Michel Visonneau

Incompressible flow calculations with a consistent physical interpolation finite volume approach

Abstract The computation of incompressible three-dimensional viscous flow is discussed. A new physically consistent method is presented for the reconstruction for velocity fluxes which arise from the mass and momentum balance discrete equations. This closure method for fluxes allows the use of a cell-centered grid in which velocity and pressure unknowns share the same location, while circumventing the occurrence of spurious pressure modes. The method is validated on several benchmark problems which include steady laminar flow predictions on a two-dimensional cartesian (lid driven 2D cavity) or curvilinear grid (circular cylinder problem at Re = 40), unsteady three-dimensional laminar flow predictions on a cartesian grid (parallelopipedic lid driven cavity) and unsteady two-dimensional turbulent flow predictions on a curvilinear grid (vortex shedding past a square cylinder at Re = 22,000).

Numerical Ship Hydrodynamics - An Assessment of the Gothenburg 2010 Workshop

The Gothenburg 2010 Workshop on CFD in Ship Hydrodynamics was the sixth in a series starting in 1980. The purpose of the Workshops is to assess the state of the art in CFD for hydrodynamic applications. Active researchers in the field worldwide are invited to provide computed results for a number of well specified test cases, and the organizers collect and present the results such that comparisons between different methods can be made easily. Detailed information about each method is also reported via a questionnaire provided by the organizers. All results are discussed at a meeting, and a final assessment of the workshop is made by the organizers. The present workshop attracted 33 groups from all over the world, and different types of computations were carried out for three hulls. It was by far the largest of the workshops in the series so far. All computed results were compiled in a volume, called Proceedings II, and distributed at the meeting, which was held in Gothenburg 8-12 December 2010. Unlike previous workshops, there was no presentation of submitted papers. Instead, the three main organizers gave reviews of the submitted results at the meeting, and most of the time was spent on discussions of these reviews. In this book, updated versions of the reviews are presented, together with a verification and validation study of the submitted resistance predictions, as well as new measurement data obtained after the workshop and a comprehensive set of additional computations carried out by the organizers to investigate topics of particular interest found at the meeting. The book has been written by the three main organizers and their co-workers. Together with supplementary information on the web site SpringerExtras (for address, se book cover) the book constitutes the final documentation of the Gothenburg 2010 Workshop and gives a state-of-the-art assessment of the CFD capabilities within the area of Ship Hydrodynamics.

Fast Dynamics of an Eel-Like Robot—Comparisons With Navier–Stokes Simulations

This paper proposes a dynamic model of the swim of elongated fish suited to the online control of biomimetic eel-like robots. The approach can be considered as an extension of the original reactive ldquolarge elongated body theoryrdquo of Lighthill to the 3-D self-propulsion to which a resistive empirical model has been added. While all the mathematical fundamentals have been detailed by Boyer . (http://www.irccyn.ec-nantes.fr/hebergement/Publications/2007/3721.pdf, 2007), this paper essentially focuses on the numerical validation and calibration of the model and the study of swimming gaits. The proposed model is coupled to an algorithm allowing us to compute the motion of the fish head and the field of internal control torque from the knowledge of the imposed internal strain fields. Based on the Newton-Euler formalism of robot dynamics, this algorithm works faster than real time. As far as precision is concerned, many tests obtained with several planar and 3-D gaits are reported and compared (in the planar case) with a Navier-Stokes solver, which, until today have been devoted to the planar swim. The comparisons obtained are very encouraging since in all the cases we tested, the differences between our simplified and reference simulations do not exceed 10%.

Optimal Location of a Synthetic Jet on an Airfoil for Stall Control

This study deals with the optimization of the location of a synthetic jet on the suction side of an airfoil to control stall. The optimal location is found by coupling a time-accurate flow solver with adaptive mesh refinement/coarsening techniques and an automatic optimization algorithm. The flow and jet are modeled by the unsteady Reynolds-averaged Navier-Stokes equations (URANSE) with a near-wall low-Reynolds number turbulence closure. An unstructured grid refinement/coarsening method is used to automatically generate meshes adapted to the presence of the synthetic jet at a prescribed location. An optimization algorithm modifies the location of the synthetic jet to determine the best actuator location to increase the time-averaged lift for high angles of attack. The proposed methodology is applied to optimize the location of a synthetic jet on the suction side of the NACA 0012 airfoil at a Reynolds number Re=2X10 6 and incidences of 18 deg and 20 deg. Finally, a physical analysis of the influence of the synthetic jet location on the control efficiency is proposed to provide some guidelines for practical jet positioning.

Three-Dimensional Flow Computation with Reynolds Stress and Algebraic Stress Models

A quadratic explicit algebraic stress model (EASM) that takes into account the variation of production-to-dissipation rate ratio is compared with an implicit algebraic stress model (ASM) and with their parent Reynolds stress model (RSM) in this paper. A new implementation of ASM model where the turbulent eddy viscosity provided by the explicit solution is employed is found to be robust. Computations for ship flows at model and full scale are performed to assess the accuracy of different models. Explicit and implicit algebraic stress models give similar prediction for the flow investigated. The RSM model provides better prediction in the region dominated by convex curvature. However, no much improvement is observed near the concave surface.

CFD in Ship Hydrodynamics—Results of the Gothenburg 2010 Workshop

The Gothenburg 2010 Workshop on Numerical Hydrodynamics gathered 33 groups with computations for one or more of 18 test cases. All results were collected and discussed at a meeting in Gothenburg in December 2010. In the present paper some representative examples from the workshop are presented. The complete results are found in the workshop Proceedings.

A new fully coupled method for computing turbulent flows

Abstract This work discusses the computation of the steady, turbulent, two-dimensional incompressible viscous flow on structured cell-centered collocated grids. A rather new computational approach – the so-called fully coupled procedure with defect correction technique – is presented as an alternative both to classical decoupled approaches (SIMPLE [Int. J. Heat Mass Transfer 15 (1972) 1787–1806], PISO [J. Comput. Phys. 62(1) (1986) 40–65] and variants) and to weakly coupled solution methods of Vanka type [Fifth symposium on Turbulent Shear flows, 1985. p. 20:27–32, J. Comput. Phys. 65 (1986) 138–158]. Its main features will be highlighted and detailed. This strategy is evaluated on two demanding test cases (the simulation of the separated flow past an AS240-B airfoil at high incidence (19°, Re=2×10 6 ) and the simulation of the wake flow behind a two-dimensional hill ( Re =60 000 )), for which documented experimental data are available. Both robustness and computational efficiency of the new approach are shown.

Influence of free surface, unsteadiness and viscous effects on oar blade hydrodynamic loads

Abstract Flow around a rowing blade is a very complex phenomenon, involving unsteady three-dimensional flow with violent motion of the free surface. However, in the literature, forces acting on blades are modelled using extreme and dubious simplifications. The aim of the present study was to evaluate the influence of free surface and unsteadiness (two physical characteristics that are commonly neglected when modelling loads on blades) as well as viscous effects. In fact, quasi-static approaches are often used, with no influence of the free surface effects. To conduct this study, computational fluid dynamics is used, supported by experimental results performed with a dedicated device reproducing a simplified rowing stroke in the towing tank. Comparisons show that both free surface flow and unsteadiness must be considered to capture the whole physics of the phenomenon accurately. In contrast, the viscous effects have a very limited influence.

RANS prediction of the KVLCC2 tanker in head waves

The present study is devoted to the computation of the KVLCC2 tanker in head wave with free heave and pitch motion. A RANS solver using finite-volume discretization and free-surface capturing approach is employed for the computation. Free ship motion is captured with a mesh deformation approach. Three different wave lengths (0.6Lpp, 1.1Lpp and 1.6Lpp) are computed. We focus on numerical uncertainty estimation in this paper. For each test case, three different meshes and at least three different time steps have been used to access both time and spatial discretization error. Additional computations with different setups aimed at identifying different numerical discretization errors will also be performed. It is demonstrated that special attention needs to be paid to time discretization. To keep the same time accuracy, time step needs to be reduced on fine mesh for such kind of unsteady free-surface computation involving important pitch or roll motion.

2-D COMPUTATIONS OF UNSTEADY FLOW PAST A SQUARE CYLINDER WITH THE BALDWIN-LOMAX MODEL

The unsteady turbulent flow past a square cylinder is calculated with the Baldwin-Lomax Model. The influence of the numerical schemes is studied. Comparisons with experimental data and with previous calculations using a Reynolds stress model and 3-D large eddy simulations are presented. It is shown that a good prediction is obtained with a Baldwin-Lomax model by using the recently proposed CPI discretization scheme.