SEARCH · Search NASA

Results for “SURFACE GEOMETRY”

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 127 records · Page 7

All sources NASA NTRS DOE OSTI

NASA NTRS1999

Data Processing for the Near Earth Asteroid Rendezvous (NEAR), X-Ray and Gamma-Ray Spectrometer (XRS) Ground System

An X-ray and Gamma-ray spectrometer (XGRS) is onboard the Near Earth Asteroid Rendezvous (NEAR) spacecraft to determine the elemental composition of the surface of the asteroid 433Eros. The Eros asteroid is highly non-spherical in physical shape and the development of data management and analysis methodologies are in several areas a divergence from traditional remotely sensed geographical information systems techniques. Field of view and asteroid surface geometry must be derived virtually and then combined with real measurements of solar, spectral and instrument calibration information to derive meaningful scientific results. Spatial resolution of planned geochemical maps will be improved from the initial conditions of low statistical significance per integration by repeated surface flyovers and regional spectral accumulation. This paper describes the results of a collaborative effort of design and development of the NEAR XGRS instrument ground system undertaken by participants at the Goddard Space Flight Center, University of Arizona, Cornell University, Applied Physics Laboratory, and Max Plank institute.

McClanahan, Timothy P.↗

NASA NTRS1985

Mechanics of a gaseous film barrier to lubricant wetting of elastohydrodynamically lubricated conjunctions

Two analytical models, one based on simple hydrodynamic lubrication and the other on soft elastohydrodynamic lubrication, are presented and compared to delineate the dominant physical parameters that govern the mechanics of a gaseous film between a small droplet of lubricant and the outer race of a ball bearing. Both models are based on the balance of gravity forces, air drag forces, and air film lubrication forces and incorporate a drag coefficient C sub D and a lubrication coefficient C sub L to be determined from experiment. The soft elastohydrodynamic lubrication (EHL) model considers the effects of droplet deformation and solid-surface geometry; the simpler hydrodynamic lubrication (HL) model assumes that the droplet remains essentially spherical. The droplet's angular position depended primarily on the ratio of gas inertia to droplet gravity forces and on the gas Reynolds number and weakly on the ratio of droplet gravity forces to surface tension forces (Bond number) and geometric ratios for the soft EHL. An experimental configuration in which an oil droplet is supported by an air film on the rotating outer race of a ball bearing within a pressure-controlled chamber produced measurements of droplet angular position as a function of outer-race velocity droplet size and type, and chamber pressure.

Prahl, J. M.↗

DOE OSTI2021

A linked-scale coupled model of mass erosion and redistribution in plasma-exposed micro-foam surfaces

Surface evolution due to exposure to harsh environments is of importance in many scientific and technological applications. In plasma-exposed materials, the surface receives charged particles from the plasma, leading to a series of processes that drive the system far from equilibrium and may lead to the severe deterioration of the surface properties. Although surface morphological changes are driven by atomic collisions taking place over picoseconds and nanometers, these processes result in mass loss and redistribution of matter over much larger length and time scales. This necessitates a multi-scale approach capable of capturing the range of processes linking primary atomic collision events with engineering-level surface geometry changes. In this paper, we develop a computational model to simulate the morphological evolution and effective erosion rate of micro-architected tungsten foams during low-energy plasma ion bombardment. Furthermore, the model acts on several length scales, with the energy and angular dependence of the sputtering yield of flat tungsten surfaces determined using the SRIM code based on the binary collision approximation. This information is introduced into a low-fluence, short-term Monte Carlo raytracing model, and further into a high-fluence, long-term particle transport model. In the latter, material particles representing billions of atoms are described in a digitized 3-D representation of the foam structure from X-ray tomography data, and are sputtered off and redeposited using the atomistic information. We show that the redeposition of sputtered atoms leads to partial self-healing in the bottom layers with a sharp reduction in the sputtering coefficient of low density foams, roughly 25% of the solid W value. This is in qualitative agreement with recent experiments on low porosity W structures. At high fluence, the foam structure degrades considerably as there are fewer ligaments available to recapture sputtered atoms and, consequently, the sputtering rate increases again.

36 MATERIALS SCIENCE↗

NASA NTRS2013

Background Oriented Schlieren Implementation in a Jet-Surface Interaction Test

Many current and future aircraft designs rely on the wing or other aircraft surfaces to shield the engine noise from observers on the ground. However the available data regarding how a planar surface interacts with a jet to shield and/or enhance the jet noise are currently limited. Therefore, the Jet-Surface Interaction Tests supported by NASA's Fundamental Aeronautics Program's Fixed Wing Project were undertaken to supply experimental data covering a wide range of surface geometries and positions interacting with high-speed jet flows in order to support the development of noise prediction methods. Phase 1 of the Test was conducted in the Aero-Acoustic Propulsion Laboratory at NASA Glenn Research Center and consisted of validating noise prediction schemes for a round nozzle interacting with a planar surface. Phased array data and far-field acoustic data were collected for both the shielded and reflected sides of the surface. Phase 1 results showed that the broadband shock noise was greatly reduced by the surface when the jet was operated at the over-expanded condition, however, it was unclear whether this reduction was due a change in the shock cell structure by the surface. In the present study, Background Oriented Schlieren is implemented in Phase 2 of the Jet-Surface Interaction Tests to investigate whether the planar surface interacts with the high-speed jet ow to change the shock cell structure. Background Oriented Schlieren data are acquired for under-expanded, ideally-expanded, and over-expanded ow regimes for multiple axial and radial positions of the surface at three different plate lengths. These data are analyzed with far-field noise measurements to relate the shock cell structure to the broadband shock noise produced by a jet near a surface.

Clem, Michelle M.↗

NASA NTRS2005

Multi-Spacecraft Observations of Interplanetary Shocks

Multi-spacecraft solar wind observations reveal that many interplanetary shocks deviate significantly from exact planarity on scale length of the magnetospheric cross section. A number of different IP shock observations with four spacecraft will be presented to demonstrate quantitatively the angular deviations between shock normals obtained from 4-spacecraft methods, using only the time and position information of shock observations but assuming a exactly planar geometry, and those obtained from a non-linear least squares fitting of the "Rankine-Hugoniot" conservation equations at each spacecraft. Moreover, the curvature of the shock fronts is strongly related to its driver, typically magnetic clouds. It will be demonstrated that small and slower moving magnetic clouds drive shocks with significantly more irregular surface geometries.

Szabo, Adam↗

NASA NTRS2019

Extrusion of Complex Surface Meshes Utilizing Face Offsetting and Mean Curvature Smoothing

Grids for three-dimensional Computational Fluid Dynamics problems frequently require a prismatic layer of cells, typically extruded in the off-body direction from a two-dimensional surface mesh to properly resolve boundary layers. When the surface geometry is complex, the extrusion process can fail, resulting in the physical boundary layer being thicker than the prismatic layer, leading to under-resolved boundary layers. To address the shortcomings of existing grid generation tools, a new tool has been developed as part of the Mesh Tools suite, that is capable of extruding complex surface meshes. The new tool uses a face offsetting method to preserve surface curvature and a mean curvature smoothing algorithm to prevent the cells from self-intersecting in concave regions. Testing of the new tool found that not only were complex surface meshes able to be extruded to the desired thickness, but extrusion of simple surface meshes was also improved, due to the face offsetting method.

mesh extrusion↗

NASA NTRS2019

Surface Flow Visualization of the High-Lift Common Research Model

A 10% scale version of the High-Lift Common Research Model (CRM-HL) was tested in the NASA Langley 14- by 22-Foot Subsonic Tunnel (14x22) in support of the NASA Advanced Air Transport Technology (AATT) Project. The CRM-HL experiment included various configurations such as conventional and simple-hinged flaps, with and without engine nacelle/pylon, with and without nacelle chine, different Active Flow Control (AFC) methods (sweeping jets, alternating pulsed jets, and preconditioned boundary layer blowing), and their various parameters. This particular study is focused on the surface flow visualization of the conventional CRM-HL model at landing configuration. The conventional CRM-HL model with the single-slotted Fowler flap system serves as a baseline for the AFC-enabled simplified high-lift configuration as well as a high-lift technology development platform due to its publicly open geometry. Surface flow visualizations were performed using fluorescent minitufts, which were found to be nonintrusive to the aerodynamic performance. Tuft flow visualizations are supplemented with the relevant pressure and force measurements in order to understand the flow characteristics developed on the conventional CRM- HL model. In addition, three dimensional, unsteady, compressible Computational Fluid Dynamic (CFD) simulations were performed for selective cases. The surface streamlines and transverse velocity fluctuations obtained by the CFD simulations are qualitatively compared to the tuft direction and tuft unsteadiness, respectively. Force measurements of the CRM-HL model show performance degradation at higher angles of attack. Surface flow visualizations revealed the performance loss due to the nacelle/pylon wake that grows with angle of attack and eventually promotes flow separation over the inboard wing. This performance loss was successfully recovered by placing a chine on the engine nacelle.

Koklu, Mehti↗

NASA NTRS1994

Computational Investigation of an F-18 Aircraft in the High-Alpha Regime

One of the goals of NASA's High Alpha Technology Program is to provide flight-validated design methods for the high-angle-of-attack regime. This is an integrated effort utilizing computational simulations, wind tunnel experiments, and flight tests using the F-18 High Alpha Research Vehicle (HARV). The dominant physics of the aircraft flows in the high alpha regime changes as the angle of attack is increased. At moderate angle of attack the flow is characterized by boundary layer separation and the formation of tight vortices. As the angle of attack is increased, these vortices break down producing unsteady wakes. With further increase in angle of attack, the, vortex breakdown moves progressively upstream until the entire flowfield becomes dominated by the unsteady wake. Previous computational work has demonstrated the ability to simulate flows about the F-18 HARV in the medium-to-high angle of attack range, where the flowfield is characterized by the vortex formation and subsequent breakdown. This paper extends the previous computations to include conditions of 45 degree angle of attack where the flowfield becomes dominated by the unsteady wake shed from the Leading Edge Extension (LEX), and regions of laminar and transitional flow appear on the fuselage forebody. A more complete surface geometry is utilized, which includes the features of the engine nacelle, inlet diffuser, and the boundary layer diverter duct. A volume grid sensitivity study was also performed to extend the accuracy of the results, most notably in the prediction of the LEX vortex breakdown position. This paper includes comparisons of computational results with both in-flight surface pressure measurements, and flow visualizations of the surface and off-surface particle trajectories.

Murman, Scott M.↗

NASA NTRS1974

Influence of mixer nozzle velocity decay characteristics on CTOL-OTW jet noise shielding

Jet noise shielding benefits for CTOL engine-over-the-wing configurations were obtained with model scale multitube and lobed mixer nozzles and various shielding surface geometries. Spectral data were obtained with jet velocities from 585 to 1110 ft/sec. Correlation equations for predicting jet noise shielding benefits with single conical nozzle installations were modified to correlate the mixer nozzle data. The modification included consideration of the number of nozzle elements and the peak axial velocity decay in the flow field adjacent to the shielding surface. The effect of forward velocity on jet noise attenuation by a shielding surface is discussed.

Vonglahn, U.↗

NASA NTRS1975

Influence of mixer nozzle velocity decay characteristics on CTOL-OTW jet noise shielding

Jet noise shielding benefits for CTOL engine-over-wing configurations were obtained with model-scale multitube and lobed mixer nozzles and various shielding surface geometries. Spectral data were obtained with jet velocities from 585 to 1110 ft/sec. Correlation equations for predicting jet noise shielding benefits with single conical nozzle installations were modified to correlate the mixer nozzle data. The modification included consideration of the number of nozzle elements and the peak axial velocity decay in the flow field adjacent to the shielding surface. The effect of forward velocity on jet noise attenuation by a shielding surface is discussed.

Von Glahn, U.↗

NASA NTRS1992

HSCT mission analysis of waverider designs

In the second quarter the development of the two waverider design tools was continued, and the groundwork necessary for the incorporation of waverider technology into the realm of the High Speed Civil Transports (HSCT's) was laid out. Advances in each of these areas is summarized. Work on the WIPAR code included the addition of an upper surface geometry generator and characteristic flow solver and the inclusion of viscous analysis in the performance computations. Details of these changes are given. In the course of the second project quarter, much of the analysis performed during the first quarter was incorporated into a working computer code. To date, utilities were developed for the definition of arbitrary 3-D shock surfaces, the computation of post-shock flow conditions, and the marching of the solution in a roughly cross-stream direction away from the shock surface. These utilities are briefly described. During the second quarter groundwork for the analysis of complete configurations was initiated. This involved the development of computational utilities for the integration of powerplants with the waverider forebodies, and the acquisition of a number of configuration analysis software packages. Work in these areas is discussed.

Source record↗

NASA NTRS1989

Interaction between Tollmien-Schlichting waves and free-stream disturbances in boundary-layer flows

A numerical study of the generation of Tollmien-Schlichting (T-S) waves due to the interaction between a small freestream disturbance and a small localized variation of the surface geometry has been carried out using finite difference methods. The nonlinear steady flow is of the viscous-inviscid interactive type while the unsteady disturbed flow is assumed to be governed by the Navier-Stokes equations linearized about this flow. Numerical solutions illustrate the growth or decay of the T-S waves generated by the interaction between the freestream disturbance and the surface distortion, depending on the value of the scaled Strouhal number. An important result of this receptivity problem is the numerical determination of the amplitude of the Tollmien-Schlichting waves.

Bodonyi, R. J.↗

NASA NTRS1997

A Feasibility Study to Control Airfoil Shape Using THUNDER

The objective of this study was to assess the capabilities of a new out-of-plane displacement piezoelectric actuator called thin-layer composite-unimorph ferroelectric driver and sensor (THUNDER) to alter the upper surface geometry of a subscale airfoil to enhance performance under aerodynamic loading. Sixty test conditions, consisting of combinations of five angles of attack, four dc applied voltages, and three tunnel velocities, were studied in a tabletop wind tunnel. Results indicated that larger magnitudes of applied voltage produced larger wafer displacements. Wind-off displacements were also consistently larger than wind-on. Higher velocities produced larger displacements than lower velocities because of increased upper surface suction. Increased suction also resulted in larger displacements at higher angles of attack. Creep and hysteresis of the wafer, which were identified at each test condition, contributed to larger negative displacements for all negative applied voltages and larger positive displacements for the smaller positive applied voltage (+102 V). An elastic membrane used to hold the wafer to the upper surface hindered displacements at the larger positive applied voltage (+170 V). Both creep and hysteresis appeared bounded based on the analysis of several displacement cycles. These results show that THUNDER can be used to alter the camber of a small airfoil under aerodynamic loads.

Pinkerton, Jennifer L.↗

DOE OSTI2024

FLARE: field line analysis and reconstruction for 3D boundary plasma modeling

The FLARE code is a magnetic mesh generator that is integrated within a suite of tools for the analysis of the magnetic geometry in toroidal fusion devices. A magnetic mesh is constructed from field line segments and permits fast reconstruction of field lines in 3D boundary plasma codes such as EMC3-EIRENE. Both intrinsically non-axisymmetric configurations (stellarators) and those with symmetry breaking perturbations of an axisymmetric equilibrium (tokamaks) are supported. The code itself is written in Modern Fortran with MPI support for parallel computing, and it incorporates object-oriented programming for the definition of the magnetic field and the material surface geometry. Extended derived types for a number of different magnetohydrodynamic equilibrium and plasma response models are implemented. The core element of FLARE is a field line tracer with adaptive step-size control, and this is integrated into tools for the construction of Poincaré maps and invariant manifolds of X-points. A collection of high-level procedures that generate output files for visualization is build on top of that. The analysis modules are build with Python frontends that facilitate customization of tasks and/or scripting of parameter scans.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1987

Wind-fetch dependence of Seasat scatterometer measurements

This work is focused on the effects of large-scale wind-generated gravity waves on scatterometer wind-measurement accuracy. Theoretical and experimental evidence of the important role played by the degree of wind-wave coupling in surface geometry and therefore in microwave signatures is presented. Seasat scatterometer wind-measurement errors are analyzed, and an error bias is found to be related to the degree of wind-wave development. Attention is focused on a dynamic measure of wind-wave development that characterizes the rate of energy transfer from the mean wind to the energy-carrying portion of the wave spectrum. An explanation of the bias is suggested based on the consideration of an additional component of surface scattering caused by electromagnetic-wave diffraction at the crests of individual, sufficiently steep wavelets.

Glazman, Roman E.↗

NASA NTRS2018

Evaluating the Assumptions in an Empirical Jet-Surface Interaction Noise Model

A set of empirical jet-surface interaction noise models, developed for single-stream round nozzles exhausting over a simple surface in a static ambient, are evaluated for use in more realistic applications that include multi-stream nozzle systems, multi-plane surface geometries, and a flight-stream. The simple-single-stream models have several advantages when used in system-level noise studies: they are robust, they are quickly computed, and they are generally applicable to a wide range of configurations. However, these models require simplifying assumptions when applied to more complex jet exhaust systems; for example, previous work on multi-stream jets used an empirical formula to compute a single-stream equivalent jet potential core length that could be used to predict the noise using simple-single-stream jet-surface interaction models. This paper considers the effect of flight and multi-plane surfaces using a similar approach: introducing assumptions to simplify the complex system, applying the simple-single-stream models, and evaluating the uncertainty.

Jet Noise↗

NASA NTRS2018

Evaluating the Assumptions in an Empirical Jet-Surface Interaction Noise Model

A set of empirical jet-surface interaction noise models, developed for single-stream round nozzles exhausting over a simple surface in a static ambient, are evaluated for use in more realistic applications that include multi-stream nozzle systems, multi-plane surface geometries, and a flight-steam. The simple-single-stream models have several advantages when used in system-level noise studies: they are robust, they are quickly computed, and they are generally applicable to a wide range of configurations. However, these models require simplifying assumptions when applied to more complex jet exhaust systems; for example, previous work on multi-stream jets used an empirical formula to compute a single-stream equivalent jet potential core length that could be used to predict the noise using simple-single-stream jet-surface interaction models. This paper considers the effect of flight and multi-plane surfaces using a similar approach: introducing assumptions to simplify the complex system, applying the simple-single-stream models, and evaluating the uncertainty.

Jet Noise↗

DOE OSTI2024

High-Throughput Microstructural Characterization and Process Correlation Using Automated Electron Backscatter Diffraction

The need to optimize the processing conditions of additively manufactured (AM) metals and alloys has driven advances in throughput capabilities for material property measurements such as tensile strength or hardness. High-throughput (HT) characterization of AM metal microstructure has fallen significantly behind the pace of property measurements due to intrinsic bottlenecks associated with the artisan and labor-intensive preparation methods required to produce highly polished surfaces. This inequality in data throughput has led to a reliance on heuristics to connect process to structure or structure to properties for AM structural materials. In this study, we show a transformative approach to achieve laser powder bed fusion (LPBF) printing, HT preparation using dry electropolishing and HT electron backscatter diffraction (EBSD). This approach was used to construct a library of > 600 experimental EBSD sample sets spanning a diverse range of LPBF process conditions for AM Kovar. This vast library is far more expansive in parameter space than most state-of-the-art studies, yet it required only approximately 10 labor hours to acquire. Build geometries, surface preparation methods, and microscopy details, as well as the entire library of >600 EBSD data sets over the two sample design versions, have been shared with intent for the materials community to leverage the data and further advance the approach. Using this library, we investigated process–structure relationships and uncovered an unexpected, strong dependence of microstructure on location within the build, when varied, using otherwise identical laser parameters.

Characterization and Analytical Technique↗