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  • 1
    Publication Date: 2013-08-31
    Description: Flow-field measurements have been made to determine the effects of core blowing on vortex breakdown and control. The results of these proof-of-concept experiments clearly demonstrate the usefulness of water tunnels as test platforms for advanced flow-field simulation and measurement.
    Keywords: AERODYNAMICS
    Type: A-87030 , NASA-TM-89410 , NAS 1.15:89410
    Format: application/pdf
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  • 2
    Publication Date: 2013-08-31
    Description: Based on the hypothesis that patterns of skin-friction lines and external streamlines reflect the properties of continuous vector fields, topology rules define a small number of singular points (nodes, saddle points, and foci) that characterize the patterns on the surface and on particular projections of the flow (e.g., the crossflow plane). The restricted number of singular points and the rules that they obey are considered as an organizing principle whose finite number of elements can be combined in various ways to connect together the properties common to all steady three dimensional viscous flows. Introduction of a distinction between local and global properties of the flow resolves an ambiguity in the proper definition of a three dimensional separated flow. Adoption of the notions of topological structure, structural stability, and bifurcation provides a framework to describe how three dimensional separated flows originate and succeed each other as the relevant parameters of the problem are varied.
    Keywords: AERODYNAMICS
    Type: A-8554 , NASA-TM-81294
    Format: application/pdf
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  • 3
    Publication Date: 2013-08-31
    Description: A compact, nonobtrusive, bi-directional, skin-friction gage was developed to measure the mean shear stress beneath a three-dimensional boundary layer. The gage works by measuring the heat flux from two orthogonal wires embedded in the surface. Such a gage was constructed and its characteristics were determined for different angles of yaw in a calibration experiment in subsonic flow with a Preston tube used as a standard. Sample gages were then used in a fully three-dimensional turbulent boundary layer on a circular cone at high relative incidence, where there were regimes of favorable and adverse pressure gradients and three-dimensional separation. Both the direction and magnitude of skin friction were then obtained on the cone surface.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-78531 , A-7637
    Format: application/pdf
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  • 4
    Publication Date: 2013-08-31
    Description: Three dimensional flow separations about a circular cone were investigated in the Mach number range 0.6 - 1.8. The cone was tested in the Ames 1.8 by 1.8 m wind tunnel at Reynolds numbers based on the cone length from 4,500,000 to 13,500,000 under nominally zero heat transfer conditions. Results indicate that: (1) the lee-side separated flow develops from initially symmetrically disposed and near-conical separation lines at angle of incidence/cone semiangle equal to approximately 1, with the free shear layers eventually rolling up into tightly coiled vortices at all Mach numbers; (2) the onset of asymmetry of the lee-side separated flow about the mean pitch plane is sensitive to Mach number, Reynolds number, and the nose bluntness; and (3) as the Mach number is increased beyond 1.8, the critical angle of incidence for the onset of asymmetry increases until at about M = 2.75 there is no longer any significant side force development.
    Keywords: AERODYNAMICS
    Type: A-7639 , NASA-TM-78532
    Format: application/pdf
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  • 5
    Publication Date: 2013-08-31
    Description: The structures of three dimensional separated flow about some chosen aerodynamic components at angle of attack are synthesized, holding strictly to the notion that streamlines in the external flow (viscous plus inviscid) and skin friction lines on the body surface may be considered as trajectories having properties consistent with those of continuous vector fields. Singular points in the fields are of limited number and are classified as simple nodes and saddles. Analogous flow structures at high angles of attack about blunt and pointed bodies, straight and swept wings, etc., are discussed, highlighting the formation of spiral nodes (foci) in the pattern of the skin friction lines. How local and global three dimensional separation lines originate and form is addressed, and the characteristics of both symmetric and asymmetric leeward wakes are described.
    Keywords: AERODYNAMICS
    Type: NASA-TM-84226 , PAPER-2 , A-8859 , NAS 1.15:84226
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  • 6
    Publication Date: 2013-08-31
    Description: The separation of three dimensional turbulent boundary layers from the lee of flight vehicles at high angles of attack is investigated. The separation results in dominant, large scale, coiled vortex motions that pass along the body in the general direction of the free stream. In all cases of three dimensional flow separation and reattachment, the assumption of continuous vector fields of skin friction lines and external flow streamlines, coupled with simple laws of topology, provides a flow grammar whose elemental constituents are the singular points: the nodes, spiral nodes (foci), and saddles. The phenomenon of three dimensional separation may be construed as either a local or a global event, depending on whether the skin friction line that becomes a line of separation originates at a node or a saddle point.
    Keywords: AERODYNAMICS
    Type: A-8845 , NAS 1.15:84221 , NASA-TM-84221
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  • 7
    Publication Date: 2013-08-31
    Description: Diverse kinds of three-dimensional regions of separation in laminar and turbulent boundary layers are discussed that exist on lifting aerodynamic configurations immersed in flows from subsonic to hypersonic speeds. In all cases of three dimensional flow separation, the assumption of continuous vector fields of skin-friction lines and external-flow streamlines, coupled with simple topology laws, provides a flow grammar whose elemental constituents are the singular points: nodes, foci, and saddles. Adopting these notions enables one to create sequences of plausible flow structures, to deduce mean flow characteristics, expose flow mechanisms, and to aid theory and experiment where lack of resolution in numerical calculations or wind tunnel observation causes imprecision in diagnosing the three dimensional flow features.
    Keywords: AERODYNAMICS
    Type: A-6035 , NASA-TM-81169
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  • 8
    Publication Date: 2017-10-02
    Description: Vortical flows in three dimensional configurations that are of typical interest to aerodynamicists and researchers in fluid mechanics are reviewed. A list of 10 issues was compiled to understanding complex vortical flows.
    Keywords: AERODYNAMICS
    Type: AGARD Aerodyn. of Vortical Type Flows in Three Dimensions; 31 p
    Format: text
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  • 9
    Publication Date: 2017-10-02
    Description: The development of the turbulent symmetric and asymmetric vortex flow about the lee side of a 5 deg semiangle conical forebody at high relative incidence was investigated. The cone was immersed in a Mach 0.6 airstream at a Reynolds number of 13.5 x 10 to the 6th power based on the 1.4 m axial length of the cone. Small amounts of air injected normally or tangentially to the cone surface, but on one side of the leeward meridian and beneath the vortex farthest from the wall, were effective in biasing the asymmetry. With this reorientation of the forebody vortices, the amplitude of the side force could be reduced to the point where its direction was reversed. This phenomenon was obtained either by changing the blowing rate at constant incidence or by changing incidence at constant blowing rate. Normal injection appeared more effective than tangential injection. The contrarotating vortices in the penetrating jet flow were of opposite hand to the rotational directions of the forebody vortices. A distinctively organized and stable flow structure emerged with the jet vortices positioned above the forebody vortices.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: AGARD Aerodyn. Characteristics of Controls; 49 p
    Format: text
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  • 10
    Publication Date: 2017-10-02
    Description: Flow-field measurements have been made to determine the effects of core blowing on vortex breakdown and control. The results of these proof-of-concept experiments clearly demonstrate the usefulness of water tunnels as test platforms for advanced flow-field simulation and measurement.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AGARD, Aerodynamic and Related Hydrodynamic Studies Using Water Facilities; 10 p
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