Catálogo de publicaciones - libros

Large Eddy Simulations of passive heat transfer in a turbine cascade with and without oncoming wakes have been performed. The computational geometry is chosen in accordance with previous experiments performed by Liu and Rodi in Karlsruhe. Oncoming wakes are found to influence the heat transfer between the outer flow and the turbine blades. The computations were carried out using 64 processors on the Hitachi-SR8000 F1.

To control the reaction progress in supersonic combustors the fuel/air mixing has to be optimized which is investigated numerically in this paper. The mixing process is strongly influenced by the design of the fuel strut injector. Optimization studies may help to improve the mixing efficiency of real size scramjet (supersonic combustion ramjet) engines. The strut design used in this paper is the result of previous experimental and numerical investigations [, , ]. It has been verified that the use of lobed strut injectors improves the mixing by generation of streamwise vortices in the core region of the combustion chamber. The present study compares two different nozzle exit designs using basically the same strut shape. 295 K cold hydrogen is injected with Mach 2.0 into a 1300 K hot Mach 2.0 supersonic air flow.

The aerodynamic performance, maneuverability and flight stability of air-crafts operating in the transonic regime are highly dependent on the deformation of their wings under aerodynamic loads. The accurate prediction of aeroelastic properties, such as aeroelastic equilibrium configurations under cruise conditions, is therefore crucial in early design stages. Due to increasing computer power and further development of numerical methods, direct numerical aeroelastic simulation, in which the governing equations for the fluid and the structure are solved consistently in time, has become feasible.

The project NHLRes ([], []) is concerned with the simulation of aircraft aerodynamics and thus belongs to the research field of computational fluid dynamics (CFD) for aerospace applications. NHLRes comprises the numerical simulation of the viscous flow around transport aircraft high lift configurations based on the solution of the Reynolds-averaged Navier-Stokes equations. The project NHLRes consists of five parts representing the analysis of complex 3D-flow features, wake vortex simulation, optimization for three-dimensional high lift flow, aerodynamic interactions between the propeller and high lift wings and finally the usage of large eddy simulation (LES) of the flow around high lift configurations.

The present annual report summarises ongoing investigations performed at the Institut für Industrielle Fertigung und Fabrikbetrieb Universität Stuttgart (IFF) on the numerical simulation of spray painting in the automotive industry. Two examples, i.e. powder coating simulation using a corona spray gun and spray-painting simulation with high-speed rotary bell are showed. Numerical models for electrostatically supported painting processes were implemented in Fluent, a commercial CFD code based on an unstructured finite volume mesh. These models account for all important effects involved in the relevant physical processes, being able to predict the film thickness distribution and the paint transfer efficiency on the work piece. The calculations were carried out using VOLVOX-Cluster in the High Performance Computing Center Stuttgart.

In the last decades, tremendous progress has been made in the area of numerical methods and computer technology but also new experimental techniques evolved and have been transferred to new application areas. This article describes the combination of two recent and innovative techniques. On the numerical side, the lattice Boltzmann method (LBM) is used for detailed simulations of the flow in complicated 3-D structures. On the experimental side, the principles of nuclear magnetic resonance (NMR) are exploited to scan the 3-D structure of arbitrary objects (e.g. random packings of spheres) with a resolution of about 0.1 mm or better (magnetic resonance imaging, MRI) and to obtain information about the velocity of the fluid in selected planes of the same object. The combination of both methods allows for the first time with justifiable effort to investigate in 3-D and on a local level exactly the same arbitrarily complicated structures experimentally and numerically. This can be utilized first to validate the methods and results mutually, second to detect artifacts, but also third to replace or complement experimental investigations by “numerical experiments” on high performance computers which can provide a larger amount of detailed 3-D information with less effort.

The 3D Parallel-Multiblock URANUS code has been extended by models for radiative exchange between the surface elements and for heat conduction within the TPS (Thermal rotection ystem). The coupling of the newly developed models with catalytic effects for the real TPS, predicted by a global catalysis model, and with temperature dependent emissivity leads to significant differences in surface temperature distribution. Results for the X-38 re-entry vehicle will be discussed in some detail. Large memory and computational time requirements arise in order to solve the non-equilibrium Navier-Stokes equations on 1.02 million cells coupled with the surface models.

Chemistry is a science of change. At the heart of a chemical reaction, chemical change happens through the formation of new bonds (and breaking of of old ones). Properties such as the electronic and geometric structure of molecules and their energies are relevant to chemistry, but these are still static proper-ties. Chemical reactions on the other hand are dynamic, that is, something happens.

The iron(III) catalyzed Michael reaction works fine with simple enones, but other Michael acceptors such as acrylic acid methyl ester did not show any reactivity in the experiments done so far. Therefore we performed quantum chemical computations to assess the reactivity of various quite different Michael acceptors. Since previous studies showed that the C-C bone forming step most likely occurs at a mononuclear iron center with two dionato ligands, the barrier heights of such steps have been calculated with hybrid density functional methods. A mixed anhydride of acrylic acid and trifluoroacetic acid was identified as a very promising candidate to carry out further experiments.

Quantum chemical calculations at the MP2/[aug]-cc-pVDZ level were used to generate a two-dimensional potential energy surface for an unusual double proton transfer reaction in which the region around the transition state is characterized by a plateau of almost constant energy. A cut of the first electronically excited singlet state potential energy surface along the ground-state reaction path was computed using time-dependent density functional theory. In addition, solvent effects which lead to significant changes of the surface were studied using a self-consistent reaction field approach.