scholarly journals An immersed boundary/level-set method for incompressible viscous flows in complex geometries with good conservation properties

2009 ◽  
pp. 561-587
Author(s):  
Yoann Cheny ◽  
Olivier Botella
Keyword(s):  
Level Set ◽  
Viscous Flows ◽  
Immersed Boundary ◽  
Implicit Representation ◽  
Irregular Boundary ◽  
Level Set Function ◽  
Incompressible Viscous Flows ◽  
Irregular Geometries ◽  
Set Function ◽  
Ib Method

This paper concerns the development of a new Cartesian grid / immersed boundary (IB) method for the computation of incompressible viscous flows in irregular geometries. In IB methods, the computational grid is not aligned with the irregular boundary, and of upmost importance for accuracy and stability is the discretization in cells which are “cut" by the boundary. In this paper, we present an IB method (the LS-STAG method) based on the Cartesian MAC method where the irregular boundary is represented by its level-set function. This implicit representation of the immersed boundary enables us to discretize efficiently the fluxes in the cut-cells by imposing the strict conservation of total kinetic energy at the discrete level. The accuracy and robustness of our method are assessed on benchmark flows.

The LS-STAG Method for Viscous Incompressible Flows in Irregular Geometries: Basics of the Discretization and Application to Viscoelastic Flows

2010 ◽  
Author(s):  
Olivier Botella ◽  
Yoann Cheny
Keyword(s):  
Level Set ◽  
Incompressible Flows ◽  
Immersed Boundary ◽  
Viscoelastic Flows ◽  
Irregular Boundary ◽  
Flow Equations ◽  
Level Set Function ◽  
Viscous Incompressible Flows ◽  
Global Invariants ◽  
Set Function

The LS-STAG method is an immersed boundary method for viscous incompressible flows based on the staggered MAC arrangement for Cartesian grids, where the irregular boundary is sharply represented by its level-set function. The level-set function enables us to compute efficiently all relevant geometry parameters of the so-called “cut-cells”, i.e. the cells that are cut by the immersed boundary, reducing thus the bookkeeping associated to the handling of complex geometries. One of the main features of the LS-STAG method is the use of a consistent and unified discretization of the flow equations in both Cartesian and cut-cells, which has been obtained by enforcing the strict conservation of global invariants of the flow such as total mass, momentum and kinetic energy in the whole fluid domain. After a short discussion on the salient features of the LS-STAG method, we will present one of its most recent application: The computation of viscoelastic flows governed by the Oldroyd-B constitutive equation.

A Method for Tracking a Solid Body in a Fluid Field in Immersed Boundary Methods

2018 ◽  
Author(s):  
Guangfa Yao
Keyword(s):  
Level Set ◽  
Solid Body ◽  
Volume Fraction ◽  
Transformation Matrix ◽  
The Body ◽  
New Method ◽  
Immersed Boundary ◽  
Body Interaction ◽  
Level Set Function ◽  
Set Function

Immersed boundary method has got increasing attention in modeling fluid-solid body interaction using computational fluid dynamics due to its robustness and simplicity. It usually simulates fluid-solid body interaction by adding a body force in the momentum equation. This eliminates the body conforming mesh generation that frequently requires a very labor-intensive and challenging task. But accurately tracking an arbitrary solid body is required to simulate most real world problems. In this paper, a few methods that are used to track a rigid solid body in a fluid domain are briefly reviewed. A new method is presented to track an arbitrary rigid solid body by solving a transformation matrix and identifying it using a level set function. Knowing level set function, the solid volume fraction can be derived if needed. A three-dimensional example is used to study a few methods used to represent and solve the transformation matrix, and demonstrate the presented new method.

scholarly journals Numerical Simulation of Wind Turbine Rotors Autorotation by Using the Modified LS-STAG Immersed Boundary Method

2017 ◽  
Vol 2017 ◽  
pp. 1-7 ◽  
Author(s):  
Ilia K. Marchevsky ◽  
Valeria V. Puzikova
Keyword(s):  
Numerical Simulation ◽  
Wind Turbine ◽  
Level Set ◽  
Immersed Boundary Method ◽  
Immersed Boundary ◽  
Pass Filter ◽  
Level Set Function ◽  
Boundary Method ◽  
Turbine Rotors ◽  
Set Function

A software package is developed for numerical simulation of wind turbine rotors autorotation by using the modified LS-STAG level-set/cut-cell immersed boundary method. The level-set function is used for immersed boundaries description. Algorithm of level-set function construction for complex-shaped airfoils, based on Bézier curves usage, is proposed. Also, algorithm for the level-set function recalculation at any time without reconstructing the Bézier curve for each new rotor position is described. The designed second-order Butterworth low-pass filter for aerodynamic torque filtration for simulations using coarse grids is presented. To verify the modified LS-STAG method, the flow past autorotating Savonius rotor with two blades was simulated at Re=1.96·105.

Droplet–particle collision mechanics with film-boiling evaporation

2007 ◽  
Vol 573 ◽  
pp. 311-337 ◽  
Author(s):  
YANG GE ◽  
L.-S. FAN
Keyword(s):  
Particle Size ◽  
Impact Velocity ◽  
Level Set ◽  
Immersed Boundary Method ◽  
Contact Time ◽  
Film Boiling ◽  
Immersed Boundary ◽  
Level Set Function ◽  
Spread Factor ◽  
Set Function

A three-dimensional numerical model is developed to simulate the process of collision between an evaporative droplet and a high-temperature particle. This phenomenon is of direct relevance to many engineering process operations, such as fluid catalytic cracking (FCC), polyethylene synthesis, and electronic materials coating. In this study, the level-set method and the immersed-boundary method are combined to describe the droplet–particle contact dynamics in a fixed Eulerian grid. The droplet deformation is captured by one level-set function while the solid–fluid boundary condition is imposed on the particle surface through the immersed-boundary method involving another level-set function. A two-dimensional vapour-layer model is developed to simulate the vapour flow dynamics. Equations for the heat transfer characteristics are formulated for each of the solid, liquid and gas phases. The incompressible flow-governing equations are solved using the finite-volume method with the ALE (arbitrary Lagrangian Eulerian) technique. The simulation results are validated through comparisons with experimental data obtained from the new experimental set-up designed in this study. An important feature of the droplet impacting on a particle with film boiling is that the droplet undergoes a spreading, recoiling and rebounding process, which is reproduced by the numerical simulation based on the model. Details of the collision such as spread factor, contact time and temperature distribution are provided. Simulations are also conducted to examine the effects of the particle size and the collision velocity. Although the value for the maximum spread factor is larger for a higher impact velocity and for a smaller particle, the contact time is independent of the impact velocity and particle size. Both the normal collision and the oblique collision are considered in this study.

scholarly journals An Image Segmentation Method Based on Improved Regularized Level Set Model

2018 ◽  
Vol 8 (12) ◽  
pp. 2393 ◽  
Author(s):  
Lin Sun ◽  
Xinchao Meng ◽  
Jiucheng Xu ◽  
Shiguang Zhang
Keyword(s):  
Image Segmentation ◽  
Level Set ◽  
Energy Functional ◽  
External Energy ◽  
Regularization Term ◽  
Level Set Function ◽  
New Energy ◽  
Segmentation Approach ◽  
Set Function ◽  
Distance Regularization

When the level set algorithm is used to segment an image, the level set function must be initialized periodically to ensure that it remains a signed distance function (SDF). To avoid this defect, an improved regularized level set method-based image segmentation approach is presented. First, a new potential function is defined and introduced to reconstruct a new distance regularization term to solve this issue of periodically initializing the level set function. Second, by combining the distance regularization term with the internal and external energy terms, a new energy functional is developed. Then, the process of the new energy functional evolution is derived by using the calculus of variations and the steepest descent approach, and a partial differential equation is designed. Finally, an improved regularized level set-based image segmentation (IRLS-IS) method is proposed. Numerical experimental results demonstrate that the IRLS-IS method is not only effective and robust to segment noise and intensity-inhomogeneous images but can also analyze complex medical images well.

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