NASA Tech Research Articles

Assessment of insulation systems for aircraft liquid hydrogen tanks

Liquid hydrogen (LH2) has ~2.8 times more energy per pound of fuel than Jet-A, however, it requires ~4 times the volume for the same energy. As a result, LH2 aircraft developments are highly dependent on the hydrogen tankage as well as the insulation system requirements. To better understand the sensitivities that hydrogen puts onto the aircraft as a system, Georgia Tech investigators, as part of a NASA preliminary evaluation activity, have developed a single-aisle LH2 passenger jet. As a part of the activity, NASA and Georgia Tech developed the ability to integrate a tank set into the aircraft including insulation systems. Assessments are made on several insulation system options to assess the amount of venting as well as the impacts to aircraft fuel consumption. Based on the results, it is observed that even though polyurethane foam is lightweight, the associated boil-off losses drove the system level mass higher than vacuum jacketed insulations. Composite tanks are observed to decrease fuel system dry mass by several hundred kg over AL5083 tanks.

MONTE: the next generation of mission design and navigation software

The Mission analysis, Operations and Navigation Toolkit Environment (MONTE) (Sunseri et al. in NASA Tech Briefs 36(9), 2012) is an astrodynamic toolkit produced by the Mission Design and Navigation Software Group at the Jet Propulsion Laboratory. It provides a single integrated environment for all phases of deep space and Earth orbiting missions. Capabilities include: trajectory optimization and analysis, operational orbit determination, flight path control, and 2D/3D visualization. MONTE is presented to the user as an importable Python language module. This allows a simple but powerful user interface via CLUI or script. In addition, the Python interface allows MONTE to be used seamlessly with other canonical scientific programming tools such as SciPy, NumPy, and Matplotlib. MONTE is the prime operational orbit determination software for all JPL navigated missions.

A model for confined vortex rings with elliptical-core vorticity distribution

We present a new model for an axisymmetric vortex ring confined in a tube. The model takes into account the elliptical (elongated) shape of the vortex ring core and thus extends our previous model (Danaila et al. J. Fluid Mech., vol. 774, 2015, pp. 267–297) derived for vortex rings with quasi-circular cores. The new model offers a more accurate description of the deformation of the vortex ring core, induced by the lateral wall, and a better approximation of the translational velocity of the vortex ring, compared with the previous model. The main ingredients of the model are the following: the description of the vorticity distribution in the vortex ring is based on the previous model of unconfined elliptical-core vortex rings (Kaplanski et al. Phys. Fluids, vol. 24, 2012, 033101); Brasseur’s approach (Brasseur, NASA Tech. Rep. JIAA TR-26, 1979) is then applied to derive a wall-induced correction for the Stokes streamfunction of the confined vortex ring flow. We derive closed formulae for the flow streamfunction and vorticity distributions. An asymptotic expression for the long-time evolution of the drift velocity of the vortex ring as a function of the ellipticity parameter is also derived. The predictions of the model are shown to be in agreement with direct numerical simulations of confined vortex rings generated by a piston–cylinder mechanism. The predictions of the model support the recently suggested heuristic relation (Krieg & Mohseni Trans. ASME J. Fluids Engng, vol. 135, 2013, 124501) between the energy and circulation of vortex rings with converging radial velocity. A new procedure for fitting experimental and numerical data with the predictions of the model is described. This opens the way for applying the model to realistic confined vortex rings in various applications including those in internal combustion engines.

On the vortex dynamics of shear-driven deep cavity flows with asymmetrical walls

The influence of the length-to-depth aspect ratio and of wall asymmetry on the main vortical flow structures evolving in rectangular two-dimensional deep cavities is studied experimentally using wall-pressure and particle image velocimetry (PIV) measurements. Wall-pressure and cavity flow statistics have been analyzed and shown that the flow features are strongly affected especially by the asymmetry. An emphasis is given concerning the behavior of the shear layer oscillations that are compared to the analytical deep-cavity model prediction proposed by P.J.W. Block (NASA Tech. Note. 1976). The results show good agreement with Block’s model if the value of the convection velocity is properly adjusted. Stochastic estimation of the cavity flows demonstrates that convective structures are involved downstream of the cavity along the wall and highlights the physical nature of the pressure-producing flow structures.

Numerical simulation of the three-dimensional screech phenomenon from a circular jet

Despite great advances on jet screech research during the past few decades, the prediction of jet screech amplitudes still remains a challenging task. The main objective of this paper is to develop an accurate three-dimensional computational aeroacoustic procedure for the simulation of screech phenomenon from an underexpanded supersonic circular jet. The three-dimensional Navier–Stokes equations and a modified two-equation standard k-ϵ turbulence model are solved in the generalized curvilinear coordinate system. A dispersion-relation-preserving scheme is utilized for space discretization. The 2N storage low-dissipation and low-dispersion Runge–Kutta scheme is applied for time marching. Numerical results are presented and compared with available experimental data over Mach number range from 1.17 to 1.60. The predicted shock cell structure and radial density profiles agree very well with the measured results by Panda and Seasholtz [“Measurement of shock structure and shock-vortex interaction in underexpanded jets using Rayleigh scattering,” Phys. Fluids 11, 3761 (1999)]. In particular, it is shown that not only the predicted wavelengths, but also the amplitudes of the flapping and helical modes are in good agreement with experimental data by Ponton et al. [“Near field pressure fluctuations in the exit plane of a choked axisymmetric nozzle,” NASA Tech. Memo TM-113137, 1997]. It is found that although the instantaneous flow fields accompanying the flapping and helical jet screech tones are not axisymmetric yet, the long time average mean flow field is still almost axisymmetric. This is because of the slow rotation of the flapping plane around the jet axis. The real time pressure signal of a Maj=1.30 screeching jet at r∕D=2 in the nozzle exit plane is analyzed. The results indicate that the acoustic field of the simulated flapping and rotating motions of the screeching jet agree well with Ponton and Seiner’s experimental measurements [“Acoustic study of B helical mode for choked axisymmetric nozzle,” AIAA J. 33, 413 (1995)].

A computational study of the near-field generation and decay of wingtip vortices

The numerical prediction of the downstream trailing vortex shed from an aircraft wingtip is a particularly challenging CFD task because, besides predicting the development of the strong vortex itself, one needs to compute accurately the flow over the wing to resolve the boundary layer roll-up and shedding which provide the initial conditions for the free vortex. Computations are here reported of the flow over a NACA 0012 half-wing with rounded wing tip and the near-field wake as measured by [Chow, J.S., Zilliac, G., Bradshaw, P., 1997. Turbulence measurements in the near-field of a wingtip vortex. NASA Tech Mem 110418, NASA.]. The aim is to assess the performance of two turbulence models which, in principle, might be seen as capable of resolving both the three dimensional boundary layer on the wing and the generation and near-field decay of the strongly accelerated vortex that develops from the wingtip. Results using linear and non-linear eddy-viscosity models are presented, but these both exhibit a far too rapid decay of the vortex core. Only a stress-transport (or second-moment) model that satisfies the “two-component limit”, [Lumley, J.L., 1978. Computational modelling of turbulent flows. Adv. Appl. Mech. 18, 123–176.], reproduces the principal features found in the experimental measurements.

Human unilateral lower limb suspension as a model for spaceflight effects on skeletal muscle

To the Editor: Widrick et al. ([18][1]) have published data from a 12-day unilateral lower limb suspension (ULLS) study conducted in 1994 using the methods originally published by Berg et al. in 1991 ([3][2]). Analyses included the morphology and contractile behavior of skinned skeletal muscle

Emergency lighting system

When power outages occurred at Landmark Plastic Corporation, it took seven to twelve minutes for the primary mercury lamps to cool down enough to relight and two to seven minutes for the ELS incandescent lamps to relight. Production could not resume for as much as seven minutes. An article in NASA Tech Briefs describing the capabilities of photosensing devices led Landmark employee, Steve Keller to design a system now activated by any voltage loss in the main lamp circuit and coupled with photosensing devices used to keep them on until the primary mercury lamps reach full brightness.

Relationships between lightning activity and various thundercloud parameters: satellite and modelling studies

The lightning frequency model developed by Baker et al. [Baker, M.B., Christian, H.J., Latham, J., 1995. A computational study of the relationships linking lightning frequency and other thundercloud parameters, Q. J. R. Meteorol. Soc., 121, 1525–1548] has been refined and extended, in an effort to provide a more realistic framework from which to examine computationally the relationships that might exist between lightning frequency f (which is now being routinely measured from a satellite, using the NASA/MSFC Optical Transient Detector (OTD)) and a variety of cloud physical parameters. Specifically, superior or more comprehensive representations were utilised of: (1) glaciation via the Hallett–Mossop (H–M) process; (2) the updraught structure of the model cloud; (3) the liquid-water-content structure of the model cloud; (4) the role of the reversal temperature T rev in influencing lightning characteristics; (5) the critical breakdown field for lightning initiation; and (6) the electrical characteristics of the ice crystal anvil of the model cloud. Although our extended studies yielded some new insights into the problem, the basic pattern of relationships between f and the other parameters was very close to that reported by Baker et al. (1995). The more elaborate treatment of T rev restricted somewhat the range of conditions under which reverse-polarity lightning could be produced if the cloud glaciated via H–M, but confirmed the earlier conclusion that such lightning would not occur if the glaciation was of the Fletcher type. The computations yielded preliminary support for the hypothesis that satellite measurements of f might be used to determine values of the ice-content of cumulonimbus anvils: a parameter of climatological importance. The successful launch and continuing satisfactory functioning of the OTD [Christian, H.J., Goodman, S., 1992. Global observations of lightning from space, Proc. 9th Int. Conf. on Atmospheric Electricity, St. Petersburg, pp. 316–321; Christian, H.J., Blakesee, R.J., Goodman, S.J., 1992. Lightning imaging sensor (LIS) for the earth observing system. NASA Tech. Memorandum, 4350] make it possible—with a high degree of precision—to measure lightning location, occurrence time and frequency f over extensive areas of the Earth's surface. Measured global distributions of lightning and associated lightning stroke radiance demonstrate that: lightning activity is particularly pronounced over the tropics, much greater over land than over the oceans, and exhibits great seasonal variability; lightning radiance tends to be greater over the oceans, less when lightning activity is high, and greater in the Northern Hemisphere winter than summer.

Retrieval of near-surface bio-optical properties of the Arabian Sea from remotely sensed ocean colour data

The use of CZCS-type band-ratio algorithms to estimate the diffuse attenuation coefficient, percentage light depths, and near-surface optically weighted phytoplankton pigment concentrations from remotely sensed ocean colour data was investigated on two cruises in the Arabian Sea and Gulf of Oman during autumn and winter 1994. The variations of upwelling radiance and downwelling irradiance with depth were measured along with phytoplankton pigment concentrations by HPLC. A spectroradiometer was used on the second cruise to investigate the feasibility of measuring water-leaving radiance from above the sea surface. Retrieval of the diffuse downwelling attenuation coefficient at 490 nm was accurate to within 22% of the actual value across both cruises. There was also a robust relationship between the diffuse attenuation coefficient and the 10, 1 and 0.1% light depths. Above-surface estimates of water-leaving radiance agreed with SeaWiFS-standard estimates to within 10% between 443 and 555 nm. The global 443 : 555 band-ratio algorithms of Aiken et al. [NASA Tech. Memo 104566, Vol. 29, SeaWiFS Technical Report Series, 34 pp] estimated near-surface chlorophyll- a and fluorometric pigment concentrations with mean absolute errors of less than 35% of the actual values (which were all less than 2.0 mg m -3). The performance of algorithms based on the 490 : 555 ratio was poorer. The estimates given by the algorithms were generally higher than the measured pigment concentrations and the variance of the accuracy of the estimates was high. There appears to be no significant change in the performance of the algorithms between cruises (approximately 2 1 2 months apart in time). There is no evidence that the Gulf of Oman should be treated as a separate bio-optical province to the Arabian Sea/Omani shelf area for the purpose of the retrieval of near-surface pigment concentrations from ocean colour observations.

A thermal analysis of traction in elastohydrodynamic rolling/sliding line contacts

An accurate thermal analysis of traction in elastohydrodynamically lubricated (EHL) line contacts has been done using an efficient numerical method based on Lobatto quadrature developed by Elrod and Brewe [H.G. Elrod, D.E. Brewe, Thermohydrodynamic analysis for laminar lubricating films, NASA Tech. Memorandum No. 88845, 1986.]. Roelands' viscosity model for P-150 and Santotrac-50 oils has been used in the present analysis. The variation of traction coefficient with slip for maximum contact pressures and rolling speeds varying between 0.4 to 1.52 GPa and 5 to 35 m s −1, respectively, are presented. Significant reduction in traction coefficient at high rolling speeds due to thermal effects have been found. Large increments in traction coefficient have been determined at high contact pressures, e.g., at 1.52 GPa as compared to 0.4 GPa at a particular rolling speed. The results of the present work have been compared with the results of Crook [A.W. Crook. The lubrication of rollers: IV. Measurements of friction and effective viscosity. Philos. Trans. R. Soc. London, Ser. A, 255 (Jan. 1963) 281–312.]. Cheng [H.S. Cheng, A refined solution to the thermal elastohydrodynamic lubrication of rolling and sliding cylinders, Trans, ASLE, 8 (4) (1965) 397–411.] and Walowit and Smith [J.A. Walowit, R.L. Smith. Traction characteristics of a MIL-L-7808 oil, Trans. ASME, J. Lubric. Technol., Oct. 1976, pp. 607–612.]. It was found that the results obtained by the present method are consistent with more elaborate theories and with the available traction data. Significant reduction in traction coefficient has been noticed at high rolling speeds (above 15 m s −1) and high slips (above 10%). The thermal effect on the sliding traction coefficient, μ, is expressed in terms of the dimensionless thermal loading parameter, Q, dimensionless load W and slip S as: μ = 2.31 W 0.80 Q −0.66 S −0.72.

A note on the leapfrogging between two coaxial vortex rings at low Reynolds numbers

In the early 1970s, Maxworthy [J. Fluid. Mech. 51, 15 (1972)] and Oshima et al. [J. Phys. Soc. Jpn. 38, 1159 (1975)] attempted to produce leapfrogging between two coaxial vortex rings at low Reynolds numbers in their laboratories. However, the rings failed to undergo the classical leapfrogging behavior and merged to form a single ring. In a recent numerical study, Shariff et al. (NASA Tech. Memo. 102257, 1989) attributed the failure partly to the effect of core distortion. They pointed out that vortex cores at low Reynolds numbers are thicker and therefore more susceptible to distortion during the leapfrogging. In this Brief Communication, it is shown through a systematic investigation that the initial generating condition also plays an important role in determining the success or failure of leapfrogging. The common belief that leapfrogging can be achieved simply by generating two vortex rings in quick succession may not be true for all flow conditions, especially when the Reynolds number is low. This finding may help to explain the results of Maxworthy and Oshima et al.

Thermal effects on film thickness and traction in rolling/sliding EHL line contacts—an accurate inlet zone analysis

Thermal analysis in an EHL line contact has been obtained using a computational method developed by Elrod and Brewe ( NASA Tech. Mem. 88845). Piezoviscous effects have been incorporated using Barus and Roelands' viscosity models for the P-150 oil used in the present analysis. A significant reduction in film thickness and traction at high rolling speeds relative to isothermal conditions has been obtained. Results are presented through figures and tables in the text. The results of the present analysis have been compared with the results of Murch and Wilson ( ASMEJ. Lubr. Technol., 97 (1975) 212), Goksem and Hargreaves ( Trans. ASME, 100 (1978) 346) and Ghosh and Hamrock ( NASA Tech. Mem. 83424). The thermal effect on film thickness reduction factor C, is expressed in terms of the dimensionless thermal loading parameter Q and slip S as: C = 1.0 [ 1.0 + 0.133 Q 0.71 ( 1.0 + 5.65 S 0.96 ) ]

Barotropic currents, vorticity, and tides in the northcentral Pacific in summer 1987 determined from long‐range acoustic transmissions

Large‐scale depth‐integrated currents, relative vorticity, and tides were measured in the northcentral Pacific Ocean during summer 1987 using long‐range reciprocal acoustic transmissions between transceivers in a triangle approximately 1000 km on a side. Tidal harmonic constants found from the acoustically determined currents agree with those found from current meters and with the tidal models of Schwiderski [E. W. Schwiderski, Mar. Geod. 3, 161–255 (1980)] and Cartwright et al. [D. E. Cartwright et al., NASA Tech. Mem. 104578 (1992)]. Sum travel times were used to calculate the baroclinic tide isotach displacement. A significant part of the derived internal tide is deterministic. Currents are calculated using the topographic Sverdrup balance with the Fleet Numerical Oceanography Center wind field. The measured time derivative of the areal‐averaged relative vorticity is insignificant to the Sverdrup balance. Currents and vorticity calculated using the Sverdrup balance are an order of magnitude smaller than the observations. The magnitude and variability of the large‐scale currents and vorticity determined from the Semtner–Chervin eddy‐resolving model of ocean circulation [A. J. Semtner and R. M. Chervin, J. Geophys. Res. 93, 15 502–15 522 (1988)] are similar to the direct measurements. [Work supported by NSF and ONR.]

NASA Patter

This selection from NASA Tech Briefs17, No. 3 ( March1993), was made by Patricia Wakeling. Further information can be obtained from NASA STI Facility, Manager TU Division, P.O. Box 8757, BWI Airport, Baltimore, Md. 21240-9985. Quote the identifying number.

Modal surface impedances for two spheres in a thermoviscous acoustic medium

Two spherical bodies are submerged in an infinite thermoviscous fluid; one body is motionless and the other is vibrating at high frequency with a surface pattern that is axisymmetric with respect to the line joining the centers of the two spheres. Both bodies are sufficiently good conductors that their surface temperatures deviate insignificantly from the ambient temperature. The acoustic stress and velocity fields on the vibrating surface may be conveniently related by a modal surface impedance matrix based on field expansions in Legendre functions. This impedance matrix, which of course accounts for the presence of the motionless sphere, is here obtained from the field equations of Epstein and Carhart [J. Acoust. Soc. Am. 25, 553–565 (1953)] through the application of translational addition theorems for bispherical coordinates [Y. A. Ivanov, DiffractionofElectromagneticWavesonTwoBodies, NASA Tech. Trans. F-597 (1970)]. Impedance matrices for fluids that exhibit thermoviscous boundary layers of various thicknesses are compared with counterparts produced by the thin-boundary-layer model [A. D. Pierce, Acoustics (McGraw-Hill, New York, 1981)]. Special attention is devoted to the case when the motionless sphere is sufficiently large relative to the vibrating sphere that it approximates a rigid wall.

Technology Transfer at NASA

There are many roles and persons responsible for effective technology transfer at NASA. The Technology Utilization Division is primarily responsible for technology transfer and it's role is described. The role of Spinoff and NASA Tech Briefs are cornerstones in a program to make NASA's technology available. The librarian's role is to bring together all of the information resources that come to bear on a topic, including NASA/RECON and ARIN. The added ingredient of a librarian in the technology transfer picture expands the horizon of inquiry beyond traditional technology transfer. At the same, time, when a librarian is exposed to technology transfer programs, it enhances his/her usefulness to patrons beyond traditional library science limits.

Surface fatigue life of carburized and hardened M50NiL and AISI 9310 spur gears and rolling-contact test bars. (Report): Townsend, D. P. and Bamberger, E. N. NASA Tech. Memo. TM-101979 1989, 16 pp

Surface fatigue life of carburized and hardened M50NiL and AISI 9310 spur gears and rolling-contact test bars. (Report): Townsend, D. P. and Bamberger, E. N. NASA Tech. Memo. TM-101979 1989, 16 pp

NASA Patter

Some developments of interest to the optics community have been selected by Charles Braun from NASA Tech Briefs13, No. 8 ( Aug.1989) Further information can be obtained by writing to NASA STI Facility, Manager TU Division, P.O. Box 8757, BWI Airport, Baltimore, MD 21240-9985, citing the identifying number.

New surface patches for minimal balance surfaces. IV. Catenoids with spout-like attachments

The way in which Schoen [Infinite Periodic Minimal Surfaces Without Self-intersections (1970), NASA Tech. Note No. D-5541] derived a simply connected surface patch for a C(H) surface cannot be generalized. One may, however, subdivide a C(H) surface into larger patches that are not simply connected. Surface patches of analogous shape give rise to five families of minimal balance surfaces unknown so far: tetragonally and orthorhombically distorted C(P) surfaces, surfaces complementary to Schoen's R2 and R3 surfaces with genus 25 and 37, respectively, and orthorhombic surfaces of a fifth family with genus 5 that are also complementary to oP surfaces.