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At least 217 records · Page 12

Flow Visualization by Elastic Light Scattering in the Boundary Layer of a Supersonic Flow

We demonstrate instantaneous flow visualization of the boundary layer region of a Mach 2.5 supersonic flow over a flat plate that is interacting with an impinging shock wave. Tests were performed in the Unitary Plan Wind Tunnel (UPWT) at NASA Langley Research Center. The technique is elastic light scattering using 10-nsec laser pulses at 532 nm. We emphasize that no seed material of any kind, including water (H2O), is purposely added to the flow. The scattered light comes from a residual impurity that normally exists in the flow medium after the air drying process. Thus, the technique described here differs from the traditional vapor-screen method, which is typically accomplished by the addition of extra H2O vapor to the airflow. The flow is visualized with a series of thin two-dimensional light sheets (oriented perpendicular to the streamwise direction) that are located at several positions downstream of the leading edge of the model. This geometry allows the direct observation of the unsteady flow structure in the spanwise dimension of the model and also allows the indirect observation of the boundary layer growth in the streamwise dimension.

Herring, G. C.↗

Active control of Boundary Layer Separation & Flow Distortion in Adverse Pressure Gradient Flows via Supersonic Microjets

Inlets to aircraft propulsion systems must supply flow to the compressor with minimal pressure loss, flow distortion or unsteadiness. Flow separation in internal flows such as inlets and ducts in aircraft propulsion systems and external flows such as over aircraft wings, is undesirable as it reduces the overall system performance. The aim of this research has been to understand the nature of separation and more importantly, to explore techniques to actively control this flow separation. In particular, the use of supersonic microjets as a means of controlling boundary layer separation was explored. The geometry used for the early part of this study was a simple diverging Stratford ramp, equipped with arrays of supersonic microjets. Initial results, based on the mean surface pressure distribution, surface flow visualization and Planar Laser Scattering (PLS) indicated a reverse flow region. We implemented supersonic microjets to control this separation and flow visualization results appeared to suggest that microjets have a favorable effect, at least to a certain extent. However, the details of the separated flow field were difficult to determine based on surface pressure distribution, surface flow patterns and PLS alone. It was also difficult to clearly determine the exact influence of the supersonic microjets on this flow. In the latter part of this study, the properties of this flow-field and the effect of supersonic microjets on its behavior were investigated in further detail using 2-component (planar) Particle Image Velocimetry (PIV). The results clearly show that the activation of microjets eliminated flow separation and resulted in a significant increase in the momentum of the fluid near the ramp surface. Also notable is the fact that the gain in momentum due to the elimination of flow separation is at least an order of magnitude larger (two orders of magnitude larger in most cases) than the momentum injected by the microjets and is accomplished with very little mass flow through the microjets.

Alvi, Farrukh S.↗

Asymmetrical boundary layer separation at the base of a two cylinder geometry

This paper reports on the experimental description of the three-dimensional horseshoe vortex system occurring at the base of two cylinder mounted side by side on an endwall. The spacing between the two cylinders is adjusted to generate a family of viscous flows. Flow visualization performed in a water tunnel provides a qualitative understanding of the flow over a range of flow variables. A detailed wind tunnel experiment provides a quantitative description of the flow at a single test condition. At Re(D) = 2.5 x 10 to the 5th the measurements show an asymmetrical primary vortex with a wide flat cross section. A small counterrotating vortex is found between the primary vortex and the cylinder leading edge.

Boyle, M. T.↗

HelioSwarm: The Swarm is the Observatory

HelioSwarm will transform our understanding of space plasma turbulence by being the first-of-its-kind simultaneous, multiscale observatory comprising multiple spacecraft. HelioSwarm was competitively selected under the Heliophysics Explorers Program 2019 Medium-Class Explorer (MIDEX) Announcement of Opportunity. The central powered-ESPA hub spacecraft is co-orbited by eight SmallSat Node spacecraft, together moving through a High Earth Orbit to obtain data in various solar wind regimes. The mission architecture is that of hub-and-spoke, with the larger hub serving as a communications relay between the nodes and DSN. Mission operations, management, and technical oversight are provided by NASA Ames Research Center; the spacecraft are provided by Northrop Grumman and BCT. The instrument suite includes foreign-contributed instruments and U.S. ones, all under the oversight of University of New Hampshire (which is also the Principal Investigator’s home institution and Science Operations Center). The mission timeline from launch through conclusion of the one-year science mission is provided along with a summarized concept of operations, with particular emphasis on placing the nodes in their proper relative orbit loops to form the geometry needed for science collection at apogee. A brief discussion of how a combination of legacy tools and custom-created swarm analysis tools are used to design the swarm and sort and visualize the collected science data and telemetry in context is provided. Finally, an exploration of the pathfinding nature of HelioSwarm and some implications for future large scientific swarms is offered.

Heliophysics↗

HelioSwarm: The Swarm is the Observatory

The HelioSwarm Mission will transform our understanding of space plasma turbulence by being the first-of-its-kind simultaneous, multiscale observatory comprising multiple spacecraft. HelioSwarm was competitively selected under the Heliophysics Explorers Program 2019 Medium-Class Explorer (MIDEX) Announcement of Opportunity. The central powered-ESPA Hub spacecraft is co-orbited by eight SmallSat Node spacecraft, together moving through a High Earth Orbit to obtain data in various solar wind regimes. The mission architecture is that of hub-and-spoke, with the larger hub serving as a communications relay between the Nodes and DSN. Mission operations, management, and technical oversight are provided by NASA Ames Research Center; the spacecraft are provided by Northrop Grumman and BCT. The instrument suite includes foreign-contributed instruments and U.S. ones, all under the oversight of University of New Hampshire (which is also the Principal Investigator’s home institution and Science Operations Center). The mission timeline from launch through conclusion of the one-year science mission is provided along with a summarized concept of operations, with particular emphasis on placing the Nodes in their proper relative orbit loops to form the geometry needed for science collection at apogee. A brief discussion of how a combination of legacy tools and custom-created swarm analysis tools are used to design the swarm and sort and visualize the collected science data and telemetry in context is provided. Finally, an exploration of the pathfinding nature of HelioSwarm and some implications for future large scientific swarms is offered.

Heliophysics↗

Computational fluid dynamics for propulsion technology: Geometric grid visualization in CFD-based propulsion technology research

The coordination is examined of necessary resources, facilities, and special personnel to provide technical integration activities in the area of computational fluid dynamics applied to propulsion technology. Involved is the coordination of CFD activities between government, industry, and universities. Current geometry modeling, grid generation, and graphical methods are established to use in the analysis of CFD design methodologies.

Ziebarth, John P.↗

Angiocardiography - Past and present

Angiocardiography is defined as an X-ray procedure which uses an intravascularly injected contrast material for visualization of the internal anatomy of the heart and great vessels. Past and present efforts in angiocardiography technology and methodology are reviewed, with special emphasis on qualitative and quantitative measurements of heart and vessel geometry. One of the more recent applications of angiographic image analysis has been for pattern recognition of margin motions over a cardiac cycle, termed contourography. Angiocardiography will continue to serve, as it has served in the past, as the principal standard of reference for calibration and/or comparison of newer methods for determining volume or dimensional change, depending on further technologic advances in X-ray equipment and means for displaying computer-processed information.

Sandler, H.↗

Far-infrared properties of dust in the reflection nebula NGC 7023

Thermal emission from dust in the reflection nebula NGC 7023 has been observed at wavelengths between 40 and 400 microns. The observed far-infrared emission comes from a region approximately 4 arcmin in diameter and shows spatial structure which correlates well with the distribution of reflected visible radiation. Temperature and optical depth maps indicate that the dust which emits the far-infrared radiation is heated by UV and visual radiation from the central star (HD 200775) and that the dust density increases steeply northwest of the star. The far-infrared data are not consistent with either the spherical or uniform slab geometries used in earlier analyses of optical observations. Comparisons of the far-infrared measurements with optical and UV measurements give a value between 2000 and 5000 for the ratio of extinction efficiency in the UV to that at 125 microns. This value is compared with the results of other observational studies and with theoretical grain models.

Whitcomb, S. E.↗

Propeller/wing interaction

The present experimental investigation of the steady-state and unsteady-state effects due to the interaction between a tractor propeller's wake and a wing employs, in the steady case, wind tunnel measurements at low subsonic speed; results are obtained which demonstrate wing performance response to variations in configuration geometry. Other steady-state results involve the propeller-hub lift and side-force due to the wing's influence on the propeller. The unsteady effects of interaction were studied through flow visualization of propeller-tip vortex distortion over a wing, again using a tractor-propeller configuration.

Witkowski, David P.↗

Angular relation of axes in perceptual space

The geometry of perceptual space needs to be known to model spatial orientation constancy or to create virtual environments. To examine one main aspect of this geometry, the angular relation between the three spatial axes was measured. Experiments were performed consisting of a perceptual task in which subjects were asked to set independently their apparent vertical and horizontal plane. The visual background provided no other stimuli to serve as optical direction cues. The task was performed in a number of different body tilt positions with pitches and rolls varied in steps of 30 degs. The results clearly show the distortion of orthogonality of the perceptual space for nonupright body positions. Large interindividual differences were found. Deviations from orthogonality up to 25 deg were detected in the pitch as well as in the roll direction. Implications of this nonorthogonality on further studies of spatial perception and on the construction of virtual environments for human interaction is also discussed.

Bucher, Urs↗

Flow and Noise from Supersonic Plug Nozzles

Nozzles with external plugs are candidates for propulsion of future supersonic aircraft. A model-scale experimental study is conducted exploring the flow and noise characteristics of various plug nozzles. For a given outer nozzle, the plug geometry is varied from conic with various half-angles (lengths) to plugs designed by the method of characteristics (MoC) as well as truncated and porous plugs. So far, noise characteristics and schlieren flow visualization data have been acquired. Limited numerical simulations have also been done addressing thrust performance. The simulations show that the MoC plugs out-perform the conic cases, especially around high Mach number cruise conditions. The experimental data, however, show that the MoC plugs are noisy relative to the conic cases at low Mach number landing and takeoff (LTO) conditions. The increased noise (with MoC at LTO) is accompanied by unsteady turbulent structures and increased jet spreading, as seen in schlieren pictures. At LTO, the longest conic plug is found to be the least noisy. Furthermore, a porous surface on the long conic plug effectively suppresses broadband shock associated noise (BBSN) at higher Mach numbers. Thus, a dilemma remains. MoC design gives best thrust performance at cruise but it is noisy at LTO. A long conic plug, on the other hand, is quieter at LTO but may have unacceptable thrust at cruise.

jets↗

Flow and noise from supersonic plug nozzles

Nozzles with external plugs are candidates for propulsion of future supersonic aircraft. A model-scale experimental study is conducted exploring the flow and noise characteristics of various plug nozzles. For a given outer nozzle, the plug geometry is varied from conic with various half-angles (lengths) to plugs designed by the method of characteristics (MoC) as well as truncated and porous plugs. So far, noise characteristics and schlieren flow visualization data have been acquired. Limited numerical simulations have also been done addressing thrust performance. The simulations show that the MoC plugs out-perform the conic cases, especially around high Mach number cruise conditions. The experimental data, however, show that the MoC plugs are noisy relative to the conic cases at low Mach number landing and takeoff (LTO) conditions. The increased noise (with MoC at LTO) is accompanied by unsteady turbulent structures and increased jet spreading, as seen in schlieren pictures. At LTO, the longest conic plug is found to be the least noisy. Furthermore, a porous surface on the long conic plug effectively suppresses broadband shock associated noise (BBSN) at higher Mach numbers. Thus, a dilemma remains. MoC design gives best thrust performance at cruise but it is noisy at LTO. A long conic plug, on the other hand, is quieter at LTO but may have unacceptable thrust at cruise.

jets↗

The broad-band spectra and variability of compact nonthermal sources

It is noted that in approximately a dozen sources, nearly simultaneous infrared and/or visual spectra are available, making it possible to examine the relationship between the infrared-visual and radio regimes. A simple transition to the steeper infrared spectra is seen as likely with a mean break wavelength of approximately 300 microns in the rest frame. These observations indicate a tapered source geometry, with the smallest structures roughly on the order of 10 to the 16th cm as estimated from the spectral break; this is consistent with scales estimated from optical variability time scales. Large amplitude variations on a six-month time interval are found to be fairly infrequent in most of the sources. A relatively model-independent way of categorizing flux variations as due to changes in source scale, or structure or the slope of the electron energy spectrum is suggested.

Jones, T. W.↗

Investigation of leading-edge flap performance on delta and double-delta wings at supersonic speeds

An investigation of the aerodynamic performance of leading-edge flaps on three clipped delta and three clipped double-delta wing planforms with aspect ratios of 1.75, 2.11, and 2.50 was conducted in the Langley Unitary Plan Wind Tunnel at Mach numbers of 1.60, 1.90, and 2.16. A primary set of fullspan leading-edge flaps with similar root and tip chords were investigated on each wing, and several alternate flap planforms were investigated on the aspect-ratio-1.75 wings. All leading-edge flap geometries were effective in reducing the drag at lifting conditions over the range of wing aspect ratios and Mach numbers tested. Application of a primary flap resulted in better flap performance with the double-delta planform than with the delta planform. The primary flap geometry generally yielded better performance than the alternate flap geometries tested. Trim drag due to flap-induced pitching moments was found to reduce the leading-edge flap performance more for the delta planform than for the double-delta planform. Flow-visualization techniques showed that leading-edge flap deflection reduces crossflow shock-induced separation effects. Finally, it was found that modified linear theory consistently predicts only the effects of leading-edge flap deflection as related to pitching moment and lift trends.

Covell, Peter F.↗

GENIE(++): A Multi-Block Structured Grid System

The computer code GENIE++ is a continuously evolving grid system containing a multitude of proven geometry/grid techniques. The generation process in GENIE++ is based on an earlier version. The process uses several techniques either separately or in combination to quickly and economically generate sculptured geometry descriptions and grids for arbitrary geometries. The computational mesh is formed by using an appropriate algebraic method. Grid clustering is accomplished with either exponential or hyperbolic tangent routines which allow the user to specify a desired point distribution. Grid smoothing can be accomplished by using an elliptic solver with proper forcing functions. B-spline and Non-Uniform Rational B-splines (NURBS) algorithms are used for surface definition and redistribution. The built in sculptured geometry definition with desired distribution of points, automatic Bezier curve/surface generation for interior boundaries/surfaces, and surface redistribution is based on NURBS. Weighted Lagrance/Hermite transfinite interpolation methods, interactive geometry/grid manipulation modules, and on-line graphical visualization of the generation process are salient features of this system which result in a significant time savings for a given geometry/grid application.

Williams, Tonya↗

Surface Generation and Cartesian Mesh Support

This document serves as the final report for the grant titled Surface Generation and Cartesian Mesh Support . This completed work was in algorithmic research into automatically generating surface triangulations from CAD geometries. NASA's OVERFLOW and Cart3D simulation packages use surface triangulations as an underlying geometry description and the ability to automatically generate these from CAD files (without translation) substantially reduces both the wall-clock time and expertise required to get geometry out of CAD and into mesh generation. This surface meshing was exercised greatly during the Shuttle investigation during the last year with success. The secondary efforts performed in this grant involve work on a visualization system cut-cell handling for Cartesian Meshes with embedded boundaries.

Haimes, Robert↗

Centrifuge in space fluid flow visualization experiment

A prototype flow visualization system is constructed to examine buoyancy driven flows during centrifugation in space. An axial density gradient is formed by imposing a thermal gradient between the two ends of the test cell. Numerical computations for this geometry showed that the Prandtl number plays a limited part in determining the flow.

Arnold, William A.↗

Free Flight and Self-Separation from the Flight Deck Perspective

The concept of "free flight", while still being developed, is intended to emphasize more, flexibility for operators in the National Airspace System (NAS) by providing more separation responsibility to pilots, New technologies, procedures, and concepts have been suggested by the aviation community to enable this task; however, much work needs to be accomplished to help define and evaluate the concept feasibility. The purpose of this simulation was to begin examining some of the communication and procedural issues associated with self-separation in the enroute environment. A simulation demonstration was conducted in the Boeing 747-400 simulator at NASA Ames Research Center. Commercial pilots (from a U.S. domestic carrier) current on the B747-400 aircraft were the participants. Ten flight crews (10 captains, 10 first officers) flew in the Denver enroute airspace environment. A new alerting logic designed to allow for airborne self-separation was created for this demonstration. This logic assumes automatic dependent surveillance broadcast (ADS-B) capability and represented aircraft up to 120 nautical miles on the display. The new flight deck display features were designed and incorporated on the existing navigational display in the simulator to allow for increased traffic and maneuvering information to the flight crew. New tools were also provided to allow the crews to assess conflicts and potential maneuvers before implementing them. Each of the flight crews flew eight different scenarios in the Denver enroute airspace. The scenarios included eight to ten other aircraft, and each scenario was created with the intent of having one of the other aircraft become an operational conflict for our simulator aircraft. Different types of conflict geometries were represented across the eight scenarios. Also, some scenarios allowed for more time to detect a potential clearance, while others allowed for less time for'detection. Additionally, the crews were asked to a ply the Visual Flight Rules (VFR) right of way rules when determining who should maneuver in a conflict situation; therefore, the scenarios were designed to test different applications of those recommendations, Data analyses include an evaluation of crew procedures and communication. The application of the VFR right-of-way rules are being explored. Timing variables are being examined to determine potential efficiency differences between scenarios and conflict types. Proximity of aircraft will be assessed as one indication of the operational safety. The intent of these evaluations is to help provide definitions and guidelines of negotiation procedures in a self-separation environment assuming automated data link technology (ADS-B). Also, definitions of likely flight crew maneuvers and application to current VFR right-of-way rules may be obtained, along with guidelines for negotiation procedures between flight crews.

Lozito, Sandra↗