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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Characterization of wind speed and directional shear at the AWAKEN field campaign site

The American wake experiment (AWAKEN) is taking place in northern Oklahoma, USA, close to the Atmospheric Radiation Measurement Southern Great Plains (ARM SGP) atmospheric observatory. The planning for the deployment of the instruments in this observational field campaign required an assessment of the wind characteristics of the site. This paper analyzes long-term data collected by instruments at the ARM SGP observatory to characterize the winds near the AWAKEN site. The analysis shows that this site experiences high wind shear and veer events with a large number of nocturnal low-level jets. A total of 7086 low-level jet wind profiles over 6 years are examined and found to be dominant from the south and southeast. Significant nocturnal wind veer is observed, which causes southerly wind near the surface to become westerly wind aloft. By identifying a strong relationship between atmospheric stability and wind shear, the wind shear at the site is predicted using the Monin–Obukhov similarity theory (MOST) and validated with the observational data collected by a scanning Doppler lidar. The results show that wind speed at a height of 91 m, a proxy hub height for wind turbines in this area, can be predicted from data collected at a height of 10 m with a bias of −0.35 and 0.65 m s−1 in unstable and stable atmospheric boundary layers, respectively. The bias of the predicted wind speed is mostly in the region of low wind speed, and wind speed above 5 m s−1 at a height of 91 m can be predicted with a bias of less than 0.2 m s−1, and the limitations of the MOST in predicting winds during the stably stratified boundary layer is well-observed.

17 WIND ENERGY↗
NASA NTRS1997

Wake Vortex Radar System Development: Overview

The objectives of the work are to: (1) Investigate microwave and millimeter wave sensors to locate, track, quantify, and observe the wake vortex hazard; (2) Develop and evaluate system concepts and designs using sensor system models and employing a theoretical reflectivity model for the wake vortex; (3) Test the validity of the theoretical model; (4) Acquire sensor systems and conduct field testing to evaluate; and to (5) Refine a system for field testing as a wake vortex sensor.

Neece, Robert T.↗
DOE OSTI2017

The Evaporation and Survival of Cluster Galaxies’ Coronae. II. The Effectiveness of Anisotropic Thermal Conduction and Survival of Stripped Galactic Tails

We simulate anisotropic thermal conduction between the intracluster medium (ICM) and the hot coronal interstellar medium (ISM) gas in cluster galaxies. In Paper I, we simulated the evaporation of the hot ISM due to isotropic (possibly saturated) conduction between the ISM and ICM. We found that hot coronae evaporate on ∼10{sup 2} Myr timescales, significantly shorter than the ∼10{sup 3} Myr gas loss times due to ram pressure stripping. No tails of stripped gas are formed. This is in tension with the observed ubiquity and implied longevity of compact X-ray coronae and stripped ISM tails, and requires the suppression of evaporation, possibly due to magnetic fields and anisotropic conduction. We perform a series of wind tunnel simulations similar to that in Paper I, now including ISM and ICM magnetic fields. We simulate the effect of anisotropic conduction for a range of extreme magnetic field configurations: parallel and perpendicular to the ICM wind, and continuous and completely disjointed between the ISM and ICM. We find that when conduction is anisotropic, gas loss due to evaporation is severely reduced; the overall gas loss rates with and without anisotropic conduction do not differ by more than 10%–20%. Magnetic fields also prevent stripped tails from evaporating in the ICM by shielding, and providing few pathways for heat transport between the ICM and ISM. The morphology of stripped tails and magnetic fields in the tails and wakes of galaxies are sensitive to the initial magnetic field configuration.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1986

Directivity and trends of noise generated by a propeller in a wake

An experimental study of the effects on far-field propeller noise of a pylon wake interaction was conducted with a scale model of a single-rotation propeller in a low-speed anechoic wind tunnel. A detailed mapping of the noise directivity was obtained at 10 test conditions covering a wide range of propeller power landings at several subsonic tip speeds. Two types of noise penalties were investigated-pulser and spacing. The pusher noise penalty is the difference in the average overall sound pressure level, OASPL, for pusher and tractor installations. (In a pusher installation, the propeller disk is downstream of a pylon or another aerodynamic surface.) The spacing noise penalty is the difference in the average OASPL for different distances between the pylon trailing edge and the propeller. The variations of these noise penalties with axial, or flyover, angle theta and circumferential angle phi are presented, and the trends in these noise penalties with tip Mach number and power loading are given for selected values of theta and phi. The circumferential directivity of the noise from a pusher installation showed that the addition noise due to the interaction of the pylon wake with the propeller had a broad peak over a wide range of circumferential angles approximately perpendicular to the pylon with a sharp minimum 90 deg. to the pylon for the majority of cases tested. The variation of the pusher noise penalty with theta had a minimum occurring near the propeller plane and maximum values of as much as 20 dB occurring toward the propeller axes. The magnitude of the pusher noise penalty generally decreased as propeller tip Mach number or power loading was increased.

Block, P. J. W.↗
NASA NTRS2002

Contrail Formation in Aircraft Wakes Using Large-Eddy Simulations

In this work we analyze the issue of the formation of condensation trails ("contrails") in the near-field of an aircraft wake. The basic configuration consists in an exhaust engine jet interacting with a wing-tip training vortex. The procedure adopted relies on a mixed Eulerian/Lagrangian two-phase flow approach; a simple micro-physics model for ice growth has been used to couple ice and vapor phases. Large eddy simulations have carried out at a realistic flight Reynolds number to evaluate the effects of turbulent mixing and wake vortex dynamics on ice-growth characteristics and vapor thermodynamic properties.

Paoli, R.↗
DOE OSTI2012

Effect of wake potential on Coulomb crystallization in the presence of magnetic field

The formation of dust crystal in plasma under the influence of repulsive Yukawa (Debye-Hueckel) potential is a well known phenomenon. The regular structure of dust particles is affected by anisotropic ion flow near the sheath region. The bombardment of the ions over dust grains distorts their Debye sphere by overshielding the dust cloud and gives rise to an attractive oscillatory wake potential. In this paper, we have obtained an expression for wake potential along with the Yukawa type of potential in a complex plasma in the presence of magnetic field, for subsonic ion flow towards the plasma sheath. In the presence of magnetic field, interaction potential gets modified and becomes anisotropic. We have studied the combined effect of the attractive wake potential as well as repulsive Yukawa potential on a 2D dust crystal, both in the presence and absence of magnetic field, using molecular dynamic simulation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1978

Lunar interaction with the solar wind - Effects on lunar electrical conductivity estimates

The lunar electromagnetic response, measured at very low frequencies with the moon in the solar wind, is used to evaluate interior electrical conductivity at great depth and to determine limits on the size of possible lunar core. A theory is developed wherein compression of the magnetic field in the lunar tail cavity caused by inflowing plasma at the lunar limbs and in the lunar wake, bends the magnetic field in the lunar interior and thereby alters the tangential component of magnetic field observed on the dayside surface. This theory strongly indicates that cavity fringing cannot explain the enhanced East-West fluctuations. It is proposed that the East-West fluctuations might be due to diamagnetic currents caused by lunar surface photoelectrons in the lunar terminator region.

Goldstein, B. E.↗
NASA NTRS1988

A multi-element vortex lattice method for calculating the geometry and effects of a helicopter rotor wake in forward flight

A method is described for the analysis of the unsteady, incompressible potential flow associated with a helicopter rotor and it's wake in forward flight. This method is particularly useful in low advance ratio flight due to the major contribution, in the near field, of the deformed wake. The rotor geometry is prescribed and the unsteady wake geometry is computed from the local flow perturbation velocities. The wake is modeled as a full vortex lattice. The rotor geometry is arbitrary and several rotor blades can be represented. The unsteady airloads on the rotor blades are computed in the presence of the deformed rotor wake by a time-stepping technique. Solution for the load distribution on the blade surfaces is found by prescribing boundary conditions in a reference system which rotates with the blade tips. Transformation tensors are used to describe the contribution of the wake in the inertial system to the rotor in the rotating reference system. The effects of blade cyclic pitch variation are computed using a rotation tensor. The deformation of the wake is computed in the inertial frame. The wake is started impulsively from rest, allowing a natural convection of the wake with time.

Berry, John D.↗
NASA NTRS1985

Fundamental study of flow field generated by rotorcraft blades using wide-field shadowgraph

The vortex trajectory and vortex wake generated by helicopter rotors are visualized using a wide-field shadowgraph technique. Use of a retro-reflective Scotchlite screen makes it possible to investigate the flow field generated by full-scale rotors. Tip vortex trajectories are visible in shadowgraphs for a range of tip Mach number of 0.38 to 0.60. The effect of the angle of attack is substantial. At an angle of attack greater than 8 degrees, the visibility of the vortex core is significant even at relatively low tip Mach numbers. The theoretical analysis of the sensitivity is carried out for a rotating blade. This analysis demonstrates that the sensitivity decreases with increasing dimensionless core radius and increases with increasing tip Mach number. The threshold value of the sensitivity is found to be 0.0015, below which the vortex core is not visible and above which it is visible. The effect of the optical path length is also discussed. Based on this investigation, it is concluded that the application of this wide-field shadowgraph technique to a large wind tunnel test should be feasible. In addition, two simultaneous shadowgraph views would allow three-dimensional reconstruction of vortex trajectories.

Parthasarathy, S. P.↗
NASA NTRS1979

Plasma diffusion into the wake of Venus

A model of the diffusion of ionosheath plasma into the wake region of Venus is presented. It is shown that particle diffusion, which is assumed to be a consequence of the fluctuating magnetic field observed in the wake of Venus by Pioneer Venus and Veneras 9 and 10, can explain the plasma observations made in the wake by Veneras 9 and 10. The pressure due to these diffusing particles when balanced against the ionospheric pressure yield ionopause heights less than 1000 km for zenith angles less than about 135 deg. The model also predicts significant fluxes of low energy electrons and ions for zenith angles less than 135 deg, which are capable of producing the observed nightside ionosphere.

Gombosi, T.↗
DOE OSTI2015

Multi-gigaelectronvolt acceleration of positrons in a self-loaded plasma wakefield

New accelerator concepts must be developed to make future particle colliders more compact and affordable. The Plasma Wakefield Accelerator (PWFA) is one such concept, where the electric field of a plasma wake excited by a charged-particle bunch is used to accelerate a trailing bunch of particles. To apply plasma acceleration to particle colliders, it is imperative that both the electrons and their antimatter counterpart, the positrons, are efficiently accelerated at high fields using plasmas1. While substantial progress has recently been reported on high-field, high-efficiency acceleration of electrons in a PWFA powered by an electron bunch 2, such an electron-driven wake is unsuitable for the acceleration and focusing of a positron bunch. Here we demonstrate a new regime of PWFA where particles in the front of a single positron bunch transfer their energy to a substantial number of those in the rear of the same bunch by exciting a wakefield in the plasma. In the process, the accelerating field is altered – self-loaded – so that about a billion positrons gain five gigaelectronvolts (GeV) of energy with a narrow energy spread in a distance of just 1.3 meters. They extract about 30% of the wake’s energy and form a spectrally distinct bunch with as low as a 1.8% r.m.s. energy spread. This demonstrated ability of positron-driven plasma wakes to efficiently accelerate a significant number of positrons with a small energy spread may overcome the long-standing challenge of positron acceleration in plasma-based accelerators.

ACCPHY↗
DOE OSTI2020

American WAKE experimeNt (AWAKEN)

The American WAKE experimeNt (AWAKEN) is an international multi-institutional wind energy field campaign to better understand wake losses within operational wind farms. Wake interactions are among the least understood physical interactions in wind plants today, leading to unexpected power and profit losses. For example, Ørsted, the world’s largest offshore wind farm developer, recently announced a downward revision in energy estimates across their energy generation portfolio, primarily caused by underprediction of energy losses from wind farm blockage and wakes. In their announcement, they noted that the standard industry models used for their original energy estimates were inaccurate, and this was likely an industry-wide issue. To help further improve and validate wind plant models across scales from individual turbines as well as interfarm interactions between plants, new observations, such as those planned for AWAKEN, are critical. These model improvements will enable both improved layout and more optimal operation of wind farms with greater power production and improved reliability, ultimately leading to lower wind energy costs.

17 WIND ENERGY↗
DOE OSTI2013

ANISOTROPY OF TeV COSMIC RAYS AND OUTER HELIOSPHERIC BOUNDARIES

Cosmic rays in the energy range from about tens of GeV to several hundreds of TeV are observed on Earth, with an energy-dependent anisotropy of order 0.01%-0.1% and a consistent topology that appears to significantly change at higher energy. The nearest and most recent galactic cosmic-ray sources might stochastically dominate the observation and possibly explain a change in orientation of the anisotropy as a function of energy. However, the diffusion approximation is not able to explain its non-dipolar structure and, in particular, the significant contribution of small angular scale features. Particle propagation within the mean free path in the local interstellar medium might have a major role in determining the properties of galactic cosmic rays, such as their arrival distribution. In particular, scattering on perturbations induced in the local interstellar magnetic field by the heliosphere wake may cause a re-distribution of anisotropic cosmic rays below about 100 TeV toward the direction of the elongated heliotail and of the local interstellar magnetic field in the outer heliosphere. Such scattering processes are considered responsible for the observed TeV cosmic-ray global anisotropy and its fine angular structure.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1975

Wind tunnel measurements in the wake of a simple structure in a simulated atmospheric flow

Measurements of longitudinal mean velocity and turbulence intensity were made in the wake of a rectangular model building in a simulated atmospheric boundary-layer wind. The model building was a 1:50 scale model of a structure used in a wake measurement program at the George C. Marshall Space Flight Center 8-tower boundary-layer facility. The approach wind profile and measurement locations were chosen to match the field site conditions. The wakes of the building in winds from azimuths of 0 and 47 degrees referenced to the normal to the building long axis were examined. The effect of two lines of trees upwind of the building on the wake and the importance of the ratio of the building height to boundary-layer thickness on the extent of the wake were determined.

Hansen, A. C.↗
NASA NTRS1985

Study for prediction of rotor/wake/fuselage interference, part 1

A method was developed which allows the fully coupled calculation of fuselage and rotor airloads for typical helicopter configurations in forward flight. To do this, an iterative solution is carried out based on a conventional panel representation of the fuselage and a blade element representation of the rotor where fuselage and rotor singularity strengths are determined simultaneously at each step and the rotor wake is allowed to relax (deform) in response to changes in rotor wake loading and fuselage presence. On completion of the iteration, rotor loading and inflow, fuselage singularity strength (and, hence, pressure and velocity distributions) and rotor wake are all consistent. The results of a fully coupled calculation of the flow around representative helicopter configurations are presented. The effect of fuselage components on the rotor flow field and the overall wake structure is detailed and the aerodynamic interference between the different parts of the aircraft is discussed.

Clark, D. R.↗
NASA NTRS1985

Study for prediction of rotor/wake/fuselage interference. Part 2: Program users guide

A method was developed which permits the fully coupled calculation of fuselage and rotor airloads for typical helicopter configurations in forward flight. To do this, an iterative solution is carried out based on a conventional panel representation of the fuselage and a blade element representation of the rotor where fuselage and rotor singularity strengths are determined simultaneously at each step and the rotor wake is allowed to relax (deform) in response to changes in rotor wake loading and fuselage presence. On completion of the iteration, rotor loading and inflow, fuselage singularity strength (and, hence, pressure and velocity distributions) and rotor wake are all consistent. The results of a fully coupled calculation of the flow around representative helicopter configurations are presented. The effect of fuselage components on the rotor flow field and the overall wake structure is discussed as well as the aerodynamic interference between the different parts of the aircraft. Details of the computer program are given.

Clark, D. R.↗
NASA NTRS1985

Overview of helicopter wake and airloads technology

An overview of helicopter aerodynamics technology is presented with emphasis on rotor wake and airloads methodology developed at the United Technologies Research Center (UTRC). The evolution over the past twenty years of various levels of computerized wake geometry models at UTRC, such as undistorted wake, prescribed empirical wake, predicted distorted wake, and generalized wake models for the hover and forward flight regimes, is reviewed. The requirement for accurate wake modeling for flow field and airload prediction is demonstrated by comparisons of theoretical and experimental results. These results include blade pressure distributions predicted from a recently developed procedure for including the rotor wake influence in a full potential flow analysis. Predictions of the interactional aerodynamics of various helicopter components (rotor, fuselage, and tail) are also presented. It is concluded that, with advanced computers and the rapidly progressing computational aerodynamics technology, significant progress toward reliable prediction of helicopter airloads is forseeable in the near future.

Landgrebe, A. J.↗
NASA NTRS1974

Development and testing of laser Doppler system components for wake vortex monitoring. Volume 1: Scanner development, laboratory and field testing and system modeling

A servo-controlled range/elevation scanner for the laser Doppler velocimeter (LDV) was developed and tested in the field to assess its performance in detecting and monitoring aircraft trailing vortices in an airport environment. The elevation scanner provides a capability to manually point the LDV telescope at operator chosen angles from 3.2 deg. to 89.6 deg within 0.2 deg, or to automatically scan the units between operator chosen limits at operator chosen rates of 0.1 Hz to 0.5 Hz. The range scanner provides a capability to manually adjust the focal point of the system from a range of 32 meters to a range of 896 meters under operator control, or to scan between operator chosen limits and at rates from 0.1 Hz to 6.9 Hz. The scanner controls are designed to allow simulataneous range and elevation scanning so as to provide finger scan patterns, arc scan patterns, and vertical line scan patterns. The development and testing of the unit is discussed, along with a fluid dynamic model of the wake vortex developed in a laser Doppler vortex sensor simulation program.

Wilson, D. J.↗