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  • 1
    Electronic Resource
    Electronic Resource
    Asymptotic growth of disturbances from spatially compact source in a skewed mixing layer (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 1153-1160 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The growth of disturbances in a skewed mixing layer, i.e., the shear layer between two streams with different velocity magnitudes and directions, is examined. Due to the three-dimensionality of the mean flow, the natural amplification direction for spatially amplifying waves needs to be determined. This issue can be resolved through investigation of the asymptotic growth of disturbances from a spatially compact source. The results show that the disturbances grow in a wedge-shaped region centered at the mean convection direction for both incompressible and compressible mixing layers. For incompressible unskewed mixing layers, the normal to the instability wave fronts is parallel to the amplification direction. The wave front normal is oblique to the amplification direction for skewed mixing layers and/or mixing layers with moderate compressibility. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869985
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  • 2
    Electronic Resource
    Electronic Resource
    Inviscid instability of compressible swirling mixing layers (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 450-461 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper, we examine the inviscid instability of a swirling mixing layer, a circular mixing layer with an additional swirl component which is present only within the shear layer. The mean flow is solved numerically using the boundary layer equations in cylindrical coordinates. Spatial inviscid stability characteristics of the base flow are studied. The results show that swirl significantly enhances the maximum amplification rate for incompressible mixing layers. This enhancement sustains under the compressible conditions. For swirling mixing layers, a significant amount of disturbance energy is extracted from the shear in the swirl component. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869861
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  • 3
    Electronic Resource
    Electronic Resource
    COMPUTATIONAL PREDICTION OF FLOW-GENERATED SOUND (2006)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Fluid Mechanics 38 (2006), S. 483-512 
    Details
    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
    Notes: This article provides a critical review of computational techniques for flow-noise prediction and the underlying theories. Hybrid approaches, in which the turbulent noise source field is computed and/or modeled separately from the far-field calculation, are afforded particular attention. Numerical methods and modern flow simulation techniques are discussed in terms of their suitability and accuracy for flow-noise calculations. Other topics highlighted include some important formulation and computational issues in the application of aeroacoustic theories, generalized acoustic analogies with better accounts of flow-sound interaction, and recent computational investigations of noise-control strategies. The review ends with an analysis of major challenges and key areas for improvement in order to advance the state of the art of computational aeroacoustics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.fluid.38.050304.092036
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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    A consistency condition for Reynolds stress closures (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 64-68 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new consistency condition is derived for the Reynolds stress turbulent closures. Recommended values of model constants used with the k-ε model and with various Reynolds stress closures do not satisfy this condition exactly. It is shown that a slight adjustment of certain computer-optimized constants would make some of these models internally consistent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865126
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  • 8
    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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  • 9
    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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  • 10
    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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