Catálogo de publicaciones - libros

In the frame of this work, the numerical investigations of the flow through the VKI turbine cascade were performed by means of Large Eddy Simulation.

The numerical simulation has delivered detailed aerodynamical information as well as showed problems and the importance of a proper mesh generation for LES. The mesh down to the wall and along the wall must be fine enough in order to resolve the expected structures.

The importance of upstream turbulence was underestimated. Therefore, no suitable inlet boundary condition was applied to the simulations. The lack of the upstream fluctuations caused deficiency of the turbulence development in the boundary layer and therefore bypass transition was impossible. In the simulations the transitions proceeded in the natural way, hence the transitions were quieter and the development of the turbulent boundary farther downstream was slower.

At the present times computational resources necessary to perform a (U)RANS simulation of the considered case does not cause a problem. Computations of flows through complex geometries at higher Reynolds numbers with LES are still the challenge for CFD and super computers.

In this project we addresses the nature of host galaxies of gammaray bursts (GRBs) through numerical simulations of galaxy formation. GRBs are the most energetic events in the universe and those longer than about 2 seconds are thought to result from the core collapse and explosion of massive stars [Pir05]. Because of the cosmologically short lifetime of the massive progenitors, GRBs are generally considered to be powerful tracers of the massive star formation history of the universe. They can therefore also be expected to provide useful insights into the understanding of the galaxy formation process. The current interest in GRB research started in 1997 with the discovery of their optical afterglow emission. To date over 40 optical detections have been made, but the number of GRB host galaxy observations is still rather limited with only about 20 positive detections.

In this paper a numerical simulation of electrostatic spray-painting with movement of the atomizer has been performed using dynamic mesh models. As atomizer the high-speed rotary bell with external charge was used. Simple movement of the atomizer and simple geometry of the substrate were considered. Numerical results with two different dynamic mesh models, i.e., dynamic layering and local remeshing are discussed. The simulated film thickness distribution was compared with the experimental result.

An overview about recent results of the DLR-Project SikMa-“Simulation of Complex Maneuvers” is presented. The objective of the SikMa-Project is to develop a numerical tool to simulate the unsteady aerodynamics of a free flying aeroelastic combat aircraft, by use of coupled aerodynamic, flight-mechanic and aeroelastic computations. To achieve this objective, the unstructured, time accurate flow-solver TAU is coupled with a computational module solving the flight-mechanic equations of motion and a structural mechanics code determining the structural deformations. By use of an overlapping grid technique (chimera), simulations of a complex configuration with movable control-surfaces is possible.

This paper presents recent developments and results in the aerodynamic and aeroelastic simulation of helicopter main rotors. Our current work focusses on two aspects which are of high relevance for the further improvement of helicopter rotors: The aeroelastic simulation of active rotor concepts and the correct reproduction and prediction of Blade Vortex Interaction.

This report describes numerical simulation of the flow around helicopter fuselage-main rotor-tail rotor configurations using the quasi-steady actuator disk approach and the time-accurate simulation that resolves the relative motion of the main and tail rotors with respect to the fuselage. The computations predict both the instantaneous and quasi-steady flow fields by solving the Reynolds-averaged Navier-Stokes (RANS) equations in three dimensions using a finite volume method and block structured grids. Turbulence effects are taken into account via a two-equation — ω model. The motion of the rotors was accomplished by an overlapping grid technique (Chimera). The DLR. CFD code FLOWer was applied in parallel mode to obtain the solution at each time step. The computations were performed on 8 processors of the NEC-SX6 at Höchstleistungsrechenzentrum Stuttgart (HLRS)

Well-resolved Large-Eddy Simulations (LES) are performed in order to investigate flow phenomena and the turbulence structure of the boundary layer along a supersonic compression ramp. The numerical simulations directly reproduce an available experiment. The compression ramp has a deflection angle of β= 25°. The mean free-stream Mach number is ∞ = 2.95. The Reynolds number based on the incoming boundary-layer thickness is δ = 63560 in accordance with the reference experiment. About 18.5 ✖ 10 grid points are used for discretizing the computational domain. For obtaining mean flow and turbulence structure the flow is sampled 1272 times over 703 characteristic time scales. Statistical data are computed from these samples. An analysis of the data shows a good agreement with the experiment in terms of mean quantities and turbulence structure. The computational data confirm theoretical and experimental results on fluctuation-amplification across the interaction region. In the wake of the main shock a shedding of shocklets is observed. The temporal behavior of the coupled shock-separation system agrees well with experimental data. Unlike previous DNS the present simulation data provide indications for a large-scale shock motion. Also evidence for the existence of threedimensional large-scale stream-wise structures, commonly referred to as Görtler-like vortices, is found.

In the “DAMPFSIM” project, a detailed simulation methodology of a fossil-fuel fired utility boiler using a Computational Fluid Dynamics code for the coal combustion process coupled with a water/steam simulation code was employed. The results are useful to analyse the influence of non-uniform heating resulting from combustion properties or operational conditions on the steam generation process in order to reduce critical conditions, and to enhance the operational performance and reliability of the boiler. For both parts, combustion and steamside simulation, in-house developed codes which have been extensively validated with experimental data in many previous projects have been used.

We used the high performance systems at HLRS in the last year for two different works. One was the hybrid implementation and optimization of ParaSPH a library for the parallel computation of particle simulations. We give details of the parallelization of ParaSPH for hybrid architectures (clustered SMPs) using MPI and OpenMP and discuss performance results for single node and speedups of the code on the Opteron Cluster and the NEC SX-6. The other work we present is the enhancement of an object-oriented framework for messages passing called TPO++ to support object-oriented parallel I/O.

The range of applications using our libraries and methods is extended continuously. At present it covers many different astrophysical phenomena, basically accretion procedures, impact simulations, the simulation of brittle material and the simulation of separated two phase flows, for example the injection of diesel jets. Recently we work on a solution to simulate granular media with SPH.

We used the high performance systems at HLRS in the last year for two different works. One was the hybrid implementation and optimization of ParaSPH a library for the parallel computation of particle simulations. We give details of the parallelization of ParaSPH for hybrid architectures (clustered SMPs) using MPI and OpenMP and discuss performance results for single node and speedups of the code on the Opteron Cluster and the NEC SX-6. The other work we present is the enhancement of an object-oriented framework for messages passing called TPO++ to support object-oriented parallel I/O.

The range of applications using our libraries and methods is extended continuously. At present it covers many different astrophysical phenomena, basically accretion procedures, impact simulations, the simulation of brittle material and the simulation of separated two phase flows, for example the injection of diesel jets. Recently we work on a solution to simulate granular media with SPH.