Standard

AIAA S-141

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Scope and Objectives of This Standard This Standard is written for developers and users of CFD codes, their managers, and those who make decisions based on results from CFD simulations. This Standard provides the relevant definitions, theoretical background, and computational procedures. It also provides generally accepted procedures for code verification. The document emphasizes practical aspects of the code verification process. The main body of the document is intentionally brief, with details and derivations relegated to appendices, and with references provided for additional or more detailed coverage of the subject. The scope and objectives of this Standard are as follows: • Explain what code verification is and explain its role in deciding whether a computational code is fit for a particular purpose. • Explain and increase awareness of the importance and need for code verification, especially when the CFD code will be used in mission-critical or high-consequence decision making. • Identify who is responsible for ensuring that code verification has been carried out and who should carry out the actual work of code verification. • Review the theoretical background and the discrete solution criteria that are relevant for code verification, including the definitions of consistency, stability, convergence, and order of accuracy. • Explain how to plan a code verification program, starting from the selection of a suitable reference solution, all the way to compiling, interpreting, and documenting the results. • Provide guidance on how to determine the observed order of accuracy. • Demonstrate how to carry out code verification for each of the three acceptable categories of reference solution; namely, (1) traditional exact analytical solutions; (2) exact manufactured solutions; and (3) benchmark computational solutions. • Provide references to literature for more detailed coverage of code verification. The concepts and practice of code verification have matured to a level that allows the formulation of a systematic process and an engineering standard for code verification. Any systematic process and any standard for code verification should nevertheless still allow for improvisation for special cases and for handling various potential complications. The terminology and the presentation in this Standard are aimed at finite difference, finite element, finite volume, and spectral element methods. The general concepts presented here are applicable for other, less common discretizations, like the Lattice Boltzmann, smoothed particle hydrodynamics, and particle-in-cell methods, but their specific verification techniques are not explicitly covered. This Standard addresses code verification for flow solvers. Code verification for pre- and post-processing codes, tools, and scripts (which will typically have their own interpolation, approximation, discretization, and other errors) requires verification techniques that may differ from the techniques used for flow solvers, and these techniques are not specifically addressed in this Standard. It should nevertheless be stated that code verification for a complete computational modeling workflow requires independent code verification for all pre- and post-processing components and any external libraries that are used with a flow solver. This Standard is focused on CFD codes. However, it also covers code verification for general multiphysics codes, and most of the concepts and methods presented in the Standard are equally applicable to codes for other categories of computational mechanics. Examples include codes for solid mechanics, electromagnetics, and radiative transport. The Standard focuses on code verification, including its theory, methods, and practices. It does not cover the use of code verification in solution verification, or uncertainty quantification, or in the assessment of suitability of a code for an application. This Standard is organized as follows: Section 1 defines code verification, explains its importance, and outlines its role within the overall VVUQ process for CFD. It also identifies the individuals who should carry out code verification and those who should ensure that it has been carried out before using computational results. It also outlines the objectives, contents, and scope of this Standard. It also provides a brief overview of the code verification process. Section 2 provides the theoretical background and the basic definitions and concepts related to code verification. Section 3 provides the recommended code verification process for CFD codes and explains the criteria for successful code verification. Section 4 specifies the requirements of this Standard (for code verification and code verification coverage), the compliance provisions, and the allowed tailoring methods. Section 5 provides a summary of this Standard and its main conclusions and recommendations. Appendix 1 provides examples of code verification using exact analytical solutions, exact manufactured solutions, and benchmark computational solutions, and discusses how to choose such solutions for code verification. Appendix 2 presents recommendations to managers, users, and developers seeking to adopt sound and effective code verification principles and practices. Appendix 3 outlines the method of manufactured solutions and its use in code verification.

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