摘要:

The equations governing the flow field that is developed when a moderately strong shock wave propagates in an oxygen–carbon suspension were developed and solved numerically using the flux‐corrected transport technique. A comparison is made between two suspensions. In one suspension the carbon particles are assumed to be inert and in the other, the combustion of the carbon particles is accounted for. In addition, the dependence of the post‐shock flow field on the initial loading ratio of the carbon particles was also investigated.

ISSN:0899-8213    

DOI:10.1063/1.857588

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Solitary waves in incompressible deep fluids are described to the first order in the wave amplitude by the Benjamin–Davis–Ono equation [J. Fluid Mech.29, 559 (1967); J. Fluid Mech.29, 593 (1967); J. Phys. Soc. Jpn.39, 1082 (1975)]. This equation describes the balance between dispersion and weak nonlinear effects for long internal waves in a density stratified layer of fluid confined in an infinitely deep fluid. A solution of this equation is the so‐called algebraic solitary wave. In the present paper the modifications of this wave due to the compressibility of the fluid are investigated. It is found that the linear (eigenvalue) problem, determining the modal function and the possible phase speeds, as well as the coefficients of the Benjamin–Davis–Ono equation, change due to the compressibility. These changes are discussed considering three special cases in detail.

ISSN:0899-8213    

DOI:10.1063/1.857589

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Transient wave phenomena in two‐phase mixtures with a liquid as the matrix and gas bubbles as the dispersed phase have been studied in a shock tube using glycerine as the liquid and He, N2, and SF6as gases having a large variation in the ratio of specific heats and the thermal diffusivity. Two different sizes of bubble radii have been produced ,R0=1.15 and 1.6 mm, with a dispersion in size of less than 5%. The void fraction was varied over one order of magnitude, &Jgr;0=0.2%–2%. The measured pressure profiles were averaged by superimposing many shots, typically 20. Speeds and profiles were measured for shock waves and for wave packets. Investigation of the wave structure allows one to approach the fundamental question of how the physics on the level of the microstructure influences the behavior on the macroscale. In the theoretical work, modeling on the basis of a hierarchy of characteristic length scales is developed. Bubble interactions, transient heat transfer, and dissipation due to molecular and bulk viscosities are included. Solutions for small void fractions and moderate amplitudes are obtained for the steady cases of shock waves and solitons and are compared with the experimental results.

ISSN:0899-8213    

DOI:10.1063/1.857590

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Accurate numerical simulations of vortex dipoles impinging on flat boundaries have revealed interesting new features. In the case of free‐slip boundaries the dipole does not rebound from the wall. In the case of nonslip walls rebounding occurs and complex interactions of secondary and tertiary vortices appear. The numerical simulation of the first dipole rebound from the wall agrees with experimental visualizations. Numerical experiments extending in time beyond the real experiments show multiple rebounding. Each rebound is associated with the detachment of a secondary vorticity layer from the wall, these layers merge, and at a value of Reynolds number Re=1600, form a new dipole. This dipole has sufficient circulation to induce on itself a motion in the opposite direction to the motion of the initial dipole.

ISSN:0899-8213    

DOI:10.1063/1.857591

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In probability density function (pdf) methods, statistics of inhomogeneous turbulent flow fields are calculated by solving a modeled transport equation for a one‐point joint probability density function. The method based on the joint pdf of velocity and fluid compositions is particularly successful since the most important processes—convection and reaction—do not have to be modeled. However, this joint pdf contains no length‐scale or time‐scale information that can be used in the modeling of other processes. This deficiency can be remedied by considering the joint pdf of velocity, dissipation, and composition. In this paper, by reference to the known properties of homogeneous turbulence, a modeled equation for the joint pdf of velocity and dissipation is developed. This is achieved by constructing stochastic models for the velocity and dissipation following a fluid particle.

ISSN:0899-8213    

DOI:10.1063/1.857592

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A database obtained by direct numerical simulation of turbulent channel flow was used to compute the three‐dimensional frequency/wave‐number spectrum of wall‐pressure fluctuations. The spectrum was used to deduce scaling laws for pressure fluctuations and to evaluate the similarity form for the power spectrum. The convection velocity as a function of frequency, wave number, and spatial and temporal separations was calculated and compared with the experimental data. The problem of artificial ‘‘acoustics’’ in numerical simulation of incompressible flows is discussed.

ISSN:0899-8213    

DOI:10.1063/1.857593

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A direct numerical simulation of the viscous incompressible flow around a circular cylinder is carried out in the Reynolds number range 2000–10 000 by solving the two‐dimensional time‐dependent Navier–Stokes equations, using a pressure–velocity finite‐volume method. Apart from the vortex shedding phenomenon, it is shown that transition waves develop in the separated shear layers and lead to mixing layer eddies. The ratio of the computed transition wave frequency over Strouhal number is in good agreement with experimental results. This allows the supposition that the instability leading to mixing layer eddies has a predominant two‐dimensional origin and is predicted by the Navier–Stokes equations.

ISSN:0899-8213    

DOI:10.1063/1.857594

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The renormalization group is applied to derive a nonlinear algebraic Reynolds stress model of anisotropic turbulence in which the Reynolds stresses are quadratic functions of the mean velocity gradients. The model results from a perturbation expansion that is truncated systematically at second order with subsequent terms contributing no further information. The resulting turbulence model applies to both low and high Reynolds number flows without requiring wall functions oradhocmodifications of the equations. All constants are derived from the renormalization group procedure; no adjustable constants arise. The model permits inequality of the Reynolds normal stresses, a necessary condition for calculating turbulence‐driven secondary flows in noncircular ducts.

ISSN:0899-8213    

DOI:10.1063/1.857595

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Vortex dynamics in plane ideal flow is strongly simplified for systems with vanishing total circulation. The additional constraint of vanishing total flow impulse leads to further simplifications. For three and four vortices, the cases are discussed where orbit shapes in properly moving configuration planes are given in closed (implicit) form. Then the remaining problems are reduced to quadratures.

ISSN:0899-8213    

DOI:10.1063/1.857596

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A fundamental property of forced, dissipative, two‐dimensional incompressible Navier–Stokes (NS) systems is the dominance at long times of the longest wavelengths available to the flow. This dominance, attributed to an inverse cascade of energy with respect to enstrophy [Kraichnan, Phys. Fluids10, 1417 (1967)], has been observed in spectrally accurate numerical simulations (see Refs. 5–7) of the incompressible NS equations. The numerical investigation of this behavior is extended to the weakly compressible regime by means of the fully compressible Fourier collocation codecomboxwith a solenoidal forcing function that imparts no net momentum and stirs the fluid in a wave‐number band in the neighborhood ofkf=11. A comparison of spectral results fromcomboxsimulations with an average Mach number of 0.22 with those from identically forced incompressible simulations, at Reynolds numbers ≤700, indicates (1) the compressible and incompressible wave‐number dependences in both the energy cascading and enstrophy cascading regions are nearly identical; (2) in the compressible calculation, a dual power law is also observed in density and pressure fluctuations; and (3) continued (kf=11) forcing leads to overall continued growth in the longest accessible velocity field wavelength, inboththe incompressible and compressible cases.

ISSN:0899-8213    

DOI:10.1063/1.857597

出版商:AIP    

年代:1990

数据来源: AIP