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  • 1
    Electronic Resource
    Electronic Resource
    Combined application of surface flow visualization and laser-Doppler anemometry to engine intake flows (1993)
    Springer
    Experiments in fluids 15 (1993), S. 323-331 
    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 Flow visualization using oil streak techniques and laser-Doppler anemometry were carried out to provide detailed information on the flow through the intake valve of a research (model) engine head under steady flow conditions. The work was partially undertaken to develop the techniques as useful tools for engine research. On the other hand, variations of the flow field with valve lift and with valve location were of interest. In the present paper it is shown that a symmetric geometry does not necessarily result in symmetric flow patterns inside the cylinder; the tendency to asymmetry increases with increasing valve lift. These characteristics of the flow should be taken into account when flow computations are performed necessitating the use of three dimensional codes in the entire flow field, not in a symmetrical half-geometry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00223410
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  • 2
    Electronic Resource
    Electronic Resource
    Counter jet stagnation flows (1991)
    Springer
    Experiments in fluids 11 (1991), S. 313-324 
    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 present paper concerns the stagnation flow produced by counter flowing air jets. Little experimental information exists on such flows in spite of their extensive employment in the theoretical treatment of diffusion flames. To remedy this situation, laser-Doppler measurements were performed to quantify the entire flow field. The experiments are described and the results of the velocity measurements presented. Differences between the investigated flow field and the ideal flow field, employed in theoretical studies, are pointed out.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00194863
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Statistical analysis of the dynamic equations for higher-order moments in turbulent wall bounded flows (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2886-2900 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The equations for the higher-order moments of turbulent velocity fluctuations are considered. These are derived utilizing truncated, cumulant expansions as an approximation for the probability density distributions of the corresponding turbulence properties. By applying different degrees of truncations to these expansions, an alternative set of equations for the moments is formulated that contains only velocity correlations. From these equations, interrelations between the higher-order moments are deduced and are experimentally verified using data available in the literature and also data measured by the authors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858698
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Flow through rotating rectangular ducts (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 770-781 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The bifurcation structure of two-dimensional, pressure-driven flows through a rectangular duct that is rotating about an axis perpendicular to its own is examined at a fixed Ekman number (Ek=ν/b2Ω) of 0.01. The solution structure for flow through a square duct (aspect ratio γ=1) is determined for Rossby numbers (Ro=U/bΩ) in the range of 0–5 using a computational scheme based on the arclength continuation method. The structure is much more complicated than reported earlier by Kheshgi and Scriven [Phys. Fluids 28, 2968 (1985)]. The primary branch with two limit points in Rossby number and a hysteresis behavior between the two- and four-cell flow structure that was computed by Kheshgi and Scriven is confirmed. An additional symmetric solution branch, which is disconnected from the primary branch (or rather connected via an asymmetric solution branch), is found. This has a two-cell flow structure at one end, a four-cell flow structure at the other and three limit points are located on the path. Two asymmetric solution branches emanating from symmetry breaking bifurcation points are also found for a square duct. Thus even within a Rossby number range of 0–5 a much richer solutions structure is found with up to five solutions at Ro=5. An eigenvalue calculation indicates that all two-dimensional solutions develop some form of unstable mode by the time Ro is increased to 5.0. In particular, the four-cell solution becomes unstable to asymmetric perturbations as found in a related problem of flow through a curved duct. The paths of the singular points are tracked with respect to variation in the aspect ratio using the fold following algorithm. A transcritical point is found at an aspect ratio of 0.815 and below which the four-cell solution is no longer on the primary branch. When the channel cross section is tilted even slightly (1°) with respect to the axis of rotation, the bifurcation points unfold and the two-cell solution evolves smoothly as Rossby number is increased. The four-cell solutions then become genuinely disconnected from the primary branch. The uniqueness range in Rossby number increases with increasing tilt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858009
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  • 5
    Electronic Resource
    Electronic Resource
    On the statistical properties of truncated Gram–Charlier series expansions in turbulent wall-bounded flows (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 118-126 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Higher-order correlations were measured in a turbulent boundary layer using the LDA measuring technique. In the paper, comparisons are made between the measured and predicted correlations obtained by utilizing the properties of truncated Gram–Charlier series expansions. Several theoretically derived relationships between correlations of different orders were confirmed by the experimental data. The experimental and theoretical results support the applicability of truncated Gram–Charlier series expansions for a refined statistical analysis of the conservation equations for higher-order moments of turbulent property fluctuations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858490
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  • 6
    Electronic Resource
    Electronic Resource
    A numerical study of the viscous supersonic flow past a flat plate at large angles of incidence (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 1553-1573 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A numerical study of the viscous supersonic flow past a flat plate is presented. The objective is to investigate the supersonic flow at high angles of incidence where large flow gradients occur. The effect of the angle of incidence and the Reynolds number (Re) in the flow structure especially in the formation of the separation region is investigated. The study is based on the solution of the full Navier–Stokes equations by high resolution schemes, and it focuses on the supersonic flow over the plate at Re≤105. Results on fine computational grids are presented for flow angles up to 20°. The calculations reveal that the flow remain attached for angles of incidence less than a=5°. For a=5° and Re=105, separation of the flow at the trailing edge appeared. Increasing the flow angle (a(approximately-greater-than)5°) moves the separation point upstream while a reverse flow region forms for the entire range of the Reynolds numbers used in this study. The results reveal that for large angles of incidence, the variation of the Reynolds number has significant effects on the variation of the flow variables. The flow behind the trailing edge is also affected from the flow angle as well as from the Reynolds number. Comparisons are also presented between viscous and inviscid solutions. The comparisons show that the viscous effects are dominant on the upper surface of the plate as well as behind the trailing edge. These effects become stronger when the flow angle is a=20°.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868269
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  • 7
    Electronic Resource
    Electronic Resource
    Measurement accuracy of semiconductor LDA systems (1990)
    Springer
    Experiments in fluids 10 (1990), S. 125-137 
    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 laser Doppler anemometer with a laser diode as the light source, has several advantages: i.e., low power consumption, compactness, and low cost. In order to be fully benefitted by these favorable characteristics, the measurement uncertainty, associated with wavefront distortion in the measuring volume, should be minimized. Furthermore, proper attention should be given to system misalignment caused by external perturbations, such as thermal expansion of the diode-collimator assembly. These considerations lead to a computational procedure for optimizing the layout of the semiconductor LDA system. Calculations are based on a generalized relation for fringe non-uniformity combined with a simulation model for the anemometry system. For this purpose, the optical field of a laser diode is described satisfactorily as a product of a Gaussian and a truncated Lorentzian distribution. The influence of various design parameters is examined by means of an extensive computational study as well as experimental evaluation involving precise scanning of the measuring volume. The performance is improved by employing a small focal length collimator and a large focal length front lens. For measurement of turbulence intensities smaller than 1%, it may become necessary to collect the signals in the side scatter and to use a frequency-domain signal processor. For such an application, temperature control may also be necessary, but it should be applied to the entire diode-collimator assembly and not just to the laser diode as suggested in previous publications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00215021
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  • 8
    Electronic Resource
    Electronic Resource
    Photodetectors for laser-Doppler measurements (1990)
    Springer
    Experiments in fluids 9 (1990), S. 13-16 
    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: Summary This short review of several papers considering signal-tonoise ratios with LDA-measurements points out that it is important to check for every experimental setup which is the optimum photodetector. A decision depends on a great variety of parameters, of which the most important are: (i) the velocity range of the fluid, which gives, together with the characteristics of the measuring control volume, the frequency range; (ii) the applied laser light power which determines, with the nature of the scattering particle, the intensity of the scattered light [Eq. (1)]; (iii) the decision in which angle the scattered light is to be received and the aperture of the receiving lens. Taking these points into account, the right application for the low velocity range, e.g. narrow frequency band, should be the photodiode, for medium velocities the photomultiplier and the avalanche photodiode for the high velocity range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00575330
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  • 9
    Electronic Resource
    Electronic Resource
    Fluid dynamically caused cycle-to-cycle variations in piston-driven pipe expansion flows (1992)
    Springer
    Experiments in fluids 13 (1992), S. 1-10 
    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 piston-driven pipe flow with a sudden expansion in cross-sectional area was studied experimentally using flow visualization and laser-Doppler anemometry as basic experimental techniques. To drive the flow, a piston was moved in the larger of the two pipes. It drew in the fluid into the pipe assembly during the upward stroke and removed fluid during the downward stroke. The time-varying flow field was investigated, yielding detailed information on the flow structure, its development, and variation with time. In the present paper, particular attention is given to those flow conditions that resulted in cycle-to-cylce variations of the flow field. For some of the conditions, repetitive cycle-to-cycle variations of the flow field occurred, yielding identical flows for even-numbered flow cycles and also for odd numbered cycles. However, the latter differed from the former. The presented data show that non-repetitive cycle-to-cycle variations of the flow field also exist and that these can be driven into a state where the flow appears to be nearly chaotic. The results of the investigation clearly demonstrate that fluid dynamically caused cycle-to-cycle flow variations can exist in piston-driven internal flows with separation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00208068
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  • 10
    Electronic Resource
    Electronic Resource
    Druckverlustminderungen in strömungen durch hochpolymere additive: Klärung einiger noch offener fragen (1991)
    Springer
    Archive of applied mechanics 61 (1991), S. 119-132 
    Details
    ISSN: 1432-0681
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Summary In this paper experimental results for drag reduction in turbulent pipe flows are reported. Drag reduction was achieved by the addition of high molecular weight polymers. The degradation of these polymers (chemically) thermally as well as mechanically was investigated and the effect of stabilizers was studied. Special emphasis is devoted to the effect of temperature on the onset of drag reduction. The influence of pipe diameter and of polymeric concentration on the critical wall shear stress (beyond which drag reduction ceases to exist) is deduced.
    Notes: Übersicht Die vorliegende Arbeit faßt Ergebnisse von experimentellen Untersuchungen zusammen, welehe durchgeführt wurden, um die reibungsmindernde Wirkung von Polymeren quantitativ zu bestimmen. Für die Durchführung der Untersuchungen sind zwei Meßeinrichtungen erstellt worden, die in der Arbeit beschrieben sind. Durch ihren Einsatz gelang es, die reibungsmindernde Wirkung von Polymeradditiven zu bestimmen und ihre mechanische Degradation sowie auch ihre Chemie-verursachte, bei erhöhten Temperaturen beschleunigt auftretende Degradation zu quantifizieren. Es werden theoretische Überlegungen zusammengefaßt, welche die mit einer Temperaturänderung auftretende Variation des Einsatzpunktes der Reibungsminderung zu erläutern erlauben. Messungen der kritischen Schubspannungsgeschwindigkeit werden angegeben, bei deren Überschreitung die reibungsmindernde Wirkung der Polymeradditive reduziert wird. Die experimentell gefundene Abhängigkeit dieser Größe vom Rohrdurchmesser und der Polymerkonzentration der Lösung wird aufgezeigt. Die für den praktischen Einsatz wichtige chemisch-thermische und mechanische Degradation der Reibungsminderung durch Polymeradditive wird quantitativ untersucht. Stabilisierende Zusätze werden hinsichtlich ihrer Wirkung im Rahmen von Meßreihen erfaßt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00787404
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