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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Effect of interjet spacing on mixing of multiple coaxial jets in supersonic flow

An experimental and analytical investigation of strut-mounted, four-nozzle, downstream facing, gaseous fuel injector assembly was conducted in a Mach 4 air-stream with P = 154 psia and T sub o 520 R. Helium was used as the injectant, and the interjet spacing (S/D) was the main parameter varied. The principal data are in the form of Helium concentration profiles at seven axial stations, Mach number distributions at three axial stations and schlieren photographs of the flow field at different interjet spacings. An approximate analysis was developed based upon a linearization in the Von Mises plane, Crocco integrals for the temperature and concentrations fields and an eddy viscosity model. Good agreement with the data was achieved. It was found that, at these conditions, interjet spacing has an effect on mixing only up to S/D of approximately 2.5, with concentration of injectant becoming smaller as S/D is increased, and the Mach number downstream of the injector tends to decrease with decreasing S/D.

Lorber, A. K.↗
NASA NTRS1977

The flow field of an underexpanded H2 jet coaxially injected into a hot free or ducted supersonic jet of air or nitrogen

Experimental data obtained in an investigation of the mixing of an underexpanded hydrogen jet in a supersonic flow both with and without combustion are presented. Tests were conducted in a Mach 2 test stream with both air and nitrogen as test media. Total temperature of the test stream was 2170 K, and static exit pressure was about one atmosphere. The static pressure at the exit of the hydrogen injector's Mach 2 nozzle was about two atmospheres. Primary measurements included shadowgraphs and pitot pressure surveys of the flow field. Pitot surveys and wall static pressures were measured for the case where the entire flow was shrouded. The results are compared to similar experimental data and theoretical predictions for the matched pressure case.

Jenkins, R. V.↗
NASA NTRS1978

Coaxial isolator has versatile interface

Approach increases system-packaging flexibility. Isolators are constructed with removable connectors that can be changed to meet user's requirements. Technique reduces development scheduling problems. Isolators can be procured before package design is firm and then readily reconfigured to meet final design requirements. Changes to existing designs to incorporate removable connectors are minimal. Small adapter plates increase size modestly; weight increase is negligible.

Olsson, D. L.↗
NASA NTRS1976

Review of coaxial flow gas core nuclear rocket fluid mechanics

The two areas where discussion and comparison of work is most useful are in (1) the factors which influence containment in cold flow studies; and (2) the effects of heat generation on containment. The work in these areas have not received any critical review in the past. The review is structured in such a way as to compare and contrast the related work of the program, rather than to preserve the chronological order of the work.

Weinstein, H.↗
NASA NTRS1978

Aerodynamic characteristics of a counter-rotating, coaxial, hingeless rotor helicopter model with auxiliary propulsion

A wind-tunnel model test at advance ratios from 0 to 0.3 with and without auxiliary jet engine thrust is reported. At each advance ratio and engine thrust, both the control power and the aircraft stability were measured. The results indicate that there is a cross-coupling for collective pitch and longitudinal cyclic pitch inputs. The control power for these inputs increased with advance ratio. There was also cross-coupling for differential collective pitch inputs. The airframe was longitudinally unstable, but the instability was less at the highest advance ratio tested. The airframe showed both positive effective dihedral and positive directional stability.

Phelps, A. E., III↗
NASA NTRS1979

Studies of the acoustic transmission characteristics of coaxial nozzles with inverted velocity profiles: Comprehensive data report

The efficiency of internal noise radiation through a coannular exhaust nozzle with an inverted velocity profile was studied. A preliminary investigation was first undertaken (1) to define the test parameters which influence the internal noise radiation; (2) to develop a test methodology which could realistically be used to examine the effects of the test parameters; and (3) to validate this methodology. The result was the choice of an acoustic impulse as the internal noise source in the jet nozzles. Noise transmission characteristics of a coannular nozzle system were then investigated. In particular, the effects of fan convergence angle, core extension length to annulus height ratio and flow Mach numbers and temperatures were studied. Relevant spectral data only is presented in the form of normalized nozzle transfer function versus nondimensional frequency.

Dean, P. D.↗
NASA NTRS1979

Studies of the acoustic transmission characteristics of coaxial nozzles with inverted velocity profiles, volume 1

The efficiency of internal noise radiation through coannular exhaust nozzle with an inverted velocity profile was studied. A preliminary investigation was first undertaken to: (1) define the test parameters which influence the internal noise radiation; (2) develop a test methodology which could realistically be used to examine the effects of the test parameters; (3) and to validate this methodology. The result was the choice of an acoustic impulse as the internal noise source in the in the jet nozzles. Noise transmission characteristics of a nozzle system were then investigated. In particular, the effects of fan nozzle convergence angle, core extention length to annulus height ratio, and flow Mach number and temperatures were studied. The results are presented as normalized directivity plots.

Dean, P. D.↗
NASA NTRS1979

Direct and inverse problems in radiation of sound from discrete random sources on two coaxial rings

An analytical model consisting of two ring sources of sound is developed to study the direct radiation in terms of correlation, coherence, and phase and also to aid in solving the inverse-radiation problem of determining the noise source in terms of farfield measurements. The rings consist of discrete sources which are either monopoles or quadrupoles with Gaussian autocorrelations. Only adjacent sources, both within and between the rings, are correlated. Results show that from the farfield information one can determine when the sources are compact or noncompact with respect to the acoustic wavelength and distinguish between the types of sources. In addition, from the inverse-radiation approach one can recover the center of mass, the location and separation distance of the ring, and the respective diameters.

Maestrello, L.↗
NASA NTRS1980

Coaxial radiative and convective heat transfer in gray and nongray gases

Coupled radiative and convective heat transfer is investigated for an absorbing gas flowing in a finite length channel and heated by blackbody radiation directed along the flow axis. The problem is formulated in one dimension and numerical solutions are obtained for the temperature profile of the gas and for the radiation escaping the channel entrance, assuming both gray and nongray absorption spectra. Due to radiation trapping, the flowing gas is found to have substantially smaller radiation losses for a given peak gas temperature than a solid surface that is radiatively heated to this temperature. A greenhouse effect is also evident whereby radiation losses are minimized for a gas having stronger absorption at long wavelengths.

Mattick, A. T.↗
NASA NTRS1981

Modal content of noise generated by a coaxial jet in a pipe

Measurements of the hydrodynamic pressure fluctuation levels showed that, for circular obstructions with a flow passage diameter less than one-half of the pipe diameter, hydrodynamic pressure fluctuations were small compared with the acoustic pressure, at locations greater than ten pipe diameters downstream of the restrictions. Thus, in the study currently reported, which was concentrated on measurement of the modal characteristics of the sound field downstream of the restrictions, special techniques to avoid contamination by hydrodynamic 'noise' were not necessary. The major results obtained in the study are scaling laws for the shape of the modal pressure spectrum and for the overall efficiency of noise generation. The characteristics of the modal pressure spectra are discussed. It is shown that the primary parameter controlling the spectrum shape is the frequency ratio (Helmholtz number/Strouhal number). The efficiency levels when plotted as a function of Mach number show a strong dependence on restriction size

Kerschen, E. J.↗
NASA NTRS1981

Performance and loads data from a wind tunnel test of a full-scale, coaxial, hingeless rotor helicopter

A full-scale XH-59A advancing blade concept helicopter was tested in Ames Research Center's 40 by 80 foot wind tunnel. The helicopter was tested with the rotor on and off, rotor hub fairings on and off, interrotor shaft fairing on and off, rotor instrumentation module on and off, and auxiliary propulsion thrust on and off. An advance ratio range of 0.25 and 0.45 with the rotor on and from 60 to 180 knots with the rotor off was investigated. Data on aerodynamic forces and moments, rotor loads, rotor control positions and vibration for the XH-59A as well as the aerodynamic performance of the isolated rotor are presented.

Felker, F. F., III↗
NASA NTRS1983

Coaxial Redundant Drives

Harmonic drives allow redundancy and high out put torque in small package. If main drive fails, standby drive takes over and produces torque along same axis as main drive. Uses include power units in robot for internal pipeline inspection, manipulators in deep submersible probes or other applications in which redundancy protects against costly failures.

Brissette, R.↗
NASA NTRS1985

Investigation of weld joint detection capabilities of a coaxial weld vision system

This report describes the second phase of a series of evaluations of a vision-based welding control sensor for the Space shuttle Main Engine Robotic Welding System. The robotic welding system is presently under development at the Marshall Space Flight Center. This evaluation determines the factors influencing the minimum joint gap required for consistent detection of the weld joint.

Gangl, K. J.↗
NASA NTRS1985

Influence of control parameters on the joint tracking performance of a coaxial weld vision system

The first phase of a series of evaluations of a vision-based welding control sensor for the Space Shuttle Main Engine Robotic Welding System is described. The robotic welding system is presently under development at the Marshall Space Flight Center. This evaluation determines the standard control response parameters necessary for proper trajectory of the welding torch along the joint.

Gangl, K. J.↗
NASA NTRS1985

Modeling of dense sprays from LOX/H2 coaxial injectors under supercritical conditions

Assumptions commonly employed in the analytical description of a thin spray become unacceptable as the droplet density and droplet volume displacement become large. Changes in the semiempirical models describing drop-drop or drop-gas interactions as well as in the basic modeling approach itself may be necessary. A number of efforts undertaken to improve such models of the atomization-evaporation process to render them applicable in the dense-spray, supercritical regime are described. The improvements include those for variable drop density, supercritical properties, stripping evaporation and drop reincorporation into the liquid stream. The models are developed for use with the ARICC three-phase finite difference combustion code. Selected results from a sample calculation are presented, demonstrating the enhanced realism achievable with the upgraded models.

Liang, P. Y.↗