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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Optimization of Acoustic Pressure Measurements for Impedance Eduction

As noise constraints become increasingly stringent, there is continued emphasis on the development of improved acoustic liner concepts to reduce the amount of fan noise radiated to communities surrounding airports. As a result, multiple analytical prediction tools and experimental rigs have been developed by industry and academia to support liner evaluation. NASA Langley has also placed considerable effort in this area over the last three decades. More recently, a finite element code (Q3D) based on a quasi-3D implementation of the convected Helmholtz equation has been combined with measured data acquired in the Langley Grazing Incidence Tube (GIT) to reduce liner impedance in the presence of grazing flow. A new Curved Duct Test Rig (CDTR) has also been developed to allow evaluation of liners in the presence of grazing flow and controlled, higher-order modes, with straight and curved waveguides. Upgraded versions of each of these two test rigs are expected to begin operation by early 2008. The Grazing Flow Impedance Tube (GFIT) will replace the GIT, and additional capabilities will be incorporated into the CDTR. The current investigation uses the Q3D finite element code to evaluate some of the key capabilities of these two test rigs. First, the Q3D code is used to evaluate the microphone distribution designed for the GFIT. Liners ranging in length from 51 to 610 mm are investigated to determine whether acceptable impedance eduction can be achieved with microphones placed on the wall opposite the liner. This analysis indicates the best results are achieved for liner lengths of at least 203 mm. Next, the effects of moving this GFIT microphone array to the wall adjacent to the liner are evaluated, and acceptable results are achieved if the microphones are placed off the centerline. Finally, the code is used to investigate potential microphone placements in the CDTR rigid wall adjacent to the wall containing an acoustic liner, to determine if sufficient fidelity can be achieved with 32 microphones available for this purpose. Initial results indicate 32 microphones can provide acceptable measurements to support impedance eduction with this test rig.

Jones, M. G.↗
NASA NTRS1989

On curve and surface stretching in turbulent flow

Cocke (1969) proved that in incompressible, isotropic turbulence the average material line (material surface) elements increase in comparison with their initial values. Good estimates of how much they increase in terms of the eigenvalues of the Green deformation tensor were rigorously obtained.

Etemadi, Nassrollah↗
NASA NTRS1989

Time-dependent Navier-Stokes computations for flow-induced vibrations of vanes

Flows over two curved vane configurations were computed using a time-accurate compressible Navier-Stokes flow model. One configuration showed the presence of strong flow-induced vibrations at Strouhal numbers near 0.19 and 0.38 for bending and torsional excitation. In the other configuration, a simple modification reduced both types of response. Laminar flows were analyzed for the effects of flow-induced vibrations, and flow fields were solved for a rigid vane and a vane undergoing forced vibrations at prescribed amplitude and frequency simulating vibration response to a coupled vortex-shedding/elastic motion feedback cycle.

Liu, B. L.↗
DOE OSTI2025

TEAMER – Enhanced Flow Measurement for Aquantis Tidal Turbine Test

The AQ10 is a floating, two-bladed, passive yawing tidal turbine developed by Aquantis that has a 10-meterrotor diameter, 160 kW rating, and employs reliable off-the-shelf powertrain and power conversion hardware. Aquantis is planning on-water turbine power performance and loads (blade loading and thrust)testing, where the turbine will be pushed through still water up to 4 knots and placed in a ‘station keeping’ tow in a tidal race up to its rated speed. On-water testing will be conducted using vessels and floating platforms on the sea surface to improve ease of testing and reduce disturbance to the environment. In this TEAMER project, Pacific Northwest National Laboratory (PNNL) will conduct water velocity and turbulence measurements in front of the turbine during on-water testing using acoustic Doppler instrumentation. By measuring both the tidal current flowing past the turbine and the resulting electrical power output, test results will provide a power curve (power vs flow speed) for the turbine up to rated power. Measurements of turbulence and velocity shear in front of the rotor will also provide information to assess the structural response of the rotor blades. With this analysis, Aquantis can use the performance and loads data to validate Tidal Bladed and OpenFAST simulations of the measured operating conditions. Measuring the power performance of a prototype turbine is a valuable step to improving device development and conducting a complete power performance assessment to IEC/TS 62600-200 standards in the future.

16 TIDAL AND WAVE POWER↗
NASA NTRS1981

The aerodynamics of circulation control

Two dimensional subsonic wind tunnel tests were conducted on a 20% thickness: chord ratio circulation controlled elliptic aerofoil section equipped with forward and reverse blowing slots. Overall performance measurements were made over a range of trailing edge blowing momentum coefficients from 0 to 0.04; some included the effect of leading edge blowing. A detailed investigation of the trailing edge wall jet, using split film probes, hot wire probes and total head tubes, provided measurements of mean velocity components, Reynolds normal and shear stresses, and radial static pressure. The closure of the two dimensional angular momentum and continuity equations was examined using the measured data, with and without correction, and the difficulty of obtaining a satisfactory solution illustrated. Suggestions regarding the nature of the flow field which should aid the understanding of Coanda effect and the theoretical solution of highly curved wall jet flows are presented.

Wood, N. J.↗
NASA NTRS1988

Plasma bulk flow in Jupiter's dayside middle magnetosphere

Using the plasma data obtained during the Voyager 1 encounter and the full response function of the Plasma Science (PLS) experiment, convective plasma velocities have been determined in the dayside middle magnetosphere of Jupiter (r = 10-25 Jupiter radii). It is found that temperature anisotropies have very little effect on plasma velocity determination and that the plasma data are well approximated by convected, isotropic Maxwellian ion distribution functions. The insensitivity of the analysis to any thermal anisotropies which may exist allows a good determination of the bulk plasma flow velocity. In addition to the subcorotational azimuthal flow, there exists a substantial nonazimuthal component of plasma flow. This nonazimuthal flow is mostly aligned (antialigned) with the local magnetic field but also exhibits a cross-field component. The velocity pattern is inconsistent with enhanced plasma outflow in the active sector, as suggested by the corotating convection model of plasma transport. The contribution of field-aligned flow along the curved magnetic field lines to the stress on the magnetic field is evaluated. In the region studied, such flow contributes up to one half the stress produced by the azimuthal plasma flow.

Sands, Mark R.↗
NASA NTRS1986

Desingularization of periodic vortex sheet roll-up

An analytical approach is used in an attempt to model the evolution of a vortex sheet past the critical time by means of a desingularization method. Evolution of the sheet, which is embedded in a two-dimensional flow, is described by approximating the total circulation between a fixed material point and an imaginary point on the curve of the flow. A linear dispersion relation is defined which shows that the short wavelength modes of the sheet are not unstable and therefore do adversely effect the computations as artifacts of round-off errors. The desingularization approach is demonstrated to converge beyond the critical time for the vortex sheet. Application of the technique for the study of the vortex sheet shed from an elliptically loaded wing is indicated.

Krasny, R.↗
NASA NTRS2007

Preliminary Investigation of Curved Liner Sample in the NASA LaRC Curved Duct Test Rig

This viewgraph presentation reviews the preliminary investigation of the curved liner sample in the NASA LaRC Curved Duct Test Rig (CDTR). It reviews the purpose of the Curved Duct Test Rig. Its purpose is to develop capability to investigate acoustic and aerodynamic properties in ducts. It has several features to accomplish that purpose: (1) Large scale (2) Flow rate to M = 0.275 (3) Higher order mode control (4) Curved flow path (5) Adaptable test section (6) Flexible test configurations. The liner has minimal effect on turbulence or boundary layer growth in duct. The curved duct sample attenuation is affected by mode scattering. In conclusion, the CDTR is valid tool for aerodynamic and acoustic evaluation of duct treatment

Gerhold, Carl H.↗
NASA NTRS1984

Turbulent boundary layers with secondary flow

An experimental analysis of the boundary layer on a plane wall, along which the flow occurs, whose potential flow lines are curved in plane parallel to the wall is discussed. According to the equation frequently applied to boundary layers in a plane flow, which is usually obtained by using the pulse law, a generalization is derived which is valid for boundary layers with spatial flow. The wall shear stresses were calculated with this equation.

Grushwitz, E.↗
NASA NTRS2002

Irradiated HMEC from A-T Heterozygous Breast Tissue

Women who are heterozygous for ataxia-telangiectasia (A-T) carry a single defective ATM gene in chromosome 11 q22-23, and have been statistically determined with high significance within a defined database to be approximately 5-fold more susceptible for developing breast cancer than their noma1 counterpart. Breast cancer susceptibility of these A-T heterozygotes has been hypothesized to include consequence of response to damage caused by low levels of ionizing radiation. Prophylactic mastectomy specimens were donated by a 41 year-old obligate A-T heterozygote who was located prior to her elective surgery through an existing pedigree. Harvest of that breast tissue provided an isolate of long-term growth human mammary epithelial cells (HMEC), designated WH612/3. An isolate of presumed normal long-term growth HMEC, designated 48R, was obtained from Dr. Martha Stampfer (Lawrence Berkeley Laboratory, University of California), and the A-T heterozygous HMEC were transformed with E6 and E7 oncogenes of human papilloma virus Type-16 in the laboratory of Dr. Ray White (Hunt- Cancer Institute, University of Utah) for use in this study. The objective of this study is to study the expression of end points that may bear on cancer outcome following irradiation of HMEC. Specific end points are cell survival, cell cycle, p53 expression, and apoptosis. Survival curves, immunostaining, and flow cytometery are used to examine these end points. Radiation-induced cell killing shows less shoulder development in the survival curve for WH61U3 compared to 48R HMEC, suggesting less repair of damage in the former HMEC. Additional information is included in the original extended abstract.

Richmond, Robert↗
NASA NTRS1973

Transmission of wave energy in curved ducts

A formation of wave energy flow was developed for motion in curved ducts. A parametric study over a range of frequencies determined the ability of circular bends to transmit energy for the case of perfectly rigid walls.

Rostafinski, W.↗
NASA NTRS1982

Velocity and flow angle measurements in the Langley 0.3-meter transonic cryogenic tunnel using a laser transit anemometer

The Laser Transit Anemometer (LTA) system is described. In the LTA system two parallel laser beams of known separation and cross sectional area are focussed at the same location or plane. When a particle in a flow field passes through both beams and the time is recorded for its transit (time of flight), its velocity can be calculated knowing the distance between the beams. By rotating the two beams (spots) around a common center and recording the number of valid events (a particle which passes through both spots in the proper sequence) at each angle the flow angle can be determined by curve fitting a predetermined number of angles or points and calculating the peak of what should be a Gaussian curve. The best angle or flow angle is defined as the angle at which the maximum number of valid events occurs. The LTA system functioned properly although conditions were less than desirable.

Honaker, W. C.↗
NASA NTRS1991

Pulmonary function in microgravity: KC-135 experience

We have commenced a KC-135 program that parallels and proceeds our Spacelab (SLS-1) pulmonary function experiment. Our first task was to elucidate the affect of normal gravitation on the shape of the maximum expiratory flow volume (MEFV) curve. Nine normal subjects performed multiple MEFV maneuvers at 0-G, 1-G, and approximately 1.7-G. The MEFV curves for each subject were filtered, aligned at RV, and ensemble-averaged to produce an average MEFV curve for each state, allowing differences to be studied. Most subjects showed a decrease in the FVC at 0-G, which we attribute to an increased intrathoracic blood volume. In most of these subjects, the mean lung volume associated with a given flow was lower at 0-G, over about the upper half of the vital capacity. This is similar to the change previously reported during heat out immersion and is consistent with the known affect of engorgement of the lung with blood, on elastic recoil. There were also consistent but highly individual changes in the position and magnitude of detailed features of the curve, the individual patterns being similar to those previously reported on transition from the erect to the supine position. This supports the idea that the location and motion of choke points which determine the detailed individual configuration of MEFV curves, can be significantly influenced by gravitational forces, presumably via the effects of change in longitudinal tension on local airway pressure-diameter behavior and wave speed. We have developed a flight mass spectrometer and have commenced a study of single breath gradients in gas exchange, inert gas washouts, and rebreathing cardiac outputs and lung volumes at 0-G, 1-G, and 1.7-G. Comparison of our results with those from SLS-1 should identify the opportunities and limitations of the KC-135 as an accessible microgravity resource.

Guy, Harold J.↗
NASA NTRS1994

Computation and modeling of aero-thermal fields in turbine cascades and strongly curved ducts

Advanced turbulence models are crucial for accurate prediction of rocket engine flows, due to existence of very large extra strain rates, such as strong streamline curvature. Numerical simulation of the turbulent flow in a strongly curved turn-around duct (TAD) has been carried out with a Reynolds stress model (RSM), an algebraic Reynolds stress model (ARSM) and a kappa-epsilon model. the RSM model and the ARSM model are found to capture the turbulence damping due to the convex curvature, but underpredict the turbulence enhancement caused by the concave curvature. To capture the concave curvature effects, it is necessary to modify the epsilon-equation. The modification of episilon-equation suggested by Launder, et.al, provides the correct trend, but over-corrects the curvature effects. A comparative study of two modes of transition in gas turbine, the by-pass transition and the separation-induced transition, has been carried out with several low-Reynolds-number (LRN) kappa-epsilon models. Effects of blade surface pressure gradient, freestream turbulence and Reynolds number on the blade boundary layer development, and particularly the inception of transition are examined in detail. The present study indicates that the turbine blade transition, in the presence of high freestream turbulence, is predicted well with LRN kappa-epsilon models employed.

Luo, J.↗
NASA NTRS1992

On turbulent flows dominated by curvature effects

A technique for improving the numerical predictions of turbulent flows with the effect of streamline curvature is developed. Separated flows and the flow in a curved duct are examples of flowfields where streamline curvature plays a dominant role. New algebraic formulations for the eddy viscosity incorporating the k-epsilon turbulence model are proposed to account for various effects of streamline curvature. The loci of flow reversal of the separated flows over various backward-facing steps are employed to test the capability of the proposed turbulence model in capturing the effect of local curvature.

Cheng, G. C.↗
NASA NTRS1990

Reduction of vortex-induced vibration in vane geometries

Computations using a time-accurate, compressible Navier-Stokes flow model were conducted to analyze both unsteady laminar and turbulent flows over two curved configurations of vanes which were shaped to treat a 4.0 kHz vibration problem which has occurred in several SSMEs. This problem involves vortex shedding from vanes which causes excessive vane vibration and cracking. The original vane configuration exhibited strong flow-induced vibrations at a Strouhal number near 0.19 for a the first bending mode excitation. Scalloping of the leading edge raised the frequency of the vane's first torsional mode, which in turn increased the onset flow velocity at lock-in. Beveling the vane's trailing edge eliminated vortex shedding at the trailing edge, which decoupled the flow oscillation from the vibrating wave. A modified vane configuration with a beveled trailing edge at a 30 deg angle was also studied.

Liu, B. L.↗