2D and 3D Turbulent Fluctuations in Open Channel Flow with Re τ = 590 Studied by Large Eddy Simulation

Well-resolved 3D Large Eddy Simulations (LES) are presented for open channel flow at a Reynolds number Re _τ  = 590 based on friction velocity u _τ and water depth h. The results are depth-averaged and thereby information is obtained on the 2D horizontal fluctuations in the channel. The total turbulence is decomposed into 2D and 3D fluctuations and the energy content of these as well as their spectral distribution is studied. It is found that only 15% of the fluctuating energy is contained in the 2D fluctuations and that these are mostly of scales larger than the water depth while the 3D fluctuations are restricted by the limited vertical extent of the water body and have scales smaller than the water depth. Information is obtained on the dispersion terms arising from the depth-averaging procedure, and scalar transport due to a vertical line source of tracer is studied thereby investigating the contribution of the 2D and 3D fluctuations to the transverse mixing of the scalar.     

A two-parameter model of turbulence,and its application to free jets

A model of turbulence is investigated in which the Reynolds stress appearing in the momentum equation is calculated from the expression \(\overline {u'\upsilon '} = - \sqrt k L(\partial U/\partial y)\) ; the kinetic energy, k, and the length scale,L, of turbulence are determined from differential transport equations for these quantities. These equations are solved for various free-jet situations, and the empirical constants involved are adjusted so as to give best agreement between predictions and experimental results. The plane mixing layer, the plane jet and the radial jet can be predicted with a single set of constants; for the round jet a different set has to be used. This suggests a dependence of the otherwise universal constants on the ratio ofL to the radiusr. Comparisons are presented of predicted and measured rates of spread, profiles forU, k and \(\overline {u'\upsilon '} \) , and energy balances. For most cases the agreement is within the experimental accuracy.     

Computation of axisymmetric confined jets in a diffuser

The paper reports on a numerical study of turbulent confined jets in a conical duct with a 5° divergence. The flow has a large ratio of jet to ambient velocities at the entrance so that it gives rise to strong recirculation. The calculations are carried out with a general finite volume method designed for calculating incompressible elliptic flows with complex boundaries. Turbulence is simulated by the standard κ–? model. The sensitivity of the solution to numerical discretization errors is examined using three convection schemes, i.e. hybrid central/upwind differencing, QUICK and SOUCUP, on two grids consisting of 68 × 50 and 102 × 82 points respectively. An examination is also made of the influence of inlet boundary conditions on the predicted flow field. The computed results are compared with experimental data for mean axial velocity, turbulent shear stress and turbulent kinetic energy profiles. It is shown that the calculations reproduce the essential features of the flow observed in the experiments.     

BIS- (N-ACY L-2-THIO-193,2-DIAZAPHOSPHO LINES), NOUVEAUX COMPLEXANTS PHOSPHORÉS D'IONS ALCALINO-TERREUX

Abstract

Nous décrivons la synthèse en quatre étapes de nouveaux 1,3-dihydrobenzodiazaphospholes 3 et 6a-c dont la particularité est de posséder un (3) ou deux (6a-c) motifs N-acyl-diazaphospholines. Seuls les ligands 6a-c présentent des propriétés complexantes vis-à-vis des ions alcalino-terreux. observables par spectrométrie IR et UV.

We describe a four step synthesis of new 1,3-dihydrobenzodiazaphospholes 3 and 6a-c which posses one (3) or two (6a-c) N-acyl diazaphospholine moieties. Only the formation of alkaline-earth cation complexes, with 6a-c has been observed by IR and UV spectroscopies.     

2,4-Dioxo(dimercapto)-1,5-benzodiazepino-13-couronne-2, Nouveau Macrocycle Complexant de L'ion Ag +

We describe herein the synthesis of new macrocycles 5 et 6 derived from 1,5-benzodiazepine-2,4-dione in a heterogenous media using phase transfer catalysis conditions. A crystallographic study by x-ray of 5 was carried out to confirm the structure suggested; moreover the macrocycle 6 presents chelating properties with respect to the ion Ag + easily observed by IR and UV spectroscopies.     

SYNTHESE DE NOUVEAUX SYSTEMES CONDENSES RENFERMANT LE 1,2,4-TRIAZOLE,LA 1,3-THIAZINE,LA 1,3-THIAZEPINE ET LA 1,3,5,7-DITHIADIAZOCINE

Une nouvelle voie de synthèse de systèmes hétérocycliques soufrés possédant le motif 1,2,4-triazole a été décrite. La réaction mise au point repose sur des conditions de la catalyse par transfert de phase solide-liquide.

Mots-clés: 1,2,4-Triazole-5-thione; 1,3,5,7-dithiadiazocine; catalyse par transfert de phase; rayons-X; thiazépine; thiazine

In this article, we described a novel route to heterocyclic systems derived from 1,2,4-triazole. The reactions were performed in heterogenous media using a phase transfer conditions.