Effiziente numerische Methoden zur Lösung von reaktiven Euler-Gleichungen für mehrere Spezies

This cumulative thesis is devoted to the efficient simulation of compressible chemically reactive flows with multiple species and reactions being involved. In addition, the mass-fraction based reactive Euler equations with multiple species can be used to describe two-phase flows with multiple 'components' (corresponding to 'species') in a diffuse-interface manner, with suitable equations of state or thermodynamical models being employed. Three numerical methods towards computational high-efficiency solution of the above equation system are proposed.Diese kumulative Doktorarbeit widmet sich der effizienten Simulation kompressibler chemisch reaktiver Strömungen, wo mehrere Arten und Reaktionen beteiligt sind. Darüber hinaus können die auf Massenfraktionen basierenden reaktiven Euler-Gleichungen für mehrere Spezies mit geeigneten Zustandsgleichungen oder thermodynamischen Modellen verwendet werden, um zweiphasige Strömungen mit mehreren "Komponenten" (entsprechend "Spezies") auf diffuse Weise zu beschreiben. Drei numerische Methoden zur numerischen hocheffizienten Lösung des obigen Gleichungssystems warden vorgeschlagen

High-performance parallel analysis of coupled problems for aircraft propulsion

This research program deals with the application of high-performance computing methods for the analysis of complete jet engines. We have entitled this program by applying the two dimensional parallel aeroelastic codes to the interior gas flow problem of a bypass jet engine. The fluid mesh generation, domain decomposition, and solution capabilities were successfully tested. We then focused attention on methodology for the partitioned analysis of the interaction of the gas flow with a flexible structure and with the fluid mesh motion that results from these structural displacements. This is treated by a new arbitrary Lagrangian-Eulerian (ALE) technique that models the fluid mesh motion as that of a fictitious mass-spring network. New partitioned analysis procedures to treat this coupled three-component problem are developed. These procedures involved delayed corrections and subcycling. Preliminary results on the stability, accuracy, and MPP computational efficiency are reported

High Performance Parallel Analysis of Coupled Problems for Aircraft Propulsion

In order to predict the dynamic response of a flexible structure in a fluid flow, the equations of motion of the structure and the fluid must be solved simultaneously. In this paper, we present several partitioned procedures for time-integrating this focus coupled problem and discuss their merits in terms of accuracy, stability, heterogeneous computing, I/O transfers, subcycling, and parallel processing. All theoretical results are derived for a one-dimensional piston model problem with a compressible flow, because the complete three-dimensional aeroelastic problem is difficult to analyze mathematically. However, the insight gained from the analysis of the coupled piston problem and the conclusions drawn from its numerical investigation are confirmed with the numerical simulation of the two-dimensional transient aeroelastic response of a flexible panel in a transonic nonlinear Euler flow regime

Etude comparative de schémas numériques pour la modélisation de phénomènes diffusifs sur maillages multiéléments

Initialement, le code de Dynamique des Fluides N3S-Natur utilisait une approche Volumes Finis/Eléments Finis, définie uniquement pour les maillages de triangles et tétraèdres. L'objectif de cette thèse est la mise au point d'une nouvelle méthode numérique qui puisse manipuler les maillages multiéléments. On a défini pour cela une métrique adéquate et étudié différentes méthodes de discrétisation de l'opérateur diffusif, le principal point délicat. Six méthodes sont analysées en consistance, précision et stabilité, théoriquement et expérimentalement par une convergence en maillage et une analyse de Fourier. Les schémas d'ordre élevé en convectif sont modifiés en conséquence et la linéarisation du flux pour l'implicite est traitée. La validation de la nouvelle version du code est menée avec succès sur un cas de plaque plane. ABSTRACT : Initially, the CFD code N3S-Natur used a Finite Volume/Finite Element approach that is only defined on triangular and tetrahedral cells. The objective of this work is to define a new numerical method that can handle hybrid meshes. First, we extend the metric to all kinds of elements. Then, six different modellings for the diffusive operator, that constitute the main issue, are proposed and tested. These methods are studied in terms of consistency, accuracy and stability. The comparison is carried out both theoretically and numerically using grid convergence and Fourier analysis. Only one method satisfies all the industrial criteria and is therefore implemented in the code. The higher order schemes for the convective operator are modified consequently and the linearisation of the new diffusive flux, that is required for the implicitation, is treated. The code is successfully validated on a flat plate test case