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  • 1
    Electronic Resource
    Electronic Resource
    The evolution of a plane mixing layer with spanwise nonuniform forcing (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 381-396 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The experimental studies of Nygaard and Glezer (AIAA Paper No. AIAA-91-0625, 1991) show that vortical structures shaped like a "chain-link fence'' form in a plane mixing layer subjected to spanwise nonuniform phase excitation. Using direct numerical simulation of temporally evolving mixing layers, initial conditions have been developed that result in flows with vortex structures similar to those observed in the experiments. The simplest initial condition that leads to the experimentally observed structures is composed of a pair of equal-strength oblique disturbances and this initial condition is a low-order Fourier approximation to the square-wave excitation used in the experiments. This simple disturbance suggests an explanation for the short wavelength cutoff observed in the experiments and allows comparison with previous stability analyses. The simulated flow fields show that the chain-link-fence vortex structures are different from the usual rib/roller mixing layer structures. Furthermore, detailed examination of the overlap region between adjacent structures shows that "local pairing'' does not occur in the chain-link-fence flow due to strong self-induction effects. By increasing the spanwise wavelength, self-induction effects can be delayed and regions of local pairing are observed. However, the local pairings do not lead to a single amalgamated vortex at late times as is observed in two-dimensional pairings. Finally, it is shown that the chain-link-fence flow produces increased mixing compared to standard rib/roller flows.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868035
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  • 2
    Electronic Resource
    Electronic Resource
    Vortex-induced disturbance field in a compressible shear layer (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 1412-1419 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The disturbance field induced by a small isolated vortex in a compressible shear layer is studied using direct simulation in a convected frame. The convective Mach number, Mc, is varied from 0.1 to 1.25. The vorticity perturbation is rapidly sheared by the mean velocity gradient. The resulting disturbance pressure field is observed to decrease both in magnitude and extent with increasing Mc, becoming a narrow transverse zone for Mc(approximately-greater-than)0.8. A similar trend is seen for the perturbation velocity magnitude and for the Reynolds shear stress. By varying the vortex size, it was verified that the decrease in perturbation levels is due to the mean-flow Mach number and not the Mach number across the vortex. At high Mc, the vortex still communicates with the edges of the shear layer, although communication in the mean-flow direction is strongly inhibited. The growth rate of perturbation kinetic energy declines with Mc primarily due to the reduction in shear stress. For Mc≥0.6, the pressure dilatation also contributes to the decrease of growth rates. Calculation of the perturbation field induced by a vortex doublet revealed the same trends as in the single-vortex case, illustrating the insensitivity of the Mach-number effect to the specific form of initial conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858576
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  • 3
    Electronic Resource
    Electronic Resource
    Simulation of spatially evolving turbulence and the applicability of Taylor's hypothesis in compressible flow (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 1521-1530 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For the numerical simulation of inhomogeneous turbulent flows, a method is developed for generating stochastic inflow boundary conditions with a prescribed power spectrum. Turbulence statistics from spatial simulations using this method with a low fluctuation Mach number are in excellent agreement with the experimental data, which validates the procedure. Turbulence statistics from spatial simulations are also compared to those from temporal simulations using Taylor's hypothesis. Statistics such as turbulence intensity, vorticity, and velocity derivative skewness compare favorably with the temporal simulation. However, the statistics of dilatation show a significant departure from those obtained in the temporal simulation. To directly check the applicability of Taylor's hypothesis, space-time correlations of fluctuations in velocity, vorticity, and dilatation are investigated. Convection velocities based on vorticity and velocity fluctuations are computed as functions of the spatial and temporal separations. The profile of the space-time correlation of dilatation fluctuations is explained via a wave propagation model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858425
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  • 4
    Electronic Resource
    Electronic Resource
    Eddy shocklets in decaying compressible turbulence (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 657-664 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The existence of eddy shocklets in three-dimensional compressible turbulence is controversial. To investigate the occurrence of eddy shocklets, numerical simulations of temporally decaying isotropic turbulence are conducted. Dilatation statistics from simulations with different initial fluctuation Mach numbers, Mt, show that dilatation is more intermittent and more negatively skewed for higher Mt. By studying instantaneous flow fields, shocklets are found and verified to have all the characteristics of a typical shock wave, such as proper jumps in pressure and density along with a local entropy peak inside the high-compression zone. Although overall compressible dissipation contributes to less than one-tenth of the total dissipation, compressible dissipation around shocklets is about an order of magnitude larger than typical values of incompressible dissipation. In the zones of eddy shocklets, pressure is highly correlated with dilatation to convert kinetic energy into internal energy. These mechanisms near shocklets should be accounted for in phenomenological modeling for highly compressible turbulence. Three-dimensional turbulence is found to be less sensitive to the initial compressibility, and requires higher initial Mt for eddy shocklets to form than for two-dimensional turbulence. Higher Mt and higher Reynolds number are found to increase the probability of shocklet occurrence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858071
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  • 5
    Electronic Resource
    Electronic Resource
    The response of anisotropic turbulence to rapid homogeneous one-dimensional compression (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 1052-1062 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Homogeneous rapid distortion theory is used to study the response of shear flows and axisymmetric turbulence to rapid one-dimensional compression. In the shear flow problem, both normal and oblique compressions are considered. The response of these anisotropic flows to compression is found to be quite different from that of isotropic turbulence. Upon normal compression, the amplification of the streamwise component of kinetic energy and the total kinetic energy in shear flows is higher than that in isotropic turbulence. Also, normal compression decreases the magnitude of the Reynolds shear stress by amplifying the pressure–strain correlation in the shear stress equation. Obliquity of compression (defined as the angle between the directions of shear and compression) is seen to significantly affect the evolution of the Reynolds stresses. For a range of oblique angles from −60° to 60°, the amplification of streamwise kinetic energy and total kinetic energy decrease with increasing magnitude of the oblique angle. Also, the tendency of the shear stress to decrease in magnitude is diminished upon increasing the oblique angle; for large oblique angles the shear stress amplifies. Upon compression along the axis of axisymmetry, the amplification of the streamwise component of kinetic energy is higher for contracted turbulence than for isotropic turbulence, while the amplification of the total kinetic energy is lower. The above results are interpreted in a more general framework. It is shown that the amplification of the streamwise component of kinetic energy is determined by the initial E11(κ1) (x1 is the direction of compression). Flows with u1 at lower κ1 have a lower effect of pressure during compression and hence, higher amplification of u21. The amplification of the total kinetic energy is determined by the initial fraction of energy along the direction of compression (u21/q2) and the initial E11(κ1). Flows with higher initial u21/q2 and with u1 at lower κ1 have a larger amplification of q2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868338
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  • 6
    Electronic Resource
    Electronic Resource
    On the density ratio effect on the growth rate of a compressible mixing layer (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 1073-1075 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A "curious reduction'' in the normalized growth rate found in recent experiments on compressible mixing layers is explained using linear stability analysis. The maximum amplification rate from the stability analysis agrees well with the growth rate measured in different experiments. No anomalous reduction is observed in the normalized maximum amplification rate, suggesting that the model of growth rate for incompressible mixing layers used to normalize the compressible mixing layer data is inaccurate for extreme density ratios.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868340
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  • 7
    Electronic Resource
    Electronic Resource
    Shock-jump relations in a turbulent flow (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2900-2905 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The exact jump relations applying across a shock in turbulent mean flow are formulated. These are analyzed to obtain answers to the following basic questions: Is the propagation speed of a shock wave which brings about a specified compression faster or slower than its classical value when moving through a turbulent medium? What is the magnitude of the turbulence associated correction? What is the magnitude of the correction to the pressure jump? Answers to these questions are developed by combining gas-dynamic analysis with homogeneous rapid distortion approximation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858343
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  • 8
    Electronic Resource
    Electronic Resource
    Vorticity form of turbulence transport equations (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 1767-1772 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The exact transport equations describing the turbulent kinetic energy, Reynolds stresses, and the dissipation rate of the turbulent kinetic energy are written in their vorticity form. The limiting behavior of the transport equations describing the irrotational fluctuations at the free-stream edges of shear flows is directly deduced from the exact transport equations. Additional relations of pure kinematic origin are also indicated. It is suggested that the formulation developed may be useful in improving the turbulence transport models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858397
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  • 9
    Electronic Resource
    Electronic Resource
    Listening while learning (1994)
    [s.l.] : Nature Publishing Group
    Nature 371 (1994), S. 454-454 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] ACCORDING to the editors of Journal of Computational Acoustics, the traditional compartmentalization of acoustics and related branches of science and engineering has not been conducive to the exchange of ideas and information. This new journal intends to provide scientists and engineers - whether ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/371454b0
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  • 10
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    Vortex‐induced disturbance field in a compressible shear layer (1993)
    American Institute of Physics
    Details
    Publication Date: 1993-06-01
    Print ISSN: 0899-8213
    Topics: Physics
    Published by American Institute of Physics
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