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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 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Two-watt radioisotope power generators for underwater applications

Materials and design considerations are discussed for a low-cost, reliable radio-isotope-fueled thermoelectric generator for use in an undersea application. Plutonium has been selected as fuel, and the generator has to meet design goals of 2 watts after 20 years with a direct output voltage of 6-8 volts. The pressed and sintered form of Bi2Te3 appears to be the most appropriate thermoelectric material. Both fibrous and multilayer foil insulation could be used with proper processing and quality control, but there is less risk with fibrous type insulation. Min-K 1400 is recommended with a nitrogen cover gas. The heat source recommended is a three-layer capsule using T-111 for both the liner and strength member with an outer liner of Hastelloy-C.

Caputo, R. S.↗
NASA NTRS1974

Investigation of the aerodynamic noise generating region of a jet engine by means of the simple source fluid dilatation model

An experiment was conducted on a full-scale jet engine to investigate the aerodynamic noise generating regions in the free jet. Cross-correlation measurements were made between the static pressure fluctuations and the farfield radiated sound. These measurements were made for two different static pressure probe positions and a large number of farfield positions (at various angles). In addition, each test geometry was run for four different jet exit velocities. The measured, normalized cross-correlation functions varied between 0.004 and 0.155. A new Q-function, based on the above normalized cross correlation is defined and plotted. This function represents the source strength per unit volume within the jet region. This Q-function shows dependence on the probe position, the angular position of the farfield microphone, and the jet exit Mach number. Third-octave analyses of both the probe signal and the farfield radiated sound were made. The results show that cross-correlation techniques are a valuable tool in the investigation of the aerodynamic noise generating regions of an actual jet engine.

Hurdle, P. M.↗
NASA NTRS1975

The convergence of theory and experiment in direct combustion generated noise

Current theories of combustion generated noise are reviewed with regard to their ability to predict the sound power output and spectral characteristics of noise generated by several flame types. New experimental information on open turbulent flames and on gas turbine combustor cans is presented. Available information on gas phase diffusion flames is reviewed. It is concluded that if some of the gross turbulence features of the flame are known and if the acoustical behavior of any flame enclosure is known, then scaling rules for behavior of the sound power output and spectral content may be quite accurately produced by theory. On the other hand, the theory is not sufficiently advanced to make absolute predictions; such predictions must await more detailed knowledge of turbulent flame structure.

Strahle, W. C.↗
NASA NTRS1975

Aerodynamic sound generation due to the interaction of an unsteady wake with a rigid surface

Some aspects of sound generation by the interaction between a wedge and the wake of a circular cylinder in a uniform incompressible stream are studied experimentally. There is a minimum separation distance between the cylinder and the wedge when a tone is first generated. As the separation distance increases beyond the minimum, the frequency increases and asymptotically approaches the frequency normally present in the free wake. The Strouhal number defined as the ratio fd/U where f is the frequency, d is the cylinder diameter and U the free-stream speed is found to be in general a function of the Reynolds number (based on d) and h/d, where h is the separation distance. The minimum distance is in general a function of the Reynolds number. Flow visualization studies show that considerable differences exist between the flow below the minimum separation distance and just above it.

Smith, C. A.↗
NASA NTRS1975

Use of numerically generated body-fitted coordinate systems for solution of the Navier-Stokes equations

A procedure for numerical solution of the time-dependent, two-dimensional incompressible Navier-Stokes equations that can treat the unsteady laminar flow about bodies of arbitrary shape, such as two-dimensional airfoils, multiple airfoils, and submerged hydrofoils, as naturally as it can deal with the flow about simple bodies. The solution is based on a method of automatic numerical generation of a general curvilinear coordinate system with coordinate lines coincident with all boundaries of a general multiconnected region containing any number of arbitrarily shaped bodies. The curvilinear coordinates are generated as the solution of two elliptical partial differential equations with Dirichlet boundary conditions, one coordinate being specified to be constant on each of the boundaries, and a distribution of the other being specified along the boundaries. The solution compares excellently with the Blasius boundary layer solution for the flow past a semiinfinite flat plate.

Thompson, J. F.↗
NASA NTRS1975

The high current transient generator, theory and operation for simulating lightning induced voltages into aerospace electrical circuits

Because of the difficulty, hazard, and cost of simulating full-scale lightning currents on flight vehicles, a nondestructive test technique using reduced-scale lightning currents was used to determine if threat level voltages will be induced into aircraft electrical circuits in the event the aircraft is actually struck by lightning. The reasoning and theory of selecting a particular simulated lightning waveshape and magnitude is given, showing that extrapolation of induced waveforms over several orders of magnitude should be avoided. The operation of high-current transient generators and hardware are described along with typical applications. The means by which voltages were generated, induced, and measured, as well as possible sources of error, are discussed.

Schulte, E. H.↗
NASA NTRS1975

Lip noise generated by flow separation from nozzle surfaces

The results of a series of experiments, performed to investigate flow separation and classic lip noise and to aid in understanding aeroacoustic noise generation are presented. Several types of nozzle-lip configurations were used to study the high frequency noise generated by small regions of flow separation at the nozzle lip. These included coaxial nozzles, and circular and slot nozzles with splitter plates. The jet flow velocity was varied and far field noise was measured for all nozzle-lip geometries (coaxial and splitter plate). The effect of a velocity difference across the lip of the coaxial nozzle and the splitter plate on the far field noise was also measured. Finally, an effort was made to find means to reduce the high frequency noise caused by flow separation at the lip.

Olsen, W.↗
NASA NTRS1975

Computer-generated animation for analysis and design

The development of computer-generated animation techniques was reviewed and some examples of the current state of the art were described. A number of ways in which computer-generated animation can be used were examined in relation to the suitability for the engineering task at hand. The examples described are primarily concerned with attempting to combine two different types of simulation: that of superposition of an engineering design on the surrounding real world, and an evaluation of this simulation both from an engineering design and an aesthetic point of view.

Feeser, L. J.↗
NASA NTRS1975

A study of sound generation in subsonic rotors, volume 1

A model for the prediction of wake related sound generation by a single airfoil is presented. It is assumed that the net force fluctuation on an airfoil may be expressed in terms of the net momentum fluctuation in the near wake of the airfoil. The forcing function for sound generation depends on the spectra of the two point velocity correlations in the turbulent region near the airfoil trailing edge. The spectra of the two point velocity correlations were measured for the longitudinal and transverse components of turbulence in the wake of a 91.4 cm chord airfoil. A scaling procedure was developed using the turbulent boundary layer thickness. The model was then used to predict the radiated sound from a 5.1 cm chord airfoil. Agreement between the predicted and measured sound radiation spectra was good. The single airfoil results were extended to a rotor geometry, and various aerodynamic parameters were studied.

Chalupnik, J. D.↗
NASA NTRS1976

Ocean foam generation and modeling

A laboratory investigation was conducted to determine the physical and microwave properties of ocean foam. Special foam generators were designed and fabricated, using porous glass sheets, known as glass frits, as the principal element. The glass frit was sealed into a water-tight vertical box, a few centimeters from the bottom. Compressed air, applied to the lower chamber, created ocean foam from sea water lying on the frit. Foam heights of 30 cm were readily achieved, with relatively low air pressures. Special photographic techniques and analytical procedures were employed to determine foam bubble size distributions. In addition, the percentage water content of ocean foam was determined with the aid of a particulate sampling procedure. A glass frit foam generator, with pore diameters in the range 70 - 100 micrometers, produced foam with bubble distributions very similar to those found on the surface of natural ocean foam patches.

Porter, R. A.↗
NASA NTRS1976

A research program in magnetogasdynamics utilizing hypervelocity coaxial plasma generators

A broadly-gauged research program in magnetogasdynamics utilizing hypervelocity coaxial plasma generators is presented. A complete hypervelocity coaxial plasma generator facility was assembled and tested. Significant progress was made in the direction of understanding the important processes in the interaction of hypervelocity MGD flow with transverse applied fields. It is now proposed to utilize the accumulated experimental capability and theoretical analysis in application to the analysis and design parameterization of pulsed magnetogasdynamic direct energy convertor configurations.

Spight, C.↗
NASA NTRS1975

Concept selection and analysis of large wind generator systems

The increasing need to develop alternative energy sources has renewed interest in the use of wind energy for the generation of utility quality electricity. This paper discusses a program to evolve a preliminary design of a cost competitive large wind generator system. An examination of a number of technically feasible alternative wind energy configurations is reported, and the rationale used in selecting the preferred system concept is presented. In addition, preliminary results of an optimization study conducted on the preferred concept are summarized. These show that considerable latitude in the selection of the system design parameters is possible. This permits design decisions to be based on other important factors such as development risk and the suitability of common component designs for systems with different power ratings.

Meier, R. C.↗
NASA NTRS1976

Wake-related sound generation from isolated airfoils

A model for the prediction of wake-related sound generation by a single airfoil is presented which assumes that the net force fluctuation on an airfoil can be expressed in terms of the net momentum fluctuation in the near wake of the airfoil. The model predicts a forcing function for sound generation which is related to the spectra of the two-point velocity correlations in the turbulent region near the airfoil trailing edge. Cross spectra were obtained from correlations of the longitudinal and transverse components of turbulence in the wake of a 36-in. chord airfoil in a wind tunnel using x-probe hot-wire sensors. Additional data were obtained from a 10-in. chord airfoil in a free-jet facility. Based on results from these tests, a scaling model was developed using the turbulent boundary-layer thickness as the primary length measure. The model was used to predict the sound radiated from a 2-in. chord airfoil for which acoustical data was available; good agreement was obtained both in level and spectral shape. The single-airfoil result is extended to a rotor geometry, and comparisons are studied for various aerodynamic parameters.

Clark, L. T.↗
NASA NTRS1976

Ballistic range experiments on superbooms generated by refraction

The enhanced sonic boom or supersonic boom generated as a result of atmospheric refraction in threshold Mach number flights was recreated in a ballistic range by firing projectiles at low supersonic speeds into a stratified medium obtained by slowly injecting carbon dioxide into air. The range was equipped with a fast-response dynamic pressure transducer and schlieren photographic equipment, and the sound speed variation with height was controlled by regulating the flow rate of the CO2. The schlieren observations of the resulting flow field indicate that the generated shocks are reflected near the sonic cutoff altitude where local sound speed equals body speed, provided such an altitude exists. Maximum shock strength occurs very nearly at the point where the incident and reflected shocks join, indicating that the presence of the reflected shock may have an appreciable effect on the magnitude of the focus factor. The largest focus factor detected was 1.7 and leads to an estimate that the constant in the Guiraud-Thery scaling law should have a value of 1.30.

Sanai, M.↗
NASA NTRS1976

Design, economic and system considerations of large wind-driven generators

The increased search for alternative energy sources has lead to renewed interest and studies of large wind-driven generators. This paper presents the results and considerations of such an investigation. The paper emphasizes the concept selection of wind-driven generators, system optimization, control system design, safety aspects, economic viability on electric utility systems and potential electric system interfacing problems.

Jorgensen, G. E.↗
NASA NTRS1976

Closed cycle MHD power generation experiments using a helium-cesium working fluid in the NASA Lewis Facility

The MHD channel in the NASA Lewis Research Center was redesigned and used in closed cycle power generation experiments with a helium-cesium working fluid. The cross sectional dimensions of the channel were reduced to 5 by 16.5 cm to allow operation over a variety of conditions. Experiments have been run at temperatures of 1900-2100 K and Mach numbers from 0.3 to 0.55 in argon and 0.2 in helium. Improvements in Hall voltage isolation and seed vaporization techniques have resulted in significant improvements in performance. Typical values obtained with helium are Faraday open circuit voltage 141 V (92% of uBh) at a magnetic field strength of 1.7 T, power outputs of 2.2 kw for tests with 28 electrodes and 2.1 kw for tests with 17 electrodes. Power densities of 0.6 MW/cu m and Hall fields of about 1100 V/m were obtained in the tests with 17 electrodes, representing a factor of 18 improvement over previously reported results. The V-I curves and current distribution data indicate that while near ideal equilibrium performance is obtained under some conditions, no nonequilibrium power has been generated to date.

Sovie, R. J.↗
NASA NTRS1976

Evaluation of the flat-plate solar collector system for electric power generation

This evaluation of the flat-plate collector system was designed to determine the number of flat-plate collectors required to generate a given amount of electricity with optimum efficiency. Variable parameters are the temperature of the heat-transport fluid, both to and from the collector field. In the analysis, the efficiency of the flat-plate collectors was coupled to the efficiency of the thermal cycle to calculate optimal overall system efficiencies. Overall system efficiencies for the system are on the order of 3.5 per cent or less. Over two million 4 ft-by-4 ft collectors would be required to produce 100,000 kW(e). Based on the results, it can be shown that the limiting factor in the use of the flat-plate collector system for electric power generation is the efficiency of the collectors. An increase in the overall system efficiency can occur only if the collector efficiency can be increased at higher surface temperatures.

Athey, R. E.↗
NASA NTRS1976

A technique for generating correlated X-band weather degradation statistics

It is, known that the X-band noise temperature of DSN receivers can go up from 20 K to over 100 K or more, if the air is heavily laden with water vapor, although that is an uncommon occurrence. It is proposed that the DSN furnish flight projects relying on X-band degradation models, one for each DSN Complex. Such models would be in the form of a random process generator, say in an MBASIC program, that would permit the project to generate X-band degradation data with the right autocorrelations for periods of interest to the Projects. The autocorrelation modeling is especially important because bursts of degradation lasting several days can affect data storage and mission sequence design strategy. One approach which works if the degradation statistics obey a half-gaussian law. That is, the random variables are formed by taking the absolute values of another set of random variables, themselves having a Gaussian distribution. The technique then permits the half-gaussian random variables to have given one and two-step correlation coefficients.

Posner, E. C.↗