DIRECT NUMERICAL SIMULATIONS OF MULTIPHASE FLOWS

INTRODUCTIONMultiphase and multifluid flows are commonin many natural and technologically importantprocesses. Rain,spray combustion,spray paint-ing,and boiling heat transfer are just a few ex-amples.While it is the overall,integral charac-teristics of such flows that are of most interest,the global behavior is determined to a large de-gree by the evolution of the smallestscales in theflow.The combustion of sprays,for example,depends on the size and the number density ofthe drops.Generally…     

Estimation of moving heat sources with a three-dimensional unsteady inverse method

This study aims at estimating a moving heat source with a three dimensional inverse model and a high spatial resolution. In order to cope with the large amount of computations required in the three dimensional case, a linear unsteady inverse model based on the principle of superposition has been made. Two concepts are used to reduce the computation time: the first is linked to the diffusion time of the heat, and the second to the redundancy of information. Firstly, numerical tests are presented. Then, a laboratory experiment, consisting in the estimation of the flux of a moving laser beam, is described.     

Updated Review of Planetary Atmospheric Electricity

This paper reviews the progress achieved in planetary atmospheric electricity, with focus on lightning observations by present operational spacecraft, aiming to fill the hiatus from the latest review published by Desch et al. (Rep. Prog. Phys. 65:955–997, 2002). The information is organized according to solid surface bodies (Earth, Venus, Mars and Titan) and gaseous planets (Jupiter, Saturn, Uranus and Neptune), and each section presents the latest results from space-based and ground-based observations as well as laboratory experiments. Finally, we review planned future space missions to Earth and other planets that will address some of the existing gaps in our knowledge.     

Asymmetric precipitation in a coronal loop as explanation of a singular observed spectrum

Almost 10 years of solar submillimeter observations have shown new aspects of solar activity, such as the presence of rapid solar spikes associated with the launch of coronal mass ejections and an increasing submillimeter spectral component in flares. We analyse the singular microwave–submillimeter spectrum of an M class solar flare on 20 December, 2002. Flux density observations measured by Sun patrol telescopes and the Solar Submillimeter Telescope are used to build the radio spectrum, which is fitted using Ramaty’s code. At submillimeter frequencies the spectrum shows a component different from the microwave classical burst. The fitting is achieved proposing two homogeneous sources of emission. This theoretical fitting is in agreement with differential precipitation through a magnetically asymmetric loop or set of loops. From a coronal magnetic field model we infer an asymmetric magnetic structure at the flare location. The model proposed to quantify the differential precipitation rates due to the asymmetry results in a total precipitation ratio Q₂/Q₁≈10⁴–10⁵, where Q₁(Q₂) represents the total precipitation in the loop foot with the high (low) magnetic field intensity. This ratio agrees with the electron total number ratio of the two sources proposed to fit the radio spectrum.     

Composition of Interstellar Neutrals and the Origin of Anomalous Cosmic Rays

Knowledge of the elemental composition of the interstellar gas is of fundamental importance for understanding galactic chemical evolution. In addition to spectroscopic determinations of certain element abundance ratios, measurements of the composition of interstellar pickup ions and Anomalous Cosmic Rays (ACRs) have provided the principal means to obtain this critical information. Recent advances in our understanding of particle acceleration processes in the heliosphere and measurements by the Voyagers of the energy spectra and composition of energetic particles in the heliosheath provide us with another means of determining the abundance of the neutral components of the local interstellar gas. Here we compare the composition at the termination shock of six elements obtained from measurements of (a) pickup ions at ～5 AU, (b) ACRs in the heliosphere at ～70 AU, and (c) energetic particles as well as (d) ACRs in the heliosheath at ～100 AU. We find consistency among these four sets of derived neutral abundances. The average interstellar neutral densities at the termination shock for H, N, O, Ne and Ar are found to be 0.055±0.021 cm^?3, (1.44±0.45)×10^?5 cm^?3, (6.46±1.89)×10^?5 cm^?3, (8.5±3.3)×10^?6 cm^?3, and (1.08±0.49)×10^?7 cm^?3, respectively, assuming the He density is 0.0148±0.002 cm^?3.     

Equivalent Electric Circuit Models of Coronal Magnetic Loops and Related Oscillatory Phenomena on the Sun

Coronal loops, which trace closed magnetic field lines, are the primary structural elements of the solar atmosphere. Complex dynamics of solar coronal magnetic loops, together with action of possible subphotospheric dynamo mechanisms, turn the majority of the coronal loops into current-carrying structures. In that connection none of the loops can be considered as isolated from the surroundings. The current-carrying loops moving relative to each other interact via the magnetic field and currents. One of the ways to take into account this interaction consists in application of the equivalent electric circuit models of coronal loops. According to these models, each loop is considered as an equivalent electric LCR-circuit with variable inductive coefficients L, capacitance C, and resistance R, which depend on shape, scale, position of the loop with respect to neighbouring loops, as well as on the plasma parameters in the magnetic tube. Such an approach enables to describe the process of electric current dynamics in the groups of coronal loops, as well as the related dynamical, energy release and radiation processes. In the present paper we describe the major principles of LCR-circuit models of coronal magnetic loops, and show their application for interpretation of the observed oscillatory phenomena in the loops and in the related radiation.     

Method for the annular gas-liquid mixture flow regime in a vertical cylindrical channel

A mathematical model for the annular gas-liquid mixture flow in the cylindrical channel is described. The influence of an upward turbulent gas flow on the downward liquid film is considered. The problem is numerically solved and the calculation results are compared with the experimental data.     

Vibrations of circular sandwich plates connected with an elastic foundation

The results of analyzing axisymmetric forced vibrations of an elastic circular sandwich plate connected with an elastic foundation under different surface loads are presented. The hypotheses of a broken normal are accepted to describe the kinematics of a package that is nonsymmetrical over the thickness. The analytical solutions of a problem for plates with a light filler are obtained and numerical analysis is carried out.     

Calculation of an unsteady jet flow around the plate cascade

In the framework of the general theory for unsteady weakly disturbed fluid flows with free boundaries, a problem is solved to calculate a jet flow around the cascade of plates executing the harmonic oscillations. We developed a program that enables us for the first time to carry out systematic calculations of flow characteristics depending on arbitrary values of determining parameters.     

Some possible techniques for improving the strength characteristics of folded cores from sheet composite materials

We consider some general problems of improving the strength characteristics of folded cores as well as the corresponding techniques for modifying the core material polymer surfaces with the use of nanotechnologies and the “mass-strength” criteria.