SEARCH · Engineering Papers

Results for “DRAG”

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.

SourceResearch connectionFrom yearThrough year

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

At least 145 records · Page 8

All sources NASA NTRS DOE OSTI

NASA NTRS2017

Differential Drag Demonstration: A Post-Mission Experiment with the EO-1 Spacecraft

Differential drag is a technique for altering the semi-major axis, velocity, and along-track position of a spacecraft in low Earth orbit. It involves varying the spacecrafts cross-sectional area relative to its velocity direction by temporarily changing attitude and solar array angles, thus varying the amount of atmospheric drag on the spacecraft. The technique has recently been proposed and used by at least three satellite systems for initial separation of constellation spacecraft after launch, stationkeeping during the mission, and potentially for conjunction avoidance. Similarly, differential drag has been proposed as a control strategy for rendezvous, removing the need for active propulsion. In theory, some operational missions that lack propulsion capability could use this approach for conjunction avoidance, though options are typically constrained for spacecraft that are already in orbit. Shortly before the spacecraft was decommissioned, an experiment was performed using NASAs EO-1 spacecraft in order to demonstrate differential drag on an operational spacecraft in orbit, and discover some of the effects differential drag might manifest. EO-1 was not designed to maintain off-nominal orientations for long periods, and as a result the team experienced unanticipated challenges during the experiment. This paper will discuss operations limitations identified before the experiment, as well as those discovered during the experiment. The effective displacement that resulted from increasing the drag area for 39 hours will be compared to predictions as well as the expected position if the spacecraft maintained nominal operations. A hypothetical scenario will also be examined, studying the relative risks of maintaining an operational spacecraft bus in order to maintain the near-maximum drag area orientation and hasten reentry.

differential drag↗

NASA NTRS2017

Differential Drag Demonstration: A Post-Mission Experiment with the EO-1 Spacecraft

Differential drag is a technique for altering the semimajor axis, velocity, and along-track position of a spacecraft in low Earth orbit. It involves varying the spacecraft's cross-sectional area relative to its velocity direction by temporarily changing attitude and solar array angles, thus varying the amount of atmospheric drag on the spacecraft. The technique has recently been proposed and used by at least three satellite systems for initial separation of constellation spacecraft after launch, stationkeeping during the mission, and potentially for conjunction avoidance. Similarly, differential drag has been proposed as a control strategy for rendezvous, removing the need for active propulsion. In theory, some operational missions that lack propulsion capability could use this approach for conjunction avoidance, though options are typically constrained for spacecraft that are already in orbit. Shortly before the spacecraft was decommissioned, an experiment was performed using NASA's EO-1 spacecraft in order to demonstrate differential drag on an operational spacecraft in orbit, and discover some of the effects differential drag might manifest. EO-1 was not designed to maintain off-nominal orientations for long periods, and as a result the team experienced unanticipated challenges during the experiment. This paper will discuss operations limitations identified before the experiment, as well as those discovered during the experiment. The effective displacement that resulted from increasing the drag area for 39 hours will be compared to predictions as well as the expected position if the spacecraft maintained nominal operations. A hypothetical scenario will also be examined, studying the relative risks of maintaining an operational spacecraft bus in order to maintain the near-maximum drag area orientation and hasten reentry.

orbital lifetim↗

DOE OSTI2015

Chiral drag force

Here, we provide a holographic evaluation of novel contributions to the drag force acting on a heavy quark moving through strongly interacting plasma. The new contributions are chiral in the sense that they act in opposite directions in plasmas containing an excess of left- or right-handed quarks. The new contributions are proportional to the coefficient of the axial anomaly, and in this sense also are chiral. These new contributions to the drag force act either parallel to or antiparallel to an external magnetic field or to the vorticity of the fluid plasma. In all these respects, these contributions to the drag force felt by a heavy quark are analogous to the chiral magnetic effect (CME) on light quarks. However, the new contribution to the drag force is independent of the electric charge of the heavy quark and is the same for heavy quarks and antiquarks, meaning that these novel effects do not in fact contribute to the CME current. We show that although the chiral drag force can be non-vanishing for heavy quarks that are at rest in the local fluid rest frame, it does vanish for heavy quarks that are at rest in a suitably chosen frame. In this frame, the heavy quark at rest sees counterpropagating momentum and charge currents, both proportional to the axial anomaly coefficient, but feels no drag force. This provides strong concrete evidence for the absence of dissipation in chiral transport, something that has been predicted previously via consideration of symmetries. Along the way to our principal results, we provide a general calculation of the corrections to the drag force due to the presence of gradients in the flowing fluid in the presence of a nonzero chemical potential. We close with a consequence of our result that is at least in principle observable in heavy ion collisions, namely an anticorrelation between the direction of the CME current for light quarks in a given event and the direction of the kick given to the momentum of all the heavy quarks and antiquarks in that event.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2021

Analytic quasi-steady evolution of marginally unstable kinetic plasma instabilities in the presence of drag and scattering

The 1D bump-on-tail problem is studied in order to determine the influence of drag on quasi-steady solutions near marginal stability (1-γ d /γ L << 1) when effective collisions are much larger than the instability growth rate (ν>>γ). In this common tokamak regime, it is rigorously shown that the paradigmatic Berk–Breizman cubic equation for the nonlinear mode evolution reduces to a much simpler differential equation, dubbed the time-local cubic equation, which can be solved directly. It is found that in addition to increasing the saturation amplitude, drag introduces a shift in the apparent oscillation frequency by modulating the saturated wave envelope. Furthermore, excellent agreement is found between the analytic solution for the mode evolution and both the numerically integrated Berk–Breizman cubic equation and fully nonlinear 1D Vlasov simulations. Experimentally isolating the contribution of drag to the saturated mode amplitude for verification purposes is explored but complicated by the reality that the amount of drag cannot be varied independently of other key parameters in realistic scenarios. While the influence of drag is modest when the ratio of effective drag to effective scattering α/ν is very small, it can become substantial when α/ν ≳ 0.5, suggesting that drag should be accounted for in quantitative models of fast-ion-driven instabilities in fusion plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Optimization-based calibration of hydrodynamic drag coefficients for a semisubmersible platform using experimental data of an irregular sea state

For the simulation of the coupled dynamic response of floating offshore wind turbines, it is crucial to calibrate the hydrodynamic damping with experimental data. The aim of this work is to find a set of hydrodynamic drag coefficients for the semisubmersible platform of the Offshore Code Comparison Collaboration, Continuation, with Correlation and unCertainity (OC6) project which provides suitable results for an irregular sea state. Due to the complex interaction of several degrees of freedom (DOF), it is common to calibrate drag coefficients with the time series of decay tests. However, applying these drag coefficients for the simulation of an irregular sea state results in misprediction of the motions. By using numerical optimization, it is possible to calibrate multiple drag coefficients simultaneously and effectively, while also considering several DOF. This work considers time series of structural displacements from wave tank tests of the OC6 project and from simulations of the same load cases in OpenFAST. Results are transferred into the frequency domain and the deviation between power spectral densities of surge, pitch and heave from experiment and numerical simulation is used as an objective function to obtain the best fitting drag coefficients. This novel numerical optimization approach enables finding one set of drag coefficients for different load cases, which is a major improvement compared to decay-test-tuned drag coefficients.

42 ENGINEERING↗

DOE OSTI2019

How drag force evolves in global common envelope simulations

ABSTRACT We compute the forces, torque, and rate of work on the companion-core binary due to drag in global simulations of common envelope (CE) evolution for three different companion masses. Our simulations help to delineate regimes when conventional analytic drag force approximations are applicable. During and just prior to the first periastron passage of the in-spiral phase, the drag force is reasonably approximated by conventional analytic theory and peaks at values proportional to the companion mass. Good agreement between global and local 3D ‘wind tunnel’ simulations, including similar net drag force and flow pattern, is obtained for comparable regions of parameter space. However, subsequent to the first periastron passage, the drag force is up to an order of magnitude smaller than theoretical predictions, quasi-steady, and depends only weakly on companion mass. The discrepancy is exacerbated for larger companion mass and when the inter-particle separation reduces to the Bondi–Hoyle–Lyttleton accretion radius, creating a turbulent thermalized region. Greater flow symmetry during this phase leads to near balance of opposing gravitational forces in front of and behind the companion, hence a small net drag. The reduced drag force at late times helps explain why companion-core separations necessary for envelope ejection are not reached by the end of limited duration CE simulations.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2024

Nonreciprocal Coulomb drag between quantum wires in the quasi-one-dimensional regime

Coulomb drag experiments have been an essential tool to study strongly interacting low-dimensional systems. Historically, this effect has been explained in terms of momentum transfer between electrons in the active and the passive layer. We report Coulomb drag measurements between laterally coupled GaAs/AlGaAs quantum wires in the multiple one-dimensional (1D) sub-band regime that break Onsager's reciprocity upon both layer and current direction reversal, in contrast to prior 1D Coulomb drag results. The drag signal shows nonlinear current-voltage (I-V) characteristics, which are well characterized by a third-order polynomial fit. These findings are qualitatively consistent with a rectified drag signal induced by charge fluctuations. However, the nonmonotonic temperature dependence of this drag signal suggests that strong electron-electron interactions, expected within the Tomonaga-Luttinger liquid framework, remain important and standard interaction models are insufficient to capture the qualitative nature of rectified 1D Coulomb drag.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2021

An Investigation of the Effects of Volume Fraction on Drag Coefficient of Non-Spherical Particles Using PR-DNS

Prediction of the drag coefficient is required in gas-particle multiphase flow modeling and simulation. Experimental data and correlations on the fixed-bed system of spherical particles with high volume fractions for various possible arrangements are available in the literature. However, the effect of volume fraction on the drag coefficient of non-spherical particles is not well studied. In solving the momentum equation, the volume fraction plays a vital role in determining the flow resistances. In this paper, we study the impact of volume fraction in the range of 0.069 to 0.65 on the drag coefficient using the computational fluid dynamics (CFD) simulation of air for Reynold number in the range of 10 to 10000 using particle resolved direct numerical solution (PR-DNS). Regular non-spherical particles such as a cube, tetrahedron, and spheroids are used in this study since their single particle’s drag coefficient data are available in the literature for comparison. For this work, the simulations are carried out in the Ansys Fluent using polyhedral mesh, which consumes significantly less computational time and power. The study showed the sphericity and volume fraction have significant impact on the bed pressure drop and average drag coefficient of the particles in the bed especially in high Reynolds number regime. The bed of the spheroid experiences the lowest drag being the most streamlined particle, and the particles with the edges result in a large drag coefficient due to flow separation at the discontinuity. The vector plots verify this behavior where large wake regions are observed behind the tetrahedron particle.

Mahyawansi, Pratik↗

DOE OSTI2015

Drag of ballistic electrons by an ion beam

Drag of electrons of a one-dimensional ballistic nanowire by a nearby one-dimensional beam of ions is considered. We assume that the ion beam is represented by an ensemble of heavy ions of the same velocity V. The ratio of the drag current to the primary current carried by the ion beam is calculated. The drag current turns out to be a nonmonotonic function of velocity V. It has a sharp maximum for V near v{sub nF}/2, where n is the number of the uppermost electron miniband (channel) taking part in conduction and v{sub nF} is the corresponding Fermi velocity. This means that the phenomenon of ion beam drag can be used for investigation of the electron spectra of ballistic nanostructures. We note that whereas observation of the Coulomb drag between two parallel quantum wires may in general be complicated by phenomena such as tunneling and phonon drag, the Coulomb drag of electrons of a one-dimensional ballistic nanowire by an ion beam is free of such spurious effects.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2019

Role of Quasi-Longitudinal and Quasi-Transverse Phonons in the Drag Thermopower of Potassium Crystals at Low Temperatures

We have analyzed the effect of elastic energy anisotropy on the electron–phonon drag and thermoelectric phenomena in potassium crystals. It is shown that focusing leads to drag thermopower anisotropy at low temperatures; when diffuse phonon scattering at the boundaries is the predominant relaxation mechanism, focusing leads to drag thermopower anisotropy. With increasing sample cross section, the competition of the boundary and bulk phonon relaxation mechanisms leads to a nonmonotonic variation of drag thermopower anisotropy: upon a transition from the Knudsen regime of the phonon gas flow, it first increases from 16% to 30%, and then vanishes upon a transition to bulk samples. We have studied the role of quasi-longitudinal and quasi-transverse phonons in the drag thermopower of potassium crystals at low temperatures. It is shown that the contribution of slow quasi-transverse phonons to the drag thermopower of bulk potassium crystals is an order of magnitude larger than the contribution of quasi-longitudinal phonons. For this reason, the isotropic medium model cannot provide a correct description of the electron–phonon drag in metals. The effect of inelastic energy anisotropy on the spectrum and of the phonon polarization vector must be taken into account.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1983

The drag coefficient of cylindrical spacecraft in orbit at altitudes greater than 150 km

The spacecraft of the Geopotential Research Mission (GRM) are cylindrical in form and designed to fly with their longitudinal axes parallel to their direction of flight. The ratio of length to diameter of these spacecraft is roughly equal to 5.0. Other spacecraft previously flown had corresponding ratios roughly equal to 1.0, and therefore the drag produced by impacts on the lateral surfaces of those spacecraft was not as large as it will be on the GRM spacecraft. Since the drag coefficient is essentially the drag force divided by the frontal area in flight, lateral impacts, when taken into account make the GRM drag coefficient significantly larger than the coefficients used before for shorter spacecraft. A simple formula is derived for the drag coefficient of a cylindrical body flying with its long axis along the direction of flight, and it is used to estimate the drag for the GRM. The formula shows that the drag due to lateral surface impacts depends on the ratio of length-to-diameter and on a coefficient C sub LS (lateral surface impact coefficient) which can be determined from previous cylindrical spacecraft flown with the same attitude, or can be obtained from laboratory measurements of momentum accommodation coefficients.

Herrero, F. A.↗

NASA NTRS1984

Interference drag in a simulated wing-fuselage juncture

The interference drag in a wing fuselage juncture as simulated by a flat plate and a body of constant thickness having a 1.5:1 elliptical leading edge is evaluated experimentally. The experimental measurements consist of mean velocity data taken with a hot wire at a streamwise location corresponding to 16 body widths downstream of the body leading edge. From these data, the interference drag is determined by calculating the total momentum deficit (momentum area) in the juncture and also in the two dimensional turbulent boundary layers on the flat plate and body at locations sufficiently far from the juncture flow effect. The interference drag caused by the juncture drag as measured at this particular streamwise station is -3% of the total drag due to the flat plate and body boundary layers in isolation. If the body is considered to be a wing having a chord and span equal to 16 body widths, the interference drag due to the juncture is only -1% of the frictional drag of one surface of such a wing.

Kubendran, L. R.↗

NASA NTRS1982

Experimental trim drag values and flow-field measurements for a wide-body transport model with conventional and supercritical wings

The purpose of this study was to determine if advanced supercritical wings incur higher trim drag values at cruise conditions than current wide body technology wings. Relative trim drag increments were measured in an experimental wind tunnel investigation conducted in the Langley 8 Foot Transonic Pressure Tunnel. The tests utilized a high aspect ratio supercritical wing and a wide body aircraft wing, in conjunction with five different horizontal tail configurations, mounted on a representative wide body fuselage. The three low tail and two T-tail configurations were designed to measure the effects of horizontal tail size, location, and camber on the trim drag increments for the two wings. Longitudinal force and moment data were taken at a Mach number of 0.82 and design cruise lift coefficients for the wide body and supercritical wings of 0.45 and 0.55, respectively. The data indicate that the supercritical wing does not have significantly higher trim drag than the wide body wing. A reduction in tail size, combined with relaxed static stability, produced trim drag reductions for both wings. The cambered tails had higher trim drag increments than the symmetrical tails for both wings, and the T-tail configurations had lower trim drag increments than the low tail configurations.

Jacobs, P. F.↗

NASA NTRS1989

Helicopter hub fairing and pylon interference drag

A wind tunnel test was conducted to study the aerodynamics of helicopter hub and pylon fairings. The test was conducted in the 7-by 10 Foot Subsonic Wind Tunnel (Number 2) at Ames Research Center using a 1/5-scale XH-59A fuselage model. The primary focus of the test was on the rotor hub fairing and pylon mutual interference drag. Parametric studies of pylon and hub fairing geometry were also conducted. This report presents the major findings of the test as well as tabulated force and moment data, flow visualization photographs, and graphical presentations of the drag data. The test results indicate that substantial drag reduction can be attained through the use of a cambered hub fairing with circular arc upper surface and flat lower surface. Furthermore, a considerable portion of the overall drag reduction is attributed to the reduction in the hub-on-pylon interference drag. It is also observed that the lower surface curvature of the fairing has a strong influence on the hub fairing and on pylon interference drag. However, the drag reduction benefit that was obtained by using the cambered hub fairing with a flat lower surface was adversely affected by the clearance between the hub fairing and the pylon.

Graham, D. R.↗

NASA NTRS1990

Supersonic aircraft drag reduction

This paper reviews aerodynamic drag reduction for friction, wave and vortex drag associated with supersonic cruise aircraft and suggests approaches and research directions. Suction laminar flow control may also enable improved low-speed, high-lift systems, improved lift-to-drag ratio for subsonic cruise, reduced parasitic viscous drag for favorable interference wave drag reduction approaches, and turbulent skin friction reduction via slot injection. Flow separation control at cruise proffers opportunities for increased leading-edge thrust, increased lift increment from upper surface, increased fuselage lift/camber for wave drag-due-to-lift reduction, improved performance of various favorable interference wave drag reduction schemes, as well as possibly better low-speed, high-lift systems and wing cruise performance.

Bushnell, D. M.↗

NASA NTRS1990

A closer look at the induced drag of crescent-shaped wings

Recent interest in the induced drag characteristics of crescent-shaped wings has led to a closer look at the methods used for determination of induced drag from computational aerodynamic methods. Induced drag may be computed by integration of surface pressure, or by evaluation of a contour integral in the Trefftz plane. A high-order panel method was used to study the induced drag of crescent and elliptical wings using both techniques. Induced drag computations using surface-pressure integration were strongly affected by panel density and angle of attack. Accurate drag computations for the crescent wing were obtained only when the spanwise as well as chordwise panel density was extremely high. Trefftz-plane results for the two wing planforms do not show this sensitivity to panel density or angle of attack. Span efficiencies of 0.994 for the crescent wing and 0.987 for the elliptical wing were computed by the Trefftz-plane technique. Substitution of a force-free, rolled-up wake geometry on the crescent wing did not change the pressure-integrated drag significantly. The slightly higher span efficiency of the crescent wing is attributed to a more nearly elliptical spanwise lift distribution. The chord distribution of the elliptical wing was modified to produce an elliptical span-loading on a wing with an unswept quarter-chord line. This wing demonstrated a span efficiency equal to that of the crescent wing.

Smith, Stephen C.↗

NASA NTRS1992

How does Fitts' Law fit pointing and dragging?

Two experiments examined selecting text using a movement sequence of pointing and dragging. Experiment 1 showed that, in the Point-Drag sequence, the pointing time was related to the pointing distance but not to the width of the text to be selected; in contrast, pointing time was related to both the pointing distance and the width of the text in the Point-Click sequence. Experiment 2 demonstrated that both the pointing and dragging times for the Point-Drag sequence were sensitive to the height of the text that was selected. The discussion of the results centers around the application of Fitts' Law to pointing and dragging in a point-drag sequence, proposing that the target for pointing is the leftmost edge of the text to be selected, and the target for dragging is the rightmost edge of the text.

Gillan, Douglas J.↗

NASA NTRS1951

An Investigation of the Drag and Pressure Recovery of a Submerged Inlet and a Nose Inlet in the Transonic Flight Range with Free-fall Models

The drag and pressure recovery of an NACA submerged-inlet model and an NACA series I nose-inlet model were investigated in the transonic flight range. The tests were conducted over a mass-flow-ratio range of 0.4 to 0.8 and a Mach number range of about 0.8 to 1.10 employing large-scale recoverable free-fall models. The results indicate that the Mach number of drag divergence of the inlet models was about the same as that of a basic model without inlets. The external drag coefficients of the nose-inlet model were less than those of the submerged-inlet model throughout the test range. The difference in drag coefficient based on the maximum cross-sectional area of the models was about 0.02 at supersonic speeds and about 0.015 at subsonic speeds. For a hypothetical airplane with a ratio of maximum fuselage cross-sectional area to wing area of 0.06, the difference in airplane drag coefficient would be relatively small, about 0.0012 at supersonic speeds and about 0.0009 at subsonic speeds. Additional drag comparisons between the two inlet models are made considering inlet incremental and additive drag.

Selna, James↗