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The flow field of a rectangular jet with a 2:1 aspect ratio was studied at a Reynolds number of 100,000 (Mach number 0.09) using three-dimensional laser Doppler velocimetry (LDV). Velocity gradients, Reynolds stress tensor components, and scalar eddy viscosities are presented for the major and minor axis planes of the jet. The eddy viscosity model was found to be applicable only in the direction of maximum mean velocity gradient.
The effects of lateral variations in the earth mantle viscosity, due to temperature- or stress-dependent rheology, on the long-wavelength geoid anomalies are examined. Results from simple perturbation theory combined with findings from numerical models for convective flow led to a conclusion that the geoid due to the very longest wavelength convective patterns (l = 2,3) on earth is probably not seriously contaminated by lateral variations due either to temperature or stress dependence. Considerable contamination of the higher-degree geoid (l value of no less than 4) is to be expected due to lateral viscosity variations in phase with the fundamental convection scale length.
A main disadvantage of using spectral methods for nonlinear conservation laws lies in the formation of Gibbs phenomenon, once spontaneous shock discontinuities appear in the solution. The global nature of spectral methods than pollutes the unstable Gibbs oscillations overall the computational domain, and the lack of entropy dissipation prevents convergences in these cases. The Spectral Viscosity method, which is based on high frequency dependent vanishing viscosity regularization of the classical spectral methods is discussed. It is shown that this method enforces the convergence of nonlinear spectral approximations without sacrificing their overall spectral accuracy.
Neutron viscosity is investigated as a possible mechanism for the dissipation of kinetic energy into luminosity in the innermost parts of accretion disks around compact objects. Simplified models are presented of the self-consistent, steady-state accretion flows in which viscosity is provided by neutron collisions with accreting ions. Ion temperatures are determined by balancing the heating of ions by viscous dissipation to their cooling by Coulomb collisions with the electrons, providing a self-consistent solution between neutron production and their impact on energy dissipation. The results indicate that neutrons can indeed provide the necessary dissipation to sustain the steady-state accretion of matter at rates of about 10 to the -8th solar mass/yr or less, and electron temperatures of about 100 keV-1 MeV. Neutrons thus present a promising way of modeling bright Galactic X-ray sources.
The extensive numerical modelling of transport phenomena was performed for the melt growth of mercury cadmium telluride. To increase the fidelity of modelling the kinematic viscosity of liquid Hg(1-x)Cd(x)Te was determined at various compositions in the range of x between 0 and 0.2 and at temperatures around and below the respective melting point. The phase diagram of Hg(1-x)Cd(x)Te shows that for this range the melting point varies from 670 C for pure HgTe to 790 C at x=0.2. The vapor pressure above the melt varies correspondingly from 15 to about 40 atm. Hence, the measurement of viscosities in this system requires a technique that allows for combinations of high temperatures and pressures. In addition, a closed isothermal system is required. The high pressure melt container must also be inert to molten Hg(1-x)Cd(x)Te to avoid possible errors from contamination of the liquid. A novel technique that largely circumvents the above experimental problems is described. Its theory is also presented.
Damped oscillations of a viscous droplet in vacuum or in an inert gas of negligible density are considered. The dependence of the complex decay factor on the properties of the liquid is investigated for the first time, and numerical results are compared with earlier studies for special cases. A new method is developed to determine both surface tension and viscosity from a single experiment in which the damping rate and frequency of oscillations are measured. The procedure to determine surface tension and viscosity from oscillating levitated liquids is outlined, and results presented for various modes of shape oscillations.
The effect of viscosity on a steady, transonic flow for which the inviscid limit has a nodal solution topology near the critical point is investigated. For the accelerating case, viscous solutions tend to repel each other, so that a very delicate choice of initial conditions is required to prevent them from diverging. Only the two critical solutions extend to arbitrarily large distances into both the subsonic and supersonic flows. For the decelerating case, the solutions tend to attract, and so an entire two-parameter family of solutions now extends over large distances. The general effect of viscosity on the solution degeneracy of a nodal topology is thus to reduce or limit it for the accelerating case and to enhance it for the decelerating case. The astrophysical implications of these findings are addressed.
A generalized transport equation is introduced which describes the transport and propagation of cosmic rays in a magnetized, collisionless medium. The equation is valid if the cosmic-ray distribution function is nearly isotropic in momentum, if the ratio of fluid speed to fluid-flow particle speed is small, and if the ratio of collision time to time for change in the macroscopic flow is small. Five independent cosmic-ray viscosity coefficients are found, and the ralationship of this viscosity to particle orbits in a magnetic field is presented.
Information is given in viewgraph form on the present state and future direction of eddy viscosity models. Topics covered include the eddy viscosity dilemma, two-equation models, equations of motion, free shear flows, incompressible free shear flows, model-predicted boundary layer structure, defect layer analysis, the effects of pressure gradients, viscous sublayer structure, wall functions and viscous damping, viscous damping for kappa-omega, the effects of compressibility, perturbation analysis of the wall layer, an alternative compressibility term, unsteady boundary layers, incompressible separation, backstep results, and compressible separation.
One major drawback of the eddy viscosity subgrid-scale stress models used in large-eddy simulations is their inability to represent correctly with a single universal constant different turbulent field in rotating or sheared flows, near solid walls, or in transitional regimes. In the present work, a new eddy viscosity model is presented which alleviates many of these drawbacks. The model coefficient is computed dynamically as the calculation progresses rather than input a priori. The model is based on an algebraic identity (Germano 1990) between the subgrid-scale stresses at two different filtered levels and the resolved turbulent stresses. The subgrid-scale stresses obtained using the proposed model vanish in laminar flow and at a solid boundary, and have the correct asymptotic behavior in the near-wall region of a turbulent boundary layer. The results of large-eddy simulations of transitional and turbulent channel flow that use the proposed model are in good agreement with the direct simulation data.
The mean velocity profile across a fully developed turbulent duct flow is obtained from an eddy viscosity relation combined with an empirical outer region wake function. Results are in good agreement with experiments and with direct numerical simulations in the same flow at two Reynolds numbers. In particular, the near-wall trend of the Reynolds shear stress and its variation with Reynolds number are similar to those of the simulations. The eddy viscosity method is more accurate than previous mixing length or implicit function methods.
The linear stability of the Batchelor (1964) vortex is examined with emphasis on new viscous modes recently found numerically by Khorrami (1991). Unlike the previously reported inviscid modes of instability, these modes are destabilized by viscosity and exhibit small growth rates at large Reynolds numbers. The analysis presented here uses a combination of asymptotic and numerical techniques. The results confirm the existence of the additional modes of instability due to viscosity.
A novel version of the capillary method for viscosity measurements of liquids is presented. Viscosity data can be deduced in a straightforward way from mass transfer data obtained by differential weighing during the gravity-induced flow of the liquid between two cylindrical chambers. Tests of this technique with water, carbon tetrachloride, and ethanol suggest that this arrangement provides an accuracy of about +/- 1 percent. The technique facilitates operation under sealed, isothermal conditions and, thus can readily be applied to reactive and/or high vapor pressure liquids.
I have set myself the task to investigate systematically the laws of motion of a fluid whose viscosity is assumed to be very small. The viscosity is supposed to be so small that it can be disregarded wherever there are no great velocity differences nor accumulative effects.
In order to clarify the viscosity effect some experiments were made in the Gottigen low-pressure tunnel with the Bruhn double-throat Venturi tube. This type of tunnel makes it possible to vary the pressure and thereby the density within wide limits and consequently, to examine the viscosity effect. This, however, did not impair the results because pressure and temperature were determined at different periods.
Both the Earth and Venus have a convecting mantle at the top of which is a relatively strong, mechanical boundary layer. The surface topography and gravity signals which result from the convection within the viscous mantle are modified by the elastic properties of this lithospheric boundary layer. In particular the ability of the lithosphere to support loads and transmit stresses from below is a function of the wavelength of the load--the lithosphere is strong to loading at shorter wavelengths. As a consequence it is usual to expect that long wavelength topography cannot be supported by the mechanical strength of the lithosphere and must be compensated--isostatically or dynamically--within the uppermost mantle or the crust. The flexural rigidity of the lithosphere can therefore be determined by estimating the greatest wavelength at which uncompensated surface topography can be supported, usually by measuring the admittance as a function of wavelength. In fact this procedure for determining the elastic thickness relies upon being able to distinguish topography with underlying support from that supported by the brittle lithosphere on the basis of their each having a characteristic value of the admittance. However, in the presence of lateral viscosity variations in the mantle, it is possible for topography to be generated which is NOT compensated by density anomalies in the underlying mantle at the same wavelength. Although this effect is not likely to be important for the Earth, on Venus, where the high surface temperatures would be expected to give a weaker lithosphere, lateral viscosity variations in the mantle can give a misleadingly large apparent elastic thickness for the lithosphere.
We consider the effects of viscosity on the inviscid stability of the Batchelor vortex in a compressible flow. The problem is tackled asymptotically, in the limit of large (streamwise and azimuthal) wavenumbers, together with large Mach numbers. Previous studies, with viscous effects neglected, found that the nature of the solution passes through different regimes as the Mach number increases, relative to the wavenumber. This structure persists when viscous effects are included in the analysis. In the present study the mode present in the incompressible case ceases to be unstable at high Mach numbers and a center mode forms, whose stability characteristics are determined primarily by conditions close to the vortex axis. We find generally that viscosity has a stabilizing influence on the flow, while in the case of center modes, viscous effects become important at much larger Reynolds numbers than for the first class of disturbance.
An oscillating-cup viscometer was developed to measure viscosity of molten HgZnTe ternary semiconductor alloys. Data were collected for the pseudobinary Hg(0.84)Zn(0.16)Te melt between 770 and 850 C. The kinematic viscosity was found to vary from approximately 1.1 to 1.4 x 10(sup -3)sq cm/s. A slow relaxation phenomena was also observed for temperatures from the melting point of 770 to approx. 800 C. Possible mechanisms for this effect are discussed.