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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 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Heat transfer characteristics for inline and staggered arrays of circular jets with crossflow of spent air

Heat transfer characteristics were measured for two dimensional arrays of jets impinging on a surface parallel to the jet orifice plate. The impinging flow was constrained to exit in a single direction along the channel formed by the jet plate and the heat transfer surface. Both mean Nusselt numbers and streamwise Nusselt number profiles are presented as a function of Reynolds number and geometric parameters. These are the streamwise and transverse hole spacings ranging from 5 to 10 and 4 to 8 jet orifice diameters, respectively; the channel height ranging from 1 to 6 diameters; and the hole pattern which includes both inline and staggered arrays. The results show that significant periodic variations occur in the streamwise Nusselt number profiles, persisting downstream for at least ten rows of jet holes. Channel height can have a significant effect on the chordwise profiles, smoothed across the periodic variations. For the smaller channel heights, Nusselt numbers first decrease and then increase downstream. Where significant differences exist, inline hole patterns provide better heat transfer than staggered ones. These and other effects of the geometric parameters are presented and discussed.

Metzger, D. E.↗
NASA NTRS1980

Investigation of the flow field surrounding circular-arc boattail nozzles at subsonic speeds

The effects of jet exhaust on the subsonic flow field surrounding boattail nozzles with attached and separated boundary layers were investigated. Measurements of local Mach numbers and flow angles were made at free-stream Mach numbers of 0.60 and 0.80 at an angle of attack of 0 deg. Jet exhaust flow was simulated with a solid cylindrical sting and with high pressure air at jet-nozzle total pressure ratios of 2.9 and 5.0. Results show strong effects of the jet-wave structure on the external flow field. The predicted local Mach numbers and flow angles for attached-flow nozzles with solid jet simulators obtained by using subsonic inviscid/viscous-flow theory are in good agreement with experimental data. Prediction of nozzle surface pressure distributions which include jet-entrainment effects also agree with experimental data for attached-flow nozzles with high pressure air jets.

Abeyounis, W. K.↗
NASA NTRS1980

Multiple band circularly polarized microstrip antenna

A multiple antenna assembly for communicating electromagnetic radiation is disclosed. An antenna element stack is constructed of a plurality of elliptical lamina antenna elements mutally separated by layers of dielectric material, and separated from a ground plane by dielectric material. The antenna assembly is coupled through a feed line in contact with the top antenna element. A conductor joins the remaining antenna elements to the ground plane. Each individual antenna element is operable for communication reception and transmission within a frequency band determined by the size of the particular antenna element. The sizes of the antenna elements may be selected to provide electromagnetic radiation communication over several distinct frequency bands, or to connect the individual bands into a broad band.

Yu, I. P.↗
NASA NTRS1979

Crosstalk cancellation on linearly and circularly polarized communications satellite links

The paper discusses the cancellation network approach for reducing crosstalk caused by depolarization on a dual-polarized communications satellite link. If the characteristics of rain depolarization are sufficiently well known, the cancellation network can be designed in a way that reduces system complexity, the most important parameter being the phase of the cross-polarized signal. Relevant theoretical calculations and experimental data are presented. The simplicity of the cancellation system proposed makes it ideal for use with small domestic or private earth terminals.

Overstreet, W. P.↗
NASA NTRS1980

Thermal conduction in a composite circular cylinder - A new technique for thermal conductivity measurements of lunar core samples

A technique is described for the measurement of the thermal conductivity of lunar core samples. According to their technique, the core sample is heated radiatively from the outside at a known rate, the temperature is measured at the surface of the core-tube, and the thermal conductivity of the sample is determined by comparing the measured temperature with the theory. The corresponding problems for a composite slab or sphere were solved and the solutions are presented for possible future application to the thermal conductivity measurements. The experimental apparatus construction and procedure are examined as well as the number of precautions taken to preserve the sample from disturbances and to improve the measurement results.

Horal, K.↗
NASA NTRS1980

Effect of wing location and strakes on stability and control characteristics of a monoplanar circular missile with low-profile tail fins at supersonic speeds

A wind tunnel test was conducted at Mach numbers from 1.70 to 2.86 to extend the aerodynamic data base for wing tail effect on stability and control characteristics of monoplanar missiles. The results are summarized to show the effects of tail fin dihedral angle, wing location, and nose body strakes. The results indicate that an increase in tail fin dihedral angle produces positive increments in directional stability that allow greater trimmed lift coefficient values (maneuver potential) to be obtained. An increase in wing tail gap for the Mach number range reduces the aerodynamic center travel and produces reductions in directional stability at the lower angles of attack. A change in wing height (vertical location) strongly influences the angle of attack at which pitch up and the most directional stability occur. The addition of strakes to the baseline configuration increases directional stability, which allows a significant increase in stable trimmed maneuver capability. The tail fins of the baseline configuration are effective in producing roll and yaw control that are accompanied by favorable yaw and roll, respectively.

Blair, A. B., Jr.↗
NASA NTRS1980

Thermal conduction in a composite circular cylinder: A new technique for thermal conductivity measurements of lunar core samples

The core sample is heated from the outside at a known rate and the rise in temperature at the surface of the core tube is measured. Because the temperature at the surface, increasing with time, is a function of the thermal properties of both the core tube and the sample, the thermal properties of the sample can be estimated by comparing the measured temperature with the theory, provided that the thermal properties of the core tube are known. Thus it is not necessary to extract the sample from the core tube to make the measurements. Neither is it necessary to insert a heater, or temperature sensor, into the sample within the core tube, as would be required if another method were applied. The sample remains intact after the measurements. The temperature change in the sample can be kept to a minimum as long as the thermal conductivity determination is possible with a reasonable precision. If the radiative method of heat transfer is chosen, the core tube will only be in mechanical contact with the sample holder and a sensor attached to the core tube to measure the surface temperature, thereby greatly reducing the possibility of disturbing the sample.

Horai, K.↗
NASA NTRS1980

Vortex pairing in a circular jet under controlled excitation. I - General jet response. II - Coherent structure dynamics

Hot-wire and flow visualization studies were performed in three air jets subjected to pure-tone excitation. The instability, vortex roll-up, and transition to the controlled excitation were investigated. The conditions most favorable to vortex parting were determined as a function of the excitation Strouhal number, the Reynolds number, and the initial shear-layer state; it was shown that the rolled-up vortex rings undergo pairing under 'the shear layer mode', and the 'jet-column mode' when the Strouhal numbers based on the initial shear-layer momentum thickness are 0.012 and 0.85, respectively. Coherent ring-like vortical structures could be educed to the end of the potential core; however, the paired vortex becomes weaker with increasing downstream distances. The transverse transport of 'u' momentum by the coherent structures was much larger during the pairing process than in regions where a single vortex is studied.

Zaman, K. B. M. Q.↗
NASA NTRS1981

Heat transfer in a periodic boundary layer near an axisymmetric stagnation point on a circular cylinder

An analysis is presented to investigate the time-mean characteristics of the laminar boundary layer near an axisymmetric stagnation point when the velocity of the oncoming flow relative to the body oscillates. Different solutions are obtained for the small and high values of the reduced frequency parameter. Numerical solutions for the velocity and temperature functions are presented and the wall values of the velocity gradients are tabulated.

Gorla, R. S. R.↗
NASA NTRS1980

Application of transmission loss concept in the evaluation of an acoustic filter for liquid-borne transverse resonance modes in a duct of circular cross section

The transmission loss concept is used in the evaluation of an acoustic filter for liquid-borne transverse modes. Tests are conducted to determine the nature of filter element designs required to suppress transverse modes, to verify the presence of transverse modes in the test assembly, to define the acoustic wave incident, and to establish data recording, processing and analysis techniques providing transmission wave filter data. The first, second, and third tangential modes, and the first radial mode are found at frequencies of 2150, 3330, 4420, and 4110 Hz, respectively, and peaks of the tangential modes recede while the radial mode peak remains, demonstrating agreement with theoretical nodal patterns. The present design is found applicable to a liquid-oxygen system, and allows the easy-to-fabricate filter to fit within the available space envelope.

Iwanicki, L. R.↗
NASA NTRS1981

An experimental investigation of the flow past a finite circular cylinder at a low subcritical Reynolds number

Results of hot wire measurements made in the near wake at a Reynolds number of 9955 are reported. The measurements include the mean velocity profiles, root mean square values of the velocity fluctuations, frequency spectra, and velocity cross correlations. The mean velocity profiles were used to determine the wake width, whose variation in the downstream and spanwise directions was examined. It is observed that close to the cylinder, the wake is narrower toward the free end than it is away from it, while further downstream the wake is wider toward the tip than it is away from it. It is found that the flow over the span can be characterized by four regions: a tip region where vortex shedding occurs at a lower frequency than that prevalent for away from the tip; an intermediate region adjacent to the first one where a frequency component of a nonshedding character is present; a third region characterized by a gradually increasing shedding frequency with increasing distance from the tip; and a two dimensional region where the shedding frequency is constant.

Budair, M.↗
NASA NTRS1981

Green's function for cracks of equal length from a circular hole in an infinite sheet

Stress-intensity factors are obtained for twin collinear cracks emanating from a hole in an infinite plate. Point forces that tend to make the crack surfaces separate and slide are applied to one of the cracks. A conformal mapping and the Muskelishvili formulation involving series representation of the Kolosov stress functions are used to derive the solutions. The variation of stress-intensity factor with crack length and with point of application of the loads is presented for both crack tips.

Shivakumar, V.↗
NASA NTRS1982

The isolated non-circular ringlets of Saturn

It is shown that the combined effect of electrodynamic and gravitational forces can account for a number of features observed by Voyagers 1 and 2 in the isolated fine dust rings of Saturn. These include the appearance and disappearance of the braids in the F-ring, the eccentricities of the F-ring and the ringlets within the Encke and Cassini divisions and a gap in the C-ring, and the kinks in the eccentric Encke ring. They may also account for the very existence of these rings.

Hill, J. R.↗
NASA NTRS1983

Sound diffraction at wall impedance discontinuities in a circular cylinder - Investigated using Wiener-Hopf technique

The results of ground observations as well as high resolution rocket electric field and particle observations during a breakup event of an intense magnetospheric substorm over northern Scandinavia are discussed. In particular, the characteristics of the substorm-associated electric field, ionospheric currents, and power dissipation during a time period about 15 minutes after substorm onset are addressed. A comparison of the observations with those of a pre-breakup event earlier in the day (Marklund et al., 1982) showed that the ionospheric substorm-related electric field could be split up into two parts: (1) an ambient LT-dependent field, probably of magnetospheric origin; and (2) a small-scale electric field associated with the bright auroral structures, which is superimposed on the LT-dependent field. The consequences for the location of the ionospheric currents and the Joule energy dissipation relative to the auroral forms are discussed. Previously announced in STAR as N83-23117

Cho, Y.-C.↗
NASA NTRS1982

Effects of free stream turbulence intensity and integral length scale on heat transfer from a circular cylinder in crossflow

A model has been proposed for the momentum eddy diffusivity induced by free stream turbulence intensity and integral length scale. The eddy diffusivity model is applied to a cylinder situated in a uniform crossflow in the presence of free stream turbulence. Numerical solution of the governing momentum and energy equations with the proposed eddy diffusivity model yielded results for the skin friction coefficient and the Nusselt number. The numerical predictions of the present work are compared with experimental data and the agreement between the two is seen to be very good.

Gorla, R. S. R.↗