Abstracts

Design and implementation of level set methods for fluid-structure interactions

Georges-Henri Cottet, Laboratoire Jean Kuntzmann, Grenoble, France 

Abstract: We will review some recent works in our group were fluid-structure interaction problems are considered from the viewpoint of immersed boundary methods. Interface motion and contacts are dealt with using level set and finite-difference or particle methods. We will discuss issues related to the numerical analysis and the computational efficiency of these methods.



An Immersed Boundary method to study the effect of roughness in supersonic boundary layers

Gianluca Iaccarino Institute for Computational Mathematical Engineering, Stanford, CA (USA)

Abstract: pdf



Using the immersed boundary method to model complex fluidstructure interaction in sperm and ciliary motility

Robert Dillon Department of Mathematics,Washington State University University, Pullman, WA (USA)

Abstract: The motility of sperm flagella and cilia are based on a common axonemal structure. We describe a fluid-mechanical model for the ciliary and sperm axoneme. This fluid-mechanical model, based on the immersed boundary method, couples the internal force generation of dynein molecular motors through the passive elastic axonemal structure with the external fluid mechanics. We show an extension of our original model for Newtonian fluids to complex viscoelastic fluids in order to model mucus transport by cilia in the respiratory tract as well as sperm motility in reproduction. These immersed boundary models for sperm and ciliary motility in complex fluids explore continuum approaches such as Oldroyd-B as well as Lagrangian moving mesh methods.

Modeling and Simulation of Fish-Like Swimming

Michel Bergmann, Institut de Mathématiques de Bordeaux and INRIA, Bordeaux, France.



Computing Complex Flows using a Front Tracking Method

Grétar Tryggvason Mechanical Engineering Department - Worcester Polytechnic Institute, Worcester, MA (USA)

Abstract: Numerical methods for tracking sharp interfaces now make it possible to conduct direct numerical simulations (DNS) of multiphase flows. Such methods have, for example, been used to examine flows with hundreds of bubbles, yielding major new insight into the dynamics of such flows. Most applications have, however, involved the flow of two incompressible Newtonian fluids, separated by a clean interface. Multiphase flows of practical interest are, however, usually considerably more complex, involving additional fields, phase changes, chemical reactions, and topology changes. Here I will describe the extension of a front tracking method to handle complex flows, including electric fields, phase change, mass transfer and chemical reactions. A multiscale approach to account for flow features too small to resolve is also presented.


Self-propelled motions of solids in a fluid: mathematical analysis, simulation and control

Marius Tucsnak, Institut Elie Cartan de Nancy and INRIA Nancy Grand Est, Nancy (France)

Abstract: pdf


Wall modeling challenges for the Immersed boundary method

Giuseppe Pascazio Politecnico di Bari (Italy)

Abstract: The Cartesian-grid immersed boundary (IB) method greatly simplifies the grid generation process for computing flows with complex and/or moving boundaries, by avoiding the need for a body-fitted mesh. The body under consideration, whose surface is described by a stereolithography format, is overlapped onto a Cartesian grid and the boundary conditions at the immersed surface are applied  explicitly at the "interface cells" by reconstructing the flow variable from the computed values of the  surrounding "fluid cells" and the prescribed values at the wall. Needless to say, the solution accuracy depends on such a reconstruction.
The aim of this work is to illustrate and address the boundary condition issues arising when applying the IB method  to two class of problems: (1) high Reynolds number flows and (2) fluid-structure interaction (FSI) problems  involving moving bodies.
For flows with moderate values of the Reynolds number (Re), a linear interpolation provides accurate results. On the other hand, such an approach would require a huge number of cells to resolve high-Re wall bounded flows. Local grid-refinement alleviates such a difficulty, but it is not fully satisfactory, especially in three dimensions. Wall functions are considered as a promising tool to render the proposed  IB method effective for high-Re flows. In this work several wall models are analyzed.  The details of such wall models will be provided along with an assessment study of their performance in the prediction of flows with pressure-induced separation regions.
For the simulation of FSI problems, one has to define an efficient and general strategy to detect when two bodies undergo a collision interaction. Then, relying on the basic mechanisms of particle-particle  and particle-wall interactions, a properly defined collision model has to be provided. Here, the case of arbitrarily shaped rigid particle transport is considered and the collision model accuracy will be assessed by solving well documented particulate flows.

An Immersed Interface Method for Simulating the Dynamics of
Inextensible Interfaces in Viscous Fluids

Boo Cheong Khoo Department of Mechanical Engineering, Faculty of Engineering, National University of Singapore (Singapore)

Abstract: pdf

A Versatile Sharp-Interface Immersed Boundary Method with Application to Complex Biological Flows

Rajat Mittal Mechanical and Aerospace Engineering, Washington (USA)

Abstract: Complex moving boundaries and fluid-structure interaction are a hallmark of biological flow configurations. Computational modeling of such flows however poses a severe challenge for conventional modeling approaches and the last decade has seen a tremendous rise in the popularity of immersed-boundary methods (IBM) for modeling such flows. The key feature of the immersed boundary method is that simulations with complex moving boundaries can be carried out on stationary, body non-conformal Cartesian grids. This approach eliminates the need for complicated re-meshing algorithms that are usually employed with conventional body-conformal methods. In our presentation we will describe the salient features of a versatile Cartesian grid-based immersed–boundary method which is especially well suited for biological flows. The IB method developed here is accurate, efficient, scalable and fast, and can handle extremely complex, moving geometries with relative ease. The solver is being use for a number of studies including fish locomotion, human swimming, insect flight and fluid-structure interaction in the human larynx, and results from these studies will be presented.


Compressible flow simulations using penalization and level set


 Haysam Telib OPTIMAD Torino (Italy)

Abstract: The point of departure of this presentation is a discussion on how the penalization method  for incompressible NS equations can be extended to compressible Euler or NS. In this framework we will derive a first order all-speed scheme for compressible flows past moving  bodies. The same ideas are further exploited to devise a simple scheme preserving sharp contact discontinuities for the computation of compressible multifluids . Finally, examples on how to improve accuracy to second order exploiting an appropriate distance function will be provided.

A numerical turbulent wind tunnel for low Reynolds number flows

Paolo Orlandi Dipartimento di Meccanica e Aeronautica, Roma (Italy)

Abstract: pdf

Imagery for 3D geometry design: application to fluid flows

Cédric Galusinski IMAT, Toulon (France)

Abstract: The goal of this talk is to introduce PDE tools in order to construct a 3D representation of tubular geometries from a 2D longitudinal view. The 3D geometry is implicitly defined by a level set function. Some image processing tools will be presented to allow identification of 2D interfaces. Then, by solving the Eikonal equation, the 2D skeleton of the 2D geometry is constructed. The 3D level set function defining the 3D geometry follows after some assumptions on sections of tubular geometries. Additional informations as boundary conditions at inlet and outlet of tubing are precised in our image processing software. Then, sufficient informations for 3D flow simulation are exported. A 3D bifluid flow solver is introduced. It uses only informations from imagery to run. Again, the level set represention on cartesian grid of the geometry and the fluids is a simple tool to allow complex flow simulation.

Global stability and control of Bluff-Body Wakes using Immersed Boundaries

Flavio Giannetti University of Salero (Italy)


Abstract: In the last decade much attention has been focused in the study of global instabilities arising in the wake of bluff bodies.  Important progress in this filed was made both through asymptotic analysis, direct numerical simulations and global stability computations. Often the numerical treatment of the problem can be substantially simplified by the use of immersed-boundary techniques, which are well suited to simulate flows behind complex bodies at moderate Reynolds number In this talk we will review some results that we have obtained in the study of global instabilities  through the use of a simple immersed-boundary technique. After a short introduction describing the particular method used in our computations, the talk will focus on the major results concerning the localization and control of the global instability occurring in bluff-body wakes, as for example those arising behind a fixed or a rotating circular cylinder. In particular we will show how to use the information contained in both the direct and adjoint modes in order to localize the core of  the global instability. Both primary and secondary instability will be discussed. Finally we will shortly describe a combined Multigrid-Immersed Boundary algorithm for the fast solution of global stability problem both in 2D and 3D configurations.