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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

The Role of the Toroidal Vortex in Cumulus Clouds' Entrainment and Mixing

Abstract Shallow convective clouds play a crucial role in Earth's energy budget, as they modulate the radiative transfer in the atmosphere and participate in the vertical transport of aerosols, energy, and humidity. The parameterizations representing these complex, vital players in weather and climate models are mostly based on a description of steady‐state plumes and are a source of major uncertainty. Recently, several studies have shown that buoyant thermals are inherent in atmospheric convection and contain a toroidal (ring) vortex. This work studies those vortices in growing shallow cumulus (Cu) clouds using high‐resolution (10 m) Large Eddy Simulations that resolve these vortices in much detail. Recent analysis of such data showed that small‐scale turbulent diffusion is unable to explain the large diluted portion of the cloud. Here we advocate for the important role of the Cu toroidal vortex (TV) in cloud dilution and present the complex dynamics and structure of a Cu TV. Nevertheless, since the vortex dominates the cloud's dilution, simplicity emerges when considering the cloud's lateral mass flux profile. The cloud mixing is quantified using direct flux calculations and Eulerian tracers. In addition, Lagrangian tracers are used to identify the origin of the entrained air and its thermodynamic properties. It shows that most of the air entrained by the vortex is not recycled by the vortex, yet is significantly more humid than the environment. We suggest that the development of new models describing thermals, together with their toroidal vortices, might improve cloud parameterizations in weather and climate models.

Meteorology & Atmospheric Sciences↗
DOE OSTI2025

Photon acceleration of high-intensity vector vortex beams into the extreme ultraviolet

Extreme ultraviolet (XUV) light sources allow for the probing of bound electron dynamics on attosecond scales, interrogation of high-energy-density matter, and access to novel regimes of strong-field quantum electrodynamics. Despite the importance of these applications, coherent XUV sources remain relatively rare, and those that do exist are limited in their peak intensity and spatio-polarization structure. Here, we demonstrate that photon acceleration of an optical vector vortex pulse in the moving density gradient of an electron beam–driven plasma wave can produce a high-intensity, tunable-wavelength XUV pulse with the same vector vortex structure as the original pulse. Quasi-3D, boosted-frame particlein- cell simulations show the transition of optical vector vortex pulses with 800-nm wavelengths and intensities below 10 18 W/cm 2 to XUV vector vortex pulses with 36-nm wavelengths and intensities exceeding 10 20 W/cm 2 over a distance of 1.2 cm. The XUV pulses have sub-femtosecond durations and nearly flat phase fronts. The production of such high-quality, high-intensity XUV vector vortex pulses could expand the utility of XUV light as a diagnostic and driver of novel light–matter interactions.

43 PARTICLE ACCELERATORS↗
NASA NTRS1972

Exploratory investigation of factors affecting the wing tip vortex

An investigation was conducted in the Langley full-scale tunnel to study some factors affecting the tip vortex of a wing. It was found that there was a pronounced effect of Reynolds number on the tip-vortex core size. An attempt was made to determine what aerodynamic parameters, such as lift, drag, or induced drag, influence the size of the vortex core, but no particular function of the parameters was found to be superior to all others. Various spoilers placed on the upper and lower surfaces of the wing to increase the boundary-layer thickness resulted in a reduction in the vorticity as determined from the tuft grid. Various solid objects placed in the vortex core downstream of the wing tip seemed to decrease the vorticity within the vortex core.

Scheiman, J.↗
NASA NTRS1971

NASA aircraft trailing vortex research

A brief description is given of NASA's comprehensive program to study the aircraft trailing vortex problem. Wind tunnel experiments are used to develop the detailed processes of wing tip vortex formation and explore different means to either prevent trailing vortices from forming or induce early break-up. Flight tests provide information on trailing vortex system behavior behind large transport aircraft, both near the ground, as in the vicinity of the airport, and at cruise/holding pattern altitudes. Results from some flight tests are used to show how pilots might avoid the dangerous areas when flying in the vicinity of large transport aircraft. Other flight tests will be made to verify and evaluate trailing vortex elimination schemes developed in the model tests. Laser Doppler velocimeters being developed for use in the research program and to locate and measure vortex winds in the airport area are discussed. Field tests have shown that the laser Doppler velocimeter measurements compare well with those from cup anemometers.

Mcgowan, W. A.↗
NASA NTRS1972

Generation and development of a viscous vortex ring.

The vorticity transport and definition of vorticity equations are derived for an axisymmetric incompressible viscous vortex ring. The coupled system is solved numerically by the Peaceman-Rachford method and the method of successive over-relaxation. Instantaneous streaklines, velocity vector fields, vorticity contours, and streamline patterns offer a detailed picture of vortex ring generation. Results compare well with experimental observations of the behavior of viscous vortex rings. The radius, trajectory, and velocity of the ring are calculated and employed to predict the propagation velocity of the vortex ring using the vortex models of Helmholtz and Hill.

Whitehead, K. D.↗
NASA NTRS1974

On the inlet vortex system

The flow field of a jet engine with an inlet vortex, which can pick up heavy debris from the ground and damage the engine, was simulated in a small water tunnel by means of the hydrogen bubble technique. It was found that the known engine inlet vortex is accompained by a vortex system, consisting of two inlet vortices (the ground based and the trailing one), secondary vortices, and ground vortices. Simulation of the ground effect by an inlet image proved that the inlet vortex feeds on free stream vorticity and can exist without the presence of a ground boundary layer. The structural form of the inlet vortex system was explained by a simple potential flow model, which showed the number, location, and the importance of the stagnation points. A retractable horizontal screen or an up-tilt of the engine is suggested as countermeasure against debris ingestion.

Bissinger, N. C.↗
NASA NTRS1974

Lift-induced wing-tip vortex attenuation

It has been shown by a new static airflow visualization method that a drogue device properly positioned downstream of the wing tip causes vortex breakdown. This same result has been obtained by mounting a jet engine simulator at the wing tip and directing the high-energy jet blast downstream into the vortex. These configurations, among others, are now under intensive investigation in the new Langley Vortex Research Facility. In this facility a balance mounted vortex generating model is propelled along the 1800-foot track while a second model trailed at 160 feet (scale distance of 1 mile) measures the far-field rolling moment induced by the vortex of the generating model.

Patterson, J. C., Jr.↗
NASA NTRS1975

Flight test investigation of the vortex wake characteristics behind a Boeing 727 during two-segment and normal ILS approaches (A joint NASA/FAA report)

Flight tests were performed to evaluate the vortex wake characteristics of a Boeing 727 aircraft during conventional and two-segment instrument landing approaches. Smoke generators were used for vortex marking. The vortex was intentionally intercepted by a Lear Jet and a Piper Comanche aircraft. The vortex location during landing approach was measured using a system of phototheodolites. The tests showed that at a given separation distance there are no readily apparent differences in the upsets resulting from deliberate vortex encounters during the two types of approaches. The effect of the aircraft configuration on the extent and severity of the vortices is discussed.

Barber, M. R.↗
NASA NTRS1976

Effects of fog droplets on wake vortex decay rate

A simple model for the motion of particles in a laminar line vortex is discussed. The energy required to accelerate a set of these particles was determined and shown to be only a small fraction of the energy content of the vortex flow. It is shown that this energy transfer is unlikely to be sufficient to significantly modify the vortex decay rate. It is further argued that the effect of the particle on the viscous properties of the resulting two phase fluid leads to a slower decay rate than in single phase air flow. However, this conclusion may not necessarily follow for turbulence flows. Results show that the migration of particles to the outer flow results in a redistribution of the velocity profile in the vortex and in a non-uniform two phase viscosity across the core. It is suggested that these effects may accelerate vortex bursting.

Moulden, T. H.↗
NASA NTRS1976

Numerical studies of three-dimensional breakdown in trailing vortex wakes

The development of dangerous vortex wakes trailing between aircraft for appreciable distance downstream, and posing hazards to following aircraft, is calculated using finite-element three-dimensional relaxation methods. Near-wake, middle-wake, and far-wake conditions are delineated. Vortex system finite lifetimes can be calculated with greater facility owing to the inclusion of a self-induction term in the solution dependent upon local curvature and vortex core radius. Looping and convergence phenomena are studied for single vortex pairs, twin pairs, and multiple pairs. Proportions of flap span and wing span are shown to affect the time to convergence of vortex pairs. The self-induction term renders the convergence time of vortices a sensitive function of wavelength. Wakes trailing between wide-body ('Jumbo') aircraft are also examined.

Hackett, J. E.↗
NASA NTRS1976

An improved method for the prediction of completely three-dimensional aerodynamic load distributions of configurations with leading edge vortex separation

The application of a higher-order subsonic potential flow panel method to the solution of three-dimensional flow about wing and wing-body combinations with leading-edge vortex separation is presented. The governing equations are the linear flow differential equation and nonlinear boundary conditions which require that the flow be parallel to the wing and body surfaces and that the free vortex sheet, springing from the leading and trailing edges, be aligned with the local flow and support no pressure jump. The vortex core is modeled as a simple line vortex which receives vorticity from the free sheet through a connecting sheet. The Kutta condition is imposed on all appropriate edges of the wing. This set of nonlinear equations is solved by an iterative procedure. The Goethert rule accounts for compressibility. The method has been programmed for the CDC 6600. Delta wings, gothic wings, arrow wings, cambered wings, and wing with body have been analyzed. Initial studies involving variations of panel density, vortex sheet sizing, Jacobian update, and initial geometry demonstrate that the present method generally exhibits good convergence characteristics.

Rubbert, p. E.↗
NASA NTRS1975

Aircraft wake vortex velocity measurements using a scanning CO2 laser Doppler velocimeter

A CO2 laser Doppler velocimeter was employed in the study of pairs of counterrotating vortices trailing aircraft in an airport air space. A laser positioned on an extended runway centerline scans a vertical plane perpendicular to the centerline. Vortex location, measurement of vortex transport, and measurement of the properties of aircraft wake vortex flow fields are achieved via spectral analysis of the data. Highest amplitude in the spectrum, the associated maximum velocity, the highest velocity above the amplitude threshold, and the total number of frequency (velocity) cells above thresholds are studied as parameters in analysis of the vortex-associated flow field. The profile of the radial variation of tangential velocity is studied, and two special problems are examined: location of the vortex center and error introduced by crosswind.

Dimarzio, C. A.↗
NASA NTRS1977

Numerical solutions of Navier-Stokes equations for the structure of a trailing vortex

The structure and decay of a trailing vortex were analyzed during the numerical solutions of the full Navier-Stokes equations. Unsteady forms of the governing equations were recast in terms of circulation, vorticity, and stream function as dependent variables, and a second upwind finite difference scheme was used to integrate them with prescribed initial and boundary conditions. The boundary conditions at the outer edge and at the outflow section of the trailing vortex were considered. Different models of the flow were postulated, and solutions were obtained describing the development of the flow as integration proceeds in time. A parametric study was undertaken with a view to understanding the various phenomena that may possibly occur in the trailing vortex. Using the Hoffman and Joubert law of circulation at the inflow section, the results of this investigation were compared with experimental data for a Convair 990 wind model and a rectangular wing. With an exponentially decaying law of circulation at the inflow section and an adverse pressure gradient at the outer edge of the trailing vortex, solutions depict vortex bursting through the sudden expansion of the core and/or through the stagnation and consequent reversal of the flow on the axis. It was found that this bursting takes place at lower values of the swirl ratio as the Reynolds number increases.

Jain, A. C.↗
NASA NTRS1976

Summary of NASA wake-vortex minimization research

NASA's effort in the area of wake-vortex minimization are reviewed. The results presented at a NASA symposium on wake-vortex minimization are summarized and additional results obtained since the symposium are included. Theoretical and experimental techniques for assessing the effectiveness of various wake-vortex minimization techniques are described. Three methods of reducing the effect of aircraft trailing vortices and a preliminary assessment of the operational suitability of employing wake-vortex minimization techniques are discussed. The application of one wake-vortex minimization technique to DC-10 and L-1011 aircraft is presented.

Dunham, R. E., Jr.↗
NASA NTRS1977

Wind-tunnel and flight evaluation of spoilers as trailing-vortex hazard alleviation devices

This paper presents the results of ground-based and flight investigations that have been performed at NASA for the purpose of development of spoilers as trailing-vortex hazard alleviation devices. Based on the results obtained in these investigations, it was found that the induced rolling moment on a trailing model can be reduced by spoilers located near the mid-semispan of a vortex-generating wing. Substantial reductions in induced rolling moment occur when the spoiler vortex attenuator is located well forward on both unswept and swept wing models. In addition, it was found by ground-based model tests and verified by full-scale flight tests that the existing flight spoilers on the B-747 aircraft are effective as trailing vortex attenuators. Based on the results of wind-tunnel investigations of the DC-10-30 and L-1011 aircraft models, the existing flight spoilers on both the DC-10-30 and L-1011 aircraft may also be effective trailing vortex attenuators.

Croom, D. R.↗
NASA NTRS1978

The role of atmospheric shear, turbulence and a ground plane on the dissipation of aircraft vortex wakes

Enhanced dispersion of two-dimensional trailed vortex pairs within simplified neutral atmospheric backgrounds is studied numerically for three conditions: when the pair is imbedded in a constant turbulent bath (constant dissipation); when the pair is subjected to a mean cross-wind shear; and when the pair is near the ground. Turbulent transport is modeled using second-order closure turbulent transport theory. The turbulent background fields are constructed using a superequilibrium approximation. The computed results allow several general conclusions to be drawn with regard to the reduction in circulation of the vortex pair and the rolling moment induced on a following aircraft: (1) the rate of decay of a vortex pair increases with increasing background dissipation rate; (2) cross-wind shear disperses the vortex whose vorticity is opposite to the background; and (3) the proximity of a ground plane reduces the hazard of the pair by scrubbing. The phenomenon of vortex bounce is explained in terms of secondary vorticity produced at the ground plane. Qualitative comparisons are made with available experimental data, and inferences of these results upon the persistence of aircraft trailing vortices are discussed.

Bilanin, A. J.↗
NASA NTRS1978

The structure of vortex breakdown

The term 'vortex breakdown', as used in the reported investigation, refers to a disturbance characterized by the formation of an internal stagnation point on the vortex axis, followed by reversed flow in a region of limited axial extent. Two forms of vortex breakdown, which predominate, are shown in photographs. One form is called 'near-axisymmetric' (sometimes 'axisymmetric'), and the other is called 'spiral'. A survey is presented of work published since the 1972 review by Hall. Most experimental data taken since Hall's review have been in tubes, and the survey deals primarily with such cases. It is found that the assumption of axial-symmetry has produced useful results. The classification of flows as supercritical or subcritical, a step that assumes symmetry, has proved universally useful. Experiments show that vortex breakdown is always preceded by an upstream supercritical flow and followed by a subcritical wake. However, a comparison between experiments and attempts at prediction is less than encouraging. For a satisfactory understanding of the structure of vortex breakdown it is apparently necessary to take into account also aspects of asymmetry.

Leibovich, S.↗
NASA NTRS1978

Motion of a curved vortex filament with decaying vortical core and axial velocity

The motion and decay of a curved vortex filament having large axial and circumferential velocity components in a three-dimensional stream are analyzed by using the method of matched asymptotic expansions of the incompressible Navier-Stokes equations. The small parameter is the square root of the ratio of the kinematic viscosity to the circulation. The outer region is analyzed by the classical Biot-Savart law, and its solution is matched to that of the inner region, where viscous effects are important. Equations describing the coupling between the inner vortex structure and the motion of the vortex filament as well as the time evolution of the inner vortex structure are obtained. Equations are derived for the motion of the vortex filament and for the change and decay in time and space of the leading-order circumferential and axial velocity and vorticity components. Solutions are constructed for these components in terms of initial data.

Callegari, A. J.↗