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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 1,531 records · Page 85

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NASA NTRS1972

Effects of the hollow cathode discharge on throttled ion thruster performance.

An experimental study performed on a 20 cm electron bombardment thruster shows substantial improvements in throttled performance can be achieved if cathode discharge region diameter and length, cathode flow rate and baffle aperture area are reduced simultaneously. This improvement is related to a thruster operating mode in which arc current does not vary significantly with arc voltage. In this mode it is possible to operate the thruster at a high arc voltage and a correspondingly high primary electron energy without the penalty of a prohibitively high arc power. Langmuir probe data indicate the arc current is limited by the cathode region plasma potential and electron density which are both nearly invariant with arc voltage.

Wilbur, P. J.↗

NASA NTRS1975

Clusius-Dickel Separations (CDS): A new look at an old technique

The history, applications, and theoretical basis of the CDS technique are reviewed. The advantage to be realized by conduction of CDSs in low-g, space environments are deduced. The results are reported of investigations aimed at further improving CDS efficiencies by altering convective flow patterns. The question of whether multicellular flow or turbulence can introduce a new separation mechanism which would boost separation efficiencies at least an order of magnitude is considered. Results are presented and discussed.

Grodzka, P. G.↗

NASA NTRS1978

An improved viscous characteristics analysis program

An improved two dimensional characteristics analysis program is presented. The program is built upon the foundation of a FORTRAN program entitled Analysis of Supersonic Combustion Flow Fields With Embedded Subsonic Regions. The major improvements are described and a listing of the new program is provided. The subroutines and their functions are given as well as the input required for the program. Several applications of the program to real problems are qualitatively described. Three runs obtained in the investigation of a real problem are presented to provide insight for the input and output of the program.

Jenkins, R. V.↗

NASA NTRS1981

Aircraft energy efficiency. Overview

Six advanced technology development projects that could cut fuel consumption of future civil air transports by as much as 50 percent are highlighted. These include improved engine components; better engine design; thin short blades for turboprop aircaft; using composite primary structures for weight reduction; the use of supercritical wings, higher aspect ratio, and winglets for improved aerodynamics; active controls; and laminar flow control. The time span of each of the six efforts and NASA's expected expenditures are also discussed.

Source record↗

NASA NTRS1981

Basic advances in the finite-volume method for transonic potential flow calculations

The finite-volume method of Jameson and Caughey provides a framework within which it is possible to calculate transonic potential flows about essentially arbitrary geometrical configurations. Improvements designed to increase the accuracy of the basic scheme and its consistency in the far field will be described. These include the incorporation of an artificial viscosity which maintains the formal second-order accuracy of the scheme in supersonic zones, and a modification of the flux balances to allow the free-stream conditions to satisfy the difference equations identically. Results of calculations illustrating the importance of these effects will be presented.

Caughey, D. A.↗

NASA NTRS1982

Performance of a 2D-CD nonaxisymmetric exhaust nozzle on a turbojet engine at altitude

Baseline thrust and cooling data obtained with a 2D-CD versatile research exhaust nozzle mounted on a turbojet engine in an altitude chamber are presented. The tests covered a range of nozzle pressure ratios, nozzle pressure ratios, nozzle throat areas, and internal expansion area ratios. The thrust data obtained show good agreement with theory and scale model results after correcting the data for leakage and bypass cooling flows. Additional work is needed to improve predictability of cooling performance.

Straight, D. M.↗

NASA NTRS1982

Characteristics of the flow in the annulus-wall region of an axial-flow compressor rotor blade passage

Three-dimensional characteristics of the mean velocity and turbulence structure in the annulus-wall region of a moderately loaded compressor rotor have been investigated experimentally by employing triaxial hot-wire probes. Results are presented which indicate that the flow within and downstream of the rotor passage is highly complex due to the interaction of the annulus-wall boundary layer, blade boundary layers, tip leakage flow, and passage secondary flow. An understanding of the reported viscous flow interactions is important for establishing improved aerodynamic design criteria and efficiency, for predicting noise levels, and for determining the stall, surge, vibration, and flutter characteristics of turbomachinery.

Davino, R. M.↗

NASA NTRS1982

Tone-excited jet: Theory and experiments

A detailed study to understand the phenomenon of broadband jet-noise amplification produced by upstream discrete-tone sound excitation has been carried out. This has been achieved by simultaneous acquisition of the acoustic, mean velocity, turbulence intensities, and instability-wave pressure data. A 5.08 cm diameter jet has been tested for this purpose under static and also flight-simulation conditions. An open-jet wind tunnel has been used to simulate the flight effects. Limited data on heated jets have also been obtained. To improve the physical understanding of the flow modifications brought about by the upstream discrete-tone excitation, ensemble-averaged schlieren photographs of the jets have also been taken. Parallel to the experimental study, a mathematical model of the processes that lead to broadband-noise amplification by upstream tones has been developed. Excitation of large-scale turbulence by upstream tones is first calculated. A model to predict the changes in small-scale turbulence is then developed. By numerically integrating the resultant set of equations, the enhanced small-scale turbulence distribution in a jet under various excitation conditions is obtained. The resulting changes in small-scale turbulence have been attributed to broadband amplification of jet noise. Excellent agreement has been found between the theory and the experiments. It has also shown that the relative velocity effects are the same for the excited and the unexcited jets.

Ahuja, K. K.↗

NASA NTRS1983

New trends in combustion research for gas turbine engines

Research on combustion is being conducted to provide improved analytical models of the complex flow and chemical reaction processes which occur in the combustor of gas turbine engines, in order to enable engine manufacturers to reduce the development time of these concepts. The elements of the combustion fundamentals program is briefly discussed with examples of research projects described more fully. Combustion research will continue to emphasize the development of analytical models and the support of these models with fundamental flow experiments to assess the models accuracy and shortcomings.

Mularz, E. J.↗

NASA NTRS1983

New trends in combustion research for gas turbine engines

Mularz, E. J.↗

NASA NTRS1983

Numerical investigation of unsteady flow development in a nozzle-duct configuration

A computational approach has been used to resolve the transient phenomena caused by a rocket engine starting up and exhausting into a short duct. The results are obtained from the finite-difference Navier-Stokes, continuity, and energy equations for a single component gas. Using a recently developed numerical technique to account for the time-varying boundary conditions at the nozzle throat and the duct openings, the numerical simulation of the idealized ignition flow model has yielded some insight into the complex interactions between the wave patterns and the vortical flow. The present findings verify the hypothesis that a lateral expansion of the jetstream outside the nozzle will generate an over-pressure pulse on the duct wall if the jetstream is restricted within the nozzle by flow separation. The numerical simulations of this complex flow problem should be useful for improving simple correlation techniques used for engineering purposes.

Li, C. P.↗

NASA NTRS1985

Combustion research for gas turbine engines

Research on combustion is being conducted at Lewis Research Center to provide improved analytical models of the complex flow and chemical reaction processes which occur in the combustor of gas turbine engines and other aeropropulsion systems. The objective of the research is to obtain a better understanding of the various physical processes that occur in the gas turbine combustor in order to develop models and numerical codes which can accurately describe these processes. Activities include in-house research projects, university grants, and industry contracts and are classified under the subject areas of advanced numerics, fuel sprays, fluid mixing, and radiation-chemistry. Results are high-lighted from several projects.

Mularz, E. J.↗

NASA NTRS1983

Combustion hot section technology

The overall objective of the Turbine Engine Hot Section Technology Combustion Project is to develop and verify improved and more accurate analysis methods for increasing the ability to design with confidence the combustion system for advanced aircraft turbine engines. The analysis methods developed will be generically applicable to combustion systems and not restricted to one specific engine or manufacturer. This project's approach was to first assess and evaluate existing combustor aerothermal analysis models by means of a contracted effort initiated during FY 1982. This evaluation effort has assessed and quantified known models' strengths and deficiencies. During FY 1984 the Aerothermal Modeling Program, Phase 2 will be initiated, which is expected to have contracted model development efforts in the areas of improved numerical methods for turbulent viscous flows, flow interactions, and fuel spray flow foekd interactions. A Phase 3 effort is planned to address remaining model deficiencies. The primary inhouse effort in this area will be the determination of high pressure flame radiation characteristics in a full annular combustor. This experiment will be conducted in the NASA LeRC High Pressure Facility with the results compiled into a comprehensive flame radiation and liner heat flux model.

Ercegovic, D. B.↗

NASA NTRS1985

Combustion research for gas turbine engines

Mularz, E. J.↗

NASA NTRS1986

Low-Reynolds number aerodynamics research at NASA Langley Research Center

The present status of various types of low-Reynolds number aerodynamics research being conducted at the Fluid Dynamics Branch of NASA Langley Research Center is reviewed. The facilities, testing techniques, airfoil design, and experimental verification are addressed, and ongoing studies of laminar separation bubbles, boundary layer stability and transition control, and low-Reynolds number juncture flow are discussed. The possibility of improving vehicle characteristics at low Reynolds numbers and the general trends of the most promising research in these areas are examined.

Harvey, William D.↗

NASA NTRS1988

The design of an air-cooled metallic high temperature radial turbine

Recent trends in small advanced gas turbine engines call for higher turbine inlet temperatures. Advances in radial turbine technology have opened the way for a cooled metallic radial turbine capable of withstanding turbine inlet temperatures of 2500 F while meeting the challenge of high efficiency in this small flow size range. In response to this need, a small air-cooled radial turbine has been designed utilizing internal blade coolant passages. The coolant flow passage design is uniquely tailored to simultaneously meet rotor cooling needs and rotor fabrication constraints. The rotor flow-path design seeks to realize improved aerodynamic blade loading characteristics and high efficiency while satisfying rotor life requirements. An up-scaled version of the final engine rotor is currently under fabrication and, after instrumentation, will be tested in the warm turbine test facility at the NASA Lewis Research Center.

Snyder, Philip H.↗

NASA NTRS1986

Aerothermal modeling program, phase 2

The main objective of the NASA sponsored Aerothermal Modeling Program, Phase 2--Element A, is to develop an improved numerical scheme for predicting combustor flow fields. This effort consists of the following three technical tasks. Task 1 involves the selection and evaluation of various candidate numerical techniques. Task 2 involves an in-depth evaluation of the selected numerical schemes. Task 3 involves the convection-diffusion scheme and the direct solver that will be incorporated in the NASA 3-D elliptic code (COM3S).

Karki, K. C.↗

NASA NTRS1989

Measurements of nitric oxide in the stratosphere at 44 N in autumn

Precision of the chemiluminescent instrument for balloon-borne NO measurement was improved by precise determinations of the flow rates of the sample air and the calibration NO in N2 gas. Based on the new calibration of these values, NO mixing ratio in the stratosphere was reanalyzed. The revision of the NO data does not at all alter the form of the diurnal variation. The average of the four NO profiles between 15 and 32 km obtained at 44 N in autumn is given.

Kondo, Y.↗