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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 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

A Novel Method for Reducing Rotor Blade-Vortex Interaction

One of the major hindrances to expansion of the rotorcraft market is the high-amplitude noise they produce, especially during low-speed descent, where blade-vortex interactions frequently occur. In an attempt to reduce the noise levels caused by blade-vortex interactions, the flip-tip rotor blade concept was devised. The flip-tip rotor increases the miss distance between the shed vortices and the rotor blades, reducing BVI noise. The distance is increased by rotating an outboard portion of the rotor tip either up or down depending on the flight condition. The proposed plan for the grant consisted of a computational simulation of the rotor aerodynamics and its wake geometry to determine the effectiveness of the concept, coupled with a series of wind tunnel experiments exploring the value of the device and validating the computer model. The computational model did in fact show that the miss distance could be increased, giving a measure of the effectiveness of the flip-tip rotor. However, the wind experiments were not able to be conducted. Increased outside demand for the 7'x lO' wind tunnel at NASA Ames and low priority at Ames for this project forced numerous postponements of the tests, eventually pushing the tests beyond the life of the grant. A design for the rotor blades to be tested in the wind tunnel was completed and an analysis of the strength of the model blades based on predicted loads, including dynamic forces, was done.

Glinka, A. T.↗
NASA NTRS2015

The Southern Argentina Agile Meteor Radar Orbital System (SAAMER-OS): An Initial Sporadic Meteoroid Orbital Survey in the Southern Sky

We present an initial survey in the southern sky of the sporadic meteoroid orbital environment obtained with the Southern Argentina Agile MEteor Radar (SAAMER) Orbital System (OS), in which over three-quarters of a million orbits of dust particles were determined from 2012 January through 2015 April. SAAMER-OS is located at the southernmost tip of Argentina and is currently the only operational radar with orbit determination capability providing continuous observations of the southern hemisphere. Distributions of the observed meteoroid speed, radiant, and heliocentric orbital parameters are presented, as well as those corrected by the observational biases associated with the SAAMER-OS operating parameters. The results are compared with those reported by three previous surveys performed with the Harvard Radio Meteor Project, the Advanced Meteor Orbit Radar, and the Canadian Meteor Orbit Radar, and they are in agreement with these previous studies. Weighted distributions for meteoroids above the thresholds for meteor trail electron line density, meteoroid mass, and meteoroid kinetic energy are also considered. Finally, the minimum line density and kinetic energy weighting factors are found to be very suitable for meteoroid applications. The outcomes of this work show that, given SAAMERs location, the system is ideal for providing crucial data to continuously study the South Toroidal and South Apex sporadic meteoroid apparent sources.

meteorites↗
NASA NTRS1973

Two-color dual-beam backscatter laser Doppler velocimeter

A laser Doppler velocimeter has been developed that uses two of the colors emitted from an argon-ion laser for the simultaneous measurement of orthogonal velocities. Designed for use in a 2.13- by 3.05-m wind tunnel, it is capable of traversing its focal volume across spatially unstable flows at scan speeds of up to 1.5 m/sec. Its optical layout and principles of operation are discussed, and the data from a typical traversal of a trailing wing-tip vortex are presented.

Grant, G. R.↗
NASA NTRS1975

Low speed aerodynamic characteristics of a lifting-body hypersonic research aircraft configuration

An experimental investigation of the low-speed longitudinal, lateral, and directional stability characteristics of a lifting-body hypersonic research airplane concept was conducted in a low-speed tunnel with a 12-foot (3.66-meter) octagonal test section at the Langley Research Center. The model was tested with two sets of horizontal and vertical tip controls having different planform areas, a center vertical tail and two sets of canard controls having trapezoidal and delta planforms, and retracted and deployed engine modules and canopy. This investigation was conducted at a dynamic pressure of 239.4 Pa (5 psf) (Mach number of 0.06) and a Reynolds number of 2 million based on the fuselage length. The tests were conducted through an angle-of-attack range of 0 deg to 30 deg and through horizontal-tail deflections of 10 deg to minus 30 deg. The complete configuration exhibited excessive positive static longitudinal stability about the design center-of-gravity location. However, the configuration was unstable laterally at low angles of attack and unstable directionally throughout the angle-of-attack range. Longitudinal control was insufficient to trim at usable angles of attack. Experiments showed that a rearward shift of the center of gravity and the use of a center-located vertical tail would result in a stable and controllable vehicle.

Penland, J. A.↗
NASA NTRS1976

Hover performance tests of full scale variable geometry rotors

Full scale whirl tests were conducted to determine the effects of interblade spatial relationships and pitch variations on the hover performance and acoustic signature of a 6-blade main rotor system. The variable geometry rotor (VGR) variations from the conventional baseline were accomplished by: (1) shifting the axial position of alternate blades by one chord-length to form two tip path planes; and (2) varying the relative azimuthal spacing from the upper rotor to the lagging hover rotor in four increments from 25.2 degrees to 62.1 degrees. For each of these four configurations, the differential collective pitch between upper and lower rotors was set at + or - 1 deg, 0 deg and -1 deg. Hover performance data for all configurations were acquired at blade tip Mach numbers of 0.523 and 0.45. Acoustic data were recorded at all test conditions, but analyzed only at 0 deg differential pitch at the higher rotor speed. The VGR configurations tested demonstrated improvements in thrust at constant power as high as 6 percent. Reductions of 3 PNdb in perceived noise level and of 4 db in blade passage frequency noise level were achieved at the higher thrust levels. Consistent correlation exists between performance and acoustic improvements. For any given azimuth spacing, performance was consistently better for the differential pitch condition of + or - 1 degree, i.e. with the upper rotor pitch one degree higher than the lower rotor.

Rorke, J. B.↗
NASA NTRS1993

Subsonic aerodynamic characteristics of the HL-20 lifting-body configuration

The HL-20 is proposed as a possible future manned spacecraft. The configuration consists of a low-aspect-ratio body with a flat undersurface. Three fins (a small centerline fin and two outboard (tip) fins set at a dihedral angle of 50 deg) are mounted on the aft body. The control system consists of elevon surfaces on the outboard fins, a set of four body flaps on the upper and lower aft body, and an all-movable center fin. Both the elevons and body flaps were capable of trimming the model to angles of attack from -2 deg to above 20 deg. The maximum trimmed lift-drag ratio was 3.6. Replacing the flat-plate tip fins with airfoil tip fins increased the maximum trimmed lift-drag ratio to 4.2. The elevons were effective as a roll control, but they produced about as much yawing moment as rolling moment because of the tip-fin dihedral angle. The body flaps produced less rolling moment than the elevons and only small values of yawing moment. A limited investigation of the effect of varying tip-fin dihedral angle indicated that a dihedral angle of 50 deg was a reasonable compromise for longitudinal and lateral stability, longitudinal trim, and performance at subsonic speeds.

Ware, George M.↗
NASA NTRS2013

Atomic Force Microscope Mediated Chromatography

The atomic force microscope (AFM) is used to inject a sample, provide shear-driven liquid flow over a functionalized substrate, and detect separated components. This is demonstrated using lipophilic dyes and normal phase chromatography. A significant reduction in both size and separation time scales is achieved with a 25-micron-length column scale, and one-second separation times. The approach has general applications to trace chemical and microfluidic analysis. The AFM is now a common tool for ultra-microscopy and nanotechnology. It has also been demonstrated to provide a number of microfluidic functions necessary for miniaturized chromatography. These include injection of sub-femtoliter samples, fluidic switching, and sheardriven pumping. The AFM probe tip can be used to selectively remove surface layers for subsequent microchemical analysis using infrared and tip-enhanced Raman spectroscopy. With its ability to image individual atoms, the AFM is a remarkably sensitive detector that can be used to detect separated components. These diverse functional components of microfluidic manipulation have been combined in this work to demonstrate AFM mediated chromatography. AFM mediated chromatography uses channel-less, shear-driven pumping. This is demonstrated with a thin, aluminum oxide substrate and a non-polar solvent system to separate a mixture of lipophilic dyes. In conventional chromatographic terms, this is analogous to thin-layer chromatography using normal phase alumina substrate with sheardriven pumping provided by the AFM tip-cantilever mechanism. The AFM detection of separated components is accomplished by exploiting the variation in the localized friction of the separated components. The AFM tip-cantilever provides the mechanism for producing shear-induced flows and rapid pumping. Shear-driven chromatography (SDC) is a relatively new concept that overcomes the speed and miniaturization limitations of conventional liquid chromatography. SDC is based on a sliding plate system, consisting of two flat surfaces, one of which has a recessed channel. A fluid flow is produced by axially sliding one plate past another, where the fluid has mechanical shear forces imposed at each point along the channel length. The shear-induced flow rates are very reproducible, and do not have pressure or voltage gradient limitations. SDC opens up a new range of enhanced separation kinetics by permitting the sample confinement with submicron dimensions. Small, highly confined liquid is advantageous for chromatographic separation because the separation rate is known to scale according to the square of the confined sample diameter. In addition, because shear-driven flows are not limited by fluid velocity, shear-driven liquid chromatography may provide up to 100,000 plate efficiency.

Anderson, Mark S.↗
NASA NTRS1975

Cold-air performance of a 12.766-centimeter-tip-diameter axial-flow cooled turbine. 1: Design and performance of a solid blade configuration

A solid blade version of a single-stage, axial-flow turbine was investigated to determine its performance over a range of speeds from 0 to 105 percent of equivalent design speed and over a range of total to static pressure ratios from 1.62 to 5.07. The results of this investigation will be used as a baseline for comparison with those obtained from a cooled version of this turbine.

Haas, J. E.↗
NASA NTRS1986

Progress in tail rotor noise analysis

Helicopter tail rotor noise generated by interactions with the main rotor tip vortices and with the fuselage separation mean wake is investigated. The tail rotor blade-main rotor tip vortex interaction is modeled as an airfoil of infinite span cutting through a moving vortex. The present results are compared to the tail rotor loading and high speed thickness noise and are found to be significant. This noise mechanism is a function of the helicopter operating conditions and the location of the tail relative to the main rotor. Tail rotor self-generated noise due to turbulent vortex shedding from blunt trailing edges is also analyzed.

Chou, S.-T.↗
NASA NTRS1996

Time Dependence of Tip Morphology during Cellular/Dendritic Arrayed Growth

Succinonitrile-1.9 wt pct acetone has been directionally solidified in 0.7 X 0.7-cm-square cross section pyrex ampoules in order to observe the cell/dendrite tip morphologies, not influenced by the 'wall effects', which are present during growth in the generally used thin (about 200 gm) crucibles. The tips do not maintain a steady-state shape, as is generally assumed. Instead, they fluctuate within a shape envelope. The extent of fluctuation increases with decreasing growth speed, as the micro structure changes from the dendritic to cellular. The influence of natural convection has been examined by comparing these morphologies with those grown, without convection, in the thin ampoules.

Song, H.↗
NASA NTRS1997

SWIFT: Multistage Turbomachinery Analysis Code Developed

A new turbomachinery analysis code called SWIFT has been developed at the NASA Lewis Research Center. SWIFT solves thin-layer Navier-Stokes equations with the Baldwin-Lomax turbulence model and an explicit finite-difference scheme. Preconditioning allows the code to be used for all speed ranges, from incompressible to supersonic flows. Multiblock capability allows three types of grids to be patched together to simulate many types of turbomachinery geometries, including hub and tip clearances. In addition, code users can analyze multistage turbomachinery by using a steady averaging-plane approach. This approach uses linearized characteristic boundary conditions to pass information accurately between the stages.

Chima, Rodrick V.↗
NASA NTRS1996

Stable Lobed Mixer With Combustion Demonstrated and Measured

The NASA Lewis Research Center collaborated with the Massachusetts Institute of Technology (MIT) on an experiment to study the use of lobed mixers to improve the fuel-air mixing process and increase combustion intensity in combustors with minimal pressure loss. This experiment is the first known stable combusting flow studied for this device, and the data show a much faster and much more uniform combustion process than for flat-plate mixers. Several potential benefits may be realized from this study in future combustors, including a reduction in NO_x emissions because of the more uniform temperature distribution. The experiment was done in Lewis' Planar Reacting Shear Layer facility, which was adapted to accept a lobed mixer in addition to the original planar tip. A graduate student at MIT provided the mixer design concept, and Lewis provided the engineering, operations, and research expertise. The experiment used hydrogen-nitrogen mixtures to react with vitiated hot air at 920 K. A flow speed of about 120 m/sec and a speed ratio of 0.5 were used. Flow diagnostics consisted of traversing fine-wire thermocouples and pitot probes for flow mapping. Supplementary fluorescence images were taken with a charged coupled device (CCD) camera to show the location and temporal behavior of the reaction zone. The data showed that the lobed mixer consumed the reactants between 3 to 10 times faster than a corresponding planar shear layer. The figure shows the dramatic difference in the measured temperature distribution with and without the lobed mixer. The increased mixing rate was due to a larger interfacial area as well as to the secondary flow from the streamwise vortices off the tips of the lobes. In addition, the fluorescence images showed that the lobes acted as flame stabilizers.

Source record↗
DOE OSTI2022

UAE6 - Wind Tunnel Tests Data - UAE6 - Sequence S - Raw Data

Sequences S, T, and U: Upwind, No Probes (F); Upwind 2° Pitch (F); Upwind 4° Pitch (F) This test sequence used an upwind, rigid turbine with a 0° cone angle. The wind speed ranged from 5 m/s to 25 m/s. Yaw angles of 0° to 180° were achieved for Sequence S, but the yaw angle remained at 0° for Sequences T and U. The blade tip pitch was 3° for Sequence S, 2° for Sequence T, and 4° for Sequence U. These three sequences were interleaved during testing because the pitch angle change was easily made by the turbine operator. The rotor rotated at 72 RPM. Blade pressure measurements were collected. The five-hole probes were removed and the plugs were installed. Plastic tape 0.03-mm-thick was used to smooth the interface between the plugs and the blade. The teeter dampers were replaced with rigid links, and these two channels were flagged as not applicable by setting the measured values in the data file to -99999.99 Nm. The teeter link load cell was pre-tensioned to 40,000 N. During post-processing, the probe channels were set to read -99999.99. In addition to the standard 30-second campaigns, yaw sweeps were done at 7 m/s and 10 m/s for the Sequence S configuration. These 6-minute campaigns were collected while the yaw drive rotated the turbine 360° at a rate of 1°/s. The file names for these campaigns use the letter designation, followed by two digits for wind speed, followed by YSU, followed by 00.

17 WIND ENERGY↗
DOE OSTI2022

UAE6 - Wind Tunnel Tests Data - UAE6 - Sequence T - Raw Data

Sequences S, T, and U: Upwind, No Probes (F); Upwind 2° Pitch (F); Upwind 4° Pitch (F) This test sequence used an upwind, rigid turbine with a 0° cone angle. The wind speed ranged from 5 m/s to 25 m/s. Yaw angles of 0° to 180° were achieved for Sequence S, but the yaw angle remained at 0° for Sequences T and U. The blade tip pitch was 3° for Sequence S, 2° for Sequence T, and 4° for Sequence U. These three sequences were interleaved during testing because the pitch angle change was easily made by the turbine operator. The rotor rotated at 72 RPM. Blade pressure measurements were collected. The five-hole probes were removed and the plugs were installed. Plastic tape 0.03-mm-thick was used to smooth the interface between the plugs and the blade. The teeter dampers were replaced with rigid links, and these two channels were flagged as not applicable by setting the measured values in the data file to -99999.99 Nm. The teeter link load cell was pre-tensioned to 40,000 N. During post-processing, the probe channels were set to read -99999.99. In addition to the standard 30-second campaigns, yaw sweeps were done at 7 m/s and 10 m/s for the Sequence S configuration. These 6-minute campaigns were collected while the yaw drive rotated the turbine 360° at a rate of 1°/s. The file names for these campaigns use the letter designation, followed by two digits for wind speed, followed by YSU, followed by 00.

17 WIND ENERGY↗
DOE OSTI2022

UAE6 - Wind Tunnel Tests Data - UAE6 - Sequence U - Raw Data

Sequences S, T, and U: Upwind, No Probes (F); Upwind 2° Pitch (F); Upwind 4° Pitch (F) This test sequence used an upwind, rigid turbine with a 0° cone angle. The wind speed ranged from 5 m/s to 25 m/s. Yaw angles of 0° to 180° were achieved for Sequence S, but the yaw angle remained at 0° for Sequences T and U. The blade tip pitch was 3° for Sequence S, 2° for Sequence T, and 4° for Sequence U. These three sequences were interleaved during testing because the pitch angle change was easily made by the turbine operator. The rotor rotated at 72 RPM. Blade pressure measurements were collected. The five-hole probes were removed and the plugs were installed. Plastic tape 0.03-mm-thick was used to smooth the interface between the plugs and the blade. The teeter dampers were replaced with rigid links, and these two channels were flagged as not applicable by setting the measured values in the data file to -99999.99 Nm. The teeter link load cell was pre-tensioned to 40,000 N. During post-processing, the probe channels were set to read -99999.99. In addition to the standard 30-second campaigns, yaw sweeps were done at 7 m/s and 10 m/s for the Sequence S configuration. These 6-minute campaigns were collected while the yaw drive rotated the turbine 360° at a rate of 1°/s. The file names for these campaigns use the letter designation, followed by two digits for wind speed, followed by YSU, followed by 00.

17 WIND ENERGY↗
NASA NTRS1973

Dual-fuselage aircraft having yawable wing and horizontal stabilizer

An aircraft configuration consisting of a pair of fuselages parallel to each other and connected by a main wing and a horizontal stabilizer which pivot on the fuselages is described. The pivotal attachment allows the wing to be yawed relative to the fuselages for high speed flight while at the same time spreading the weight and volume distribution of the aircraft along the direction of flight. The main wing is curved upward at the tips to compensate for any roll tendencies caused by its yawed position.

Jones, R. T.↗
NASA NTRS1991

NACA 0015 wing pressure and trailing vortex measurements

A NACA 0015 semispan wing was placed in a low-speed wind tunnel, and measurements were made of the pressure on the upper and lower surface of the wing and of velocity across the vortex trailing downstream from the tip of the wing. Pressure data were obtained for both 2-D and 3-D configurations. These data feature a detailed comparison between wing tips with square and round lateral edges. A two-component laser velocimeter was used to measure velocity profiles across the vortex at numerous stations behind the wing and for various combinations of conditions. These conditions include three aspect ratios, three chord lengths, a square- and a round lateral-tip, presence or absence of a boundary-layer trip, and three image plane positions located opposite the wing tip. Both pressure and velocity measurements were made for the angles of attack 4 deg less than or equal to alpha less than or equal to 12 deg and for Reynolds numbers 1 x 10(exp 6) less than or equal to Re less than or equal to 3 x 10(exp 6).

Mcalister, K. W.↗