GRIDDLER and VISTA with CGNS interface

-This developer's and user's note has been written to help developers and users of GRIDDLER and VISTA to maintain and use their recent CGNS (CFD General Notation System) interface. The present note contains a description of the first version of GRIDDLER and VISTA with this option. This version has implemented CGNS formatted GRIDDLER output and VISTA input of an arbitrary multi-block structured 3D grid with block connectivity and boundary conditions. In later versions, other options of the CGNS system will be included as well. The main reason for making a CGNS output format option available to GRIDDLER was the need for making a blocked gridfrom a GRIDDLER model. Even though GRIDDLER is a multi-block grid generator, implemented with the use of object-oriented programming; until now, the final result has been a global gridthat collects the points from all the blocks. A trigger for making this blocked grid option to GRIDDLER was the requirement of the parallel VISTA CFD code - based on the algorithm of domain decomposition -to be able to contain just the grid of its own domain (possibly with overlaps to its neighbouring domains or blocks) and not the whole grid as was required in the first place. Some examples are given in the appendices. Oppdragsgiver UNINETT/SIGMA A

A Comprehensive Simulation Methodology for Fluid-Structure Interaction of Offshore Wind Turbines

This paper gives an overview of a comprehensive simulation methodology for fluid-structure interaction (FSI) of offshore wind turbines that is being developed at the Applied Mathematics Department of SINTEF ICT. The methodology will account for most of the scales ranging from mesoscale meteorology through microscale meteorology to the aerodynamics of wind turbine blades. The meso and micro scales are handled through a unidirectional coupling of a meso and micro scale atmospheric code while the fluid structure interaction part is dealt with an isogeometric finite element based fluid-structure simulation code IFEM. In the current work we have shown the potential of the coupled system which is actually meant to generate realistic boundary condition as a wind forecasting tool. Also we present a comparison of the IFEM computed drag, lift and moment coefficients against experimental data for flow around a 3-D oscillating airfoil.publishedVersio

Implementation and comparison of three isogeometric Navier–Stokes solvers applied to simulation of flow past a fixed 2D NACA0012 airfoil at high Reynolds number

Implementation of three different Navier–Stokes solvers in an isogeometric finite element framework is presented in this paper. The three solvers Chorin projection method and Coupled formulation , both with the Spalart–Allmaras turbulence model, and Variational Multiscale (VMS) method have been applied to simulate flow past a two-dimensional NACA0012 airfoil at a high Reynolds number (Re=3×106Re=3×106) for four different angles of attack. The predicted flow characteristics have been compared and the effects of increasing the order of the spline element on the accuracy of prediction and computational efficiency are evaluated. In this study it turns out that flow separation does not take place up to an angle of attack of 16°. Up to this angle of attack all three solvers predict similar results in good agreement with each other and with available experimental results. However, a big spread in lift and drag coefficients is observed in the stall regime. Our study also shows that for linear spline elements all three solvers are computationally similar. For quadratic spline elements the Chorin solver compares favorably to the others based on the results presented here.acceptedVersio

Simulation of airflow past a 2D NACA0015 airfoil using an isogeometric incompressible Navier-Stokes solver with the Spalart-Allmaras turbulence model

The work presented in this paper concerns the efforts of conducting a computational fluid dynamics (CFD) simulation of air flow past a fixed 2D NACA0015 airfoil at high Reynolds number (Re=2.5×106Re=2.5×106) using an isogeometric finite element methodology with linear, quadratic and cubic spline elements. Flow simulations at such high Reynolds numbers require turbulence models or very high resolution. The present work employs the Spalart–Allmaras turbulence model combined with a Navier–Stokes solver based on a Chorin projection method, the first development of its kind in an isogeometric finite element framework. The obtained results from the simulations are compared with two sets of experimental results available in the literature.acceptedVersio

Unconditionally Stable Splitting Methods For The Shallow Water Equations

. The front tracking method for hyperbolic conservation laws is combined with operator splitting in order to study the shallow water equations. Furthermore, the method includes adaptive grid refinement. The front tracking method is unconditionally stable, but for practical computations feasible cfl numbers are moderately above unity (typically between 1 and 5). The method resolves shocks sharply and is highly efficient. The numerical technique is applied to four test cases, the first being an expanding bore with rotational symmetry. The second problem addresses the question of describing the time-development of two constant water levels separated by a dam that breaks instantaneously. The third problem compares the front tracking method with an explicit analytic solution of water waves rotating over a parabolic bottom profile. Finally, we study flow over an obstacle in one-dimension. 1. Introduction The shallow water equations model free surface flow for a fluid under the influence of ..

Implementation and comparison of three isogeometric Navier–Stokes solvers applied to simulation of flow past a fixed 2D NACA0012 airfoil at high Reynolds number

Implementation of three different Navier–Stokes solvers in an isogeometric finite element framework is presented in this paper. The three solvers Chorin projection method and Coupled formulation , both with the Spalart–Allmaras turbulence model, and Variational Multiscale (VMS) method have been applied to simulate flow past a two-dimensional NACA0012 airfoil at a high Reynolds number (Re=3×106Re=3×106) for four different angles of attack. The predicted flow characteristics have been compared and the effects of increasing the order of the spline element on the accuracy of prediction and computational efficiency are evaluated. In this study it turns out that flow separation does not take place up to an angle of attack of 16°. Up to this angle of attack all three solvers predict similar results in good agreement with each other and with available experimental results. However, a big spread in lift and drag coefficients is observed in the stall regime. Our study also shows that for linear spline elements all three solvers are computationally similar. For quadratic spline elements the Chorin solver compares favorably to the others based on the results presented here

Simulation of airflow past a 2D NACA0015 airfoil using an isogeometric incompressible Navier-Stokes solver with the Spalart-Allmaras turbulence model

The work presented in this paper concerns the efforts of conducting a computational fluid dynamics (CFD) simulation of air flow past a fixed 2D NACA0015 airfoil at high Reynolds number (Re=2.5×106Re=2.5×106) using an isogeometric finite element methodology with linear, quadratic and cubic spline elements. Flow simulations at such high Reynolds numbers require turbulence models or very high resolution. The present work employs the Spalart–Allmaras turbulence model combined with a Navier–Stokes solver based on a Chorin projection method, the first development of its kind in an isogeometric finite element framework. The obtained results from the simulations are compared with two sets of experimental results available in the literature

Numerical benchmarking of fluid–structure interaction: An isogeometric finite element approach

In this paper we describe and evaluate an isogeometric finite element program, IFEM-FSI, for doing coupled fluid–structure interaction simulations. We investigate the role played by employing higher polynomial orders and higher regularity for solving a well known benchmark problem for flow past a circular cylinder with an attached flexible bar at Reynolds number Re=100. Furthermore, we investigate the sensitivity to resolution in the fluid mesh as well as stiffness distribution in the mesh movement algorithm. Mesh quality is also assessed. Our simulations indicate that quadratic and cubic spline elements give better estimation of lift, drag and displacements than linear spline element