摘要:

The equation describing the evolution of the probability density function of the temperature field in a turbulent axisymmetric heated jet is presented. A closure problem is present and some possible ways of attacking it are suggested. A closure at the first‐order level is then tentatively tried and similarity arguments are exploited. A hyperbolic first‐order variable‐coefficient quasi‐self‐preserving partial differential equation is obtained. The constants appearing in those coefficients are evaluated from available experiments. Some questions are raised on the uncertainty of the computed constants due to the experimental scattering of the velocity‐temperature correlation at the centerline. The probability density function is obtained analytically as a function of downstream location along the centerline if it is prescribed at a reference centerline position. In particular, the probability density function is taken as Gaussian at ten diameters downstream. The computed mean and variance are compared with existing experiments and display a reasonably good agreement. Values for the skewness and flatness factor tend to indicate that deviations from Gaussianity along the centerline are very small.

ISSN:0031-9171    

DOI:10.1063/1.861163

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Turbulence and heat transfer were measured in a heated jet of air and development of self‐similarity was determined. Temperature fluctuation balance was measured across the jet. Turbulent velocity and temperature spectra and their dependence on jet Reynolds number and location across the jet were measured. The jet nozzles with length to width ratios of 20, 40, and 140 were used and the effect of aspect ratio on turbulent structure was determined.

ISSN:0031-9171    

DOI:10.1063/1.861164

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Turbulence behind a biplanar grid with jets of air injected at the grid surface either in the upstream or the downstream direction was found to be nearly isotropic forx/M≳ 20. Turbulence level increases with the injection rate for both upstream and downstream injection. The shape of the energy spectrum functions and microscales do not vary with the injection rate. The microscales for upstream injection are larger than those for downstream injection.

ISSN:0031-9171    

DOI:10.1063/1.861165

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Model turbulent kinetic energy profiles expected during drag reduction are synthesized from similarity arguments. At low drag reduction, it is postulated that the radial transport of turbulent kinetic energy and of axial momentum are analogous. Thus, in nondimensional terms, the maximum kinetic energy during drag reduction must exceed the Newtonian maximum kinetic energy by an amount proportional to the ’’effective slip,’’ which latter is the amount whereby the mean velocity during drag reduction exceeds that during Newtonian turbulent flow. At maximum drag reduction, the turbulent kinetic energy profile is related to the Newtonian profile by means of the respective mixing length constants,XmandXn; in the former case, the maximum turbulent kinetic energy is predicted to beXn/Xm= 4.7 times the Newtonian. The model profiles are in accord with the (few) available experimental measurements of turbulence during drag reduction.

ISSN:0031-9171    

DOI:10.1063/1.861166

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The creeping flow equations have been solved to account for effects of shear on drop shape when the influence of neighboring drops is considered. A cell model is used to account for finite concentrations of the dispersed phase. From these results a constitutive equation is derived and implications for several flows are discussed. The shape and orientation of drops are computed and compared with existing data. Finally, dynamic viscosity and rigidity are obtained for nondilute suspensions of viscoelastic particles in an oscillatory shear flow.

ISSN:0031-9171    

DOI:10.1063/1.861167

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A perturbation analysis of the capillary instability of an inviscid liquid jet of circular cross section was carried out to third order. The results show that the nonlinear terms are responsible for the presence of satellite drops. The dimensionless cutoff wavenumber, which separates regions of stability and instability, remains unity to third order. The present theory was used in a computer simulation of jet breakup, and it was found that predicted surface wave profiles, disturbance amplification rates and drop sizes are in excellent agreement with the data of previous investigators. New experimental results are presented as additional support of the theory.

ISSN:0031-9171    

DOI:10.1063/1.861168

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Laboratory observations of the interaction between pairs of vortex rings during certain collisions are described. A theory is advanced, based on the resonance of the forced motion with the elliptical mode of oscillation of a single vortex, and is found to be in agreement with the observed behavior.

ISSN:0031-9171    

DOI:10.1063/1.861169

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A technique is described by which the flow properties in a conventional diaphragm shock tube were determined from an analysis of the particle trajectories within the flow. The particle trajectories were obtained by high‐speed photography of smoke tracers placed at 10 cm intervals along the 8 m length of the tube. The subsequent analysis gave the space and time variation of pressure, density, velocity, and temperature of the gas throughout the tube, for a shock of intermediate strength. The results are compared with those made using other measurement devices for pressure and density and it is concluded that the technique gives the flow properties to an accuracy of about 5%. The technique also revealed some aberrations of the flow which had not been detected by other means.

ISSN:0031-9171    

DOI:10.1063/1.861170

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A theory is developed for inviscid supersonic flow past blunt bodies of revolution containing small spherical cloud particles of uniform size. It is assumed that there are no collisions between the particles. The only interactions between the gas and the particles are drag force and heat exchange. The problem is solved by using the direct method of a given body and the technique of series truncation. The convergence of the series is improved by recasting it in a modified Euler transformation. It is found that the relaxation zone is much larger than the shock layer thickness, hence the flow is nonequilibrium in the entire subsonic region. The solutions for the case without the particles agree with the known blunt‐body solutions, and those with the particles resemble the known dusty air solutions behind a normal shock wave.

ISSN:0031-9171    

DOI:10.1063/1.861171

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The results of the two‐dimensional numerical simulation of an ideal magnetohydrodynamic high beta shock tube plasma with a magnetic dam are presented. The dam is created by an external coil and drives into the plasma behind the shock, preventing the immediate loss of the shock‐heated plasma. The problem corresponds mathematically to a hyperbolic transverse flow plasma region coupled across several free boundaries to various elliptic vacuum regions, and is solved using a particle code for the plasma dynamics, and over relaxation for the vacuum regions. The results obtained show that such a dam will lengthen the lifetime of the shock‐heated plasma.

ISSN:0031-9171    

DOI:10.1063/1.861172

出版商:AIP    

年代:1975

数据来源: AIP