A negatively-buoyant jet discharged horizontally into an ambient fluid at res in a large rectangular water tank has been investigated numerically using a non-isotropic Smagorinskii model of the large eddy simulation (LES). The turbulent jet discharged continuously out of a straight horizontal nozzle with a square cross-section spreads so that it mixes with the surrounding fluid and gradually sinks down as it moves forward. The purpose of this work is to clarify the dynamical structure of such a spreading jet consisting of a heavier fluid numerically. The analysis has been carried out for two cases of the ambient fluid : (1) homogeneous, and (2) stably stratified. The validity of the present numerical method for analyzing the negatively-buoyant turbulent jet is first confirmed by comparing a numerical result for the case (1) with the experimental one by Davies and Ahmed⁹⁾ . In case (2), the paths as well as forms of the jet and the velocity distributions in the spreading jet are found at different values of a parameter (1m /h) depending on the initial velocity and density of a discharged jet. The analysis shows that an initially negatively-buoyant jet can take a complicated path as it becomes neutrally-buoyant by entraining the surrounding fluid. The effects of the background density gradient on the jet forms are also clarified when 1M/h is constant.

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This paper describes a computational parametric study showing how the preceding heat release position affects aerodynamic characteristics of a hemisphere in a hypersonic flow. A thermal and chemical nonequilibrium viscous flow is assumed. For this purpose, finite-rate chemical reactions with seven species are considered to treat chemical non-equilibrium. Park's two temperature model is used to take account of thermal non-equilibrium. Results show that an increase in the distance between heat release and hemisphere causes both the drag and the amount of heating rate to decrease monotonically. These reductions saturate when the distance becomes longer than 14 times the radius of the hemisphere.

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In order to reveal the underlying statistics describing properly the fully developed turbulence, the probability density function of the local dissipation is derived by taking extremal of a generalized entropy (Tsallis entropy). It is shown that the scaling exponent ζ_m of velocity structure function, determined non-perturbatively with the help of the derived probability density function, explains experimental data very well. It is also revealed that the asymptotic expression of ζ_m for m >> 1. has a log term. The present analysis strongly suggests that the underlying statistics of fully developed turbulence is the non-extensive one.

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