Abstract:The bimetallic ruthenium complex [(1,3,5-i-Pr 3 C 6 H 3 )Ru(m-Cl) 3 RuCl(C 2 H 4 )(PCy 3 )] has been synthesized by reaction of [(1,3,5-i-Pr 3 C 6 H 3 )RuCl 2 )] 2 with one equivalent of PCy 3 in the presence of ethylene. It can be used as a catalyst precursor for the controlled atom transfer radical polymerization of methacrylates at 35 8C. The resulting polymers show low polydispersities.Keywords: acrylates; bimetallic complex; polymerization; radical reaction; ruthenium Starting with seminal publications in the mid 1990s, [1] transition metal-catalyzed atom transfer radical polymerizations (ATRP) have become ubiquitous in modern macromolecular chemistry.[2] For most applications, Cu(I) complexes with amine-based ligands are used as the catalysts.[3] Nevertheless, there are a number of other transition metals which are known to catalyze ATRP reactions.[2] Among those, ruthenium complexes are of special interest because some of them were found to display very high activities. [4,5] In continuation of our efforts to develop new catalysts for ruthenium-catalyzed radical reactions, [5a,6] we have recently described the homobimetallic complex [(cymene)Ru(m-Cl) 3 RuCl(C 2 H 4 )(PCy 3 )] (1). [7] This complex shows an outstanding catalytic activity in atom transfer radical addition (ATRA) reactions. Since ATRP and ATRA are mechanistically closely related, [2] we were interested to see whether complex 1 can also be used for the controlled polymerization of acrylates. Unfortunately, complex 1 showed a very limited solubility in the monomer-toluene starting mixtures. We therefore investigated possibilities to increase the solubility of complex 1. A modification of the p-ligand appeared to be a suitable strategy because the catalytically relevant RuCl 2 (C 2 H 4 )(PCy 3 ) fragment would not be directly affected. Consequently, the well-soluble dimer [(1,3,5-i-Pr 3 C 6 H 3 )RuCl 2 ] 2 (2) [8] was chosen as the starting material. When a solution of complex 2 in isooctane was heated to 50 8C with one equivalent of PCy 3 in the presence of an atmosphere of ethylene, the desired bimetallic complex 3 was formed (Scheme 1). The product precipitates from solution and can be isolated by filtration (yield: 90%).The new complex was comprehensively characterized by 1 H and 13 C NMR spectroscopy, elemental analysis and single-crystal X-ray crystallography. The 13 C NMR spectrum of 3 in CD 2 Cl 2 showed two signals of equal intensity for the methyl groups of the i-Pr 3 C 6 H 3 p-ligand. This can be explained by the fact that complex 3 is chiral and configurationally stable on the NMR time scale. The methyl groups are thus diastereotopic. In the 1 H NMR spectrum, however, the difference between the two CH 3 groups was not resolved and only one doublet was observed at d ¼ 1.39 ppm. In order to avoid partial dissociation of the labile ethylene ligand, all spectra were recorded under an atmosphere of C 2 H 4 . Analysis of complex 3 by X-ray crystallography confirmed the expected dinuclear structure with three chloro bridges (Fi...

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In this paper, the modelling of leakages through a compressor stator penny cavity, and their effect on the aerodynamics within the compressor are studied. The penny, sometimes also referred to as ‘button’, is the cylindrical platform feature of a variable stator normally found between a vane’s airfoil and spindle. The pennies nominally lie recessed into the compressor endwalls at hub and casing, with a surrounding clearance to ensure the vane’s stagger angle can be adjusted. RANS-simulations, with these clearances included, have shown a significant impact from the penny cavity leakages on compressor efficiency and surge line. Neglecting this secondary flow path through the penny cavities results in an under prediction of the losses close to the endwalls. The prediction of the penny cavity effect on the stator row is based on a Reynolds-Averaged-Navier-Stokes (RANS) study, using a hybrid structured-unstructured mesh to provide adequate resolution of the local flow phenomena. The complex geometry and pressure field result in flows that are unevenly distributed within the penny cavity. The outflow or leakage is focused in a concentrated area leading to a high local velocity that strongly impacts the stator losses and turning. Since such geometries lie beyond the normal validated cases, the modelling uncertainties are discussed and the plausibility of the results is checked. In order to provide an experimental database and validate the turbulent mixing of leakage and main flow, which is seen as the main contributor to loss production, a validation test case — ‘Jet-In-Crossflow’ was chosen. As well as the standard RANS code, this validation case was run as a time-accurate high-order Lattice Boltzmann (LBM) simulation (PowerFLOW), using Very-Large-Eddy-Simulation (VLES) turbulence modelling. The LBM simulation showed significant unsteady flow features and was considerably closer to the test data than the RANS calculations. A future test campaign, currently being prepared at the annular cascade test facility of the Institute of Jet Propulsion and Turbomachinery (IST) at RWTH Aachen university, will be briefly presented. This focuses on investigating the penny flows in a typical engine design.

Film Cooling is a crucial technology for engine manufacturer to develop high-efficiency gas turbine engines by raising turbine entry temperature. A lot of cooling holes geometries have been studied in the past few years in tests, as well as numerical simulations. Shaped holes are nowadays a standard geometry for protecting the blades, given the performance improvement compared to cylindrical holes. Numerical correlation with physical tests is challenging due to the high sensitivity to thermal mixing and adequate boundary condition predictions. This paper is devoted to numerical simulation comparisons of the 777 shaped holes configuration of Pennsylvania State University, for an incompressible flow with a density ratio of 1.5, a blowing ratio of 1.5 and a free stream turbulence intensity of 0.5%. Two different simulations have been chosen: a state-of-the-art RANS simulation with k-e Realizable model computed with ANSYS Fluent and a high fidelity solver Lattice-Boltzmann Method computed with Simulia PowerFLOW. In order to improve the accuracy of numerical simulations against test results, this article deals with an aerothermal model of the complete test bench. This additional modeling allows to strongly improve thermal prediction and to understand initial discrepancies related to test bench environment. Results show that k-ε Realizable simulation provides a good prediction of average effectiveness, but local differences appear due to inherent RANS modeling limitations. On the other hand, LBM simulation provides excellent results for both aerodynamic and thermal quantities: tests results are very well reproduced.

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