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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 2249-2259 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In nearly isothermal, compressible turbulence of a nondense gas the mass fraction of an embedded passive scalar satisfies the same formal conservation equation as a passive scalar in incompressible turbulence. Direct numerical simulation of this system shows that the compressible turbulence modes are less efficient than the incompressible in transporting scalar spectral content from large to small scales. It is argued that the cause of this outcome is the reduced size of the integral length scale of the compressible velocity components vis á vis that of the incompressible velocity components, and this also explains the experimentally observed ineffectiveness of the dilatational velocity modes in determining scalar flux in homogeneous, compressible turbulence with a uniform mean scalar gradient. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 9 (1997), S. 1754-1763 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Direct numerical simulation of decaying, isotropic, compressible turbulence in three dimensions is used to examine the behavior of fluctuations in density, temperature and pressure when the initial conditions include temperature fluctuations larger than pressure fluctuations. The numerical procedure is described elsewhere, the initial turbulent Mach number is subsonic, 0.3 to 0.7, and the initial compressible turbulence is characterized as being in one of three states in which the ratios of initial kinetic energy in the compressible modes to total kinetic energy are, respectively, very small, moderate or nearly unity. Only at the lowest values of initial turbulent Mach number and energy ratio do thermodynamic scalings follow the predictions in the literature. For turbulent Mach numbers above 0.3, or for finite values of the kinetic energy ratio, the scalings are more complex. A relationship between turbulent Mach number, compressible pressure and energy ratio, which has been proposed previously for isothermal problems, appears to hold, on average, for the cases computed in this study, all of which are non-isothermal. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 8 (1996), S. 2555-2557 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An asymptotic self-similar solution is obtained for the one-point probability density function (pdf) equation, of a passive scalar with uniform mean gradient in incompressible homogeneous turbulence. It is argued that the same solution should be a valid approximation when turbulence is generated in a high-quality wind tunnel. The asymptotic pdf shape is a unique function of the conditional expectation of the normalized scalar dissipation rate. The mean scalar gradient modifies the scalar pdf shape only if the conditional expected velocity component in the direction of the mean gradient is a nonlinear function of scalar fluctuation value. Experimental data from wind tunnel studies are consistent with the sign and scale of the changes produced by these nonlinearities. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of scientific computing 11 (1996), S. 179-205 
    ISSN: 1573-7691
    Keywords: Compressible flows ; direct numerical simulation ; essentially non-oscillatory ; parallel processing ; turbulence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract In this paper, a finite-difference based ENO (essentially nonoscillatory) procedure has been chosen for the direct numerical simulation (DNS) of compressible turbulence. The implementation of the ENO scheme follows the relatively efficient procedure in Shuet al. (1992), but the latter has been modified in the present paper to admit scalar conservation equations and to run on the iPSC/860 Paragon parallel supercomputer. DNS results with our procedure are in excellent agreement with pseudo-spectral and Padé approximation calculations in two and three dimensions. This is the case for a variety of initial conditions for compressible turbulence. The parallel algorithms presented are simple but quite efficient for DNS, with a speedup that approaches the theoretical value. Some of the attractive features include 1) minimum communication whereby a processor only communicates with two neighbors, 2) almost one hundred percent load balancing, 3) a checker-board approach to solve the Poisson equation reduces communication by a factor of approximately 2, and, 4) obtaining turbulence statistics is based on a ‘global collect’ approach, which is implemented to ensure that a single number, rather than a large matrix of numbers, is communicated between processors. The ENO code presented in this paper should be quite useful in its own right, while the parallel implementation should allow the simulation of fairly realistic problems.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 7 (1994), S. 419-432 
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper presents a new finite element formulation in the Laplace domain for both diffusion and wave equations with applications in the field of electrical engineering. With the aid of congruence transformation of matrices, the finite element equations in the Laplace domain are solved and time-domain results can be obtained through the inverse Laplace transform. In a test problem, good agreement between the numerical results derived with the present method and the analytical solutions has been found. For applications in which only Dirichlet and Neumann boundary conditions are involved, this new finite element approach can be applied and provide both frequency-domain and time-domain results in one run without any timestepping scheme. The limitations of using the congruence transformation in solving propagation problems are also addressed in this paper.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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