Workshop on Verification and Validation of CFD for Offshore Flows

2012 ◽  
Author(s):  
L. Eça ◽  
G. Vaz
Keyword(s):  
Reynolds Numbers ◽  
Verification And Validation ◽  
Test Cases ◽  
Code Verification ◽  
Complex Flow ◽  
Solution Verification ◽  
Manufactured Solution ◽  
Cylinder Flow ◽  
Flow Case ◽  
Paper Submission

This document introduces the Workshop on Verification and Validation (V&V) of CFD for Offshore Flows, to be held during OMAE2012. It presents a brief introduction to the purpose of Verification and Validation with the identification of the goals of code and solution verification and validation. Within this context, three test-cases are proposed: Case-I of code verification, Case-II of solution verification and Case-III of solution verification and validation. Case-I consists on a 3D manufactured solution of an unsteady turbulent flow. Case-II is an exercise on the canonical problem of the infinite smooth circular cylinder flow at different Reynolds numbers. Case-III is a more complex flow around a straked-riser. The participants are asked to perform at least one of these test-cases. The objectives for the three proposed test-cases are presented, together with a detailed description of the numerical settings to be used, and the results to be obtained and sent to the Workshop organization. At the end some considerations on general conditions, paper submission, deadlines, and encouragements are stated.

Modeling Transition for the Cylinder Flow With Verification and Validation

2015 ◽  
Author(s):  
Guilherme F. Rosetti ◽  
Guilherme Vaz ◽  
André L. C. Fujarra
Keyword(s):  
Turbulence Models ◽  
Reynolds Numbers ◽  
Verification And Validation ◽  
Transition Model ◽  
Physical Conditions ◽  
Turbulent Transition ◽  
Solution Verification ◽  
Sst Turbulence Model ◽  
High Reynolds ◽  
Cylinder Flow

The widespread use of Computational Fluid Dynamics (CFD) tools for engineering applications is certainly positive. However, users must also be aware of the physics of the problems being modeled, as well as the shortcomings of turbulence models in use. New state-of-the-art turbulence models are currently being developed with the aim of enhancing the turbulent flow predictions but the laminar-turbulent transition is still out of the scope of most the models. Bearing upon those ideas, this paper investigates the performance of the Local Correlation Transition Model (LCTM) for the cylinder flow with Solution Verification and Validation at high Reynolds numbers. Furthermore, attention is paid to characteristics of the setup, numerics and physical conditions and we study how these features alter the results. We also bring recommendations on the use of the transition model regarding grid, setup and physical conditions. The results show much better comparison of numerical and experimental results regarding drag coefficients than seen with the SST turbulence model, even with the two-dimensional calculations done herein.

Code Verification, Solution Verification and Validation in RANS Solvers

2010 ◽  
Author(s):  
Lui´s Ec¸a ◽  
Guilherme Vaz ◽  
Martin Hoekstra
Keyword(s):  
Turbulent Flows ◽  
Verification And Validation ◽  
Test Cases ◽  
Simple Test ◽  
Error Evaluation ◽  
Code Verification ◽  
Engineering Activity ◽  
Solution Verification ◽  
The Right ◽  
Comparison With Experimental Data

The maturing of CFD codes for practical calculations of complex turbulent flows implies the need to establish the credibility of the results by Verification & Validation. These two activities have different goals: Verification is a purely mathematical exercise that intends to show that we are “solving the equations right”, whereas Validation is a science/engineering activity that intends to show that we are “solving the right equations”. Verification is in fact composed of two different activities: Code Verification and Solution Verification. Code Verification intends to verify that a given code solves correctly the equations of the model that it contains by error evaluation. On the other hand, Solution Verification intends to estimate the error of a given calculation, for which in general the exact solution is not known. Validation intends to estimate modelling errors by comparison with experimental data. The paper gives an overview of procedures for Code Verification, Solution Verification and Validation. Examples of the three types of exercises are presented for simple test cases demonstrating the advantages of performing Verification and Validation exercises.

URANS Calculations for Smooth Circular Cylinder Flow in a Wide Range of Reynolds Numbers: Solution Verification and Validation

2012 ◽  
Vol 134 (12) ◽  
Author(s):  
Guilherme F. Rosetti ◽  
Guilherme Vaz ◽  
André L. C. Fujarra
Keyword(s):  
Large Range ◽  
Reynolds Numbers ◽  
Uncertainty Estimation ◽  
Wide Range ◽  
Modeling Errors ◽  
Solution Verification ◽  
Sst Turbulence Model ◽  
Validation Procedure ◽  
Cylinder Flow ◽  
Fixed Cylinder

The flow around circular smooth fixed cylinder in a large range of Reynolds numbers is considered in this paper. In order to investigate this canonical case, we perform CFD calculations and apply verification & validation (V&V) procedures to draw conclusions regarding numerical error and, afterwards, assess the modeling errors and capabilities of this (U)RANS method to solve the problem. Eight Reynolds numbers between Re = 10 and Re=5×105 will be presented with, at least, four geometrically similar grids and five discretization in time for each case (when unsteady), together with strict control of iterative and round-off errors, allowing a consistent verification analysis with uncertainty estimation. Two-dimensional RANS, steady or unsteady, laminar or turbulent calculations are performed. The original 1994 k-ω SST turbulence model by Menter is used to model turbulence. The validation procedure is performed by comparing the numerical results with an extensive set of experimental results compiled from the literature.

URANS Calculations for Smooth Circular Cylinder Flow in a Wide Range of Reynolds Numbers: Solution Verification and Validation

2012 ◽  
Author(s):  
Guilherme F. Rosetti ◽  
Guilherme Vaz ◽  
André L. C. Fujarra
Keyword(s):  
Large Range ◽  
Reynolds Numbers ◽  
Data Repository ◽  
Wide Range ◽  
Solution Verification ◽  
Sst Turbulence Model ◽  
Validation Procedure ◽  
Unsteady Rans ◽  
Cylinder Flow ◽  
Fixed Cylinder

The flow around circular smooth fixed cylinder in a large range of Reynolds numbers is considered in this paper. In order to investigate this canonical case, we perform CFD calculations and apply Verification & Validation (V&V) procedures to draw some conclusions regarding numerical error, and afterwards, assess the modelling errors and capabilities of URANS method to solve this problem. Eight Reynolds numbers between Re = 10 and Re = 5×105 will be presented with five geometrically similar grids and five time steps for each case, together with strict control of iterative and round-off errors, allowing a consistent verification analysis with uncertainty estimation. In these calculations, two-dimensional Unsteady RANS calculations were performed making use of the k–ω SST turbulence model. The Validation procedure is performed by comparing the numerical results with an extensive set of experimental results compiled from the literature and also made available in the VIV Data Repository website (http://oe.mit.edu/VIV/).

Effective Use of V&V20 Solution Verification Methodology

2010 ◽  
Author(s):  
Christopher J. Freitas
Keyword(s):  
Heat Transfer ◽  
Verification And Validation ◽  
Code Verification ◽  
Flow And Heat Transfer ◽  
Time Period ◽  
Solution Verification ◽  
Particular Solution ◽  
American Society ◽  
Effective Use ◽  
Verification Methodology

Methods for the quantification of numerical uncertainty have been a subject of interest to the American Society of Mechanical Engineers (ASME) and the mechanical engineering community as a whole for over a decade. During this time period, ASME has promulgated three statements of standards for the reporting of numerical uncertainty in archival publications (Journal of Fluids Engineering). This paper summarizes the work that has gone into the specification of these standards and the continuing effort in formulation of methods and procedures for quantifying numerical uncertainty. Specifically, this paper discusses the efforts of the ASME V&V 20 Committee (Verification and Validation in Computational Fluid Dynamics and Heat Transfer) to lay a foundation and structure to verification and validation for fluid flow and heat transfer simulations. Issues and methods related to code verification and in particular solution verification are presented and discussed in the context of the recently released V&V20 Standard.

An Example of Code Verification in the Simulation of Wave Propagation

2011 ◽  
Author(s):  
Fahd Fathi ◽  
Lui´s Ec¸a ◽  
Mart Borsboom
Keyword(s):  
Wave Propagation ◽  
Numerical Solution ◽  
Physical Reality ◽  
Verification And Validation ◽  
Cfd Modeling ◽  
Code Verification ◽  
Complex Flows ◽  
Solution Verification ◽  
The Mathematical Model

Thanks to advances in modeling and hardware the range of applications available to CFD modeling is continuously increasing. As CFD has moved from demonstration of capability to production of engineering results of practical value, there is an increased awareness in the field that Verification and Validation are systematically required. Verification deals with the numerical accuracy of a given set of results. Its object is the assessment of the numerical uncertainty due to discretization and iterative errors of a numerical solution (Solution Verification) performed with a Code that has been previously checked to be free of errors (Code Verification). Both activities are required to ensure that errors are controlled and that quality of the results is maintained. Complementarily, Validation addresses the modeling error, i.e. the comparison of the mathematical model with the (physical) reality. Therefore, it requires comparison with experimental data. Validating CFD results is only meaningful when preceded by carefully verified calculations (Solution Verification) with verified codes (Code Verification). The topic of Verification and Validation is developing and standardized procedures are still under discussion. Nevertheless, there are techniques available to perform careful Code and Solution Verification for flows with engineering relevance. This paper presents a Code Verification exercise for the simulation of wave propagation with a VOF code. Systematically refined grids and time steps are applied in the calculation of waves with a known analytical solution to assess the convergence properties of the numerical solution. The aim of the exercise is to demonstrate the advantages of such exercises for the knowledge of the numerical properties of a code that is applied in complex flows. The study is not a pure Code Verification exercise. Modeling errors introduced by approximate outlet boundary conditions (allowing wave reflections) are also quantified for a linear and a high-order wave. However, these are still based on (numerical) error evaluations for known analytical solutions and so they can still be classified as Code Verification.

scholarly journals On the prospects of improving the numerical analysis of symmetric airfoils at low Reynolds numbers and high angles of attack by a LES approach: the case of NACA0021 profile

2020 ◽  
Vol 197 ◽  
pp. 08015
Author(s):  
Simone Giaccherini ◽  
Filippo Mariotti ◽  
Lorenzo Pinelli ◽  
Michele Marconcini ◽  
Alessandro Bianchini
Keyword(s):  
Turbine Blades ◽  
Separated Flow ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Operating Conditions ◽  
High Fidelity ◽  
Complex Flow ◽  
Energy Applications ◽  
Low Reynolds ◽  
High Angles Of Attack

The working conditions of airfoils along modern wind turbine blades are putting new focus on the importance of properly characterizing the aerodynamic performance of different airfoil families also at high angles of attack (AoAs) beyond stall and at Reynolds numbers much lower (from few thousands to one million) than those commonly analyzed before. Several test cases are showing that even higher-order computational methods (like RANS/URANS CFD) are unable to properly capture the complex flow physics taking place past the blades, when deep stall occurs or when the AoA changes so rapidly to provoke the onset of dynamic stall. To fill this gap, the use of high-fidelity methods, like the Large Eddy Simulation (LES) is proposed, even though it implies a massive increase of the calculation cost. In order to analyze the prospects of using LES in comparison to RANS for low Reynolds, high AoAs, this work presents an in-depth study of the NACA 0021 aerodynamics at the Reynolds number of 80,000, by means of both traditional RANS approaches and high-fidelity (LES) simulations using the OpenFOAM suite. The selected airfoil has been showing in fact several issues in the correct characterization of its performance in similar conditions in many recent wind energy applications. The LES approach showed the ability to overcome the limitations of traditional RANS simulations, improving the accuracy of the results and reducing their dispersion thanks to the fact that the flow structures in the separated-flow regions are properly captured. Overall, this work underlines that accurate investigations of the aerodynamic performance of the NACA 0021 at low Reynolds require multiple sensitivity studies when RANS approaches are used, and suggests the use of LES simulations in order to increase the accuracy of estimations, especially when studying the stalledflow operating conditions of the airfoil.

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