Verifikationsmethodik für die rechnerische Windtechnik Vorhersage von Windlasten an Tragwerken

In this thesis, a new credibility assessment framework is developed for computational wind engineering (CWE) simulations. The framework is mainly developed for testing code implementation correctness and estimation of the discretization uncertainty for eddy-resolving, and unsteady simulations. The framework is composed of two main milestones. First, a modular and flexible procedure for code verification is developed with the ability of testing black box codes. The code verification procedure focuses on the consistency of the code implementation and convergence of field variables. The procedure for code verification consists of analytical benchmarks, either exact or manufactured, with increasing complexity to test the implementation of each term in the Navier-Stokes equation. Second, the credibility assessment framework has a guideline for the quantification of discretization error/uncertainty. More precisely, guidelines are defined for solution verification. The discretization error/uncertainty estimation is based on Richardson Extrapolation approach. A solution biased uncertainty estimator is used to account for using unstructured grids, non-uniform refinement, and non-asymptotic solutions. The newly developed framework has a new definition for the measurement of grid size, handling simulation data with anomalous behavior, and for the safety factor definition in the uncertainty quantification of the discretization error. The assessment methodology is suited to both well- and ill-behaved sequences of simulations. The performance of the assessment methodology is checked with a glimpse on validation with experimental data. Finally, it can be concluded that the developed verification methodology is highly qualified to judge the quality of CWE simulations. Moreover, the generality and modularity of the framework makes it applicable to any software environment regardless of the discretization scheme. Consequently, the methodology encourages further research on the identification of the reliability of CWE simulations.In dieser Arbeit wird ein neues Rahmenwerk zur Glaubwürdigkeitsbewertung für rechnergestützte Windsimulationen (CWE) entwickelt. Der Rahmen wird hauptsächlich für die Prüfung der Korrektheit der Code-Implementierung und die Abschätzung der Diskretisierungsunsicherheit für wirbelauflösende und instationäre Simulationen entwickelt. Das Framework besteht aus zwei Hauptmeilensteinen. Erstens wird ein modulares und flexibles Verfahren zur Code-Verifikation entwickelt, das die Möglichkeit bietet, Black-Box-Codes zu testen. Das Code-Verifikationsverfahren konzentriert sich auf die Konsistenz der Code-Implementierung und die Konvergenz der Feldvariablen. Das Verfahren zur Codeverifizierung besteht aus analytischen Benchmarks, entweder exakt oder hergestellt, mit zunehmender Komplexität, um die Implementierung jedes Terms in der Navier-Stokes-Gleichung zu testen. Zweitens verfügt das Rahmenwerk zur Glaubwürdigkeitsbewertung über einen Leitfaden zur Quantifizierung von Diskretisierungsfehlern/Unsicherheiten. Genauer gesagt, werden Richtlinien für die Verifizierung der Lösung definiert. Die Schätzung des Diskretisierungsfehlers/der Unsicherheit basiert auf dem Richardson-Extrapolationsansatz. Ein lösungsverzerrter Unsicherheitsschätzer wird verwendet, um die Verwendung unstrukturierter Gitter, ungleichmäßiger Verfeinerung und nicht asymptotischer Lösungen zu berücksichtigen. Der neu entwickelte Rahmen hat eine neue Definition für die Messung der Gittergröße, die Behandlung von Simulationsdaten mit anomalem Verhalten und für die Definition des Sicherheitsfaktors bei der Unsicherheitsquantifizierung des Diskretisierungsfehlers. Die Bewertungsmethodik eignet sich sowohl für gut als auch für schlecht verhaltene Simulationsfolgen. Die Leistungsfähigkeit der Bewertungsmethodik wird mit einem Blick auf die Validierung mit experimentellen Daten überprüft. Abschließend kann festgestellt werden, dass die entwickelte Verifikationsmethodik hoch qualifiziert ist, um die Qualität von CWE-Simulationen zu beurteilen. Darüber hinaus macht die Allgemeingültigkeit und Modularität des Rahmens es für jede Softwareumgebung unabhängig vom Diskretisierungsschema anwendbar. Folglich fördert die Methodik weitere Forschungen zur Identifizierung der Zuverlässigkeit von CWE-Simulationen

Influence of local and adaptive mesh refinement on the tip vortex characteristics of a wing and propeller

Two different methods to obtain nearly grid independent solutions for tip vortex flow were tested for a wing and a propeller. A priory mesh refinement inside a tube with a helix shaped centre line worked quite well, reducing the grid dependency of the minimum pressure in the vortex core significantly but the accuracy still depends on the initial mesh. Better results were obtained with adaptive mesh refinement using the jump based estimator. Projection of new created nodes to the exact geometry is required to obtain high accuracy

Technical Evaluation Report for Symposium AVT-147: Computational Uncertainty in Military Vehicle Design

The complexity of modern military systems, as well as the cost and difficulty associated with experimentally verifying system and subsystem design makes the use of high-fidelity based simulation a future alternative for design and development. The predictive ability of such simulations such as computational fluid dynamics (CFD) and computational structural mechanics (CSM) have matured significantly. However, for numerical simulations to be used with confidence in design and development, quantitative measures of uncertainty must be available. The AVT 147 Symposium has been established to compile state-of-the art methods of assessing computational uncertainty, to identify future research and development needs associated with these methods, and to present examples of how these needs are being addressed and how the methods are being applied. Papers were solicited that address uncertainty estimation associated with high fidelity, physics-based simulations. The solicitation included papers that identify sources of error and uncertainty in numerical simulation from either the industry perspective or from the disciplinary or cross-disciplinary research perspective. Examples of the industry perspective were to include how computational uncertainty methods are used to reduce system risk in various stages of design or development

Development of code evaluation criteria for assessing predictive capability and performance

Computational Fluid Dynamics (CFD), because of its unique ability to predict complex three-dimensional flows, is being applied with increasing frequency in the aerospace industry. Currently, no consistent code validation procedure is applied within the industry. Such a procedure is needed to increase confidence in CFD and reduce risk in the use of these codes as a design and analysis tool. This final contract report defines classifications for three levels of code validation, directly relating the use of CFD codes to the engineering design cycle. Evaluation criteria by which codes are measured and classified are recommended and discussed. Criteria for selecting experimental data against which CFD results can be compared are outlined. A four phase CFD code validation procedure is described in detail. Finally, the code validation procedure is demonstrated through application of the REACT CFD code to a series of cases culminating in a code to data comparison on the Space Shuttle Main Engine High Pressure Fuel Turbopump Impeller

The prospect of using LES and DES in engineering design, and the research required to get there

In this paper we try to look into the future to divine how large eddy and detached eddy simulations (LES and DES, respectively) will be used in the engineering design process about 20-30 years from now. Some key challenges specific to the engineering design process are identified, and some of the critical outstanding problems and promising research directions are discussed.Comment: accepted for publication in the Royal Society Philosophical Transactions

Validation of full-scale delivered power CFD simulations

Verification and Validation of CFD simulations of delivered power at full-scale are carried out for a single screw cargo vessel. Numerical simulations are performed with a steady-state RANS method coupled with a body force propeller model based on a lifting line theory. There are no significant differences in the uncertainty levels between model and full-scale computations. The finest grid exhibits the numerical uncertainty of 1.40% at full-scale. Computed results are compared with sea trial data for three sister ships. Special attention is paid to the effect of roughness on the hull and propeller. The comparison error for the delivered power is about 1% which is significantly lower than the experimental uncertainty