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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 24 (1968), S. 233-242 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract This report describes the karyotypes of fourteen species of the tribe Chrysotoxini (Diptera, Syrphidae) with the single genus Chrysotoxum. The species are listed in the Table on p. 240. All have 2n=10 chromosomes, usually consisting of short apparently telocentric sex chromosomes plus two subtelocentric and two submetacentric pairs of autosomes.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Fluid Mechanics 17 (1985), S. 151-189 
    ISSN: 0066-4189
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2716-2724 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An experimental study has been conducted to investigate the effects of swirl on the streamwise development of an axisymmetric turbulent mixing layer. The initial boundary layer was tripped well upstream of the lip. All three mean velocities and the six independent components of the Reynolds stress tensor were measured using a rotatable cross-wire probe for three swirl numbers (0, 0.2, and 0.4). The zero swirl case was found to develop as expected, with a linear growth rate and the peak Reynolds stresses approaching constant asymptotic levels. The results show that the swirling mixing layer is affected by the angular momentum instability over almost the whole layer. The effect of the instability is to increase all the peak Reynolds stresses within the mixing layer, with the peaks increasing monotonically with swirl number. The largest increases occurred in the spanwise normal stress and the two secondary shear stresses. A part of the increase in the turbulence stresses is attributed to "extra'' production through terms activated by the angular momentum instability. The thickness and growth rate for the lower swirl rate were found to be comparable to the zero swirl case, while those for the higher swirl rate were increased significantly, in line with the increased Reynolds stresses. This nonmonotonic behavior of the mixing layer growth rate is attributed to the effects of a favorable pressure gradient in the core flow.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 2054-2062 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Some studies of forced and unforced plane turbulent mixing layers have been conducted using two experimental and two computational approaches. The present paper contains an overall comparison and discussion of the measured and computed results. The experimental results include flow-visualization data using the smoke-laser technique and mean flow and turbulence measurements obtained with hot X wires and a two-component laser-Doppler velocimeter (LDV). The mean flow and turbulence results indicate that the two experimental techniques agree reasonably well for this shear flow. Two-dimensional computations of the measured mixing layers have also been conducted in a coordinated effort; one method uses the inviscid discrete vortex technique for a spatially developing layer and the other is based on an approximation to the Reynolds-averaged Navier–Stokes equations. The vortex method was found to give excellent results for the forced mixing layer while the Reynolds-averaged computations, with a modified turbulence model, were particularly successful at capturing the near-field viscous behavior that included the splitter plate wake.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Experiments in fluids 14 (1993), S. 286-288 
    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: Conclusions An experimental study which shows the effects of relatively small changes in the initial conditions on the development of the three-dimensional structure of a plane mixing layer originating from laminar boundary layers has been completed. It was shown that while the exact shapes and positions of the streamwise vortex structures are not the same for the two initial conditions, their overall distribution, reorganization and decay are very similar. The present results imply that while some of the specific details of the streamwise vortex structure may be facility dependent, a relatively strong structure, which produces significant three-dimensionality, should form in all mixing layers originating from laminar boundary layers. After some initial readjustments, the structure will appear in the form of counter-rotating pairs of streamwise vortices which, in the mean, grow with the mixing layer and decay in strength. The present results also serve as a warning that small changes in initial conditions may significantly affect the Reynolds stress distributions in the near-field. The most likely mechanism for this is through the effects of very small changes in initial boundary layer properties on the details (strength and location) of the spanwise vortex roll-up. Despite these relatively large differences in the near-field, both mixing layers attain comparable turbulence structure and growth rates in the far-field. In addition, the behavior of the streamwise vortex structure does not appear to be affected by the differences in the near-field Reynolds stress distributions.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Experiments in fluids 17 (1994), S. 32-38 
    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 Traditionally, linear mean-square (MS or stochastic) estimation coefficients are calculated using cross-correlations between each of the data at reference and estimation locations. Since the cross-correlation between data at reference and estimation locations typically decreases rapidly with increasing separation distance, the resulting estimated fluctuations diminish away from the reference locations. Two new schemes have been developed to optimally determine estimation coefficients which yield an improved estimated energy representation. One approach involves a non-linear least-square fit toboth the estimation covariance and the cross-correlation between data at reference and estimation locations. By also minimizing the error in the estimation covariance, realistic energy levels can be estimated without significantly altering the correlation between true and estimated velocity signals as given by the traditional MS method. Another scheme, developed for use with a single-point, two-component reference, maximizes the correlation coefficient between the estimate and its measured counterpart. It is shown that for this simple case, the estimated covariance can be setequal to the measured covariance without compromising the correlation coefficientat all. The effectiveness of the proposed techniques is demonstrated by comparing their estimates with those given by the MS method in a plane turbulent mixing layer. In general, the estimation schemes appear to give improved results when references from the edge of the mixing layer are employed. It is also demonstrated how the results of the proposed estimation methods can be used to infer details regarding the mixing layer structure and kinematics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Experiments in fluids 4 (1986), S. 257-266 
    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 Detailed mean flow and turbulence measurements have been made in the near-field of two plane mixing layers in air with a maximum velocity of 21 m/s. The experimental rig enabled mixing layers of velocity ratios 0 and 0.46 to be generated simultaneously. Cases with both tripped and untripped initial boundary layers were studied. In all cases, it was found that the two-stream layer developed to the self-preserving state in a distance much shorter than the single-stream layer, which followed accepted criteria for the development distance. The asymptotic levels of the turbulence quantities in the two-stream layer and the development of the single-stream layer showed agreement with existing data. The results suggest that the two-stream mixing layer should provide a better test case for the development of turbulence models and calculation methods than the single-stream mixing layer.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Experiments in fluids 5 (1987), S. 358-358 
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Experiments in fluids 7 (1989), S. 405-411 
    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 oscillating vortex embedded within a turbulent boundary layer was generated experimentally by forcing a periodic lateral translation of a half-delta wing vortex generator. The objective of the experiment was to investigate the possibility that a natural oscillation, or meander, might be responsible for flattened vortex cores observed in previous work, which could also have contaminated previous turbulence measurements. The effect of this forced oscillation was characterized by comparison of measurements of the mean velocities and Reynolds stresses at two streamwise stations, for cases with and without forcing. The Reynolds stresses, especially ′w′, were affected significantly by the forced oscillation, mainly through contributions from the individual production terms, provided the vortex was not too diffuse.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Experiments in fluids 8 (1990), S. 354-356 
    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 comparison method is proposed for the verification of mean flow and turbulence measurements obtained with a three-dimensional laser Doppler velocimeter system. Such measurements can include large errors caused by problems unique to three-dimensional systems. Direct comparisons of laser and hot cross-wire measurements obtained in two-dimensional flows, as is the common practice, will not bear out all the errors associated with three-dimensional laser systems. It is proposed here that the errors may be adequately quantified by making the direct comparisons in a weakly three-dimensional turbulent shear flow. The weak three-dimensional flow ensures high accuracy of the cross-wire data while still generating sufficiently strong secondary mean flow and Reynolds shear stresses so that all the laser measurements may be fully verified. This type of shear flow is easily generated by introducing a weak streamwise vortex into a nominally two-dimensional turbulent shear layer.
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