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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Experiments in fluids 7 (1989), S. 453-463 
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract An experimental study has been made on the interaction of a vortex ring with a plane solid boundary which is inclined to the axis of the ring. Dye visualizations of the ring during the interaction revealed (i) the formation of bi-helical vortex lines around the circumferential axis of the ring, and (ii) that these vortex lines were constantly being displaced along the circumferential axis on either side of the plane of symmetry and towards the region of the ring furthest away from the wall. Key factors which may be responsible for this phenomenon have been identified and are discussed in this paper.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract It is well documented that a trailing vortex pair approaching the ground, and a vortex ring colliding head-on with a rigid plane, experience a reversal in axial velocity which is commonly referred to as “rebound”. One explanation of this phenomenon suggests that it is essentially an inviscid process due to the effect of the finite core-size, whereas another and more widely accepted explanation attributes it to the influence of a secondary vortex which is generated at the surface by viscous effects. The aim of this paper is to assess experimentally the validity of these competing explanations. To achieve this, flow visualization studies of the collision of a vortex ring with a wall are compared with those of the head-on collision of two identical rings. The head-on collision is designed to mimic the inviscid, free-slip case of a ring/wall interaction. This paper describes the experimental findings.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Experiments in fluids 16 (1994), S. 181-186 
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A new flying hot-wire system has been developed for the measurement of highly turbulent and reversing flows. The apparatus is of rectilinear design, incorporating many features which extend its range of application beyond the range of previous designs. One of the advantages of this system is that it is mounted on a flow visualization wind tunnel which allows complementary qualitative and quantitative studies to be performed. This system has been used successfully to measure turbulent and reversing flows including the flow past a fence. Some results are presented.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 357 (1992), S. 225-227 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The experiment was conducted in water in a glass tank (1.22 m long, 0.36 m wide and 0.47 m deep) in which were immersed two horizontally opposed nozzles spaced 220 mm apart. The position of one nozzle could be finely adjusted to make the rings collide exactly head-on. Both nozzles were connected ...
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  • 5
    Publication Date: 2013-08-31
    Description: A flow visualization study in water was completed on the interaction of a streamwise vortex with a laminar boundary layer on a two-dimensional wing. The vortex was generated at the tip of a finite wing at incidence, mounted perpendicular to the main wing, and having the same chord as the main wing. The Reynolds number based on wing chord was about 5000. Two different visualization techniques were used. One involved the injection of two different colored dyes into the vortex and the boundary layer. The other technique utilized hydrogen bubbles as an indicator. The position of the vortex was varied in a directional normal to the wing. The angle of attack of the main wing was varied from -5 to +12.5 deg. The vortex induced noticeable cross flows in the wing boundary layer from a distance equivalent to 0.75 chords. When very close to the wing, the vortex entrained boundary layer fluid and caused a cross flow separation which resulted in a secondary vortex.
    Keywords: AERODYNAMICS
    Type: NAS 1.15:86656 , NASA-TM-86656 , REPT-85013
    Format: application/pdf
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  • 6
    ISSN: 1752-1688
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: : Grazed pastures represent a potential source of non-point pollution. In comparison to other nonpoint sources (e.g., row-cropped lands), relatively little information exists regarding possible magnitudes of pollution from grazed pasture; how that pollution is affected by weather, soil, management and other variables; and how the pollution can be minimized. The objective of this study was to assess how the quality of runoff from fescue plots is influenced by duration of cattle manure application (4–12 weeks) and manure application strategy (none, weekly application of 1.4 kg/plot, and monthly application at 5.6 kg/plot). Additional analyses were performed to relate runoff quality to the timing of sample collection. The study was conducted at the University of Kentucky Maine Chance Agricultural Experiment Station north of Lexington. Plots (2.4 m wide by 6.1 m long) were constructed and established in Kentucky 31 fescue (Festuca arundinacea Schreb.) to represent pasture. Grazing was simulated by application of beef cattle manure to the plots. Runoff was generated by applying simulated rainfall approximately 4, S and 12 weeks following initiation of manure application. Runoff samples were collected and analyzed according to standard methods for nitrogen (N), phosphorus (P) and fecal coliforms (FC). Runoff concentrations of N and P from manure-treated plots were low and generally not consistently different from control plot concentrations or related to manure application strategy. Runoff FC concentrations from manure-treated plots were higher than from control plot concentrations. Runoff concentrations of ammonia N, total Kjeldahl N, ortho-P and FC decreased approximately exponentially in response to increasing time of sample collection. These findings suggest that manure deposition on well-managed pasture at the rates used in this study might have a negligible impact on nutrient content of runoff.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 13 (2001), S. 770-775 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is well known that vortex rings are the dominant flow structures in the near field of a free jet, and this has led many researchers to believe that they also occur in a jet in cross flow (JICF). Previous studies have postulated that these vortex rings deform and fold as they convect downstream, which culminates in the formation of vortex loops at both the upstream and the lee-side of the jet column. In this paper, we take a fresh look at the vortical structures of JICF in water by releasing dye at strategic locations around the jet exit. The results show that there is no evidence of ring vortices in JICF, and the postulation that vortex loops are formed from the folding of the vortex rings does not reflect the actual flow behavior. The presence of a counter-rotating vortex pair (CVP) at the jet exit is found to inhibit the formation of the vortex rings. Instead, vortex loops are formed directly from the deformation of the cylindrical vortex sheet or jet column, without going through the vortex rings, in a process similar to the buoyant jet and wake structures studied by Perry and Lim [J. Fluid Mech. 88, 451 (1978)]. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 1666-1671 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In a recent experimental investigation, Webster and Longmire [Phys. Fluids 9, 655 (1997)] reported that the large-scale jet structures from inclined nozzles, which consisted of continuous inclined vortex rings, would undergo breakdown if the inclined angle of the nozzle was sufficiently large. They attributed the breakdown to the presence of longitudinal vorticity, but did not elaborate on the mechanism involved. In this paper, we examined the above issue by focusing primarily on the large-scale structures of the inclined jet (i.e., the inclined vortex rings). To the author's knowledge, this area of research remains relatively unexplored. A study of it would certainly help to shed light on the mechanism involved in the breakdown of the inclined jets. Here we investigated the effects of the Reynolds number, the nozzle's inclined angle, and L/D (see below) on the evolution of inclined vortex rings. Nozzles with the inclined angle of 5°, 10°, 20°, and 45° were considered, and the Reynolds number of the flow ranged from 1447 to 4824. The L/D was varied from 0.77 to 1.92, where L is the length of the slug of fluid ejected through the nozzle of diameter D. The results showed that when inclined vortex rings were formed, they were subjected to a differential rate of vortex stretching, due in part to a nonaxisymmetric vortex roll-up. As a result, circumferential flow was produced in the vortex core which increased with the nozzle angle and the Reynolds number. If sufficiently large, the circumferential flow was found to lead to core breakdown by initiating a wavy instability in the vortex filament which subsequently developed into a "bubble-type" breakdown and then a "double-helix"-type breakdown before the ring disintegrated into a chaotic motion. A simple physical model describing this transition process is proposed. However, if the circumferential flow was low, core bulging (or core swelling) might occur instead. A breakdown chart plotted using the Reynolds number and L/D for different nozzle angles is presented. The chart enables one to determine the flow conditions under which the core breakdown would occur. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 9 (1997), S. 239-241 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the early 1970s, Maxworthy [J. Fluid. Mech. 51, 15 (1972)] and Oshima et al. [J. Phys. Soc. Jpn. 38, 1159 (1975)] attempted to produce leapfrogging between two coaxial vortex rings at low Reynolds numbers in their laboratories. However, the rings failed to undergo the classical leapfrogging behavior and merged to form a single ring. In a recent numerical study, Shariff et al. (NASA Tech. Memo. 102257, 1989) attributed the failure partly to the effect of core distortion. They pointed out that vortex cores at low Reynolds numbers are thicker and therefore more susceptible to distortion during the leapfrogging. In this Brief Communication, it is shown through a systematic investigation that the initial generating condition also plays an important role in determining the success or failure of leapfrogging. The common belief that leapfrogging can be achieved simply by generating two vortex rings in quick succession may not be true for all flow conditions, especially when the Reynolds number is low. This finding may help to explain the results of Maxworthy and Oshima et al. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 14 (2002), S. 1537-1539 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper is motivated by our earlier investigation on the stability of Taylor–Couette flow in which we discovered a previously unidentified flow regime, which we refer to as "Second Taylor vortex flow" (STVF) when an inner cylinder is subjected to some critical acceleration [Lim, Chew, and Xiao, Phys. Fluids 10, 3233 (1998)]. The aim here is to explore how the STVF regime is affected by changes in radius ratio and aspect ratio. Results show that the STVF regime is sensitive to the gap size between the two cylinders, and does not exist for some radius ratios, whereas it increases with decreasing aspect ratio. © 2002 American Institute of Physics.
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