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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Riblets for aircraft skin-friction reduction

Energy conservation and aerodynamic efficiency are the driving forces behind research into methods to reduce turbulent skin friction drag on aircraft fuselages. Fuselage skin friction reductions as small as 10 percent provide the potential for a 250 million dollar per year fuel savings for the commercial airline fleet. One passive drag reduction concept which is relatively simple to implement and retrofit is that of longitudinally grooved surfaces aligned with the stream velocity. These grooves (riblets) have heights and spacings on the order of the turbulent wall streak and burst dimensions. The riblet performance (8 percent net drag reduction thus far), sensitivity to operational/application considerations such as yaw and Reynolds number variation, an alternative fabrication technique, results of extensive parametric experiments for geometrical optimization, and flight test applications are summarized.

Walsh, Michael J.↗
NASA NTRS1988

Data reduction and analysis of HELIOS plasma wave data

Reduction of data acquired from the HELIOS Solar Wind Plasma Wave Experiments on HELIOS 1 and 2 was continued. Production of 24 hour survey plots of the HELIOS 1 plasma wave data were continued and microfilm copies were submitted to the National Space Science Data Center. Much of the effort involved the shock memory from both HELIOS 1 and 2. This data had to be deconvoluted and time ordered before it could be displayed and plotted in an organized form. The UNIVAX 418-III computer was replaced by a DEC VAX 11/780 computer. In order to continue the reduction and analysis of the data set, all data reduction and analysis computer programs had to be rewritten.

Anderson, Roger R.↗
NASA NTRS1988

Enhanced viscous flow drag reduction using acoustic excitation

Large eddy break up devices (LEBUs) constitute a promising method of obtaining drag reduction in a turbulent boundary layer. Enhancement of the LEBU effectiveness by exciting its trailing edge with acoustic waves phase locked to the large scale structure influencing the momentum transfer to the wall is sought. An initial estimate of the required sound pressure level for an effective pulse was obtained by considering the magnitude of the pressure perturbations at the near wake of a thin plate in inviscid flow. Detailed skin friction measurments were obtained in the flow region downstream of a LEBU excited with acoustic waves. The data are compared with skin friction measurements of a simply manipulated flow, without acoustic excitation and with a plain flow configuration. The properties and the scales of motion in the flow regime downstream of the acoustically excited LEBU are studied. A parametric study based upon the characteristics of the acoustic input was pursued in addition to the careful mapping of the drag reduction phenomenon within the acoustically manipulated boundary layer. This study of boundary layer manipulation has lead to improved skin friction drag reduction and further understanding of the turbulent boundary layer.

Nagel, R. T.↗
NASA NTRS1988

Model reduction methods for control design

Several different model reduction methods are developed and detailed implementation information is provided for those methods. Command files to implement the model reduction methods in a proprietary control law analysis and design package are presented. A comparison and discussion of the various reduction techniques is included.

Dunipace, K. R.↗
NASA NTRS1988

Comparison of experimental rotor damping data-reduction techniques

The ability of existing data reduction techniques to determine frequency and damping from transient time-history records was evaluated. Analog data records representative of small-scale helicopter aeroelastic stability tests were analyzed. The data records were selected to provide information on the accuracy of reduced frequency and decay coefficients as a function of modal damping level, modal frequency, number of modes present in the time history record, proximity to other modes with different frequencies, steady offset in time history, and signal-to-noise ratio. The study utilized the results from each of the major U.S. helicopter manufacturers, the U.S. Army Aeroflightdynamics Directorate, and NASA Ames Research Center using their inhouse data reduction and analysis techniques. Consequently, the accuracy of different data analysis techniques and the manner in which they were implemented were also evaluated. It was found that modal frequencies can be accurately determined even in the presence of significant random and periodic noise. Identified decay coefficients do, however, show considerable variation, particularly for highly damped modes. The manner in which the data are reduced and the role of the data analyst was shown to be important. Although several different damping determination methods were used, no clear trends were evident for the observed differences between the individual analysis techniques. It is concluded that the data reduction of modal-damping characteristics from transient time histories results in a range of damping values.

Warmbrodt, William↗
NASA NTRS1988

A preliminary investigation of drag reduction and mechanism for a blunt body of revolution with slanted base

This is a preliminary study of the drag reduction effect and its mechanism of a blunt body of revolution with a 21-deg slant angle by using a series of base plates. Drag coefficients were measured to investigate the effect of base installation position and plate height. An effective drag reduction device was found. Through the measurement of base pressure and total pressure distribution and flow pattern display, flow characteristics and drag reduction mechanism in the vortex near the wake were investigated.

Xia, Xuejian↗
NASA NTRS1987

InP based solar cells for space application: Reduction of external losses

Although InP-based solar cells have considerable potential for space applications, it is necessary to improve efficiencies to around the level of GaAs or Si cells before their excellent radiation resistance can be regarded as a dominant advantage. The authors concentrate on indium-tin-oxide/InP cells, presenting data relating to reduction of the contact resistance of the rear surface metallization, reduction of reflectance losses by choosing indium-tin-oxide deposition conditions to give specific optical properties, and reduction of losses associated with the grid. Simultaneous optimization of all of these has led to improved values of Jsc. For devices of approximately 1 cm2 in area, the largest Jsc achieved to date is 28.1 mA/aq cm (AM1.5, SERI/NASA direct normal spectrum, 25 C, total area, 100 mW/sq cm). For this particular cell, the equivalent AM0 value of Jsc was 34.6 mA/sq cm, which appears to be the largest reported for any InP-based cell.

Wu, X.↗
NASA NTRS1989

Real gas flow computations using algebraic reduction

It is shown that algebraic reduction can be extensively used in the computation of source terms for chemical species in chemically reacting flow fields. Cases of computation from chemical equilibrium and frozen chemistry are considered. For the case of chemical equilibrium the implementation of algebraic reduction method is shown to produce satisfactory results with computational efficiency better than comparable methods. For the case of finite rate chemistry, algebraic reduction of the source term expression for the species is used to obtain a directly integrable expression.

Nagaraj, N.↗
NASA NTRS1989

Noise reduction of a composite cylinder subjected to random acoustic excitation

Interior and exterior noise measurements were conducted on a stiffened composite floor-equipped cylinder, with and without an interior trim installed. Noise reduction was obtained for the case of random acoustic excitation in a diffuse field; the frequency range of interest was 100-800-Hz one-third octave bands. The measured data were compared with noise reduction predictions from the Propeller Aircraft Interior Noise (PAIN) program and from a statistical energy analysis. Structural model parameters were not predicted well by the PAIN program for the given input parameters; this resulted in incorrect noise reduction predictions for the lower one-third octave bands where the power flow into the interior of the cylinder was predicted on a mode-per-mode basis.

Grosveld, Ferdinand W.↗
NASA NTRS1989

Component mode synthesis for model order reduction of nonclassically damped systems

Based on a component mode synthesis approach, a model-order-reduction method for linear structures with arbitrary linear damping has been developed. Projection matrices are introduced to make the method applicable to systems having rigid-body freedom. To test the method, eigenvalues of a reduced-order model of a free-free beam with nonproportional damping were compared to exact eigenvalues and to eigenvalues obtained using two other model-reduction strategies. The present model-reduction strategy proved to be decidedly superior.

Craig, Roy R., Jr.↗
NASA NTRS1989

Controller reduction by preserving impulse response energy

A model order reduction algorithm based on a Krylov recurrence formulation is developed to reduce order of controllers. The reduced-order controller is obtained by projecting the full-order LQG controller onto a Krylov subspace in which either the controllability or the observability grammian is equal to the identity matrix. The reduced-order controller preserves the impulse response energy of the full-order controller and has a parameter-matching property. Two numerical examples drawn from other controller reduction literature are used to illustrate the efficacy of the proposed reduction algorithm.

Craig, Roy R., Jr.↗
NASA NTRS1989

The reduction correction in North America

An inverse Poisson integral technique was used to determine a gravity field on the geoid which, when continued by analytic free space methods to the topographic surface, agrees with the observed field. The computation is performed in three stages, each stage refining the previous solution using data at progressively increasing resolution (1 x 1 deg, 5 x 5', 5/8 x 5/8') from a decreasing area of integration. Reduction corrections are computed at 5/8 x 5/8' granularity by differencing the geoidal and surface values, smoothed by low-pass filtering and sub-sampled at 5' intervals. The 1 x 1 deg averages of the reduction corrections thus obtained for 172 1 x 1 deg squares in western North America are discussed. The 1 x 1 deg mean reduction corrections are predominantly positive, varying from -3 to +15 mgal, with values in excess of 5 mgal for 26 squares. Their mean and rms values are +2.4 and 3.6 mgal respectively and they correlate well with the mean terrain corrections. The mean and rms contributions from the three stages of computation are: 1 x 1 deg stage +0.15 and 0.7 mgal; 5 x 5' stage + 1.0 and 1.6 mgal; and 5/8 x 5/8' stage +1.3 and 1.8 mgal. These results reflect a tendency for the contributions to become larger and more systematically positive as the wavelengths involved become shorter. The results are discussed in terms of two mechanisms; the first is a tendency for the absolute values of both positive and negative anomalies to become larger when continued downwards and, the second, a non-linear rectification, due to the correlation between gravity anomaly and topographic height, which results in the values continued to a level surface being systematically more positive than those on the topography.

Martzen, P. D.↗
NASA NTRS1990

Characterization study of polycrystalline tin oxide surfaces before and after reduction in CO

Polycrystalline tin oxide surfaces have been examined before and after reduction in 40 Torr of CO at 100 and 175 C using Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA), ion scattering spectroscopy (ISS) and electron stimulated desorption (ESD). The changes in the surface composition and chemical states of the surface species generally are subtle for the reductive conditions used. However, significant changes do occur with regard to the amounts and the chemical forms of the hydrogen-containing species remaining after both the 100 and 175 C reductions.

Drawdy, Jean E.↗
NASA NTRS1991

Experimental reduction of simulated lunar glass by carbon and hydrogen and implications for lunar base oxygen production

The most abundant element in lunar rocks and soils is oxygen which makes up approximately 45 percent by weight of the typical lunar samples returned during the Apollo missions. This oxygen is not present as a gas but is tightly bound to other elements in mineral or glass. When people return to the Moon to explore and live, the extraction of this oxygen at a lunar outpost may be a major goal during the early years of operation. Among the most studied processes for oxygen extraction is the reduction of ilmenite by hydrogen gas to form metallic iron, titanium oxide, and oxygen. A related process is proposed which overcomes some of the disadvantages of ilmenite reduction. It is proposed that oxygen can be extracted by direct reduction of native lunar pyroclactic glass using either carbon, carbon monoxide, or hydrogen. In order to evaluate the feasibility of this proposed process a series of experiments on synthetic lunar glass are presented. The results and a discussion of the experiments are presented.

Mckay, David S.↗
NASA NTRS1990

Outer-layer manipulators for turbulent drag reduction

The last ten years have yielded intriguing research results on aerodynamic boundary outer-layer manipulators as local skin friction reduction devices at low Reynolds numbers; net drag reduction device systems for entire aerodynamic configurations are nevertheless noted to remain elusive. Evidence has emerged for dramatic alterations of the structure of a turbulent boundary layer which persist for long distances downstream and reduce wall shear as a results of any one of several theoretically possible mechanisms. Reduced effectiveness at high Reynolds numbers may, however, limit the applicability of outer-layer manipulators to practical aircraft drag reduction.

Anders, J. B., Jr.↗
NASA NTRS1990

Finite element model reduction application to parametric studies and optimization of rotorcraft structures

As a result of this work, a reduction procedure has been developed which can be applied to large finite element model of airframe type structures. This procedure, which is tailored to be used with MSC/NASTRAN finite element code, is applied to the full airframe dynamic finite element model of AH-64A Attack Helicopter. The applicability of the resulting reduced model to parametric and optimization studies is examined. Through application of the design sensitivity analysis, the viability and efficiency of this reduction technique has been demonstrated in a vibration reduction study.

Hashemi-Kia, M.↗
NASA NTRS1991

Model order reduction applied to a hot-bench simulation of an aeroelastic wind-tunnel model

Simulations of an aeroelastically scaled wind-tunnel model were developed for hot-bench testing of a digital controller. The digital controller provided active flutter-suppression, rolling-maneuver-load alleviation, and plant estimation. To achieve an acceptable time scale for the hot-bench application, the mathematical model of the wind-tunnel model was reduced from 220 states to approximately 130 states while assuring that the required accuracy was preserved for all combinations of 10 inputs and 56 outputs. The reduction was achieved by focussing on a linear, aeroelastic submodel of the full mathematical model and by applying a method based on the internally balanced realization of a dynamic system. The error-bound properties of the internally balanced realization significantly contribute to its utility in the model reduction process. The reduction method and the results achieved are described.

Buttrill, Carey S.↗
NASA NTRS1992

Special Course on Skin Friction Drag Reduction

Lecture notes for the AGARD Fluid Dynamics Panel (FDP) Special Course on 'Skin Friction Drag Reduction' have been assembled in this report. The aim and scope of this course was to provide an overview of the state of the art of current technology programs focused on reducing aircraft drag caused by skin friction. This report provides a review of recent progress in the field of skin friction drag reduction for transport aircraft. It provides a general introduction to the technology and then focuses on two specific aspects of drag reduction: maintaining laminar flow by controlling transition and manipulating the turbulence structure in boundary layers to help reduce skin friction. Technology associated with the use of riblets, LEBU, polymers, additives, etc., is also reviewed.

Advisory Group for Aerospace Research and Developm↗