IUTAM Symposium on Variable Density Low-Speed Turbulent Flows

The General Assembly of the International Union of Theoretical and Applied Mechanics in its meeting on August 28, 1994, selected for 1996 only four Mechanics Symposia, of which ours is the only one related to Fluid Mechanics: Variable Density Low Speed Turbulent Flows. This IUTAM Symposium, organized by the Institut de Recherche sur les Phenomenes Hors Equilibre (Marseille), is the logical continuation of the meetings previously organized or co-organized - on the French or European level, such as Euromech 237, Marseille, 1988 - by the same research group ofMarseille. This meeting focused specifically on the structure of turbulent flows in which density varies strongly : the effect of this variation on the velocity and scalar fields is in no sense negligible. We were mainly concerned with low-speed flows subjected to strong local changes of density as a consequence of heat or mass transfer or of chemical reactions. Compressible turbulent flows - such a!" supersonic ones - were also considered in order to underline their similarities to and their differences from low-speed variable density flows.

Klappentext

This book contains the proceedings of an IUTAM Symposium on turbulent flows at low Mach number, in which fluctuations in density occur as a result of heat transfer or of mixing of different fluids. Such flows occur in the atmosphere, the ocean, and in chemical engineering. In addition, in combustion large fluctuations in density occur as a result of heat release; the flows that are considered here do not involve heat release, for the most part, but the variable density flows that are considered can serve as a paradigm for many of the problems that arise in combustion as a result of the density fluctuations. Compressible flows - such as supersonic ones - are also considered in order to underline their similarities to and their differences from low-speed variable density flows. The book will be of interest to mechanical, aerospace, civil, and chemical engineers, meteorologists and oceanographers - in fact, anyone who deals with fluids in which fluctuations of density occur. The book will be accessible to professional and graduate students. There are no other works that deal with this interesting area.

Inhalt
I. Instabilities.- Instabilities and bifurcations in variable density flows.- Global self-excited oscillations in a two-dimensional heated jet : a numerical simulation.- Mixing behavior of absolutely unstable axisymmetric shear layers forming side jets.- Influence of density contrast on instability and mixing in coaxial jets.- A wake behind a heated cylinder at small Mach numbers : bifurcations of the vortex street and potentialities of acoustic diagnostics.- Experimental study of the Benard-Karman instability downwind of a heated cylinder.- Direct simulation of multiphase flows with density variations.- Self-turbulent flame simulation by a cellular automaton.- II. Modelling and Experiments.- Some problems on single point modelling of turbulent, low-speed, variable density fluid motions.- Turbulent kinetic energy in variable density jets and the modelling issue.- Second-order turbulence modelling and numerical simulation of volume variable turbulent flows.- Second order modelling of variable density jets : Favre averaged closures versus Reynolds averaged closures.- Averaging procedures for the large eddy simulation of variable density flows.- Numerical predictions of mixing phenomena in turbulent variable density flows with second-order closure turbulence models.- Variation of the effective nozzle diameter in round turbulent jets with variable density.- Mixing in coaxial jets with large density differences.- Forces on bodies moving in a weak density gradient without buoyancy effects.- Experimental investigation of the interaction between scalar dissipation and strain rate in a counterflow geometry.- Analytical solution of the equation for the probability density function of a scalar in decaying grid-generated turbulence with a uniform mean scalar gradient.- Pdf and highest concentration evolution in turbulent jets.- III. Modelling and Experiments. Buoyancy Effects.- Turbulent transfer modelling in turbulent flows with density variations and buoyancy forces.- Buoyancy-generated variable-density turbulence.- Turbulence structure and its modelling of a natural convection boundary layer.- Turbulent structure in horizontal channel flow under unstable density stratification.- Second order modelling of incompressible turbulent buoyant flows : some comments on the maximum principle.- Variable density effects in axisymmetric turbulent jets and diffusion flames.- Numerical modelling of turbulent convective heat and mass transfer in two-layer systems.- An experimental investigation of quasi-2D turbulence with or without buoyancy effects.- Penetrative convection in water near 4°C.- IV. Modelling and Experiments. Industrial Applications.- Studying and modelling variable density turbulent flows for industrial applications.- V. Experiments and Measurement Methods.- Optical diagnostics for flows with density variations.- Large scale characterisation of the concentration field of supercritical jets of hydrogen and methane.- Unsteady measurement of static pressure, velocity and temperature in the vicinity of the nozzle in a vacuum-wind-tunnel.- Improvement of the response of a fine cold-wire for the measurement of high-frequency temperature fluctuations.- Measurements of velocity in the turbulent stage of gaseous mixtures induced by shock waves.- VI. Compressible Flows.- Flows with density variations and compressibility: similarities and differences.- Balance of kinetic energy in a supersonic mixing layer compared to subsonic mixing layer and subsonic jets with variable density.- Compressibility versus density variations and the structure ofturbulence : a viewpoint from experiments.- A numerical method for computing flows for arbitrarily small and medium Mach numbers.- On density and pressure fluctuations in uniformly sheared compressible flow.- A structural approach to the effects of compressibility in turbulent flows subjected to external compression or high shear.- Conclusion.- Concluding remarks.- List of Participants.- Author Index.