Search NASA⌕ Search

SEARCH · Search NASA

Results for “vortex structures”

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.

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

At least 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

THE FORMATION AND ERUPTION OF A SMALL CIRCULAR FILAMENT DRIVEN BY ROTATING MAGNETIC STRUCTURES IN THE QUIET SUN

We present the first observation of the formation and eruption of a small circular filament driven by a rotating network magnetic field (RNF) in the quiet Sun. In the negative footpoint region of an inverse J-shaped dextral filament, the RNF was formed by the convergence to supergranular junctions of several magnetic flux patches of the same polarity, and it then rotated counterclockwise (CCW) for approximately 11 hr and showed up as a CCW rotating EUV cyclone, during which time the filament gradually evolved into a circular filament that surrounded the cyclone. When the calculated convergence and vortex flows appeared around the RNF during its formation and rotation phases, the injected magnetic helicity calculation also showed negative helicity accumulation during the RNF rotation that was consistent with the dextral chirality of the filament. Finally, the RNF rotation stopped and the cyclone disappeared, and, probably due to an emerging bipole and its forced cancellation with the RNF, the closure filament underwent an eruption along its axis in the (clockwise) direction opposite to the rotation directions of the RNF and cyclone. These observations suggest that the RNFs might play an important role in the formation of nearby small-scale circular filaments as they transport and inject magnetic energy and helicity, and the formation of the EUV cyclones may be a further manifestation of the helicity injected into the corona by the rotation of the RNFs in the photosphere. In addition, the new emerging bipole observed before the filament eruption might be responsible for destabilizing the system and triggering the magnetic reconnection which proves useful for the filament eruption.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Observation of magnetic adatom-induced Majorana vortex and its hybridization with field-induced Majorana vortex in an iron-based superconductor

Braiding Majorana zero modes is essential for fault-tolerant topological quantum computing. Iron-based superconductors with nontrivial band topology have recently emerged as a surprisingly promising platform for creating distinct Majorana zero modes in magnetic vortices in a single material and at relatively high temperatures. The magnetic field-induced Abrikosov vortex lattice makes it difficult to braid a set of Majorana zero modes or to study the coupling of a Majorana doublet due to overlapping wave functions. Here we report the observation of the proposed quantum anomalous vortex with integer quantized vortex core states and the Majorana zero mode induced by magnetic Fe adatoms deposited on the surface. We observe its hybridization with a nearby field-induced Majorana vortex in iron-based superconductor FeTe 0.55 Se 0.45 . We also observe vortex-free Yu-Shiba-Rusinov bound states at the Fe adatoms with a weaker coupling to the substrate, and discover a reversible transition between Yu-Shiba-Rusinov states and Majorana zero mode by manipulating the exchange coupling strength. The dual origin of the Majorana zero modes, from magnetic adatoms and external magnetic field, provides a new single-material platform for studying their interactions and braiding in superconductors bearing topological band structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1980

Influence of pressure driven secondary flows on the behavior of turbofan forced mixers

A finite difference procedure was developed to analyze the three dimensional subsonic turbulent flows in turbofan forced mixer nozzles. The method is based on a decomposition of the velocity field into primary and secondary flow components which are determined by solution of the equations governing primary momentum, secondary vorticity, thermal energy, and continuity. Experimentally, a strong secondary flow pattern was identified which is associated with the radial inflow and outflow characteristics of the core and fan streams and forms a very strong vortex system aligned with the radial interface between the core and fan regions. A procedure was developed to generate a similar generic secondary flow pattern in terms of two constants representing the average radial outflow or inflow in the core and fan streams as a percentage of the local streamwise velocity. This description of the initial secondary flow gave excellent agreement with experimental data. By identifying the nature of large scale secondary flow structure and associating it with characteristic mixer nozzle behavior, it is felt that the cause and effect relationship between lobe design and nozzle performance can be understood.

Anderson, B.↗
NASA NTRS1990

SAM II aerosol measurements during the 1989 AASE

The Stratospheric Aerosol Measurement II (SAM II) satellite experiment measures 14 daily 1.0-micron aerosol extinction profiles in the high northern latitudes. These SAM II data were used to spot the locations of polar stratospheric clouds (PSCs) and provide an overview of the vertical structure of the upper tropospheric and stratospheric aerosols during the 1989 Airborne Arctic Stratospheric Expedition (AASE). Although SAM II measured a higher than average number of PSCs in January 1989 as compared to the previous 10 years, the number of PSCs sighted during the entire 1989 winter season is only slightly above average. Also discussed is the vertical gradient in aerosol extinction which occurs as the SAM II measurement locations cross the polar vortex.

Osborn, M. T.↗
NASA NTRS1995

Evaluation of the impact of noise metrics on tiltrotor aircraft design

A subjective noise evaluation was conducted in which the test participants evaluated the annoyance of simulated sounds representative of future civil tiltrotor aircraft. The subjective responses were correlated with the noise metrics of A-weighted sound pressure level, overall sound pressure level, and perceived level. The results indicated that correlation between subjective response and A-weighted sound pressure level is considerably enhanced by combining it in a multiple regression with overall sound pressure level. As a single metric, perceived level correlated better than A-weighted sound pressure level due to greater emphasis on low frequency noise components. This latter finding was especially true for indoor noise where the mid and high frequency noise components are attenuated by typical building structure. Using the results of the subjective noise evaluation, the impact on tiltrotor aircraft design was also evaluated. While A-weighted sound pressure level can be reduced by reduction in tip speed, an increase in number of rotor blades is required to achieve significant reduction of low frequency noise as measured by overall sound pressure level. Additional research, however, is required to achieve comparable reductions in impulsive noise due to blade-vortex interaction, and also to achieve reduction in broad band noise.

Sternfeld, H.↗
NASA NTRS1993

Numerical simulation of laminar-turbulent transition in a spatially-developing flat plate wake

Laminar-turbulent transition of an incompressible flat-plate wake is investigated by direct numerical integration of the Navier-Stokes equations. For the numerical integration, a combination of finite-difference and spectral methods along with an ADI/Crank-Nicolson/Adams-Bashforth time integration scheme is employed. Subject to 2D forcing, the wake exhibited a rapidly-growing fundamental disturbance that quickly saturated. This saturation was due partly to the stabilizing effect of the mean flow distortion. Downstream of the saturation point, disturbance energy was concentrated in the fundamental disturbance, the second harmonic, and the mean flow distortion component. At large amplitude levels, a Karman vortex street formed. Variations in the 2D forcing level did not alter the qualitative behavior of the disturbances. Simulations of 3D breakdown indicates that the presence of large-amplitude, 2D disturbances tends to initially suppress small-amplitude 3D disturbance growth. Following this initial suppression, a resumption of 3D growth is observed that may have been due to a secondary instability mechanism. For high levels of 3D disturbance energy, lambda-shaped vortical structures formed between adjacent Karman vortices.

Dratler, D. I.↗
NASA NTRS2008

CFD Analyses and Jet-Noise Predictions of Chevron Nozzles with Vortex Stabilization

The wind computational fluid dynamics code was used to perform a series of analyses on a single-flow plug nozzle with chevrons. Air was injected from tubes tangent to the nozzle outer surface at three different points along the chevron at the nozzle exit: near the chevron notch, at the chevron mid-point, and near the chevron tip. Three injection pressures were used for each injection tube location--10, 30, and 50 psig-giving injection mass flow rates of 0.1, 0.2, and 0.3 percent of the nozzle mass flow. The results showed subtle changes in the jet plume s turbulence and vorticity structure in the region immediately downstream of the nozzle exit. Distinctive patterns in the plume structure emerged from each injection location, and these became more pronounced as the injection pressure was increased. However, no significant changes in centerline velocity decay or turbulent kinetic energy were observed in the jet plume as a result of flow injection. Furthermore, computational acoustics calculations performed with the JeNo code showed no real reduction in jet noise relative to the baseline chevron nozzle.

Dippold, Vance↗
NASA NTRS1979

Analytic studies on satellite detection of severe, two-cell tornadoes

From funnel-cloud-length interpretation, the severe tornado is characterized by peak swirl speed relative to the axis of rotation of about 90 m/s. Thermohydrodynamic achievement of the pressure deficit from ambient necessary to sustain such swirls requires that a dry, compressionally heated, non-rotating downdraft of initially tropopause-level air lie within an annulus of rapidly swirling, originally low-level air ascending on a near-moist-adiabatic locus of thermodynamic states. The two-cell structure furnishes an observable parameter possibly accessible to a passively instrumented, geosynchronous meteorological satellite with mesoscale resolution, for early detection of a severe tornado. Accordingly, the low-level turnaround region, in which the surface inflow layer separates to become a free ascending layer and for which inviscid modeling suffices, is examined quantitatively. Preliminary results indicate that swirl overshoot, i.e., swirl speeds in the turnaround region in excess of the maximum achieved in the potential vortex, is modest.

Carrier, G. F.↗
NASA NTRS1996

A Structured Grid Based Solution-Adaptive Technique for Complex Separated Flows

The objective of this work was to enhance the predictive capability of widely used computational fluid dynamic (CFD) codes through the use of solution adaptive gridding. Most problems of engineering interest involve multi-block grids and widely disparate length scales. Hence, it is desirable that the adaptive grid feature detection algorithm be developed to recognize flow structures of different type as well as differing intensity, and adequately address scaling and normalization across blocks. In order to study the accuracy and efficiency improvements due to the grid adaptation, it is necessary to quantify grid size and distribution requirements as well as computational times of non-adapted solutions. Flow fields about launch vehicles of practical interest often involve supersonic freestream conditions at angle of attack exhibiting large scale separate vortical flow, vortex-vortex and vortex-surface interactions, separated shear layers and multiple shocks of different intensity. In this work, a weight function and an associated mesh redistribution procedure is presented which detects and resolves these features without user intervention. Particular emphasis has been placed upon accurate resolution of expansion regions and boundary layers. Flow past a wedge at Mach=2.0 is used to illustrate the enhanced detection capabilities of this newly developed weight function.

Thornburg, Hugh↗
NASA NTRS2003

Flame-Generated Vorticity Production in Premixed Flame-Vortex Interactions

In this study, we use detailed time-dependent, multi-dimensional numerical simulations to investigate the relative importance of the processes leading to FGV in flame-vortex interactions in normal gravity and microgravity and to determine if the production of vorticity in flames in gravity is the same as that in zero gravity except for the contribution of the gravity term. The numerical simulations will be performed using the computational model developed at NRL, FLAME3D. FLAME3D is a parallel, multi-dimensional (either two- or three-dimensional) flame model based on FLIC2D, which has been used extensively to study the structure and stability of premixed hydrogen and methane flames.

Patnaik, G.↗
NASA NTRSDate not supplied

Flutter Analysis of the Transonic Truss-Braced Wing Aircraft Using Transonic Correction

This paper describes a flutter analysis method for the Transonic Truss-Braced Wing aircraft using a vortex lattice method coupled to an unsteady transonic correction method to account for unsteady aerodynamics in transonic flow. A steady-state vortex-lattice model of the Truss-Braced Wing aircraft is developed using vortex lattice code VSPAERO. A transonic and viscous flow correction method is implemented in the VSPAERO model to account for steady-state transonic and viscous flow effects using transonic small disturbance code TSFOIL coupled to an in-house integral boundary layer code. In addition, a wing-strut interference correction method is developed to account for the transonic interference aerodynamics in the strut juncture region using high-fidelity CFD code FUN3D. A structural dynamic finite-element model of the Truss-Braced Wing aircraft is developed using BEAM3D in-house finite-element code and is coupled to the VSPAERO. The BEAM3D model includes a geometric nonlinearity due to the tension in the strut which causes a deflection-dependent nonlinear stiffness. An unsteady transonic correction method is developed to better capture the unsteady aerodynamics in transonic flow. The unsteady transonic correction method makes use of the Theodorsen’s theory to account for the amplitude and phase shift of the unsteady lift coefficient in transonic flow. A preliminary flutter analysis of the Truss-Braced Wing aircraft is conduct to illustrate the unsteady transonic correction approach.

Nhan Nguyen↗
NASA NTRSDate not supplied

Optical and Near-Infrared Coronagraphy of the Quasar 3C 273

We present preliminary results of our observations of the ultraluminous quasar 3C 273 using the HST/STIS coronagraph and the Keck/NIRC2 vortex coronagraph to provide high-contrast imaging of the inner regions of the host galaxy in the optical and near-infrared. We use reference star differential imaging (RDI) techniques developed for high-contrast imaging of exoplanets and circumstellar disks to observe the morphology of features down to the inner few tenths of arcseconds (inner few 100s of pc) around the quasar point source. Broadband optical (50CORON) coronagraphy with STIS reveals the inner structure of jets and shocks, while Ks-band coronagraphy with NIRC2 suggests the presence of a candidate kpc-scale circumnuclear disk. If confirmed, this disk plays a potentially important role in driving the extreme feedback state of 3C 273 by up-regulating accretion, and its presence is consistent with recent observations of atomic and molecular gas in this system at larger spatial scales. We conclude by discussing potential applications of the observing techniques we applied to 3C 273 to other PSF-dominated systems at moderate redshifts to detect features such as circumnuclear disks and multiple nuclei with direct imaging.

Kevin Fogarty↗
NASA NTRS1985

An experimental study of airfoil-spoiler aerodynamics

The steady/unsteady flow field generated by a typical two dimensional airfoil with a statically deflected flap type spoiler was investigated. Subsonic wind tunnel tests were made over a range of parameters: spoiler deflection, angle of attack, and two Reynolds numbers; and comprehensive measurements of the mean and fluctuating surface pressures, velocities in the boundary layer, and velocities in the wake. Schlieren flow visualization of the near wake structure was performed. The mean lift, moment, and surface pressure characteristics are in agreement with previous investigations of spoiler aerodynamics. At large spoiler deflections, boundary layer character affects the static pressure distribution in the spoiler hingeline region; and, the wake mean velocity fields reveals a closed region of reversed flow aft of the spoiler. It is shown that the unsteady flow field characteristics are as follows: (1) the unsteady nature of the wake is characterized by vortex shedding; (2) the character of the vortex shedding changes with spoiler deflection; (3) the vortex shedding characteristics are in agreement with other bluff body investigations; and (4) the vortex shedding frequency component of the fluctuating surface pressure field is of appreciable magnitude at large spoiler deflections. The flow past an airfoil with deflected spoiler is a particular problem in bluff body aerodynamics is considered.

Mclachlan, B. G.↗
NASA NTRS1991

Unsteady vortex-dominated flow around wings with oscillating leading-edge flaps

Unsteady vortex-dominated flow around delta wings with oscillating leading-edge flaps represents an important classs of problems for supermaneuverability and flow control of advanced aircraft. The problem is solved using time accurate integration of the unsteady, compressible, thin-layer Navier-Stokes equations in conjunction with the unsteady, linearized, Navier-displacement equations. Starting with an initial configuration of the wing and its flaps, the Navier-Stokes equations are solved on an initial structured grid for the steady flow. The forced oscillation of the flaps is then applied, and the problem is solved accurately in time. The Navier-displacement equations are solved for the grid deformation and the Navier-Stokes equations are solved for the flowfield. Symmetric and anti-symmetric flaps oscillations are presented to study the effect of the flaps oscillation on the leading-edge vortical flow.

Kandil, Osama A.↗
NASA NTRS1998

Computational Investigation and Validation of Twin-Tail Buffet Response Including Dynamics and Control

Multidisciplinary tools for prediction of single rectangular-tail buffet are extended to single swept-back-tail buffet in transonic-speed flow, and multidisciplinary tools for prediction and control of twin-tail buffet are developed and presented. The configuration model consists of a sharp-edged delta wing with single or twin tails that are oriented normal to the wing surface. The tails are treated as cantilevered beams fixed at the root and allowed to oscillate in both bending and torsion. This complex multidisciplinary problem is solved sequentially using three sets of equations on a dynamic single or multi-block grid structure. The first set is the unsteady, compressible, Reynolds-averaged Navier-Stokes equations which are used for obtaining the flow field vector and the aerodynamic loads on the tails. The Navier-Stokes equations are solved accurately in time using the implicit, upwind, flux-difference splitting, finite volume scheme. The second set is the coupled bending and torsion aeroelastic equations of cantilevered beams which are used for obtaining the bending and torsion deflections of the tails. The aeroelastic equations'are solved accurately in time using, a fifth-order-accurate Runge-Kutta scheme. The third set is the grid-displacement equations and the rigid-body dynamics equations, which are used for updating the grid coordinates due to the tail deflections and rigid-body motions. The tail-buffet phenomenon is predicted for highly-swept, single vertical tail placed at the plane of geometric symmetry, and for highly-swept, vertical twin tails placed at three different spanwise separation distances. The investigation demonstrates the effects of structural inertial coupling and uncoupling of the bending and torsion modes of vibration, spanwise positions of the twin-tail, angle of attack, and pitching and rolling dynamic motions of the configuration model on the tail buffet loading and response. The fundamental issue of twin-tail buffet alleviation is addressed using two active flow-control methods. These methods are the tangential leading-edge blowing and the flow suction from the leading-edge vortex cores along their paths. Qualitative and quantitative comparisons with the available experimental data are presented. The comparisons indicate that the present multidisciplinary aeroelastic analysis tools are robust, accurate and efficient.

Kandil, Osama A.↗
NASA NTRS2016

Experimental Verification of Buffet Calculation Procedure Using Unsteady PSP

Typically a limited number of dynamic pressure sensors are employed to determine the unsteady aerodynamic forces on large, slender aerospace structures. The estimated forces are known to be very sensitive to the number of the dynamic pressure sensors and the details of the integration scheme. This report describes a robust calculation procedure, based on frequency-specific correlation lengths, that is found to produce good estimation of fluctuating forces from a few dynamic pressure sensors. The validation test was conducted on a flat panel, placed on the floor of a wind tunnel, and was subjected to vortex shedding from a rectangular bluff-body. The panel was coated with fast response Pressure Sensitive Paint (PSP), which allowed time-resolved measurements of unsteady pressure fluctuations on a dense grid of spatial points. The first part of the report describes the detail procedure used to analyze the high-speed, PSP camera images. The procedure includes steps to reduce contamination by electronic shot noise, correction for spatial non-uniformities, and lamp brightness variation, and finally conversion of fluctuating light intensity to fluctuating pressure. The latter involved applying calibration constants from a few dynamic pressure sensors placed at selective points on the plate. Excellent comparison in the spectra, coherence and phase, calculated via PSP and dynamic pressure sensors validated the PSP processing steps. The second part of the report describes the buffet validation process, for which the first step was to use pressure histories from all PSP points to determine the "true" force fluctuations. In the next step only a selected number of pixels were chosen as "virtual sensors" and a correlation-length based buffet calculation procedure was applied to determine "modeled" force fluctuations. By progressively decreasing the number of virtual sensors it was observed that the present calculation procedure was able to make a close estimate of the "true" unsteady forces only from four sensors. It is believed that the present work provides the first validation of the buffet calculation procedure which has been used for the development of many space vehicles.

Buffet↗
NASA NTRS1980

Vertical structure of the atmosphere of Venus from Pioneer Venus orbiter radio occultations

Between December 1978 and February 1979 the Pioneer Venus orbiter spacecraft returned some 140 S band and X band radio occultation measurements of the Venus atmosphere. Results from 13 measurements, covering diverse latitudes from near equatorial to polar, are presented in this paper in the form of vertical profiles of temperature. The temperature profiles show a pronounced inversion at the tropopause for latitudes higher than about 50 deg, with the deepest inversions occurring between the latitudes of 60 deg and 70 deg, the latitudes at which the cold collar cloud feature was observed by the Pioneer Venus Vortex instrument. A comparison of the temperature profiles derived from radio occultation measurements with the stratospheric infrared temperature soundings of the Vortex instrument and the in situ measurements of tropospheric temperature and pressure by the North, Sounder, and Day probes indicates excellent agreement.

Kliore, A. J.↗
NASA NTRS2015

Fundamental Study of a Single Point Lean Direct Injector. Part I: Effect of Air Swirler Angle and Injector Tip Location on Spray Characteristics

Lean direct injection (LDI) is a combustion concept to reduce oxides of nitrogen (NOx) for next generation aircraft gas turbine engines. These newer engines have cycles that increase fuel efficiency through increased operating pressures, which increase combustor inlet temperatures. NOx formation rates increase with higher temperatures; the LDI strategy avoids high temperature by staying fuel lean and away from stoichiometric burning. Thus, LDI relies on rapid and uniform fuel/air mixing. To understand this mixing process, a series of fundamental experiments are underway in the Combustion and Dynamics Facility at NASA Glenn Research Center. This first set of experiments examines cold flow (non-combusting) mixing using air and water. Using laser diagnostics, the effects of air swirler angle and injector tip location on the spray distribution, recirculation zone, and droplet size distribution are examined. Of the three swirler angles examined, 60 degrees is determined to have the most even spray distribution. The injector tip location primarily shifts the flow without changing the structure, unless the flow includes a recirculation zone. When a recirculation zone is present, minimum axial velocity decreases as the injector tip moves downstream towards the venturi exit; also the droplets become more uniform in size and angular distribution.

vortex↗