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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 253 records · Page 14

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NASA NTRS1991

Cascade flutter analysis with transient response aerodynamics

Two methods for calculating linear frequency domain aerodynamic coefficients from a time marching Full Potential cascade solver are developed and verified. In the first method, the Influence Coefficient, solutions to elemental problems are superposed to obtain the solutions for a cascade in which all blades are vibrating with a constant interblade phase angle. The elemental problem consists of a single blade in the cascade oscillating while the other blades remain stationary. In the second method, the Pulse Response, the response to the transient motion of a blade is used to calculate influence coefficients. This is done by calculating the Fourier Transforms of the blade motion and the response. Both methods are validated by comparison with the Harmonic Oscillation method and give accurate results. The aerodynamic coefficients obtained from these methods are used for frequency domain flutter calculations involving a typical section blade structural model. An eigenvalue problem is solved for each interblade phase angle mode and the eigenvalues are used to determine aeroelastic stability. Flutter calculations are performed for two examples over a range of subsonic Mach numbers.

Bakhle, M. A.↗

NASA NTRS1991

Cascade flutter analysis with transient response aerodynamics

Two methods for calculating linear frequency domain aerodynamic coefficients from a time-marching Full-Potential cascade solver are developed and verified. In the first method, the Influence Coefficient method, solutions to elemental problems are superposed to obtain the solutions for a cascade in which all blades are vibrating with a constant interblade phase angle. The elemental problem consists of a single blade in the cascade oscillating while the other blades remain stationary. In the second method, the Pulse Response method, the response to the transient motion of a blade is used to calculate influence coefficients. This is done by calculating the Fourier transforms of the blade motion and the response. Both methods are validated by comparison with the Harmonic Oscillation method and give accurate results. The aerodynamic coefficients obtained from these methods are used for frequency domain flutter calculations involving a typical section blade structural model. An eigenvalue problem is solved for each interblade phase angle mode and the eigenvalues are used to determine aeroelastic stability. Flutter calculations are performed for two examples over a range of subsonic Mach numbers using both flat plates and actual airfoils.

Bakhle, Milind A.↗

NASA NTRS1986

Excitation of nearly steady finite-amplitude barotropic waves

An exact nonlinear stationary solution is obtained for barotropic waves in a beta-plane channel and it is shown that it can be excited under a range of initial conditions. Results show that a finite-amplitude wave in a constant shear flow, given an initial phase tilt against the shear and a sufficient initial amplitude, interacts with the mean flow to produce a nearly steady state close to the exact stationary solution. This equilibration process involves nonlinear transients; in particular, as the flow equilibrates, the emergence of critical levels is accompanied by the neutralization of local mean vorticity gradients at these levels, thus allowing the solution to attain a nonsingular modal structure.

Hou, A. Y.↗

NASA NTRS1979

Changes in apparent body orientation and sensory localization induced by vibration of postural muscles - Vibratory myesthetic illusions

Human experiments are carried out which support the observation of Goodwin (1973) and Goodwin et al. (1972) that vibration of skeletal muscles can elicit illusory limb motion. These experiments extend the class of possible myesthetic illusions by showing that vibration of the appropriate muscles can produce illusory body motion in nearly any desired direction. Such illusory changes in posture occur only when visual information about body orientation is absent; these changes in apparent posture are sometimes accompanied by a slow-phase nystagmus that compensates for the direction of apparent body motion. During illusory body motion a stationary target light that is fixated will appear to move with the body at the same apparent velocity. However, this pattern of apparent body motion and conjoint visual - defined as propriogyral illusion - is suppressed if the subject is in a fully illuminated environment providing cues about true body orientation. Persuasive evidence is thus provided for the contribution of both muscle afferent and touch-pressure information to the supraspinal mechanisms that determine apparent orientation on the basis of ongoing patterns of interoceptive and exteroceptive activity.

Lackner, J. R.↗

NASA NTRS1983

Solitary waves and double layers on auroral field lines

Time stationary solutions to the Vlasov-Poisson equations for ion holes and double layers are examined along with particle simulations that pertain to recent observations of small amplitude electric field structures on auroral field lines. Both the time stationary analysis and the simulations suggest that the observed double layers evolve from holes in ion phase space. Multiple small amplitude double layers, as seen in long simulation systems, are observed to propagate past the spacecraft and may account for the acceleration of plasma sheet electrons to produce inverted-V precipitation.

Hudson, M. K.↗

NASA NTRS1992

Energetic ion phase space densities in Neptune's magnetosphere

Ion phase densities of Neptune are presently ascertained at the first and second adiabatic invariants of charged-particle motion on the basis of an analysis of Voyager 2 measurements. The profiles thus obtained are interpreted as indicative of generally inward radial diffusion, with an energetic ion source near L = 10. Excellent agreement is obtained between inbound and outbound phase-space density profiles at the values of the invariants; this suggests approximately axisymmetric, quasi-stationary radiation belts. The inward diffusing power carried by energetic ions appears adequate for powering Neptune's aurora, if enough of the ions are lost to the Neptune atmosphere.

Cheng, Andrew F.↗

NASA NTRS2022

Biofilm Study Under Simulated Microgravity

The goal of this study was to understand biofilm formation under microgravity (µg), in support of biofilm mitigation efforts in exploration water recovery systems. The technical approach was to conduct a mass transfer and bacterial culture study under both simulated µg and ambient gravity. The aim was to correlate nutrient consumption to gene expression to better understand biofilm formation. A representative species of bacteria that is commonly cultured from the International Space Station (ISS) Water Processor Assembly (WPA) was cultured in a WPA influent water ersatz formulation that is tailored for microbiology studies. A mass transfer rate study was carried out using the ersatz WPA influent water by introducing a water-soluble dye to represent dissolved nutrients and nutrient particles. Imaging of dye diffusion over time allowed for the comparison of mass transport rates under a series of rotation per minute (RPM) speeds for the High Aspect Ratio Vessels (HARVs) on a Rotating Wall Vessel (RWV). This was done to determine the speed that will most accurately simulate the low convective rates experienced under actual µg conditions. Three biological replicates of the Burkholderia contaminans (B. contaminans) microbe were cultured under simulated µg with a rotating (R) control in the horizontal plane at the determined optimal RPM of 15, along with a stationary (S) reference culture. At T=0, and then at T=1,2,3 (in exponential phase) and T=4 (in S phase), the bacterial culture and ersatz were harvested for transcriptomic and nutrient content analysis, respectively. The experimental results illustrated that phosphate is a limiting nutrient in the WPA ersatz formula. Nutrient analysis illustrated that the µg treatment culture took up essential nutrients more rapidly than the R and S control cultures, yet non-essential nutrients remained higher in the µg treatment than in the controls at later timepoints. The rapid uptake and subsequent starvation of phosphate in the culture under µg conditions is further illustrated in the transcriptomic response when compared to that of the R control condition. The subsequent starvation response may serve as one element to explain a moderate enhancement of biofilm formation in the µg treatment. One implication of this work is that biofilm mitigation in the ISS environment could be supported by ensuring a steady flow of water as a vehicle for phosphate within the WPA to avoid complete phosphate consumption, which occurs in times of no flow and leads to undesired biofilm formation.

Aubrie O’Rourke↗

NASA NTRS2004

Measuring Gravitation Using Polarization Spectroscopy

A proposed method of measuring gravitational acceleration would involve the application of polarization spectroscopy to an ultracold, vertically moving cloud of atoms (an atomic fountain). A related proposed method involving measurements of absorption of light pulses like those used in conventional atomic interferometry would yield an estimate of the number of atoms participating in the interferometric interaction. The basis of the first-mentioned proposed method is that the rotation of polarization of light is affected by the acceleration of atoms along the path of propagation of the light. The rotation of polarization is associated with a phase shift: When an atom moving in a laboratory reference interacts with an electromagnetic wave, the energy levels of the atom are Doppler-shifted, relative to where they would be if the atom were stationary. The Doppler shift gives rise to changes in the detuning of the light from the corresponding atomic transitions. This detuning, in turn, causes the electromagnetic wave to undergo a phase shift that can be measured by conventional means. One would infer the gravitational acceleration and/or the gradient of the gravitational acceleration from the phase measurements.

Matsko, Andrey↗

DOE OSTI2026

Non-resonant Raman optical activity from phase-space electronic structure theory

In order to model experimental non-resonant Raman optical activity, chemists must compute a host of second-order response tensors (e.g., the electric-dipole–magnetic-dipole polarizability) and their nuclear derivatives along a set of vibrational modes. While these response functions are almost always computed within a Born–Oppenheimer (BO) framework, here we provide a natural interpretation of the electric-dipole–magnetic-dipole polarizability within phase space electronic structure theory, a beyond-BO model whereby the electronic structure depends on nuclear momentum (P) in addition to nuclear position (R). By coupling to nuclear momentum, phase space electronic structure theory is able to capture the asymmetric response of the electronic properties to an external field, in so far as for a vibrating (non-stationary) molecule, $\frac{∂μ}{∂B}$≠$\frac{∂m}{∂F}$, where μ and m are the electrical linear and magnetic dipoles, and F and B are electric and magnetic fields. As an example, for a prototypical methyloxirane molecule, we show that phase space electronic structure theory is able to deliver a reasonably good match with experimental results in a manner that is formally invariant to gauge origin G 0 —provided that one uses a complete basis or, alternatively, gauge invariant atomic orbitals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1992

An interface tracking method applied to morphological evolution during phase change

The focus of this work is the numerical simulation of interface motion during solidification of pure materials. First, the applicability of the oft-used quasi-stationary approximation for interface motion is assessed. It is seen that such an approximation results in poor accuracy for nontrivial Stefan numbers. Solution of the full set of equations including grid movement terms yields close agreement with analytical results. Next, a generic interface tracking procedure is designed, which overcomes restrictions of single-valuedness of the interface imposed by commonly used mapping methods. This method incorporates with ease interface phenomena involving curvature, which assume importance at the smaller scales of a deformed interface. The method is then applied to study the development of a morphologically unstable phase interface. The issue of appropriate scaling has been addressed. The Gibbs-Thomson effect for curved interfaces has been included. The evolution of the interface, with the competing mechanisms of undercooling and surface tension is found to culminate in tip-splitting, cusp formation and persistent cellular development.

Shyy, W.↗

DOE OSTI2023

A novel approach to identify the ionomer phase in PEMFC by EELS

Proton exchange membrane fuel cells are one of the most promising technologies of energy conversion for both automotive and stationary applications, due to their ultimate cleanness and high efficiency. A critical factor, which strongly affects the fuel cell performance, is the ionomer distribution and coverage over the carbon support, since the catalysts, which are typically Pt and/or Pt-alloy nanoparticles, must be located at the carbon support/ionomer interface to catalyze the sluggish oxygen reduction reaction. However, the characterization and identification of the ionomer film, in terms of ionomer distribution and coverage over the carbon surface, is a long standing challenge. This is because the ionomer film may suffer from beam damage during the characterization, either from x-rays, neutrons or an electron beam, which causes morphological changes. In this regard, we report here a novel approach to identify and differentiate the ionomer, using the carbon signal produced by STEMEELS. Using this approach, not only the ionomer distribution, but also the carbon support distribution, can be probed at high spatial resolutions. In addition, this new approach allows us to identify ionomer-rich and carbon-support rich regions, which are quite challenging to determine using other methods.

08 HYDROGEN↗

NASA NTRS1989

Two-component phase-averaged turbulence statistics downstream of a rotating spoked-wheel wake generator

Flow-field measurements of unsteady turbulent flow downstream of a rotating spoked-wheel wake generator were performed in a short-duration light-piston tunnel, and the instantaneous-velocity data were phase averaged based on a signal synchronized with the bar-passing frequency. Mean axial velocities were found to agree well with those obtained from measurements behind a stationary cylinder and to be independent of both Reynolds and bar-passing Strouhal numbers. Reynolds stresses were found to be consistent with related cylinder-wake measurements, but were significantly higher than corresponding measurements obtained in large-scale research turbomachines. Phase-averaged triple velocity correlations were calculated from the digital velocity records, revealing the sign and the magnitude of skewness in the velocity probability density distributions for the two components.

O'Brien, J. E.↗

NASA NTRS1985

Reverberation effects on directionality and response of stationary monopole and dipole sources in a wind tunnel

Analytical solutions for the three dimensional inhomogeneous wave equation with flow in a hardwall rectangular wind tunnel and in the free field are presented for a stationary monopole noise source. Dipole noise sources are calculated by combining two monopoles 180 deg out of phase. Numerical calculations for the modal content, spectral response and directivity for both monopole and dipole sources are presented. In addition, the effect of tunnel alterations, such as the addition of a mounting plate, on the tunnels reverberant response are considered. In the frequency range of practical importance for the turboprop response, important features of the free field directivity can be approximated in a hardwall wind tunnel with flow if the major lobe of the noise source is not directed upstream. However, for an omnidirectional source, such as a monopole, the hardwall wind tunnel and free field response are not comparable.

Baumeister, K. J.↗

NASA NTRS1986

Reverberation effects on directionality and response of stationary monopole and dipole sources in a wind tunnel

Baumeister, K. J.↗

NASA NTRSDate not supplied

Computational Study of Low-Speed Boundary-Layer Laminar-Turbulent Transition over a 30º Swept Plate in a Channel

Reliable boundary-layer laminar-turbulent transition predictions are critical for the design of aircraft that use natural or controlled laminar flow to achieve low drag and better fuel efficiency. During cruise flight through low turbulence, the three-dimensional boundary layer over swept surfaces can transition prematurely due to stationary crossflow instabilities induced by surface roughness. Parabolized stability equations analyses have been successfully used to explain the different phases of the transition process under well controlled perturbations such as steps or discrete roughness elements. However, methodologies are still lacking to model the boundary layer receptivity to distributed random roughness, and the following non-linear instability stages leading to transition. For engineering applications, several semi-empirical methods based on linear amplification factors or local helicity have found growing adoption, but their reliability is limited by their level of simplification and the sparsity of data they are based on. To address this gap, a new study of the effect of distributed random surface roughness on crossflow transition was started, using a 30◦ swept plate as a test vehicle. The plate, which is mounted in the 2 Foot × 3 Foot Low-Speed Boundary-Layer Channel at the NASA Langley Research Center, has been tested with micro-scale roughness of varied geometry near the leading edge. In order to analyze the flow in the test section and prepare Direct Numerical Simulations with resolved roughness, Reynolds-Averaged Navier-Stokes (RANS) simulations of the flow over the plate installed in the wind tunnel test section were performed using the Langtry-Menter transition model with stationary crossflow extension. This paper presents the results of these simulations, with comparison to the experiment.

ARMD↗

NASA NTRS1999

Yaw and pitch visual-vestibular interaction in weightlessness

Both yaw and pitch visual-vestibular interactions at two separate frequencies of chair rotation (0.2 and 0.8 Hz) in combination with a single velocity of optokinetic stimulus (36 degrees/s) were used to investigate the effects of sustained weightlessness on neural strategies adopted by astronaut subjects to cope with the stimulus rearrangement of spaceflight. Pitch and yaw oscillation in darkness at 0.2 and 0.8 Hz without optokinetic stimulation, and constant velocity linear optokinetic stimulation at 18, 36, and 54 degrees/s presented relative to the head with the subject stationary, were used as controls for the visual-vestibular interactions. The results following 8 days of space flight showed no significant changes in: (1) either the horizontal and vertical vestibulo-ocular reflex (VOR) gain, phase, or bias; (2) the yaw visual-vestibular response (VVR); or (3) the horizontal or vertical optokinetic (OKN) slow phase velocity (SPV). However, significant changes were observed: (1) when during pitch VVR at 0.2 Hz late inflight, the contribution of the optokinetic input to the combined oculomotor response was smaller than during the stationary OKN SPV measurements, followed by an increased contribution during the immediate postflight testing; and (2) when during pitch VVR at 0.8 Hz, the component of the combined oculomotor response due to the underlying vertical VOR was more efficiently suppressed early inflight and less suppressed immediately postflight compared with preflight observations. The larger OKN response during pitch VVR at 0.2 Hz and the better suppression of VOR during pitch VVR at 0.8 Hz postflight are presumably due to the increased role of vision early inflight and immediately after spaceflight, as previously observed in various studies. These results suggest that the subjects adopted a neural strategy to structure their spatial orientation in weightlessness by reweighting visual, otolith, and perhaps tactile/somatic signals.

NASA Center JSC↗

NASA NTRS1989

Inviscid spatial stability of a compressible mixing layer. Part 2: The flame sheet model

The results of an inviscid spatial calculation for a compressible reacting mixing layer are reported. The limit of infinitive activation energy is taken and the diffusion flame is approximated by a flame sheet. Results are reported for the phase speeds of the neutral waves and maximum growth rates of the unstable waves as a function of the parameters of the problem: the ratio of the temperature of the stationary stream to that of the moving stream, the Mach number of the moving streams, the heat release per unit mass fraction of the reactant, the equivalence ratio of the reaction, and the frequency of the disturbance. These results are compared to the phase speeds and growth rates of the corresponding nonreacting mixing layer. We show that the addition of combustion has important, and complex effects on the flow stability.

Jackson, T. L.↗

NASA NTRS1990

Inviscid spatial stability of a compressible mixing layer. II - The flame sheet model

Jackson, T. L.↗