Review of numerical simulations for high-speed, turbulent cavity flows

High speed flows inside cavities are encountered in many aerospace applications including weapon bays of combat aircraft as well as landing gear. The flow field inside these cavities is associated with strong acoustic effects, unsteadiness and turbulence. With increasing emphasis on stealth operation of unmanned combat air vehicles and noise concerns near airports, cavity flows attracted the interest of many researchers in aerodynamics and aeroacoustics. Several attempts were made using wind tunnel experimentation and computational fluid dynamics analyses to understand the complex flow physics associated with cavity flows and alleviate their adverse effects via flow control. The problem proved to be complex, and current research revealed a very complex flow with several flow phenomena taking place. With the aid of experiments, CFD methods were validated and then used for simulations of several cavity configurations. The detached-eddy and large-eddy simulation methods proved invaluable for these studies and their application highlights the need for advanced turbulence simulation techniques in aerospace. The success of these methods and a summary of the current status of the experimental and computational progress over the past twenty years is summarised in this paper.     

Observations of auroral kilometric radio emission on the <Emphasis Type="Italic">Interball-1</Emphasis> satellite in the active Sun period 1999–2000

Results of almost two years (January 1999–October 2000) of continuous observations of auroral kilometric radio emission with the instrument AKR-X onboard the high-apogee satellite of the Earth Interball-1 are presented. The observations were conducted at the growth stage (in 1999) and in the maximum (2000) of solar activity within the 100–1500 kHz frequency band. The results of AKR detection in the vicinity of the maximum of its spectrum at a frequency of 252 kHz are presented. Both similarity (for example, the character of global directivity) and important differences from the AKR emission observed during the solar activity minimum [5] are found. Together with very high sporadicity, strong seasonal changes in the intensity are typical for the emission. It is completely absent in the spring-summer period in the Northern Hemisphere and is strongly suppressed in this period in the Southern Hemisphere. Probable nature of these features of AKR is discussed.     

Kink-like mode of a double gradient instability in a compressible plasma current sheet

A linear MHD instability of the electric current sheet, characterized by a small normal magnetic field component, varying along the sheet, is investigated. The tangential magnetic field component is modeled by a hyperbolic function, describing Harris-like variations of the field across the sheet. For this problem, which is formulated in a 3D domain, the conventional compressible ideal MHD equations are applied. By assuming Fourier harmonics along the electric current, the linearized 3D equations are reduced to 2D ones. A finite difference numerical scheme is applied to examine the time evolution of small initial perturbations of the plasma parameters. This work is an extended numerical study of the so called “double gradient instability”, – a possible candidate for the explanation of flapping oscillations in the magnetotail current sheet, which has been analyzed previously in the framework of a simplified analytical approach for an incompressible plasma. The dispersion curve is obtained for the kink-like mode of the instability. It is shown that this curve demonstrates a quantitative agreement with the previous analytical result. The development of the instability is investigated also for various enhanced values of the normal magnetic field component. It is found that the characteristic values of the growth rate of the instability shows a linear dependence on the square root of the parameter, which scales uniformly the normal component of the magnetic field in the current sheet.     

HORACE: A compact cold atom clock for Galileo

HORACE (HOrloge à Refroidissement d’Atomes en Cellule = clock based on atoms cooled from vapour cell) is a compact cold caesium atom clock developed in SYRTE at Paris Observatory. This clock can operate both on ground and in microgravity environment. Design of HORACE is based on isotropic light cooling, allowing performing the whole clock sequence (cooling, atomic preparation, Ramsey interrogation and detection) at the same place. Compared to more conventional cold atom clocks such as atomic fountains, the use of isotropic light cooling simplifies both the optical part of the setup and the detection sequence, and leads to a drastic size reduction of the physics package. Very good short-term performances have been demonstrated at SYRTE since relative frequency instability of 2.2 × 10⁻¹³ τ^−1/2 has been obtained. Optimization of the long term stability is still under progress and current results show relative frequency instability around 3 × 10⁻¹⁵ in 10⁴ s of integration. With these performances, HORACE appears as a good candidate both for Galileo’s ground segment clock and for onboard Galileo clock.     

Optical Processing Techniques for Simultaneous Pulse Compression and Beam Sharpening

A technique is described in which the separate techniques of beam sharpening (by synthetic antenna methods) and pulse compression are converted into a single two-dimensional operation, which is carried out with a coherent optical processor.     

On the concept of a future carrier-based light fighter

The peculiarities of future light fighter concept generation, reflecting tendencies of fighter aviation development and potentialities of scientific and research background are considered.     

Study of isotropic shell survivability by the analytical method

Shells with a through-thickness macrocrack are considered. The algorithms for determining the specific radius r _c in the crack-tip vicinity, the limiting load p _c (the attainment of which makes the crack unstable), and the direction of macrocrack growth θ _c are presented. We study the carrying capacity of a lengthy circular cylindrical shell under the internal pressure and with an arbitrarily oriented macrocrack.     

Some peculiarities of the wave beams in wireless power transmission

Some wave beam peculiarities which usually are wasted are useful in wireless power transmission systems. These peculiarities-the focusing of the beam, the taper distribution of the radiating field, and the discontinuous antenna-are discussed     

Structural regularities of stress-strain state variations in a hardened surface of turbine blade roots at service conditions

Some results obtained in the course of structural investigations with the use of the methods of scanning electron microscopy and X-ray structure analysis of operating temperature influence upon dynamics of the hardened state relaxation in the turbine blade roots are discribed. Also considered are the data on determining the residual surface stresses by Davidenkov’s method and that of the X-ray diffractometry.