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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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NASA NTRS2020

Streak Instabilities on HIFiRE-5 Elliptic Cone

The Hypersonic International Flight Research and Experimentation (HIFiRE) 5 flight experiment by the Air Force Research Laboratories and Australian Defense Science and Technology Organization yielded inflight, hypersonic transition data for a canonical, 3D configuration in the form of an elliptic cone at various combinations of angle-of-attack and yaw. Previous analysis has shown that boundary-layer stability calculations for the as-flown, zero-yaw flight conditions are able to capture the second mode dominated transition along the attachment line as well as the crossflow induced transition in between the attachment line and the minor axis symmetry plane. However, there is still a need to understand the transition in the vicinity of the minor axis plane of symmetry, where the boundary layer thickness exhibits an azimuthally compact bulge due to the collision of the secondary flow approaching from the attachment lines on both sides. This paper reports a computational analysis of the stability of the boundary layer flow along the bulge regions on both the leeward and windward sides of the vehicle surface. At a representative flight condition corresponding to a time instant of t = 514.813 seconds, computations are performed to identify several different unstable modes within the bulge regions, with the eventual goal of developing a linear stability correlation for the transition onset near the minor axis symmetry plane. The most amplified flow instabilities in the pretransitional region correspond to a “stem” mode that is concentrated within a pair of nearly vertical shear layers below the cap of the mushroom shaped bulge in the mean velocity contours. An excellent agreement is found between the predictions of instability amplification based on the plane marching parabolized stability equations (PSE) and the direct numerical solutions (DNS). Given the large number of unstable modes within the bulge region, the observed agreement demonstrates, for first time, that the PSE can provide accurate predictions for the development of flow instabilities in streak-like flow features over three-dimensional bodies. The peak N-factor of approximately 15 at the transition location estimated from the thermocouple measurements along the leeward centerline is close to the transition N-factor for Mack mode transition during the HIFiRE-1 circular cone flight experiment with nearly zero degrees angle of attack.

Meelan Choudhari↗
NASA NTRS2003

Active Control of Low-Speed Fan Tonal Noise Using Actuators Mounted in Stator Vanes: Part III Results

A test program to demonstrate simplification of Active Noise Control (ANC) systems relative to standard techniques was performed on the NASA Glenn Active Noise Control Fan from May through September 2001. The target mode was the m = 2 circumferential mode generated by the rotor-stator interaction at 2BPF. Seven radials (combined inlet and exhaust) were present at this condition. Several different error-sensing strategies were implemented. Integration of the error-sensors with passive treatment was investigated. These were: (i) an in-duct linear axial array, (ii) an induct steering array, (iii) a pylon-mounted array, and (iv) a near-field boom array. The effect of incorporating passive treatment was investigated as well as reducing the actuator count. These simplified systems were compared to a fully ANC specified system. Modal data acquired using the Rotating Rake are presented for a range of corrected fan rpm. Simplified control has been demonstrated to be possible but requires a well-known and dominant mode signature. The documented results here in are part III of a three-part series of reports with the same base title. Part I and II document the control system and error-sensing design and implementation.

Sutliff, Daniel L.↗
NASA NTRS1982

Mechanisms for lithospheric heat transport on Venus Implications for tectonic style and volcanism

The mechanisms of plate recycling, lithospheric conduction, and hot spot volcanism are each evaluated to determine which is the dominant mode of lithospheric heat transfer on Venus, with attention given to the implications of each mechanism for the interpretation of Venus surface features. It is thought that plate recycling on Venus cannot be excluded on the basis of either theoretical arguments or present observations on topography and radar backscatter. Landforms caused by plate convergence and divergence on Venus, it is noted, would differ substantially from those on the earth owing to the high surface temperature and the absence of oceans on Venus, the lack of free or hydrated water in subducted material, the possibility that subduction would more commonly be accompanied by lithospheric delamination, and the rapid spreading rates that would be required if plate recycling removed a significant fraction of the internal heat. The possibility that the dominant mechanism early in the history of the planet was different from the one at work now is thought to merit consideration.

Solomon, S. C.↗
NASA NTRS2010

Shallow and Deep Latent Heating Modes Over Tropical Oceans Observed with TRMM PR Spectral Latent Heating Data

The global hydrological cycle is central to the Earth's climate system, with rainfall and the physics of its formation acting as the key links in the cycle. Two-thirds of global rainfall occurs in the Tropics. Associated with this rainfall is a vast amount of heat, which is known as latent heat. It arises mainly due to the phase change of water vapor condensing into liquid droplets; three-fourths of the total heat energy available to the Earth's atmosphere comes from tropical rainfall. In addition, fresh water provided by tropical rainfall and its variability exerts a large impact upon the structure and motions of the upper ocean layer. Three-dimensional distributions of latent heating estimated from Tropical Rainfall Measuring Mission Precipitation Radar (TRMM PR)utilizing the Spectral Latent Heating (SLH) algorithm are analyzed. Mass-weighted and vertically integrated latent heating averaged over the tropical oceans is estimated as approx.72.6 J/s (approx.2.51 mm/day), and that over tropical land is approx.73.7 J/s (approx.2.55 mm/day), for 30degN-30degS. It is shown that non-drizzle precipitation over tropical and subtropical oceans consists of two dominant modes of rainfall systems, deep systems and congestus. A rough estimate of shallow mode contribution against the total heating is about 46.7 % for the average tropical oceans, which is substantially larger than 23.7 % over tropical land. While cumulus congestus heating linearly correlates with the SST, deep mode is dynamically bounded by large-scale subsidence. It is notable that substantial amount of rain, as large as 2.38 mm day-1 in average, is brought from congestus clouds under the large-scale subsiding circulation. It is also notable that even in the region with SST warmer than 28 oC, large-scale subsidence effectively suppresses the deep convection, remaining the heating by congestus clouds. Our results support that the entrainment of mid-to-lower-tropospheric dry air, which accompanies the large-scale subsidence is the major factor suppressing the deep convection. Therefore, representation of the realistic entrainment is very important for proper reproduction of precipitation distribution and resultant large-scale circulation.

Takayabu, Yukari N.↗
NASA NTRS1985

Electron-cyclotron maser emission during solar and stellar flares

Radio bursts, with high brightness temperature 10 to the 10th power K and high degree of polarization, and the heating of the solar and stellar coronae during flares have been attributed to emission from the semirelativistic maser instability. In plasmas where the electron-plasma frequency, p, omega sub p, and the electron-cyclotron frequency, Omega sub e, are such that omego sup 2 sub p/Omega sup 2 sub e 1, x-mode growth dominates while z-mode growth dominates if omega sup 2 sub p/Omega sup 2 sub e at which x-mode growth dominates is shown to be dependent on the plasma temperature with x-mode growth dominating at higher omega sub p/Omega sub e as the plasma temperature increases. Observations from a set of 20 impulsive flares indicate that the derived conditions for the dominance of x-mode growth are satisfied in about 75 percent of the flares.

Winglee, R. M.↗
NASA NTRS1965

Waveguide feeder system for the Goonhilly satellite-communication earth station

There are two features which distinguish the feeder arrangements at a satellite earth station from those used in conventional microwave line-of-sight links. The first is the importance of low loss in all waveguides and components and the second is the need for rotating joints. Losses are important in the receive direction because they contribute significantly to the overall system noise temperature while, in the transmit direction, not only do they waste expensive transmitter power but localized points of high loss can give rise to the formation of arcs when the power is applied. Rotating joints are required on the elevation axis of the aerial to permit waveguide connection between apparatus in the turntable cabin and on the dish. In the installation at Goonhilly, three separate waveguide connections are required between the turntable cabin and the focus platform; one each for the Telstar and Relay transmitters operating at 6390 and 1725 Mc/s respectively, and one for the receiver feed, routed via the maser cabin on the back of the dish and operating at 4170 and 4080 Mc/s. Dominate-mode rectangular waveguide is used for these runs, and the components and installation practices used follow normal practice as far as possible.

GROUND STATION↗
NASA NTRS1972

Atmospheric helium and geomagnetic field reversals.

The problem of the earth's helium budget is examined in the light of recent work on the interaction of the solar wind with nonmagnetic planets. It is proposed that the dominant mode of helium (He4) loss is ion pumping by the solar wind during geomagnetic field reversals, when the earth's magnetic field is very small. The interaction of the solar wind with the earth's upper atmosphere during such a period is found to involve the formation of a bow shock. The penetration altitude of the shock-heated solar plasma is calculated to be about 700 km, and ionization rates above this level are estimated for a cascade ionization (electron avalanche) process to average 10 to the 9th power ions/sq cm/sec. The calculated ionization rates and the capacity of the solar wind to remove ionized helium (He4) from the upper atmosphere during geomagnetic dipole reversals are sufficient to yield a secular equilibrium over geologic time scales. The upward transport of helium from the lower atmosphere under these conditions is found to be adequate to sustain the proposed loss rate.

Sheldon, W. R.↗
NASA NTRS1972

A computer-aided regulator design.

A unified computer-aided method for the design of linear and nonlinear regulators is discussed. The general mathematical programming approach considered involves the determination of a vector that solves the problem of minimizing the objective function subject to constraints. Classical design problems stated are related to stability design, dominant mode design, and comprehensive design. A computer algorithm is also developed.

Karmarkar, J. S.↗
NASA NTRS1973

Ammonium perchlorate gasification and combustion at high heating rates and low pressures.

Mass-spectrometric and linear regression rate characterizations are reported, derived from CO2 laser pyrolyses of pressed NH2ClO4 (AP) at incident heat fluxes ranging from 25 to 4000 cal/sq cm sec. Product evolution-rate histories were obtained in vacuo by time-resolved (5 msec) mass spectrometry during (1) transient heat-up, and (2) subsequent quasi-steady vaporization (QSV). Vaporization induction times were obtained for (1); these, coupled with heat-transfer approximations neglecting thermochemical heat release, indicated that optical absorption at 10.6 microns dominated over conduction for heat fluxes much greater than 300. Conclusions applying in vacuo were: preferential desorption of NH3, with net accumulation of adsorbed HClO4, occurred during transient heat-up and onset of condensed phase decomposition (CPD), but preferential decomposition of adsorbed HClO4 (compared to NH3) occurred during QSV when CPD was significant. CPD was the dominant mode of QSV at moderate heat fluxes.

Pellett, G. L.↗
NASA NTRS1971

Control theory analysis of a three-axis VTOL flight director

A control theory analysis of a VTOL flight director and the results of a fixed-based simulator evaluation of the flight-director commands are discussed. The VTOL configuration selected for this study is a helicopter-type VTOL which controls the direction of the thrust vector by means of vehicle-attitude changes and, furthermore, employs high-gain attitude stabilization. This configuration is the same as one which was simulated in actual instrument flight tests with a variable stability helicopter. Stability analyses are made for each of the flight-director commands, assuming a single input-output, multi-loop system model for each control axis. The analyses proceed from the inner-loops to the outer-loops, using an analytical pilot model selected on the basis of the innermost-loop dynamics. The time response of the analytical model of the system is primarily used to adjust system gains, while root locus plots are used to identify dominant modes and mode interactions.

Niessen, F. R.↗
NASA NTRS1975

The solid-state Ku-band power amplifier

A survey of IMPATT diodes and negative resistance amplifiers is presented. The first phase of the amplifier effort is discussed in which a single diode reflection amplifier delivering 0.5 watt at 15 GHz with 10-dB gain over a 1-GHz band was developed. The design of a dominant mode resonant combiner is described along with the characterization of the IMPATT diodes. Results are given on the complete amplifier and on the thermal and graceful failure characteristics of the unit.

Geller, B. D.↗
NASA NTRS1975

Film boiling of mercury droplets

Vaporization times of mercury droplets in Leidenfrost film boiling on a flat horizontal plate are measured in an air atmosphere. Extreme care was used to prevent large amplitude droplet vibrations and surface wetting; therefore, these data can be compared to film boiling theory. Diffusion from the upper surface of the drop appears as a dominant mode of mass transfer from the drop. A closed-form analytical film boiling theory is developed to account for the diffusive evaporation. Reasonable agreement between data and theory is seen.

Baumeister, K. J.↗
NASA NTRS1975

Film boiling of mercury droplets

Vaporization times of mercury droplets in Leidenfrost film boiling on a flat horizontal plate are measured in an air atmosphere. Extreme care was used to prevent large amplitude droplet vibrations and surface wetting; therefore, these data can be compared to film boiling theory. For these data, diffusion from the upper surface of the drop is a dominant mode of mass transfer from the drop. A closed-form analytical film boiling theory is developed to account for the diffusive evaporation. Reasonable agreement between data and theory is seen.

Baumeister, K. J.↗
NASA NTRS1975

A Monte Carlo model for the gardening of the lunar regolith

The processes of movement and turnover of the lunar regolith are described by a Monte Carlo model. The movement of material by the direct cratering process is the dominant mode, but slumping is also included for angles exceeding the static angle of repose. Using a group of interrelated computer programs, a large number of properties are calculated, including topography, formation of layers, depth of the disturbed layer, nuclear-track distributions, and cosmogenic nuclides. In the most complex program, the history of a 36-point square array is followed for times up to 400 million years. The histories generated are complex and exhibit great variety. Because a crater covers much less area than its ejecta blanket, there is a tendency for the height change at a test point to exhibit periods of slow accumulation followed by sudden excavation. In general, the agreement with experiment and observation seems good, but two areas of disagreement stand out. First, the calculated surface is rougher than that observed. Second, the observed bombardment ages, of the order 400 million are shorter than expected (by perhaps a factor of 5).

Arnold, J. R.↗
NASA NTRS1976

Influence of planetary-scale topography on the diurnal thermal tide during the 1971 Martian dust storm

Data obtained with the Mariner 9 infrared spectroscopy experiment during the Martian Dust Storm of 1971 to 1972 are examined for evidence of topographic influence on the atmospheric thermal structure. Temperature perturbations which are well correlated with the planetary scale topography are found superposed on the large amplitude diurnal thermal tide. Applications of tidal theory to the data indicate that the observed perturbations result from the kinematic interaction of the westward traveling diurnal wave with the large scale components of topography. The dominant mode is excited by the wave-number two topography component and is a vertically evanescent eastward traveling wave with an equivalent depth comparable to the atmospheric scale height. The principle dynamic effect of this mode is the enhancement of the amplitude of the near-surface diurnal wind to over 40m/sec in limited areas near 30 deg south latitude. It appears likely that dust was injected into the atmosphere in these regions during the storm.

Conrath, B. J.↗
NASA NTRS1976

Influence of planetary-scale topography on the diurnal thermal tide during the 1971 Martian dust storm

Data obtained with the Mariner 9 infrared spectroscopy experiment during the Martian dust storm of 1971-72 are examined for evidence of topographic influence on the atmospheric thermal structure. Temperature perturbations which are well correlated with the planetary-scale topography are found superposed on the large-amplitude diurnal thermal tide previously reported. Applications of tidal theory to the data indicate that the observed perturbations result from the kinematic interaction of the westward traveling diurnal wave with the large-scale components of topography. The dominant mode is excited by the wavenumber 2 topography component and is a vertically evanescent, eastward traveling wave with an equivalent depth comparable to the atmospheric-scale height. The principle dynamic effect of this mode is the enhancement of the amplitude of the near-surface diurnal wind to over 40 m/s in limited areas near 30 deg S latitude. Thus, it appears likely that dust was injected into the atmosphere in these regions during the storm. Other waves excited include vertically propagating modes which produce little effect in the lower atmosphere, but may represent a source of energy for the upper atmosphere during dust storm conditions.

Conrath, B. J.↗