will provide a set of useful equations, relationships, and physical interpretations direct from the damped two-mode interaction problem. We will demonstrate that the results from the two-mode interaction problem are in direct agreement with observed test data. Practical methods for estimating the parameters driving the relations direct from modal test data are provided. We finalize with two examples demonstrating weak and strong interactions.

spaceflight hardware↗

NASA NTRS1984

Hybrid approach to steady transonic normal-shock compressible laminar boundary-layer interactions over airfoils

A simulation of steady transonic viscous-inviscid interactions through a combination of zonal solution methods (involving different equation sets and numerical regions for various flow regions) is used in an investigation of a fluid mechanics problem in which the pressure distribution is determined by the interaction between transonic inviscid flow and an inner laminar viscous layer. The results obtained are in good agreement with laminar experimental data. Both attached and separated boundary layer flows are considered for either weak or strong interactions.

Ram, R. B.↗

NASA NTRS1986

Some topics in the magnetohydrodynamics of accreting magnetic compact objects

Magnetic compact objects (neutron stars or white dwarfs) are currently thought to be present in many accreting systems that are releasing large amounts of energy. The magnetic field of the compact star may interact strongly with the accretion flow and play an essential role in the physics of these systems. Some magnetohydrodynamic (MHD) problems that are likely to be relevant in building up self-consistent models of the interaction between the accreting plasma and the star's magnetosphere are addressed in this series of lectures. The basic principles of MHD are first introduced and some important MHD mechanisms (Rayleigh-Taylor and Kelvin-Helmholtz instabilities; reconnection) are discussed, with particular reference to their role in allowing the infalling matter to penetrate the magnetosphere and mix with the field. The structure of a force-free magnetosphere and the possibility of quasistatic momentum and energy transfer between regions linked by field-aligned currents are then studied in some detail. Finally, the structure of axisymmetric accretion flows onto magnetic compact objects is considered.

Aly, J. J.↗

NASA NTRS1991

Optical and ultraviolet spectroscopy of three F + B binary stars

Optical and ultraviolet spectroscopy is presented for three F + B objects that are members of the first group of strongly interacting, F II + B systems. The data obtained confirm that HD 59771, HD 242257, and CoD -30 5135 are all binary star systems consisting of a luminous F-type component and a B star. Strong, variable H-alpha emission is seen in all the stars. It is found that the UV spectrum of HD 59771 resembles the spectrum of HD 207739. CoD -30 5135 has the most dramatic mid-UV spectrum seen among the scores of observed cool + hot star systems.

Bopp, Bernard W.↗

NASA NTRS1993

Supersonic shock wave/vortex interaction

Although shock wave/vortex interaction is a basic and important fluid dynamics problem, very little research has been conducted on this topic. Therefore, a detailed experimental study of the interaction between a supersonic streamwise turbulent vortex and a shock wave was carried out at the Penn State Gas Dynamics Laboratory. A vortex is produced by replaceable swirl vanes located upstream of the throat of various converging-diverging nozzles. The supersonic vortex is then injected into either a coflowing supersonic stream or ambient air. The structure of the isolated vortex is investigated in a supersonic wind tunnel using miniature, fast-response, five-hole and total temperature probes and in a free jet using laser Doppler velocimetry. The cases tested have unit Reynolds numbers in excess of 25 million per meter, axial Mach numbers ranging from 2.5 to 4.0, and peak tangential Mach numbers from 0 (i.e., a pure jet) to about 0.7. The results show that the typical supersonic wake-like vortex consists of a non-isentropic, rotational core, where the reduced circulation distribution is self similar, and an outer isentropic, irrotational region. The vortex core is also a region of significant turbulent fluctuations. Radial profiles of turbulent kinetic energy and axial-tangential Reynolds stress are presented. The interactions between the vortex and both oblique and normal shock waves are investigated using nonintrusive optical diagnostics (i.e. schlieren, planar laser scattering, and laser Doppler velocimetry). Of the various types, two Mach 2.5 overexpanded-nozzle Mach disc interactions are examined in detail. Below a certain vortex strength, a 'weak' interaction exists in which the normal shock is perturbed locally into an unsteady 'bubble' shock near the vortex axis, but vortex breakdown (i.e., a stagnation point) does not occur. For stronger vortices, a random unsteady 'strong' interaction results that causes vortex breakdown. The vortex core reforms downstream of the rear stagnation point, and the reduced circulation distribution once again becomes self-similar in this region. A-new model of this interaction is proposed. Finally, a curve defining the approximate limits of supersonic vortex breakdown is presented.

Settles, G. S.↗

NASA NTRS1993

A numerical investigation of supersonic strut/endwall interactions in annular flow with varying strut thickness

A full 3D Navier-Stokes numerical investigation has been conducted of the shock-wave/boundary-layer flow interactions caused by four diamond-shaped struts, of varying thickness, in an annular duct with Mach 3 core flow and turbulent boundary-layers on both walls. Secondary flows caused by weak-to-strong interactions are examined in the vicinity of a strut which is bounded by curved endwalls. The duct endwall boundary-layer separated for the strongest interaction. The struts studied had maximum thickness-to-chord ratios of 0.125, 0.188, 0.250, and 0.500. The duct gap height is 0.7 strut chords, the duct inner-to-outer wall radius ratio is 0.7, and the Reynolds number is 3 x 10 exp 5 based on the strut chord length which was held constant for all interactions considered. The effects of strut thickness on the secondary flows are discussed, including: trajectories for the leading and trailing edge horseshoe vortices, strut/endwall corner vortices, and boundary-layer separation. The line of coalescence discussed in the literature, previously ascribed to boundary-layer separation, is shown to be caused by the leading edge horseshoe vortex convecting along the shock front.

Williams, K. E.↗