Search NASA⌕ Search

SEARCH · Search NASA

Results for “SCALE EFFECT”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Scaled centrifugal compressor, collector and running gear program

The Scaled Centrifugal Compressor, Collector and Running gear Program was conducted in support of an overall NASA strategy to improve small-compressor performance, durability, and reliability while reducing initial and life-cycle costs. Accordingly, Garrett designed and provided a test rig, gearbox coupling, and facility collector for a new NASA facility, and provided a scaled model of an existing, high-performance impeller for evaluation scaling effects on aerodynamic performance and for obtaining other performance data. Test-rig shafting was designed to operate smoothly throughout a speed range up to 60,000 rpm. Pressurized components were designed to operate at pressures up to 300 psia and at temperatures to 1000 F. Nonrotating components were designed to provide a margin-of-safety of 0.05 or greater; rotating components, for a margin-of-safety based on allowable yield and ultimate strengths. Design activities were supported by complete design analysis, and the finished hardware was subjected to check-runs to confirm proper operation. The test rig will support a wide range of compressor tests and evaluations.

Kenehan, J. G.↗
NASA NTRS1985

Variational assimilation of VAS data into a mesoscale model Assimilation method and sensitivity experiments

The assimilation of temperature and moisture gradient information from the Visible IR Spin-Scan Radiometer's Atmospheric Sounder (VAS) into a mesoscale model is presently undertaken by means of a variational method and followed by tests of the sensitivity of both diabatic and adiabatic versions of the model to VAS data assimilations for the case of July 20-21, 1981. The synoptic scale effects of the assimilation of VAS data are noted to be negligible; the greatest impact was instead on mesoscale forecasts of convective instability patterns. The additional assimilation of relative humidity gradients did not significantly change the patterns of the forecast instabilities. The greatest improvements from assimilation resulted from the resolution of the strong mesoscale temperature gradients by the asynoptic VAS data.

Cram, J. M.↗
NASA NTRS1984

The influence of gravity on structure and function of animals

Gravity is the only environmental parameter that has remained constant during the period of evolution of living matter on earth. Thus, it must have been a major force in shaping living things. The influence of gravitational loading on evolution of the vertebrate skeleton is well recognized, and scale effects have been studied. This paper, however, considers in addition four pivotal events in early evolution that would seem to have been significant for the later success and diversifcation of animal life. These are evolution of the cytoskeleton, cell motility (flagellae and cilia), gravity detecting devices (accelerometers), and biomineralization. All are functionally calcium dependent in eukaryotes and all occurred or were foreshadowed in prokaryotes. A major question is why calcium was selected as an ion of great importance to the structure and function of living matter; another is whether gravity played a role in its selection.

Ross, M. D.↗
NASA NTRS1986

Exploratory investigation of deflectable forebody strakes for high angle of attack yaw control

A deflectable strake concept was investigated on a conical forebody to evaluate its yaw control potential at high angles of attack. In exploratory low-speed tunnel tests using a generic delta wing fighter configuration, antisymmetrically deflected strakes provided useful levels of yaw power at angles of attack when the conventional rudder became totally degraded. Symmetrical strakes prevented side force development at high angles of attack, and provided pitch control through symmetrical deflection. The strake performance was sensitive to its circumferential position on the forebody due to varying interaction of strake vortices with the wing and vertical tail. The low Reynolds number results of this study provided a favorable initial validation of the concept, subject to verification in regard to scale effects.

Rao, D. M.↗
NASA NTRS1987

Some aspects of double layer formation in a plasma constrained by a magnetic mirror

The shift from wave-generated anomalous resistivity toward the more large-scale effects of magnetic confinement of current carrying plasmas was inspired by the more extensive data on auroral particle distribution functions that were made available, data that may often seem consistent with a dissipation-free acceleration of auroral electrons over an extended altitude range. Efforts to interpret these data have brought new vigor to the concept that a smooth and static electric field can be self-consistently generated by suitable pitch angle anisotropies among the high altitude particle populations, different for electrons and ions, and that such an electric field is both necessary and sufficient to maintain the plasma in a quasi-neutral steady state. Certain aspects of this concept are reviewed and criticized, both from a general theoretical standpoint and from the standpoint of what is known about the magnetospheric environment. It is argued that this concept has flaws and that the actual physical problem is considerably more complicated, requiring a more complex electric field, possibly including double layer structures.

Lennartsson, W.↗
NASA NTRS1989

Real-Time Optimization Of Receiver Bandwidth

Estimates of signal and noise spectra enhance reception of weak signals. Carrier-tracking phase-locked loop represented by linear mathematical model at small rms phase errors. Loop continuously generates estimates of received phase. Bandwidth (in effect, scale of complex-frequency variable p) optimized to minimize rms phase error. Minimum signals tracked 5 to 15 dB below those tracked by current receivers. Improvement accomplished by use of bandwidths of 0.1 to 1.0 Hz, in contrast with 3-Hz bandwidth in current use. Principle of real-time optimization of bandwidth adapted to other situations to enhance reception of weak signals otherwise "buried" in noise.

Vilnrotter, V. A.↗
NASA NTRS1988

Snow cover, snowmelt and runoff in the Himalayan River basins

Not withstanding the seasonal vagaries of both rainfall amount and snowcover extent, the Himalayan rivers retain their basic perennial character. However, it is the component of snowmelt yield that accounts for some 60 to 70 percent of the total annual flow volumes from Hamilayan watersheds. On this large hydropotential predominantly depends the temporal performance of hydropower generation and major irrigation projects. The large scale effects of Himalayan snowcover on the hydrologic responses of a few selected catchments in western Himalayas was studied. The antecedent effects of snowcover area on long and short term meltwater yields can best be analyzed by developing appropriate hydrologic models forecasting the pattern of snowmelt as a function of variations in snowcover area. It is hoped that these models would be of practical value in the management of water resources. The predictability of meltwater for the entire snowmelt season was studied, as was the concurrent flow variation in adjacent watersheds, and their hydrologic significance. And the applicability of the Snowmelt-Runoff Model for real time forecast of daily discharges during the major part of the snowmelt season is examined.

Dey, B.↗
NASA NTRS1988

Active microwave measurements of artificial sea ice

A 5 m x 15 m outdoor tank of 1.2 m depth was filled with sea water, and polarimetric radar backscatter data were collected at 1.8, 5, and 10 GHz for incidence angles 0 to 60 deg. Observations commenced with open water and continued until 30 cm of sea ice formed. The roughness of the ice surface is important in determining the general backscatter level for first-year ice. Experiments were performed to study the change in backscatter with various roughness scales. Effects of freeze and thaw conditions were also examined. Absolute backscatter levels for new to gray ice are small, except for the large, coherent returns at vertical. The backscatter responses of new, gray, rough grey, and desalinated first-year ice at linear polarization are dissimilar. This is confirmed by examining their polarization signatures.

Onstott, R. G.↗
NASA NTRS1989

The acoustics of a small-scale helicopter rotor in hover

A 2.1 m diameter, 1/6-scale model helicopter main rotor was tested in hover in the test section of the NASA Ames 40- by 80-foot wind tunnel. Performance and noise data on a small-scale rotor at various thrust coefficients and tip Mach numbers were obtained for comparison with existing data on similar full-scale helicopter rotors. These data form part of a data base to permit the estimation of scaling effects on various rotor noise mechanisms. Another objective was to contribute to a data base that will permit the estimation of facility effects on acoustic testing. Acoustic 1/3-octave-band spectra are presented, together with variations of overall acoustic levels with rotor performance, microphone distance, and directivity angle.

Kitaplioglu, Cahit↗
NASA NTRS1987

Advanced experimental techniques for transonic testing

Problems common to wind tunnels, including low Reynolds numbers, wall interference, support interference, and flow unsteadiness are discussed, and it is noted that with increasing aircraft size, existing transonic tunnels are becoming more inadequate in terms of their Reynolds-number capability. Problems attributed to scale effect are covered, and techniques for increasing Reynolds number are presented. These include operating with a heavy gas or a mixture of gases, increasing the operating pressure in the tunnel, increasing the size of the model, and/or reducing the test temperature. Acceptable levels of flow unsteadiness are reviewed, along with the problems associated with the flow over wind-tunnel models influenced by flow unsteadiness. Sources of flow unsteadiness present in a continuous transonic tunnel driven by a compressor or a fan are listed, and rules for ensuring low levels of flow unsteadiness are given.

Kilgore, Robert A.↗
NASA NTRS1991

The geomagnetic tail

A review is presented of the plasma sheet and lobe regions of the magnetotail, focusing principally on large-scale processes or microprocesses with some large-scale effects. Consideration is given to quiet and average structures, not necessarily related to activity phases, with quasi-steady convection aspects, and with the characteristics of dynamic phases including acceleration mechanisms and single particle aspects. Attention is given to various activity models, average and quiet time properties, properties and effects of magnetospheric convection, dynamics of the magnetotail, and the near tail, substorm current wedge.

Birn, Joachim↗
NASA NTRS1992

Scaling Of Responses Of Composite Beams

Report describes series of experiments in which scale-model composite beams made of matrix/fiber composite materials tested to failure under combined axial compressive and bending loads. Discusses scaling effects in static large-deflection response of composite beams.

Jackson, Karen E.↗
NASA NTRS1992

Lab-scale Lidar Sensing of Diesel Engines Exhausts

Combustion technology and its environmental concerns are being considered with increasing attention, not only for global-scale effects, but also for toxicological implications, particularly in the lift conditions of traffic-congested areas and industrial sites. Majority combustion by-products (CO, NO(sub x)) and unburned hydrocarbons (HC), are already subject to increasingly severe regulations; however other, non-regulated minority species, mainly soot and heavy aromatic molecules, involve higher health risks, as they are suspected to be agents of serious pathologies and even mutagenic effects. This is but one of the reasons why much research work is being carried out worldwide on the physical properties of these substances. Correspondingly, the need arises to detect their presence in urban environments, with as high a sensitivity as is required by their low concentrations, proper time- and space-resolutions, and 'real-time' capabilities. Lidar techniques are excellent candidates to this purpose, although severe constraints limit their applicability, eye-safety problems and aerosol Mie scattering uncertainties above all. At CNR's Istituto Motori in Napels, a Lidar-like diagnostic system is being developed, aimed primarily at monitoring the dynamic behavior of internal combustion engines, particularly diesel exhausts, and at exploring the feasibility of a so-called 'Downtown Lidar'.

Borghese, A.↗
NASA NTRS1990

X-29 high angle of attack

Flight test program highlights are discussed for the X-29 high angle-of-attack (AOA) aircraft. The AOA envelope extended from 10 to 66 deg; the X-29 exhibited precise pitch control, allowing AOA to be maintained within 1 deg during stabilized points as well as permitting rapid recoveries from all AOAs. Attention is given to controllability degradation above 40-deg AOA due to asymmetric yawing moments. The use of this aircraft as a fundamental research tool which complements analytical methods is powerfully justified by the obviation of scaling effects.

Ishmael, Stephen D.↗
NASA NTRS1992

Scaling of energy absorbing composite plates

The energy absorption response and crushing characteristics of geometrically scaled graphite-Kevlar epoxy composite plates were investigated. Three different trigger mechanisms including chamfer, notch, and steeple geometries were incorporated into the plate specimens to initiate crushing. Sustained crushing was achieved with a simple test fixture which provided lateral support to prevent global buckling. Values of specific sustained crushing stress (SSCS) were obtained which were comparable to values reported for tube specimens from previously published data. Two sizes of hybrid plates were fabricated; a baseline or model plate, and a full-scale plate with in-plane dimensions scaled by a factor of two. The thickness dimension of the full-scale plates was increased using two different techniques; the ply-level method in which each ply orientation in the baseline laminate stacking sequence is doubled, and the sublaminate technique in which the baseline laminate stacking sequence is repeated as a group. Results indicated that the SSCS is independent of trigger mechanism geometry. However, a reduction in the SSCS of 10-25 percent was observed for the full-scale plates as compared with the baseline specimens, indicating a scaling effect in the crushing response.

Jackson, Karen↗
NASA NTRS1927

Mass distribution and performance of free flight models

This note deals with the mass distribution and performance of free flight models. An airplane model which is to be used in free flight tests must be balanced dynamically as well as statically, e.g., it must not only have a given weight and the proper center of gravity but also a given ellipsoid of inertia. Equations which relate the motions of an airplane and its model are given. Neglecting scale effect, these equations may be used to predict the performance of an airplane, under the action of gravity alone, from data obtained in making dropping tests of a correctly balanced model.

Scherberg, Max↗
NASA NTRS1926

The characteristics of the NACA M-12 airfoil section

The data obtained on the NACA M-12 airfoil, tested at twenty atmosphere density in the NACA variable density wind tunnel, have been extended by additional tests at one and at twenty atmospheres under improved conditions. The results of these tests are given. Considerable scale effect was found.

AIRFOILS - CLARK Y - CHAR & C P↗
NASA NTRS1928

Resistance of streamline wires

This note contains the results of tests to determine the resistance of four sizes of streamline wire. The investigation was conducted in the six-inch wind tunnel of the National Advisory Committee for Aeronautics. The tests were made at various velocities and it was found that the resistance of streamline wires was considerably less than that of round wires of equivalent strength. Scale effect was also found since, with an increase of Reynolds Number, a decrease in the resistance coefficient was obtained.

Defoe, George L↗