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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

An experimental and analytical investigation of a hypersonic cruise vehicle at Mach 6

Flow field properties over a hypersonic vehicle are measured and compared with results from the numerical analysis of inviscid supersonic flow theory. Good agreement between theory and experiment at zero angle of attack, and significant discrepancy at angles of attack greater than or equal to 5 deg are found. The experiments indicate that turbulent boundary layer without flow separation exists over the model surface at zero angle of attack. Vortex lift-off, flow separation, and shock boundary layer interaction occur over the leeward surface, and near the wing-fuselage junction with angles of attack greater than or equal to 5 deg. Improvements of the existing numerical method to compute hypersonic cruise vehicle flow field at large angle of attack are presented.

Wang, C. R.↗
NASA NTRS1980

The 17th JANNAF Combustion Meeting, Volume 1

The combustion of solid rocket propellants and combustion in ramjets is addressed. Subjects discussed include metal burning, steady-state combustion of composite propellants, velocity coupling and nonlinear instability, vortex shedding and flow effects on combustion instability, combustion instability in solid rocket motors, combustion diagnostics, subsonic and supersonic ramjet combustion, characterization of ramburner flowfields, and injection and combustion of ramjet fuels.

Eggleston, D. S.↗
NASA NTRS1981

System for sterilizing objects

A system for producing a stream of humidified sterilizing gas for sterilizing objects such as the water systems of space vehicles and the like includes a source of sterilant gas which is fed to a mixing chamber which has inlet and outlet ports. The level of the water only partially fills the mixing chamber so as to provide an empty space adjacent the top of the chamber. A heater is provided for heating the water in the chamber so as to produce a humidified atmosphere. The sterilant gas is fed through an arcuate shaped tubular member connected to the inlet port of the mixing chamber for producing a vortex type of flow of sterilant gas into the chamber for humidification. A tubular member extends from the mixing chamber for supplying the humidified sterilant gas to the object for being sterilized. Scrubbers are provided for removing the sterilant gas after use.

Bryan, C. J.↗
NASA NTRS1985

Quasi-Porous Plug With Vortex Chamber

Pressure-letdown valve combines quasi-porous-plug and vortex-chamber in one controllable unit. Valve useful in fossil-energy plants for reducing pressures in such erosive two-phase process streams as steam/water, coal slurries, or combustion gases with entrained particles. Quasi-Porous Plug consists of plenums separated by perforated plates. Number or size of perforations increases with each succeeding stage to compensate for expansion. In Vortex Chamber, control flow varies to control swirl and therefore difference between inlet and outlet pressures.

Walsh, J. V.↗
NASA NTRS1987

Summary of STOL ground vortex investigation

An experimental facility was developed in the 1.23 (48 inch) wind tunnel of the Applied Research Lab. at the Pennsylvania State Univ. to model the ground vortex. The purpose of the facility was to study the effect of various parameters on the location and characteristics of a ground vortex. An experimental investigation was conducted in the tunnel into the formation, stability and strength of the ground vortex for several flow parameters. The design of the facility, special instrumentation and results are summarized.

Billet, Michael L.↗
NASA NTRS1987

Numerical simulation of shock wave diffraction by TVD schemes

An upwind total variation diminishing (TVD) scheme and a predictor-corrector symmetric TVD scheme were used to numerically simulate the blast wave diffraction on a stationary object. The objective is to help design an optimum configuration so that lateral motion is minimized and at the same time vortex shedding and flow separation are reduced during a blast wave encounter. Results are presented for a generic configuration for both a coarse grid and a fine grid to illustrate the global and local diffraction flow fields. Numerical experiments for the shock wave reflection on a wedge are also included to validate the current approach. Numerical study indicated that these TVD schemes are more stable and produced higher shock resolution than classical shock capturing methods such as the explicit MacCormack scheme.

Young, Victor Y. C.↗
NASA NTRS1989

Transonic Unsteady Aerodynamics and Aeroelasticity 1987, part 2

This two part document contains copies of the text and figures for the papers presented at the symposium held at NASA Langley on 20 to 22 May, 1987. The papers are grouped in five subject areas. The areas covered by this part includes the following: Methods for vortex and viscous flows; Aeroelastic applications, and Experimental results and cascade flows.

Bland, Samuel R.↗
NASA NTRS1989

On the onset of three-dimensionality and time-dependence in Goertler vortices

The secondary instability of large-amplitude Goertler vortices in a growing boundary layer is discussed in the fully nonlinear regime. It is shown that the three-dimensional breakdown to a flow with wavy vortex boundaries, similar to that which occurs in the Taylor vortex problem takes place. However, the instability is confined to the thin shear layers which were shown by Hall & Lakin (1988) to trap the region of vortex activity. The disturbance eigenfunctions decay exponentially away from the center of these layers, so that the upper and lower shear layers can support independent modes of instability. The structure of the instability, in particular its location and speed of downstream propagation, is found to be entirely consistent with recent experimental results. Furthermore, it is shown that the upper and lower layers support wavy vortex instabilities with quite different frequencies. This result is again consistent with the available experimental observations.

Hall, Philip↗
NASA NTRS1989

A note concerning the onset of three dimensionality and time dependence in Goertler vortices

Recently Hall and Seddougui (1989) considered the secondary instability of large amplitude Goertler vortices in a growing boundary layer evolving into a three-dimensional flow with wavy vortex boundaries. They obtained a pair of coupled, linear ordinary differential equations for this instability which constituted an eigenproblem for the wavelength and frequency of this wavy mode. Investigations into the nonlinear version of this problem by Seddougui and Bassom have revealed several omissions in the numerical work of Hall and Seddougui. These issues are addressed in this note. In particular, it is found that many neutrally stable modes are possible. The properties of such modes are derived in a high wavenumber limit and it is shown that the combination of the results of Hall and Seddougui and the modifications made here lead to conclusions which are consistent with the available experimental observations.

Bassom, Andrew P.↗
NASA NTRS1990

Plasma heating, electric fields and plasma flow by electron beam ionospheric injection

The electric fields and the floating potentials of a Plasma Diagnostics Payload (PDP) located near a powerful electron beam injected from a large sounding rocket into the auroral zone ionosphere have been studied. As the PDP drifted away from the beam laterally, it surveyed a region of hot plasma extending nearly to 60 m radius. Large polarization electric fields transverse to B were imbedded in this hot plasma, which displayed large ELF wave variations and also an average pattern which has led to a model of the plasma flow about the negative line potential of the beam resembling a hydrodynamic vortex in a uniform flow field. Most of the present results are derived from the ECHO 6 sounding rocket mission.

Winckler, J. R.↗
NASA NTRS1989

Advances in fluid dynamics

Various papers on advances in fluid dynamics are presented. Individual topics addressed include: nonunique solutions of the Euler equations; numerical solution of the biharmonic equation using a spectral multigrid method; finite-volume shape and placement for efficiency, accuracy, and physics; NND schemes and their application to numerical simulation of complex plume flow problems; symbolic analysis and computational algorithm construction; and velocity and mass flux distribution measurements of spherical glass beads in air flow in a 90-deg vertical-to-horizontal bend. Also discussed are: hyperbolic solution adaptive mesh generation; progress and future directions in CFD; numerical simulation of shock focusing; microbubble formation and splitting in a turbulent boundary layer for turbulence reduction; numerical study of spherical Taylor-Couette flow, trajectories of vortex lines beneath a free surface or above a plane; and a mathematical model for response of the coronary circulation to high sustained gravitational force fields.

Ballhaus, W. F., Jr.↗
NASA NTRS1990

The onset of three-dimensionality and time-dependence in Goertler vortices - Neutrally stable wavy modes

Recently Hall and Seddougui (1989) considered the secondary instability of large-amplitude Goertler vortices in a growing boundary layer into a three-dimensional flow with wavy vortex boundaries. A pair of coupled, linear ordinary differential equations was obtained for this instability which constituted an eigenproblem for the wavelength and frequency of this wavy mode. In the course of investigating the nonlinear version of this problem (Seddougui and Bassom 1990), it has been found that the numerical work of Hall and Seddougui (1989) is incomplete; this deficiency is rectified here. In particular, it is found that many neutrally stable modes are possible; the properties of such modes are derived in a high-wavenumber limit, and it is shown that the combination of the results of Hall and Seddougui and the present modifications lead to conclusions which are consistent with the available experimental observations.

Bassom, Andrew P.↗
NASA NTRS1993

On the receptivity problem for 0(1) wavelength Goertler vortices

In this paper, we make an investigation of the receptivity of boundary layer flows to Gortler vortex modes. A study by Denier, Hall, and Seddougui (1991) of the generation of vortices by wall roughness elements concluded that such elements are extremely poor as mechanisms to stimulate short wavelength modes, but that analysis was in error. We re-examine this problem and demonstrate how the form of the wall roughness is crucial in determining the vortex stability characteristics downstream of the roughness. In particular, we investigate the cases of both isolated and distributed forcing functions and show that, in general, a distributed function is much more important in generating vortices than are either isolated roughness or freestream disturbances.

Bassom, Andrew P.↗
NASA NTRS1995

Tracking a turbulent spot in an immersive environment

We describe an interactive, immersive 3D system called Tracktur, which allows a viewer to track the development of a turbulent flow. Tracktur displays time-varying vortex structures extracted from a numerical flow simulation. The user navigates the space and probes the data within a windy 3D landscape. In order to sustain a constant frame rate, we enforce a fixed polygon budget on the geometry. We supplement the interactive system with interactive, hypertext documentation available on the World Wide Web. In actual use by a fluid dynamicist, the system has yielded new insights into the transition to turbulence in a laminar flow.

Banks, David C.↗
NASA NTRS1982

Hypersonic Laminar Viscous Flow Past Spinning Cones at Angle of Attack

Computational results are presented for hypersonic viscous flow past spinning sharp and blunt cones of angle of attack, obtained with a parabolic Navier-Stokes marching code. The code takes into account the asymmetries in the flowfield resulting from spinning motion and computes the asymmetric shock shape, cross-flow and streamwise shear, heat transfer, cross-flow separation, and vortex structure. The Magnus force and moments are also computed. Comparisons are made with other theoretical analyses based on boundary-layer and boundary-region equations, and an anomaly is discovered in the displacement thickness contribution to the Magnus force when compared with boundary-layer results.

Agarwal, Ramesh↗
NASA NTRS1999

Implicit and Multigrid Method for Ideal Multigrid Convergence: Direct Numerical Simulation of Separated Flow Around NACA 0012 Airfoil

Numerical investigation of flow separation over a NACA 0012 airfoil at large angles of attack has been carried out. The numerical calculation is performed by solving the full Navier-Stokes equations in generalized curvilinear coordinates. The second-order LU-SGS implicit scheme is applied for time integration. This scheme requires no tridiagonal inversion and is capable of being completely vectorized, provided the corresponding Jacobian matrices are properly selected. A fourth-order centered compact scheme is used for spatial derivatives. In order to reduce numerical oscillation, a sixth-order implicit filter is employed. Non-reflecting boundary conditions are imposed at the far-field and outlet boundaries to avoid possible non-physical wave reflection. Complex flow separation and vortex shedding phenomenon have been observed and discussed.

Liu, Chao-Qun↗
NASA NTRS2002

Macrostructure of Friction Stir Welds

This paper will discuss two of the well know large scale features of friction stir welds: the "onion rings" seen in transverse sections, and the striations on the surface of the work piece. It will be shown that the surface features (sometimes called "tool marks") are the result of irregularities on the rotating shoulder of the pin tool and disappear when the shoulder is polished. The "onion ring" structure seen in transverse cross sections is formed by parts of the "carousel", the zone of material adjacent to and rotating with the pin tool, that are shed off in each rotation. The relation between the carousel and the "ring vortex", a rotational flow extending both in and out of the carousel and resembling a smoke-ring with the hole centered on the pin tool, will be discussed.

Aloor, S.↗
NASA NTRS1998

Impact of Fuselage Cross Section on the Stability of a Generic Fighter

Many traditional data bases, which involved smooth-sided forebodies, are no longer relevant for designing advanced aircraft. The current work provides data on the impact of chined-shaped fuselage cross section on the stability of a generic fighter configuration. Two different chined-shaped fuselages were tested upright and inverted. It was found that a fuselage with a 30" included chine angle resulted in significantly higher values of fuselage with a 100" included chine angle. This difference was attributed to the more beneficial vortical interaction between the stronger forebody vortices coming off of the sharper chine edges and the wing vortices. The longitudinal stability of the configuration with the sharper chine angle was also better because, based on pressures and flow visualization, the vortex burst over the wing was delayed until significantly higher values of a. Unstable rolling moment derivatives were also delayed to higher values of a for the sharper chine angle cross section. Furthermore, it was found that directional stability of both of the upright configurations, which had larger lofts in cross section above the chine lines than below the chine lines. was better than for the inverted configurations.

Hall, Robert M.↗