Direct Computations of Boundary Layers Distorted by Migrating Wakes in a Linear Compressor Cascade

A Direct Numerical Simulation (DNS) of flow in the V103 Low-Pressure (LP) compressor cascade with incoming wakes was performed. The computational geometry was chosen largely in accordance with the setup of the experiments performed by Hilgenfeld and Pfitzner (J Turbomach 126:493–500, 2004) at the University of the Armed Forces in Munich. The computations were carried out on the NEC-SX8 in Stuttgart using 64 processors and 85 million grid points. The incoming wakes stemmed from a separate DNS of incompressible flow around a circular cylinder with a Reynolds number of Re _d  = 3300 (based on mean inflow velocity and cylinder diameter). The boundary layer along the suction surface of the blade was found to separate and roll up due to a Kelvin–Helmholtz instability triggered by the periodically passing wakes. Inside the rolls further transition to turbulence was found to occur. The boundary-layer flow along the pressure surface did not separate, instead it underwent by-pass transition.     

Simulation of vortex shedding past a square cylinder with different turbulence models

This paper presents the results of numerical simulations of vortex shedding past a free-standing square cylinder at Re_D=22 000, obtained with different turbulence models. Using wall functions, the standard k–ε model is compared with a modification suggested by Kato and Launder (Proc. 9th Symp. Turbulent Shear Flows, Kyoto, 10-4-1 (1993)). In addition, both versions are used in a two-layer approach, in which the flow close to the cylinder is computed with a locally more suitable one-equation turbulence model and only outside the viscous near-wall layer with the two mentioned high-Re model versions. To allow a comparison, the simulations are performed first using the same computational domain and boundary conditions as in previous investigations. Then results are presented that were obtained on a computational domain and with boundary conditions more suitable for a comparison with the experiments. © 1998 John Wiley & Sons, Ltd.     

Forced Convection Heat Transfer from a Finite-Height Cylinder

This paper presents a large eddy simulation of forced convection heat transfer in the flow around a surface-mounted finite-height circular cylinder. The study was carried out for a cylinder with height-to-diameter ratio of 2.5, a Reynolds number based on the cylinder diameter of 44 000 and a Prandtl number of 1. Only the surface of the cylinder is heated while the bottom wall and the inflow are kept at a lower fixed temperature. The approach flow boundary layer had a thickness of about 10% of the cylinder height. Local and averaged heat transfer coefficients are presented. The heat transfer coefficient is strongly affected by the free-end of the cylinder. As a result of the flow over the top being downwashed behind the cylinder, a vortex-shedding process does not occur in the upper part, leading to a lower value of the local heat transfer coefficient in that region. In the lower region, vortex-shedding takes place leading to higher values of the local heat transfer coefficient. The circumferentially averaged heat transfer coefficient is 20 % higher near the ground than near the top of the cylinder. The spreading and dilution of the mean temperature field in the wake of the cylinder are also discussed.     

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.     

Conformationally restricted goniofufurone mimics with halogen,azido or benzoyloxy groups at the C-7 position: Design,synthesis and antiproliferative activity

A series of new conformationally restricted goniofufurone mimics, bearing an additional 1,3-dioxan ring and a halogen, azido or benzoyloxy functionality at the C-7 position has been designed and synthesized. The Appel reaction was used for replacement of 7-OH group with Cl or Br functions in tricyclic lactone (3). 7-Iodo derivative (3d) was prepared by using the Ph₃P/I₂/2,6-lutidine reagent system. 7-Fluoro group was introduced by treatment of 3 with DAST, while the corresponding 7-azido and 7-benzoyloxy derivatives have been prepared by multistep sequences. Synthesized products were evaluated for their ability to inhibit growth of selected human malignant cell lines. Structure-activity relationships demonstrated that the nature of a substituent at the C-7 position could enhance the antiproliferative activity of the analogues. The preliminary study on the mechanisms indicated that all synthesized compounds induced apoptosis in 61–77% of K562?cells.