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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Development of a takeoff performance monitoring system

The development and testing of a real-time takeoff performance monitoring system is discussed. The algorithm is madeup of two segments: a pretakeoff segment and a real-time segment. One-time inputs of ambient conditions and airplane configuration information are used in the pretakeoff segment to generate schedule performance data for that takeoff. The real-time segment uses the scheduled performance data generated in the pretakeoff segment, runway length data, and measured parameters to monitor the performance of the airplane throughout the takeoff roll. Airplane and engine performance deficiencies are detected and annunciated. An important feature of this algorithm is the one-time estimation of the runway rolling friction coefficient. The algorithm was tested using a six degree of freedom airplane model in a computer simulation. Results from a series of sensitivity analysis are also included.

Srivatsan, R.↗
NASA NTRS1985

Heavy ion beam-ionosphere interactions - Electron acceleration

Moore et al. (1982) described a number of unexpected effects which were observed during the first Argon Release Controlled Study (ARCS 1, or rocket flight 29:014). The present paper provides a description of detailed analyses of the interaction of the argon beam with the ionosphere. An important feature of the considered test was that all detectors and the Ar(+) gun remained attached to the rocket throughout the flight. It is pointed out that the most dramatic effect of ion gun operation on ARCS 1 involved large changes in the fluxes of electrons with energies below about 600 eV. The observations are discussed, taking into account the distribution functions, azimuth dependence, and electron and ion trajectories. Attention is given to the perpendicular ion beam, the parallel ion beam, the acceleration of downgoing and upgoing electrons, and aspects of wave generation.

Kaufmann, R. L.↗
NASA NTRS1985

An analysis of a separation bubble transition criterion at low Reynolds numbers

Factors which influence the criterion governing the length of the laminar region of a separation bubble on an airfoil at low Re were investigated. The criterion is the onset of separation when a critical Re value is surpassed. Wind tunnel data were gathered for the flow around a NACA 66(3)-018 airfoil at Re from 50,000-200,000. The data were taken with either hot-wire anemometers or pressure taps. The value of the critical Re was influenced by the chord Re, the angle of attack and the level of turbulence in the free stream. However, the turbulence levels examined, up to 0.184 percent, did not greatly affect the critical Re. Further characterizations of the effects of the three factors on the critical Re are necessary before the important features of separation bubbles can be identified with an acceptable level of certainty.

Schmidt, G. S.↗
NASA NTRS1985

A refractory inclusion in the Kaba CV3 chondrite - Some implications for the origin of spinel-rich objects in chondrites

The first detailed petrographic and mineralogical study of a Ca, Al-rich inclusion (CAI) from the Kaba CV3 chondrite is reported. This 'fine-grained' CAI contains abundant small, rounded, rimmed, spinel-rich objects which have important features in common with the spinel-rich objects in other carbonaceous and ordinary chondrites. These nodules are interpreted as fractionated distillation residues of primitive dust. However, the available data do not unambiguously rule out a condensation origin for at least some of these objects. Finally, the preservation of distinct diopside-hedenbergite rims on the spinel-rich bodies and the small grain size of many minerals in the CAI matrix material both suggest that the CAI accreted cool and had a relatively cool thermal history in the Kaba parent body.

Fegley, B., Jr.↗
NASA NTRS1985

Numerical algorithms for transonic inviscid flow calculations

It is pointed out that the supercritical wing is one of the most important features of modern transonic aerodynamics. The design of its shock free airfoil section depends on potential flow calculations. The present paper is concerned with the development of inviscid flow simulation methods based on potential formulations, taking into account also the problem of nonuniqueness of the potential solution. Nonisentropic and nonisoenergetic models are considered, and an alternative approach using the stream function is discussed. Attention is given to transonic small disturbance calculations, calculations based on the full potential equation, iterative methods, wave drag calculations, and an alternative form of Euler equations.

Hafez, M. M.↗
NASA NTRS1986

Reverberation effects on directionality and response of stationary monopole and dipole sources in a wind tunnel

Analytical solutions for the three dimensional inhomogeneous wave equation with flow in a hardwall rectangular wind tunnel and in the free field are presented for a stationary monopole noise source. Dipole noise sources are calculated by combining two monopoles 180 deg out of phase. Numerical calculations for the modal content, spectral response and directivity for both monopole and dipole sources are presented. In addition, the effect of tunnel alterations, such as the addition of a mounting plate, on the tunnels reverberant response are considered. In the frequency range of practical importance for the turboprop response, important features of the free field directivity can be approximated in a hardwall wind tunnel with flow if the major lobe of the noise source is not directed upstream. However, for an omnidirectional source, such as a monopole, the hardwall wind tunnel and free field response are not comparable.

Baumeister, K. J.↗
NASA NTRS1984

The utility of Head-Up Displays - Eye-focus vs decision times

Instrument-panel information is presented by a Head-Up Display (HUD) to pilots in such a way that the symbols appear far away (at optical infinity) superimposed upon the landscape. The use of a HUD makes it, therefore, unnecessary for the pilot to take his eyes off the changing scene in order to look down and refocus on the instrument panel. It is pointed out that the HUD has proved superior to the conventional instrument-panel display. An experiment was conducted with the objective to help to determine which of the differences between HUD and conventional instrument-panel display are mainly responsible for the superiority of the HUD. Important features of this experiment are that the format of each virtual-image display, its luminance, and its angle subtended at the eye, remained the same as the optical distance and location were varied. It was found that the HUD symbology at optical infinity does reduce decision times compared to the same format at the location of a conventional instrument panel.

Weintraub, D. J.↗
NASA NTRS1986

Comment on electric field evidence on the viscous interaction at the magnetopause, by F. S. Mozer

In his paper on ISEE-1 electric field measurements in the low-latitude boundary layer (LLBL), Mozer (1984) concluded that LLBL contributes only about 10 percent of the average cross-tail potential difference Delta phi, and thus that viscous effects associated with the boundary layer are not very important as compared to the competing process of magnetic reconnection. Here, it is pointed out that Mozer may not have recognized an important feature of the LLBL, in that the maximum or minimum values of Delta phi (BL) may have occurred tailward of the spacecraft orbit. It is also pointed out that the sum of the viscous interaction potentials across the dawn and dusk low latitude boundary layers is closer to 30 kV than the 6 kV reported by Mozer. In his reply, Mozer gives reasons why the values he used are correct and that his earlier conclusions need no revision.

Heikkila, W. J.↗
NASA NTRS1985

Using the ET for gamma-ray astronomy

A gamma-ray-telescope design is presented which makes use of the normally spent external tank (ET) of the Space Shuttle as the spacecraft and Cerenkov pressure vessel. The ET would be configured into the telescope once onorbit, using the Space Station as the base of operations for carrying out the assembly activities. The telescope provides a continuation to the NASA program in high-energy astrophysics, providing for follow-on observations to the survey work of the EGRET instrument on GRO. The most important features of the gamma-ray imaging telescope system are its collecting area of 250,000 sq cm per ET (40 times that of the EGRET instrument) and its ability to locate point sources to within several arc minutes.

Koch, D.↗
NASA NTRS1986

An Eigensystem Realization Algorithm in Frequency Domain for modal parameter identification

This paper demonstrates the close conceptual relationships between time domain and frequency domain approaches to identification of modal parameters for linear systems. A frequency domain eigensystem realization algorithm, via transfer functions, is developed using a known procedure formulated for a time domain eigensystem realization algorithm, via free decay measurement data. An important feature is the capability of windowing to concentrate analysis on the frequency range of interest. The procedure of overlap averaging is used to produce smoother spectra to reduce the effect of noise on identified modal parameters. Examples from simulation and experiments are given to illustrate the validity of formulations derived in the paper.

Juang, J.-N.↗
NASA NTRS1987

Solar Thermoelectric Converters

Existing technologies combined to exploit solar power. Report discusses design concepts for alkali metal thermoelectric power converters heated by Sun. Several alternative configurations of equipment presented, with brief analyses of engineering problems and important features of each.

Selcuk, M. Kudret↗
NASA NTRS1987

Improved Flux-Gate Magnetometer

Simplified circuit drives heading indicator and senses magnetic field of Earth. Simple flux-gate magnetometer supplies digital readout of magnetic heading of vehicle, developed to drive heading indicator, or supply heading information to autopilot or to other navigational instruments. Important feature is core driven into saturation in one direction only by alternating drive voltage, which swings from zero to one polarity and back. Made in part of commercially available integrated circuits.

Garner, H. Douglas↗
NASA NTRS1987

Development of a takeoff performance monitoring system

Discussed are the development and testing of a real-time takeoff performance monitoring algorithm. The algorithm is made up of two segments: a pretakeoff segment and a real-time segment. One-time imputs of ambient conditions and airplane configuration information are used in the pretakeoff segment to generate scheduled performance data for that takeoff. The real-time segment uses the scheduled performance data generated in the pretakeoff segment, runway length data, and measured parameters to monitor the performance of the airplane throughout the takeoff roll. Airplane and engine performance deficiencies are detected and annunciated. An important feature of this algorithm is the one-time estimation of the runway rolling friction coefficient. The algorithm was tested using a six-degree-of-freedom airplane model in a computer simulation. Results from a series of sensitivity analyses are also included.

Srivatsan, Raghavachari↗
NASA NTRS1987

A transport model of the turbulent scalar-velocity

Performance tests of the third-order turbulence closure for predictions of separating and recirculating flows in backward-facing steps were studied. Computations of the momentum and temperature fields in the flow domain being considered entail the solution of time-averaged transport equations containing the second-order turbulent fluctuating products. The triple products, which are responsible for the diffusive transport of the second-order products, attain greater significance in separating and reattaching flows. The computations are compared with several algebraic models and with the experimental data. The prediction was improved considerably, particularly in the separated shear layer. Computations are further made for the temperature-velocity double products and triple products. Finally, several advantages were observed in the usage of the transport equations for the evaluation of the turbulence triple products; one of the most important features is that the transport model can always take the effects of convection and diffusion into account in strong convective shear flows such as reattaching separated layers while conventional algebraic models cannot account for these effects in the evaluation of turbulence variables.

Amano, R. S.↗
NASA NTRS1987

A linearized Euler analysis of unsteady flows in turbomachinery

A method for calculating unsteady flows in cascades is presented. The model, which is based on the linearized unsteady Euler equations, accounts for blade loading shock motion, wake motion, and blade geometry. The mean flow through the cascade is determined by solving the full nonlinear Euler equations. Assuming the unsteadiness in the flow is small, then the Euler equations are linearized about the mean flow to obtain a set of linear variable coefficient equations which describe the small amplitude, harmonic motion of the flow. These equations are discretized on a computational grid via a finite volume operator and solved directly subject to an appropriate set of linearized boundary conditions. The steady flow, which is calculated prior to the unsteady flow, is found via a Newton iteration procedure. An important feature of the analysis is the use of shock fitting to model steady and unsteady shocks. Use of the Euler equations with the unsteady Rankine-Hugoniot shock jump conditions correctly models the generation of steady and unsteady entropy and vorticity at shocks. In particular, the low frequency shock displacement is correctly predicted. Results of this method are presented for a variety of test cases. Predicted unsteady transonic flows in channels are compared to full nonlinear Euler solutions obtained using time-accurate, time-marching methods. The agreement between the two methods is excellent for small to moderate levels of flow unsteadiness. The method is also used to predict unsteady flows in cascades due to blade motion (flutter problem) and incoming disturbances (gust response problem).

Hall, Kenneth C.↗
NASA NTRS1987

Modified independent modal space control method for active control of flexible systems

A modified independent modal space control (MIMSC) method is developed for designing active vibration control systems for large flexible structures. The method accounts for the interaction between the controlled and residual modes. It incorporates also optimal placement procedures for selecting the optimal locations of the actuators in the structure in order to minimize the structural vibrations as well as the actuation energy. The MIMSC method relies on an important feature which is based on time sharing of a small number of actuators, in the modal space, to control effectively a large number of modes. Numerical examples are presented to illustrate the application of the method to generic flexible systems. The results obtained suggest the potential of the devised method in designing efficient active control systems for large flexible structures.

Baz, A.↗
NASA NTRS1987

Calculations of inlet distortion induced compressor flowfield instability

Calculations are presented predicting the onset of flow instability for a multistage low speed axial compressor operating in circumferentially distorted inlet flow. The most important feature of the model used is that it attempts to properly account for the fluid dynamic interaction between the spoiled and unspoiled sectors of the compressor. The calculations show that there is an approximate stability criterion, the annulus averaged slope of the compressor pressure rise characteristic equal to zero, that is valid whenever the dynamics of the compressor distorted flowfield can be considered independent of the compressor environment. This approximate criterion is used to investigate the relationship between the present model and the parallel compressor model. Further calculations are performed to investigate cases of interest when the dynamics of the flowfield are coupled to the environment. Resonant cases and cases when the distortion is unsteady are studied. In particular, it is shown that rotating distortions which propagate in the rotor direction can have a greater effect on stability margin than stationary or counter-rotational ones. Finally, it is shown that the general predictions of the model are insensitive to the details of the unsteady bladerow dynamics.

Hynes, T. P.↗
NASA NTRS1986

Angular and energy distribution of low energy cometary ions measured in the outer coma of Comet Halley

During the early phase of the Giotto encounter with comet Halley, at distances from the nucleus greater than 350,000 km, the neutral mass spectrometer was operated in a mode allowing the measurement of low energy ions. Data reveal two important features of the outer coma: the presence of a sharp discontinuity in the plasma flow at 550,000 km from the nucleus which results in a significant decrease of the plasma flow accompanied by an increase in temperature; and the detection of newly born ions identified as O(+) and CO(+), at distances from the comet greater than 800,000 km.

Berthelier, J. J.↗