SEARCH · Search NASA

Results for “Vortex”

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 199 records · Page 11

All sources NASA NTRS DOE OSTI

NASA NTRS1972

Feasibility of wake vortex monitoring systems for air terminals

Wake vortex monitoring systems, especially those using laser Doppler sensors, were investigated. The initial phases of the effort involved talking with potential users (air traffic controllers, pilots, etc.) of a wake vortex monitoring system to determine system requirements from the user's viewpoint. These discussions involved the volumes of airspace to be monitored for vortices, and potential methods of using the monitored vortex data once the data are available. A subsequent task led to determining a suitable mathematical model of the vortex phenomena and developing a mathematical model of the laser Doppler sensor for monitoring the vortex flow field. The mathematical models were used in combination to help evaluate the capability of laser Doppler instrumentation in monitoring vortex flow fields both in the near vicinity of the sensor (within 1 kilometer and at long ranges(10 kilometers).

Wilson, D. J.↗

NASA NTRS1973

Vortex age as a wake turbulence scaling parameter

Research which was conducted to determine the significance of vortex age as a scaling parameter in wake turbulence development and dissipation is reported. Tests were conducted at three angles of attack, three free stream speeds, and seven downstream positions from 2 to 30 chordlengths using an NACA 0012 wing and a five hole yawhead pitot probe. The end surface of the wing tip was flat. Speeds were selected to give a predetermined range of vortex ages. The complete velocity structure of the vortex was measured at each station and speed. The resulting plots of maximum tangential velocity and vortex core diameter versus downstream distance and vortex age indicate that vortex age is not a self sufficient scaling parameter. In addition to the expected effect of lift coefficient there is also a definite free stream speed influence at high wing angles of attack. The exact cause and nature of this effect is not fully understood, but it does not appear to be explainable in terms of Mach number or Reynolds number; however, the influence of tip edge shape on spanwise flow separation appears to be an important factor.

Marshall, J. R.↗

NASA NTRS1973

Aircraft wake dissipation by sinusoidal instability and vortex breakdown.

Sinusoidal instability of aircraft trailing vortices was induced by differentially oscillating inboard and outboard flaps on a model wing in a ship towing tank. Measured amplification rates qualitatively agree with theoretical predictions. Axial velocities in the vortex core were directed towards the wing and measured to be approximately 25% of the tow speed. Vortex breakdown was observed to occur along trailers undergoing sinusoidal instability near but ahead (towards the wing) of positions of maximum trailer separation. It is shown that axisymmetric pressure gradients are imposed along the vortex core by the other sinusoidally deformed trailer and are responsible for the observed changes in core diameter. A theoretical model predicts the short-time behavior of the vortex core and shows that the response of the vortex depends crucially on the axial velocity in the vortex.

Bilanin, A. J.↗

NASA NTRS1975

Vortex information display system program description manual

A vortex information display system is described which provides flexible control through system-user interaction for collecting wing-tip-trailing vortex data, processing this data in real time, displaying the processed data, storing raw data on magnetic tape, and post processing raw data. The data is received from two asynchronous laser Doppler velocimeters (LDV's) and includes position, velocity, and intensity information. The raw data is written onto magnetic tape for permanent storage and is also processed in real time to locate vortices and plot their positions as a function of time. The interactive capability enables the user to make real time adjustments in processing data and provides a better definition of vortex behavior. Displaying the vortex information in real time produces a feedback capability to the LDV system operator allowing adjustments to be made in the collection of raw data. Both raw data and processing can be continually upgraded during flyby testing to improve vortex behavior studies. The post-analysis capability permits the analyst to perform in-depth studies of test data and to modify vortex behavior models to improve transport predictions.

Conway, R.↗

NASA NTRS1977

Vortex interactions and decay in aircraft wakes

The dynamic interactions of aircraft wake vortices are investigated using both inviscid and viscous models. The phenomenon of vortex merging resulting in the rapid aging of a vortex wake is examined in detail. It is shown that the redistribution of vorticity from convection and diffusion during merging is a mechanism effective in reducing the hazard of a wake. Inviscid computations show that the merging phenomenon may be sensitive to small changes in spanwise load distribution and that the fuselage vortex shed from the wing-fuselage junction can play a significant role in promoting merging of wing-tip and flap vortices. Vortex-wake-merging computations using a second-order closure model of turbulent transport indicate that a low-hazard wake occurs when the generating aircraft flap and wing-tip vortices of the same strength and sign. This optimum is achieved when the flap vortex is located outboard approximately 40% of the distance to the tip vortex.

Bilanin, A. J.↗

NASA NTRS1977

Thrust-augmented vortex attenuation

An experimental investigation was conducted to determine the vortex attenuating effect of engine thrust. Tests were made using a 0.03-scale model of the Boeing 747 transport aircraft as a vortex generating model. A Learjet-class probe model was used to measure the vortex induced rolling moment at a scale separation distance of 1.63 km. These tests were conducted at a lift coefficient of 1.4 at a model velocity of 30.48 m/s. The data presented indicate that engine thrust is effective as a vortex attenuating device when the engines are operated at high thrust levels and are positioned to direct the high energy engine wake into the core of the vortex. The greatest thrust vortex attenuation was obtained by operating the inboard engine thrust reversers at one-quarter thrust and the outboard engines at maximum forward thrust.

Patterson, J. C., Jr.↗

NASA NTRS1977

A generalized vortex lattice method for subsonic and supersonic flow applications

If the discrete vortex lattice is considered as an approximation to the surface-distributed vorticity, then the concept of the generalized principal part of an integral yields a residual term to the vorticity-induced velocity field. The proper incorporation of this term to the velocity field generated by the discrete vortex lines renders the present vortex lattice method valid for supersonic flow. Special techniques for simulating nonzero thickness lifting surfaces and fusiform bodies with vortex lattice elements are included. Thickness effects of wing-like components are simulated by a double (biplanar) vortex lattice layer, and fusiform bodies are represented by a vortex grid arranged on a series of concentrical cylindrical surfaces. The analysis of sideslip effects by the subject method is described. Numerical considerations peculiar to the application of these techniques are also discussed. The method has been implemented in a digital computer code. A users manual is included along with a complete FORTRAN compilation, an executed case, and conversion programs for transforming input for the NASA wave drag program.

Miranda, L. R.↗

NASA NTRS1982

Analytical study of vortex flaps on highly swept delta wings

This paper highlights some current results from ongoing analytical studies of vortex flaps on highly swept delta wings. A brief discussion of the vortex flow analysis tools is given along with comparisons of the theories to vortex flap force and pressure data. Theoretical trends in surface pressure distribution for both angle-of-attack variation and flap deflection are correctly predicted by Free Vortex Sheet theory. Also shown are some interesting calculations for attached-flow and vortex-flow flap hinge moments that indicate flaps utilizing vortex flow may generate less hinge moment than attached flow flaps. Finally, trailing-edge flap effects on leading-edge flap thrust potential are investigated and theory-experiment comparisons made.

Frink, N. T.↗

NASA NTRS1983

An experimental study of pressures on 60 deg Delta wings with leading edge vortex flaps

An experimental study was conducted in the Virginia Tech Stability Wind Tunnel to determine surface pressures over a 60 deg sweep delta wing with three vortex flap designs. Extensive pressure data was collected to provide a base data set for comparison with computational design codes and to allow a better understanding of the flow over vortex flaps. The results indicated that vortex flaps can be designed which will contain the leading edge vortex with no spillage onto the wing upper surface. However, the tests also showed that flaps designed without accounting for flap thickness will not be optimum and the result can be oversized flaps, early flap vortex reattachment and a second separation and vortex at the wing/flap hinge line.

Marchman, J. F., III↗

NASA NTRS1984

Identification of vortex-induced clear-air turbulence using airline flight records

The nature and cause of clear-air turbulence is being investigated, in cooperation with the National Transportation Safety Board, using the flight records available from airline encounters with severe turbulence. This paper presents two case studies of severe turbulence which indicate that the airplanes involved encountered vortex arrays which were generated by destabilized wind-shear layers near the tropopause. In order to identify and analyze vortex patterns (i.e., vortex strength, size, and spacings), potential-flow models of vortex arrays were developed that describe reasonably well the wind patterns derived from the airliner flight records. The results of this analysis indicate that in the two cases studied, the vortex cores had diameters in the range of 900 to 1,200 ft with tangential velocities in the range of 70 to 85 ft/sec. This study presents the first identification and analysis of vortex arrays from airline flight data. The results are compared with theoretical predictions and previous observations.

Parks, E. K.↗

NASA NTRS1984

Vortex flaps - Advanced control devices for supercruise fighters

Prompted by the extensive experience obtained with vortex lift-generating leading edges in the SR-71, Concorde and F-16 supersonic aircraft, development efforts have recently been made toward the use of variable incidence angle delta wing leading edge 'vortex flaps' for supersonic cruise and maneuvering performance improvements in fighter aircraft. Vortex lift flaps have been wind tunnel tested on scale models, and it has been noted that a variety of effects can be obtained through the use of folding, hinged, and tabbed flap designs. Flap planforms can, moreover, be varied in length and in total area, as well as segmented, to yield unique combinations of drag reduction, vortex generation, longitudinal stability, and vortex flow reattachment. It is speculated that the vortex flap may be applicable to multimission fighters, and promote STOL performance.

Lamar, J. E.↗

NASA NTRS1984

An experimental investigation of the parallel blade-vortex interaction

A scheme for investigating the parallel blade vortex interaction (BVI) has been designed and tested. The scheme involves setting a vortex generator upstream of a nonlifting rotor so that the vortex interacts with the blade at the forward azimuth. The method has revealed two propagation mechanisms: a type C shock propagation from the leading edge induced by the vortex at high tip speeds, and a rapid but continuous pressure pulse associated with the proximity of the vortex to the leading edge. The latter is thought to be the more important source. The effects of Mach number and vortex proximity are discussed.

Caradonna, F. X.↗

NASA NTRS1985

Computations of two-dimensional airfoil-vortex interactions

A procedure for calculating the interaction of a vortex with a two dimensional airfoil in a uniform free stream is presented along with results for several test cases. A Lamb like anaytical vortex having a finite core and convect in a uniform free stream interacts with the flowfield of NACA 0012 or NACA 64A006 airfoil in transonic and subsonic flow. Euler and thin layer Navier-Stokes solutions are computed and the results are compared with the results from transonic small disturbance code and available experimental results. For interactions within the limits of transonic small disturbance assumptions, the three methods gave qualitatively similar results of a two bladed helicopter rotor and suggest that the time lag effects of the free stream velocity approaching the blade may be important and should be considered in the analysis. In general, the results show a tremendous influence of the interacting vortex on the flowfield around the airfoil. This is particularly true when the vortex is stationary. For a convecting vortex, the most dramatic changes in the flowfield seem to occur when the vortex is within one chord of the airfoil.

Srinivasan, G. R.↗

NASA NTRS1984

Aeroacoustic interaction of a distributed vortex with a lifting Joukowski airfoil

A first principles computational aeroacoustics calculation of the flow and noise fields produced by the interaction of a distributed vortex with a lifting Joukowski airfoil is accomplished at the Reynolds number of 200. The case considered is that where the circulations of the vortex and the airfoil are of opposite sign, corresponding to blade vortex interaction on the retreating side of a single helicopter rotor. The results show that the flow is unsteady, even in the absence of the incoming vortex, resulting in trailing edge noise generation. After the vortex is input, it initially experiences a quite rapid apparent diffusion rate produced by stretching in the airfoil velocity gradients. Consideration of the effects of finite vortex size and viscosity causes the noise radiation during the encounter to be much less impulsive than predicted by previous analyses.

Hardin, J. C.↗

NASA NTRS1984

Two dimensional blade-vortex interaction flow visualization study

Blade-vortex interaction occurs when a rotor blade encounters the tip vortex from a previous rotor blade. To obtain details of the close encounter process, the results from a flow visualization study of an airfoil representing a rotor blade in the wake of an oscillating airfoil serving as a vortex generator are described. A distinguishing feature of this study is that the vortex filament is oriented parallel to the blade span, orthogonal to the test section free stream velocity. This orientation simulates the case of two-dimensional blade-vortex interaction, which is known to produce the most impulsive and most intensive BVI noise. Photographic data are examined to deduce qualitative and quantitative details of the close encounter interaction process with emphasis on structural changes in the vortex filament and its trajectory.

Booth, E. R., Jr.↗

NASA NTRS1986

Water tunnel results of leading-edge vortex flap tests on a delta wing vehicle

A water tunnel flow visualization test on leading edge vortex flaps was conducted at the flow visualization facility of the NASA Ames Research Center's Dryden Flight Research Facility. The purpose of the test was to visually examine the vortex structures caused by various leading edge vortex flaps on the delta wing of an F-106 model. The vortex flaps tested were designed analytically and empirically at the NASA Langley Research Center. The three flap designs were designated as full-span gothic flap, full-span untapered flap, and part-span flap. The test was conducted at a Reynolds number of 76,000/m (25,000/ft). This low Reynolds number was used because of the 0.076-m/s (0.25-ft/s) test section flow speed necessary for high quality flow visualization. However, this low Reynolds number may have influenced the results. Of the three vortex flaps tested, the part-span flap produced what appeared to be the strongest vortex structure over the flap area. The full-span gothic flap provided the next best performance.

Delfrate, J. H.↗

NASA NTRS1986

Measurements of a turbulent horseshoe vortex formed around a cylinder

An experimental investigation was conducted to characterize a symmetrical horseshoe vortex system in front of and around a single large-diameter right cylinder centered between the sidewalls of a wind tunnel. Surface flow visualization and surface static pressure measurements as well as extensive mean velocity and pressure measurements in and around the vortex system were acquired. The results lend new insight into the formation and development of the vortex system. Contrary to what has been assumed previously, a strong vortex was not identified in the streamwise plane of symmetry, but started a significant angular distance away from it. Rather than the multiple vortex systems reported by others, only a single primary vortex and saddle point were found. The scale of the separation process at the saddle point was much smaller than the scale of the approaching boundary layer thickness. Results of the present study not only shed light on such phenomena as the nonsymmetrical endwall flow in axial turbomachinery but can also be used as a test case for three-dimensional computational fluid mechanics computer codes.

Eckerle, W. A.↗

NASA NTRS1984

An experimental investigation of the parallel blade-vortex interaction

Caradonna, F. X.↗