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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS2020

Development of a Flow Field for Testing a Boundary-Layer-Ingesting Propulsor

In order to test embedded-propulsor technology, modifications were required of the 8x6 Supersonic Wind tunnel at NASA Glenn Research Center. The extent of the modifications required that a new tunnel calibration be completed to generate a new calibration dataset and operational procedures for the tunnel, as well as to map the boundary layer on the raised floor. This report describes the propulsor inflow that was to be simulated, documents the tunnel modifications that were required, and conveys the results of the calibration test that was completed to measure the resulting flow properties.

boundary layer↗
NASA NTRS2022

Interaction of a Tunnel-like Acoustic Disturbance Field with a Blunt Cone Boundary Layer at Mach 8

The existing measurements of laminar-to-turbulent transition over circular cones in conventional (i.e., “noisy”) hypersonic wind tunnels have established that the transition location moves downstream when the nose radius is increased from zero. However, this initially downstream movement slows down and ultimately reverses beyond a critical value of the nose radius, and may be related to external forcing in the form of freestream disturbances and/or surface roughness. To understand the effects of freestream acoustic disturbances on transition reversal over a blunt body, hypersonic boundary-layer receptivity to broadband freestream acoustic disturbances from the nozzle wall of a digital conventional wind tunnel is investigated by both direct numerical simulations (DNS) and modal and nonmodal stability analysis. A Mach 8 flow over a 7 deg half-angle cone with a nose radius of 𝑅 𝑛 = 5.2mm and freestream Reynolds number of 12.2 × 10 6 m -1 is considered. The results show that the broadband tunnel noise in the free stream of a convectional hypersonic wind tunnel (i.e., outside of the nozzle-wall turbulent boundary layer) can be well represented by an acoustic model with an ansatz of slow acoustic waves. With successful calibration of the model parameters against the precursor tunnel DNS, such an acoustic ansatz can successfully reproduce both the frequency-wavenumber spectra and the temporal evolution of the broadband tunnel noise radiated from the nozzle wall. Additionally, the DNS of the Mach 8 blunt cone with tunnel-like acoustic input above the bow shock showed that the spectra of wall-pressure and heat-transfer fluctuations recovers the signature of the axisymmetric waves predicted by the nonmodal analysis. Furthermore, the azimuthal wavenumber and frequency spectrum of the temperature fluctuations as a function of the wall-normal distance show higher amplitudes for three-dimensional waves above the boundary-layer edge. The numerical schlieren contours show the inclined structures commonly observed in blunt cone experiments, demonstrating that they correspond to three-dimensional structures due to freestream disturbances in the presence of an entropy layer.

Boundary-layer transition↗
NASA NTRS2022

Interaction of a Tunnel-like Acoustic Disturbance Field with a Blunt Cone Boundary Layer at Mach 8

The existing measurements of laminar-to-turbulent transition over circular cones in conventional (i.e., “noisy”) hypersonic wind tunnels have established that the transition location moves downstream when the nose radius is increased from zero. However, this initially downstream movement slows down and ultimately reverses beyond a critical value of the nose radius, and may be related to external forcing in the form of freestream disturbances and/or surface roughness. To understand the effects of freestream acoustic disturbances on transition reversal over a blunt body, hypersonic boundary-layer receptivity to broadband freestream acoustic disturbances from the nozzle wall of a digital conventional wind tunnel is investigated by both direct numerical simulations (DNS) and modal and nonmodal stability analysis. A Mach 8 flow over a 7 deg half-angle cone with a nose radius of 𝑅 𝑛 = 5.2mm and freestream Reynolds number of 12.2 × 10 6 m -1 is considered. The results show that the broadband tunnel noise in the free stream of a convectional hypersonic wind tunnel (i.e., outside of the nozzle-wall turbulent boundary layer) can be well represented by an acoustic model with an ansatz of slow acoustic waves. With successful calibration of the model parameters against the precursor tunnel DNS, such an acoustic ansatz can successfully reproduce both the frequency-wavenumber spectra and the temporal evolution of the broadband tunnel noise radiated from the nozzle wall. Additionally, the DNS of the Mach 8 blunt cone with tunnel-like acoustic input above the bow shock showed that the spectra of wall-pressure and heat-transfer fluctuations recovers the signature of the axisymmetric waves predicted by the nonmodal analysis. Furthermore, the azimuthal wavenumber and frequency spectrum of the temperature fluctuations as a function of the wall-normal distance show higher amplitudes for three-dimensional waves above the boundary-layer edge. The numerical schlieren contours show the inclined structures commonly observed in blunt cone experiments, demonstrating that they correspond to three-dimensional structures due to freestream disturbances in the presence of an entropy layer.

Boundary layer transition↗
NASA NTRS1987

Experimental study of laminar boundary layer receptivity to a traveling pressure field

Study is made of the production of Tollmien-Schlichting (T-S) waves within a Blasius boundary layer by an externally-imposed, two-dimensional, pressure field of a particular type. The field is that due to flow past a relatively small cylinder aligned parallel to the test plate and normal to the flow. The cylinder was carried on a circular path about an axis located well above the plate and such that the closest approach of the cylinder to the layer was several times the layer thickness or cylinder diameter. The turbulent wake did not, therefore, directly perturb the layer. Through adjustment of the circumferential velocity, the pressure field was swept along a certain region of the plate with controllable speed. Both the pressure field and the layer response are described in detail. It is shown that the production of T-S waves was sharply maximal for the case of circumferential speed near that of freely-propagating T-S waves, and that the coupling efficiency was extremely high for this case of resonance. The relevance of this energy transfer process to T-S wave production by the unsteady pressure fields resulting from wind tunnel wall turbulent boundary layers for both subsonic and supersonic flow is mentioned.

Kendall, James M.↗
NASA NTRS1994

The velocity field created by a shallow bump in a boundary layer

We report the results of measurements of the disturbance velocity field generated in a boundary layer by a shallow three-dimensional bump oscillating at a very low frequency on the surface of a flat plate. Profiles of the mean velocity, the disturbance velocity at the fundamental frequency and at the first harmonic are presented. These profiles were measured both upstream and downstream of the oscillating bump. Measurements of the disturbance velocity were also made at various spanwise and downstream locations at a fixed distance from the boundary of one displacement thickness. Finally, the spanwise spectrum of the disturbances at three locations downstream of the bump are presented.

Gaster, Michael↗
NASA NTRS1991

Steady state toroidal magnetic field at earth's core-mantle boundary

Measurements of the dc electrical potential near the top of earth's mantle have been extrapolated into the deep mantle in order to estimate the strength of the toroidal magnetic field component at the core-mantle interface. Recent measurements have been interpreted as indicating that at the core-mantle interface, the magnetic toroidal and poloidal field components are approximately equal in magnitude. A motivation for such measurements is to obtain an estimate of the strength of the toroidal magnetic field in the core, a quantity important to our understanding of the geomagnetic field's dynamo generation. Through the use of several simple and idealized calculation, this paper discusses the theoretical relationship between the amplitude of the toroidal magnetic field at the core-mantle boundary and the actual amplitude within the core. Even with a very low inferred value of the toroidal field amplitude at the core-mantle boundary, (a few gauss), the toroidal field amplitude within the core could be consistent with a magnetohydrodynamic dynamo dominated by nonuniform rotation and having a strong toroidal magnetic field.

Levy, Eugene H.↗
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 NTRS1979

Outline of research on oscillating boundary layers

The state of the art in the field of unsteady boundary layers is outlined with emphasis on turbulent boundary layers. The unsteady flows considered are mainly periodic with the external velocity varying around a zero or nonzero mean time value. The principal results obtained on laminar boundary layers are also presented.

Cousteix, J.↗
DOE OSTI2022

Defect redistribution along grain boundaries in SrTiO 3 by externally applied electric fields

During thermal annealing at 1425 °C nominal electric field strengths of 50 V/mm and 150 V/mm were applied along the grain boundary planes of a near 45° (100) twist grain boundary in SrTiO 3 . Electron microscopy characterization revealed interface expansions near the positive electrode around 0.8 nm for either field strength. While the interface width decreased to roughly 0.4 nm after annealing at 50 V/mm, the higher field strength caused decomposition of the boundary structure close to the negative electrode. Electron energy-loss and X-ray photoelectron spectroscopies demonstrated an increased degree of oxygen sublattice distortion at the negative electrode side, and enhanced concentrations of Ti 3+ and Ti 2+ compared to bulk for both single crystals and bicrystals annealed with an external electric field, respectively. Oxygen migration due to the applied electric field causes the observed alteration of grain boundary structures. At sufficiently high field strength the agglomeration of anion vacancies may lead to the decomposition of the grain boundary.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Wind loads on flat plate photovoltaic array fields

The results of an experimental analysis (boundary layer wind tunnel test) of the aerodynamic forces resulting from winds acting on flat plate photovoltaic arrays are presented. Local pressure coefficient distributions and normal force coefficients on the arrays are shown and compared to theoretical results. Parameters that were varied when determining the aerodynamic forces included tilt angle, array separation, ground clearance, protective wind barriers, and the effect of the wind velocity profile. Recommended design wind forces and pressures are presented, which envelop the test results for winds perpendicular to the array's longitudinal axis. This wind direction produces the maximum wind loads on the arrays except at the array edge where oblique winds produce larger edge pressure loads. The arrays located at the outer boundary of an array field have a protective influence on the interior arrays of the field. A significant decrease of the array wind loads were recorded in the wind tunnel test on array panels located behind a fence and/or interior to the array field compared to the arrays on the boundary and unprotected from the wind. The magnitude of this decrease was the same whether caused by a fence or upwind arrays.

Miller, R. D.↗
NASA NTRS1985

Observations of field-aligned currents at the plasma sheet boundary - An ISEE-1 and 2 survey

Using ISEE-1 and 2 magnetometer data, a survey of field-aligned currents at the boundary of the plasma sheet between 10 and 22 earth radii down the magnetotail was performed. Most cases are observed as the plasma sheet expands across the spacecraft. It is found that the currents are most often observed flowing earthward throughout this region of the tail; however, a fraction of the cases corresponds to tailward flowing currents and these tend to be found dawnward of midnight. Toward dusk no tailward currents are found. The currents at the plasma sheet boundary should map to the high latitude boundary of the auroral zone, and consequently one might expect them to have a Region 1 polarity; just the opposite is observed. Typical sheet current densities for these cases are roughly 5 mA/m.

Elphic, R. C.↗
DOE OSTI2022

Boundary Modes from Periodic Magnetic and Pseudomagnetic Fields in Graphene

Single-layer graphene subject to periodic lateral strains is an artificial crystal that can support boundary spectra with an intrinsic polarity. This is analyzed by comparing the effects of periodic magnetic fields and strain-induced pseudomagnetic fields that, respectively, break and preserve time-reversal symmetry. In the former case, a Chern classification of the superlattice minibands with zero total magnetic flux enforces single counterpropagating modes traversing each bulk gap on opposite boundaries of a nanoribbon. For the pseudomagnetic field, pairs of counterpropagating modes migrate to the same boundary where they provide well-developed valley-helical transport channels on a single zigzag edge. Here, we discuss possible schemes for implementing this situation and their experimental signatures.

36 MATERIALS SCIENCE↗
NASA NTRS1993

Flow field measurements in a crossing shockwave turbulent boundary layer interaction at Mach 3

An experimental study has been conducted to examine the flow field of the 3D crossing shock wave/turbulent boundary layer interaction. A symmetric pair of 9-deg fins were used to generate the crossing shocks. The incoming boundary layer was developed on the tunnel sidewall and thus was relatively thick, 0.49 arcsec, and suited for pitot probe surveys. The test conditions were a nominal Mach number of 3 and unit Reynolds number of 1.2 x 10 exp 7/ft. The measurements obtained included surface oil flow visualizations, surface static pressures, and boundary layer pitot pressure profiles. The results showed that downstream of the crossing shock intersection, the stagnation pressure losses were significant and the stagnation pressure profiles were highly nonuniform. Despite the severe shock disturbances, the law of the wall and the law of the wake were found to give relatively good agreement with the experimental data.

Lachowicz, Jason T.↗
NASA NTRS1992

Detecting surface roughness effects on the atmospheric boundary layer via AIRSAR data: A field experiment in Death Valley, California

The part of the troposphere influenced by the surface of the earth is termed the atmospheric boundary layer. Flow within this layer is influenced by the roughness of the surface; rougher surfaces induce more turbulence than smoother surfaces and, hence, higher atmospheric transfer rates across the surface. Roughness elements also shield erodible particles, thus decreasing the transport of windblown particles. Therefore, the aerodynamic roughness length (z(sub 0)) is an important parameter in aeolian and atmospheric boundary layer processes as it describes the aerodynamic properties of the underlying surface. z(sub 0) is assumed to be independent of wind velocity or height, and dependent only on the surface topography. It is determined using in situ measurements of the wind speed distribution as a function of height. For dry, unvegetated soils the intensity of the radar backscatter (sigma(sup 0)) is affected primarily by surface roughness at a scale comparable with the radar wavelength. Thus, both wind and radar respond to surface roughness variations on a scale of a few meters or less. Greeley showed the existence of a correlation between z(sub 0) and sigma(sup 0). This correlation was based on measurements over lava flows, alluvial fans, and playas in the southwest deserts of the United States. It is shown that the two parameters behave similarly also when there are small changes over a relatively homogeneous surface.

Blumberg, Dan G.↗
NASA NTRS1982

Three dimensional flow field inside compressor rotor, including blade boundary layers

The flow in a turbomachinery blade passage has a predominant flow direction. The viscous diffusion in the streamwise direction is usually small and the elliptic influence is transmitted upstream through the pressure field. Starting with a guessed pressure field, it is possible to converge on the full elliptic solution by iterating between a parabolic solution and an iteration of the pressure field. The main steps of the calculation are given. The blade boundary layers which are three dimensional with laminar, transitional, turbulent, and separation zones are investigated. The kinetic energy is analyzed, and the dissipation equation is presented. Measurements were made of the three dimensional flow inside an axial flow compressor passage.

Pouagare, M.↗
NASA NTRS1990

Observations of rotational discontinuity - Slow expansion fan structure of the magnetotail boundary

This paper gives the first explicit test of the rotational discontinuity-slow expansion fan structure predicted by MHD models of the open tail boundary. The magnetic field and plasma data collected by IMP 8 during its magnetotail boundary crossings at geocentric distances near 25 Re and high latitudes are analyzed. Many crossings show the particle and field signatures of the paired MHD tail boundary structure. The openness of the tail is revealed by rotational discontinuities. They often show relatively large normal magnetic field components. Other crossings show properties that suggest a tangential discontinuity and reveal regions where, or times when, the tail is closed. Examples of each are given here.

Sanchez, E. R.↗