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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Altitude engine test of a turbofan exhaust gas mixer to conserve fuel

A comparison of the specific fuel consumption was made with and without an internal mixer installed in a low bypass ratio, confluent flow turbofan engine. Tests were conducted at several Mach numbers and altitudes for core to fan stream total temperature ratios of 2.0 and 2.5 and mixing lengths of L/D = 0.95 and 1.74. For these test conditions, the specific fuel consumption improvement varied from 2.5 to 4.0 percent.

Cullom, R. R.↗
NASA NTRS1980

Computation of three-dimensional flow in turbofan mixers and comparison with experimental data

A three dimensional, viscous computer code was used to calculate the mixing downstream of a typical turbofan mixer geometry. Experimental data obtained using pressure and temperature rakes at the lobe and nozzle exit stations were used to validate the computer results. The relative importance of turbulence in the mixing phenomenon as compared with the streamwise vorticity set up by the secondary flows was determined. The observations suggest that the generation of streamwise vorticity plays a significant role in determining the temperature distribution at the nozzle exit plane.

Povinelli, L. A.↗
NASA NTRS1980

Computation of three-dimensional flow in turbofan mixers and comparison with experimental data

A three-dimensional, viscous computer code was used to calculate the mixing downstream of a typical turbofan mixer geometry. Experimental data were obtained using pressure and temperature rakes at the lobe and nozzle exit stations. Secondary flow velocities were also obtained. These data were used to validate the computer results. An assessment was also made to determine the relative importance of turbulence in the mixing phenomenon as compared with the streamwise vorticity set up by the secondary flows. The observations suggest that the generation of streamwise vorticity appears to play a significant role in determining the temperature distribution at the nozzle exit plane.

Povinelli, L. A.↗
NASA NTRS1980

Influence of pressure driven secondary flows on the behavior of turbofan forced mixers

An analytical and experimental study was performed to determine the influence of pressure driven secondary flows on the behavior of turbofan forced mixer nozzles. The basic secondary flow structure entering the nozzle was identified experimentally and was composed of a strong vortex system aligned with the radial interface between the fan and core streams. A generic secondary flow vortex structure was constructed for input to the analysis to represent the large scale structure of this inflow condition. Comparison between experiment and analysis at five axial stations showed very good agreement and indicated that this vortex system was convected downstream and dominated the mixing process.

Anderson, B.↗
NASA NTRS1980

Projected noise in submillimeter-wave mixers with InSb Schottky diodes

The reduction of the equivalent noise temperature in liquid-nitrogen-cooled submillimeter-wave mixers by the use of Schottky barriers on InSb instead of GaAs is evaluated by an analytical model that assumes limited local oscillator power and matched impedances. The calculations, executed at 1.0 and 1.8 THz, take plasma resonance and skin effect into account. For single and multiple contacts on homogeneous semiconductor materials of optimum doping, the noise of InSb diodes is smaller than that of GaAs diodes by a factor of 3 to 14. A simplified model is used to predict the performance of epitaxial structures as well as alternative materials.

Lieneweg, U.↗
NASA NTRS1981

Super-Schottky mixer performance at 92 GHz

As part of a program to investigate the behavior of superconducting Schottky mixers at high frequencies, the mixing and video performance of several super-Schottky diodes (a 3-micron active diameter, and a doping concentration of 2 x 10 to the 19th per cu cm) have been tested at 92 GHz. At 92 GHz, video responsivities were typically 80 A/W (corrected for RF mismatch). Conversion loss (corrected for both RF and IF mismatches) was typically not less than 18 dB. As expected, diode temperature was low (less than 5 K). Video responsivity and conversion loss were also measured at an RF frequency of 3.95 GHz. These data were used with the measured volt-ampere characteristics of the diodes to compare theoretical predictions of diode performance at 92 GHz, in both the video and mixing modes, with the high-frequency data

Dickman, R. L.↗
NASA NTRS1981

Improved liquid phase epitaxial GaAs for low series resistance Schottky barrier mixer diodes

Millimeter wave Schottky barrier mixer diodes are extremely important devices for radio astronomy. The performance of the Schottky diodes depends largely on the characteristics and quality of the GaAs epitaxial materials used. Systematic manipulation of the liquid phase epitaxial growth conditions and substrate surface treatments has yielded significantly improved surface morphology. Initial problems of high resistivity interfacial layers have been reduced without the use of an in situ etchback. Two-micron diameter Schottky diodes fabricated from epitaxial layers grown at 725 C exhibit a 9-ohm series resistance very near the theoretical minimum.

Binari, S. C.↗
NASA NTRS1982

Turbofan forced mixer-nozzle internal flowfield. Volume 2: Computational fluid dynamic predictions

A general program was conducted to develop and assess a computational method for predicting the flow properties in a turbofan forced mixed duct. The detail assessment of the resulting computer code is presented. It was found that the code provided excellent predictions of the kinematics of the mixing process throughout the entire length of the mixer nozzle. The thermal mixing process between the hot core and cold fan flows was found to be well represented in the low speed portion of the flowfield.

Werle, M. J.↗
NASA NTRS1982

Experiments on high bypass internal mixer nozzle jet noise

Model scale jet noise data are presented for a variety of internal lobed mixer nozzle configurations for take off power settings in a static environment. The results are presented for a 17.5 cm diameter fan nozzle to show the effect on noise levels caused by changes in geometric shape of the internal, or core flow, nozzle. The geometric variables include the lobe discharge angle, the number of lobes, spacing between the center plug and lobe valley, lobe side wall shape and axial contour of the lobes. An annular plug core flow nozzle was also tested and is used as a baseline for comparative purposes. Comparison of data from the internal lobed configurations showed that for comparative effect, in terms of the effect on full scale perceived noise levels, was caused by a change in the lobe discharge angle. The results showed that increasing the discharge angle caused an increase as large as 7 dB in sound pressure levels in the high frequency portion of the spectra. Changes in the other geometric variables cause negligible effects.

Goodykoontz, J. H.↗
NASA NTRS1983

Further development of a method for computing three-dimensional subsonic viscous flows in turbofan lobe mixers

Procedure for computing subsonic, turbulent flow in turbofan lobe mixers was extended to allow consideration of flow fields in which a swirl component of velocity may be present. Additional, an optional k-lambda turbulence model was added to the procedure. The method of specifying the initial flow field was also modified, allowing parametric specification or radial secondary flow velocities, and making it possible to consider initial flow fields which have significant inlet secondary flow vorticity. A series of example calculations was performed which demonstrate the various capabilities of the modified code. These calculations demonstrate the effects of initial secondary flows of various magnitudes, the effects of swirl, and the effects of turbulence model on the mixing process. The results of these calculations indicate that the initial secondary flows, presumed to be generated within the lobes, play a dominant role in the mixing process, and that the predicted results are relatively insensitive to the turbulence model used.

Lin, S. J.↗
NASA NTRS1982

Automatic millimeter wave mixer noise figure measurements

Systems for making automatic noise figure measurements of millimeter wave mixers have been developed using both analog and digital techniques. The effect of IF mismatch on the measured noise figures is also determined with these methods (Forsythe, 1982). The measurement systems are versatile enough to be used to measure the noise figure of receivers anywhere from 30 to 300 GHz.

Forsythe, R. E.↗
NASA NTRS1985

Mechanical Mixer for Rudder/Braking Wedge

Right and left rudder panels moved separately. Mechanical mixer enables panels of two-panel rudder to rotate in same direction for steering or in opposite directions for dynamic braking. Steering and braking inputs separate so any combination of steering and braking motions executed simultaneously. Developed for aerodynamic braking of Space Shuttle orbiter, steering/braking drive train and rudder arrangement used for similar purposes on aircraft, thereby reducing sizes of thrust reversers.

Grimm, D.↗
NASA NTRS1984

Formation of planar n(+) pockets in GaAs for mixer diode fabrication

A novel technique has been developed to produce n(+) 'pockets' in semiinsulating GaAs bulk material. This technique has produced thick pockets of highly conducting epitaxial material on the substrate surface. The pockets were formed by the growth of a liquid-phase epitaxial (LPE) layer into holes which had been etched into the substrate. Surface uniformity was obtained by chemo-mechanically polishing the substrate surface under tightly controlled conditions. Polishing rates as low as 0.2 micron/min have been obtained. Photographs taken of the pocket cross-sectional area have revealed that growth occurred throughout the entire pocket region. Growth was even found to have occurred along the irregularly shape walls of the packets. The continuous growth throughout the pockets coupled with the subsequent polishing of the substrate have produced exceptionally smooth and planar surfaces. Thicknesses as great as 10 microns have been obtained for the n(+) pockets using this technique. Mixer diodes have been fabricated onto these layers and tested. Preliminary dc measurements taken on these devices have yielded a zero-biased cutoff frequency (Fco) of 800 GHz with a series resistance (Rs) of 6 omega and a zero-biased capacitance (Co) of 30 fF.

Griffin, J. A.↗
NASA NTRS1986

Forced mixer lobes in ejector designs

Forced mixer lobes in augmentor primary ejectors obtain a 100-percent increase in pumping over conventional design, together with nearly complete mixing in very short mixing ducts, through the generation of large scale axial vorticity in the mixing duct. The vorticity causes rapid mixing of the primary and secondary flows with low losses; since mixing length is minimized, wall friction losses are reduced, allowing more secondary flow to be pumped for a given total pressure in the primary flow. Analytical results are presented that are judged to have significant implications for future ejector test work.

Presz, W. M., Jr.↗
NASA NTRS1989

Multiplying Video Mixer

Video mixing circuit places transparent overlay image on all or portion of normal image on television screen. Overlay computer-generated graphics, text, or another image. Background video brightness signal fed into one input terminal of circuit, while overlay brightness signal fed into other input terminal. Amplitude of background brightness signal modulated by overlay brightness signal, resulting in video image in which background image appears as though viewed through overlay. Multiplying video mixer, combined with additional circuitry, places transparent or opaque overlay images on normal (background) video images.

Heckt, Neil W.↗
NASA NTRS1989

A corner-reflector mixer mount for far infrared wavelengths

A new type of corner-reflector mixer mount, which has the advantages of ease of fabrication and assembly as well as frequency versatility, has been designed and constructed. The predicted response patterns have been experimentally verified for various antenna lengths and operating frequencies between 800 and 2000 GHz. An important design feature is the incorporation of a microstrip matching network which eliminates IF impedance mismatch and provides mechanical isolation for the whisker antenna.

Zmuidzinas, J.↗
NASA NTRS1990

Temperature automation for a propellant mixer

The analysis and installation of an automatic temperature controller on a propellant mixer is presented. Ultimately, the entire mixing process will come under automation, but since precise adherence to the temperature profile is very difficult to sustain manually, this was the first component to be automated. Automation is not only important for producing a uniform product, but it is necessary for envisioned space-based propellant production.

Vincent, T. L.↗