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  • 1
    Electronic Resource
    Electronic Resource
    The influence of kinematic waves on jet break down (1992)
    Springer
    Experiments in fluids 12 (1992), S. 173-180 
    Details
    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 The breakdown of a liquid jet is commonly considered as an effect of the surface tension. However, essential aspects of the boundary wave amplification and the final disintegration of velocity modulated jets can be explained by non-linear travelling time effects, which are of purely kinematic nature. The experiments are carried out on jets with radii between 1.2 to 2.5 mm and Weber numbers between 17 to 200. The experimental results are compared with a theoretical solution which neglects the surface tension.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00188256
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  • 2
    Electronic Resource
    Electronic Resource
    Computer aided evaluation of interferograms (1993)
    Springer
    Experiments in fluids 16 (1993), S. 46-53 
    Details
    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 semi-automatic technique is presented for obtaining the density field from interferograms provided by a Mach-Zehnder setup in infinite fringe width adjustment using short exposure times. The algorithm relies on extracting the fringe edges from the original image and then numbering the resulting polygons according to their order of interference using a graphical editor. The density field is then interpolated between the polygons by calculating its value from the intensity in the original interferogram. This results in highly accurate, high resolution scalar data fields. The results may then be presented in a quasi three-dimensional form using a shading model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00188506
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  • 3
    Electronic Resource
    Electronic Resource
    A refined droplet approach to the problem of homogeneous nucleation from the vapor phase (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3872-3884 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theory of homogeneous nucleation from the vapor phase is presented, which is based on an extension of Fisher's semiphenomenological droplet model for the Gibbs free energy of formation of a cluster. This droplet model allows translational, rotational, vibrational, and configurational degrees of freedom of the cluster as well as the variation of surface tension with cluster size. By suitable choice of the three free model parameters, known nucleation theories such as the classical Becker–Döring–Zeldovich theory and others are obtained as special cases. Since, however, an ansatz for the Gibbs free energy of formation allows the construction of an equation of state for real gases below the critical point, a new method of determining the model parameters is suggested, which is based on the idea of forcing the identity of the constructed equation of state with an experimentally verified one. Thus, all free model parameters can be determined purely from well-known handbook properties. It is shown that the new theory gives a better prediction of observed nucleation rates than the classical one.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460663
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  • 4
    Electronic Resource
    Electronic Resource
    An electronic Cranz–Schardin camera (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 364-368 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An electronic high-speed multiple-image camera based on the Cranz–Schardin principle has been developed. High-power LEDs are used as a light source. Frames are recorded by a system of eight CCDs and an eight channel image processor enabling a series of eight subsequent images at full-frame (512× 512) resolution or more images (up to 80) at a lower resolution. The maximum framing frequency is 10 MHz. The advantages upon the classical spark illumination and photographic techniques are mainly the precise electronic control, the immediate access to the frames, the on-line image processing and the low cost of the system. Examples of gas- and two-phase flow visualization are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142129
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of ventilation on the flowfield around a sphere (1995)
    Springer
    Experiments in fluids 19 (1995), S. 78-88 
    Details
    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 The flowfield around a sphere with and without ventilation was investigated in a wind tunnel over a range of Reynolds numbers in an incompressible flow. At supercritical Re, the pressure drag of a sphere can be nearly nullified by venting only 2% of the frontal area of the sphere to the base through a smooth internal duct. The drag reduction is achieved by increased pressures in the separated flow region close to the base. At high Re, the vent flow breaks through the near wake and brings about symmetry in the global flowfield. When the internal shear is increased by using a rough internal duct, the base pressure is unchanged, but the external flow is accelerated to velocities beyond that achieved by the potential flow around the basic sphere. The findings can be explained by a flow model in which the near wake is aerodynamically streamlined by a pair of counterrotating vortex rings at the base. A roughness element can be made to partially destroy the vortex system at the base and result in a steady asymmetric wake. A 1.2 mm diameter wire placed at 70° was found to overtrip the boundary layer and completely destroy the vortex system. Simultaneously, the turbulent separation is advanced and the drag increased. At subcritical Re, ventilation marginally increases static pressures all over the surface. Since the large pressure differential between the windward and leeward sides is not reduced, the internal flow has a rapid acceleration to a velocity close to that of the free stream. The reverse flow associated with the near wake forces the vent flow to rest within itself and the wake profile is unchanged. The main features of subcritical flow around the basic sphere are retained in spite of ventilation. The upstream effects of ventilation are greater for subcritical flow than for supercritical flow.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00193853
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  • 6
    Electronic Resource
    Electronic Resource
    Flow visualisation studies on growth of area of deflected jets (1997)
    Springer
    Experiments in fluids 23 (1997), S. 105-112 
    Details
    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  Laser light sheet visualisation, coupled with image processing, was utilised to understand the effect of exit geometry on the integral properties of jets in cross flow. The study involved jets emanating from circular and rectangular nozzles of different aspect ratios deflected by a uniform free-stream. The investigation considers incompressible momentum jets with exit Reynolds number in the range of 4400–9200, the velocity ratios being 3.9, 5.9 and 7.8. In contrast to a deflected circular jet, those jets emanating from blunt configurations tend to have higher growth rates initially and are devoid of the horse-shoe or the bound vortex system in their cross section.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003480050091
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  • 7
    Electronic Resource
    Electronic Resource
    Forced oscillations of airfoil flows (1996)
    Springer
    Experiments in fluids 21 (1996), S. 457-464 
    Details
    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 The effect of background flow oscillations on a transonic airfoil (NACA 0012) flow was investigated experimentally. The oscillations were generated by means of a rotating plate placed downstream of the airfoil. Owing to the expansion and compression waves generated at the plate, the flow over the airfoil flow was drastically disturbed. This resulted in the presence of high intensity oscillations of a shock wave and a separation bubble on the suction surface of the airfoil. For relatively large values of the airfoil angle of attack, weak shock waves (transonic sound waves) were periodically shed upstream of the airfoil. This work was supported by Commission of the European Communities (Communit's Action for Cooperation in Science and Technology with Central and Eastern European Countries).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00189048
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  • 8
    Electronic Resource
    Electronic Resource
    Bluff-body drag reduction by passive ventilation (1993)
    Springer
    Experiments in fluids 16 (1993), S. 73-81 
    Details
    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 The drag of a sphere at highRe can be reduced to more than half its value by passive ventilation from the stagnation region to the base. Simultaneously, the flow field around the base is stabilized and made symmetric, leading to reduction of unsteady aerodynamic forces. At highRe, the vent flow breaks through the dead water region associated with the near wake and aerodynamically streamlines the base. The streamlining is done by virtue of a base-vortex-ring beyond the point of turbulent boundary layer separation. A mean flow model for the flow around the vented sphere is proposed. Smoke flow visualized on a laser light screen placed at two diameters behind the base of the sphere shows the effectiveness of the method in suppressing the flow oscillations. The drag reduction achieved is very sensitive to the quality of the external surface and relatively insensitive to disturbances in the internal flow. Surface roughness or boundary layer tripping wire on the external flow can completely offset the benefit obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00944909
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  • 9
    Electronic Resource
    Electronic Resource
    Oscillation modes of laval nozzle flow (1995)
    Springer
    Experiments in fluids 18 (1995), S. 145-152 
    Details
    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 Experimental investigations of Laval nozzle flow show for relatively low supply to exit pressure ratios, which correspond to shock wave positions close to the nozzle throat, three different, oscillatory instabilities. (i) Shock pattern oscillations where the root of a λ-like shock front remains nearly in constant position, but where the proportion between the normal part and the oblique part of the shock changes periodically. (ii) Shock wave and separation bubble oscillations where the motion of the shock wave is accompanied by displacements of the separation bubble. (iii) Flow rate oscillations where the shock waves leave periodically through the nozzle throat in upstream direction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00230258
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  • 10
    Electronic Resource
    Electronic Resource
    Velocity measurement of compressible air flows utilizing a high-speed video camera (1995)
    Springer
    Experiments in fluids 18 (1995), S. 204-206 
    Details
    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 PIV-measurements of the flow above a pitching airfoil were conducted in a transonic wind tunnel. An ultra high-speed video camera was used for separate recording of two exposures. The data was analysed using the cross-correlation method. The results show the applicability of the technique in high speed flows.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00230266
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