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The laminar breakdown of the boundary-layer flow of an axisymmetric sharp cone in a Mach 8 flow is simulated by a synergistic approach that combines the parabolized stability equation (PSE) method and spatial direct numerical simulation (DNS). The transitional state is triggered by a symmetric pair of oblique second-mode disturbances whose nonlinear interactions generate strong streamwise vorticity, which leads in turn to severe spanwise variations in the flow and eventual laminar breakdown. The PSE method is used to compute the weakly and moderately nonlinear initial stages of the transition process and, thereby, to derive a harmonically rich inflow condition for the DNS. The strongly nonlinear and laminar-breakdown stages of transition are then computed by well-resolved DNS, with a highly accurate algorithm that exploits spectral collocation and high-order compact-difference methods. Evolution of the flow is presented in terms of modal energies, mean quantities (e.g., skin friction), Reynolds stresses, turbulent kinetic energy, and flow visualization. The numerical test case is an approximate computational analog of one of the few stability experiments performed for hypersonic boundary-layer flows. Comparisons and contrasts are drawn between the experimental and the computational results. Rope-like waves similar to those observed in schlieren images of high-speed transitional flows are also observed in the numerical experiment and are shown to be visual manifestations of second-mode instability waves.This research was supported under NASA Contracts NAS1-19831 and NAS1-20059 for the first and second authors, respectively. 相似文献
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The reaction of acetic [13C]formic anhydride with sodiumpentacarbonylmanganate proceeds rapidly at 0°C to give 13CO substituted pentacarbonylmanganese hydride as the predominant product. The results are consistent with the formation of a short-lived neutral formyl complex, (CO)5Mn13CHO. 相似文献
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C. Pruett 《Theoretical and Computational Fluid Dynamics》2008,22(3-4):275-304
Large-eddy simulation (LES) has relied almost exclusively on spatial filtering to separate resolved and unresolved scales.
For many reasons, temporal filtering may be more natural, particularly for flows of engineering interest. The paper develops
the theory of temporal LES (TLES) and provides a demonstration of the concept by simulations of viscous Burger’s flow and
incompressible plane-channel flow. The latter is accomplished by adapting the approximate deconvolution model (ADM) of Stolz
and Adams (Phys. Fluids 11:1699, 1999) to causal, time-domain filtering. The temporal variant of the ADM is termed the TADM.
相似文献
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R.L. Pruett R.C. Schoening J.L. Vidal R.A. Fiato 《Journal of organometallic chemistry》1979,182(4):C57-C60
The reaction of LiBH(C2H5)3 with Os3(CO)12 or Ir4(CO)12 leads to the formation of spectroscopically detectable formyl complexes. In the latter case, the complex is smoothly converted to [Ir4(CO)11H]?, an expected decompositioFn complex of the corresponding polynuclear formyl complex, [Ir4(CO)11CHO]?. 相似文献
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Experience with fluid-flow simulation suggests that, in some instances, under-resolved direct numerical simulation (DNS), without a residual-stress model per se but with artificial damping of small scales to account for energy lost in the cascade from resolved to unresolved scales, may be as reliable as simulations based on more complex models of turbulence. One efficient and versatile manner to selectively damp under-resolved spatial scales is by a relaxation regularization, e.g. Stolz and Adams [S. Stolz, N.A. Adams, An approximate deconvolution procedure for large eddy simulation, Phys. Fluids II (1999) 1699-1701]. We consider the analogous approach based on time scales, time filtering and damping of under-resolved temporal features. The paper explores theoretical and practical aspects of temporally damped fluid-flow simulations. We prove existence of solutions to the resulting continuum model. We also establish the effect of the damping of under-resolved temporal features as the energy balance and dissipation and prove that the time fluctuations → 0 in a precise sense. The method is then demonstrated to obtain both steady-state and time-dependent coarse-grid solutions of the Navier-Stokes equations. 相似文献
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The forced transition of the boundary layer on an axisymmetric flared cone in Mach 6 flow is simulated by the method of spatial
direct numerical simulation (DNS). The full effects of the flared afterbody are incorporated into the governing equations
and boundary conditions; these effects include nonzero streamwise surface curvature, adverse streamwise pressure gradient,
and decreasing boundary-layer edge Mach number. Transition is precipitated by periodic forcing at the computational inflow
boundary with perturbations derived from parabolized stability equation (PSE) methodology and based, in part, on frequency
spectra available from physical experiments. Significant qualitative differences are shown to exist between the present results
and those obtained previously for a cone without afterbody flare. In both cases, the primary instability is of second-mode
type; however, frequencies are much higher for the flared cone because of the decrease in boundary-layer thickness in the
flared region. Moreover, Goertler modes, which are linearly stable for the straight cone, are unstable in regions of concave
body flare. Reynolds stresses, which peak near the critical layer for the straight cone, exhibit peaks close to the wall for
the flared cone. The cumulative effect appears to be that transition onset is shifted upstream for the flared cone. However,
the length of the transition zone may possibly be greater because of the seemingly more gradual nature of the transition process
on the flared cone.
Received 20 March 1997 and accepted 21 May 1997 相似文献
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The functional Ito formula, in the form df() = f( + d ) f(),is formulated and proved in the context of a Lie algebra L associatedwith a quantum (non-commutative) stochastic calculus. Here fis an element of the universal enveloping algebra U of L, andf() + d() f() is given a meaning using the coproductstructure of U even though the individual terms of this expressionhave no meaning. The Ito formula is equivalent to a chaoticexpansion formula for f() which is found explicitly. 1991 MathematicsSubject Classification: primary 81S25; secondary 60H05; tertiary18B25. 相似文献