Simulation of incompressible viscous flows around moving objects by a variant of immersed boundary-Lattice Boltzmann method

A variant of immersed boundary-lattice Boltzmann method (IB-LBM) is presented in this paper to simulate incompressible viscous flows around moving objects. As compared with the conventional IB-LBM where the force density is computed explicitly by Hook's law or the direct forcing method and the non-slip condition is only approximately satisfied, in the present work, the force density term is considered as the velocity correction which is determined by enforcing the non-slip condition at the boundary. The lift and drag forces on the moving object can be easily calculated via the velocity correction on the boundary points. The capability of the present method for moving objects is well demonstrated through its application to simulate flows around a moving circular cylinder, a rotationally oscillating cylinder, and an elliptic flapping wing. Furthermore, the simulation of flows around a flapping flexible airfoil is carried out to exhibit the ability of the present method for implementing the elastic boundary condition. It was found that under certain conditions, the flapping flexible airfoil can generate larger propulsive force than the flapping rigid airfoil

A Ghost Fluid Approach for Thermal Lattice Boltzmann Method in Dealing with Heat Flux Boundary Condition in Thermal Problems with Complex Geometries

In this paper, the ghost fluid thermal lattice Boltzmann method is improved to properly impose the heat flux boundary condition on complex geometries [Khazaeli, R., S. Mortazavi and M. Ashrafizaadeh (2013). Application of a ghost fluid approach for a thermal lattice Boltzmann method, J. Comput. Phys. 250, 126– 140]. A double-population thermal lattice Boltzmann method is used to handle both the flow and temperature fields on a Cartesian grid and the boundary conditions are imposed using a ghost fluid method. The method is based on the decomposition of the unknown distribution functions into their equilibrium and non-equilibrium parts at every ghost point. The equilibrium parts are determined by performing an extrapolation of major quantities from the image points to the associated ghost points. The bounce-back scheme is then used to determine the non- equilibrium parts. The method benefits from some features such as easy implementation and second order accuracy. The method is applied to simulate natural convection within annuluses with different shapes and boundary conditions,. The obtained results are generally in a good agreement with those predicted by other numerical efforts

A coupled 3-dimensional bonded discrete element and lattice Boltzmann method for fluid-solid coupling in cohesive geomaterials

This paper presents a 3D bonded discrete element and lattice Boltzmann method for resolving the fluid‐solid interaction involving complicated fluid‐particle coupling in geomaterials. In the coupled technique, the solid material is treated as an assembly of bonded and/or granular particles. A bond model accounting for strain softening in normal contact is incorporated into the discrete element method to simulate the mechanical behaviour of geomaterials, whilst the fluid flow is solved by the lattice Boltzmann method based on kinetic theory and statistical mechanics. To provide a bridge between theory and application, a 3D algorithm of immersed moving boundary scheme was proposed for resolving fluid‐particle interaction. To demonstrate the applicability and accuracy of this coupled method, a benchmark called quicksand, in which particles become fluidised under the driving of upward fluid flow, is first carried out. The critical hydraulic gradient obtained from the numerical results matches the theoretical value. Then, numerical investigation of the performance of granular filters generated according to the well‐acknowledged design criteria is given. It is found that the proposed 3D technique is promising, and the instantaneous migration of the protected soils can be readily observed. Numerical results prove that the filters which comply with the design criteria can effectively alleviate or eliminate the appearance of particle erosion in dams

Application of an Immersed Boundary Treatment in Simulation of Natural Convection Problems with Complex Geometry via the Lattice Boltzmann Method

In this study, a version of thermal immersed boundary-Lattice Boltzmann method (TIB-LBM) is used to simulate thermal flow problems within complex geometries. The present approach is a combination of the immersed boundary method (IBM) and the thermal lattice Boltzmann method (TLBM) under the double population approach. The method combines two different grid systems, an Eulerian grid for the flow domain and a Lagrangian grid for the boundary points immersed in the flow. In the present method, an unknown velocity correction is considered on the boundary points to impose the no-slip boundary condition. As a similar approach, an unknown internal energy correction on the boundary points is applied to satisfy the constant temperature boundary condition. The advantages of this approach are its second-order accuracy and straightforward calculation of the Nusselt number. The natural convection in an annulus with various outer cylinder shapes for different Rayleigh numbers have been simulated to demonstrate the capability and the accuracy of present approach. In terms of accuracy, the predicted results show an excellent agreement with those predicted by other experimental and numerical approaches

Application of multi-block approach in the immersed boundary-lattice Boltzmann method for viscous fluid flows

10.1016/j.jcp.2006.02.017Journal of Computational Physics2182460-478JCTP

Computational Study of Free Jets Emanating from Circular and Lobed Orifice-Lattice Boltzmann Method

The Lattice Boltzmann method is an effective computational fluid dynamics tool to study complex flows. Unlike conventional numerical schemes based on discretization of macroscopic continuum equations, the Lattice Boltzmann method is based on particles and mesoscopic kinetic equations. Single-Relaxation Time Lattice Boltzmann Method (SRTLBM) with Smagorinsky LES model is applied to simulate high Reynolds number jet flows of single and multiphase flows emanating. The multi-block approach is implemented to refine the mesh when the high resolution is needed in the region around the core jet. An 2nd order accurate interface treatment between neighboring blocks is derived to satisfy the conservation of mass momentum and the continuity of the stresses across the interface. The bounce back boundary condition and curve boundary condition using extrapolation approach based on the idea of bounce back of the non-equilibrium part is implemented to impose the velocity boundary conditions at surfaces. The core jet length, velocity decay, turbulence intensity, vortex generation, jet breakup and noise spectrum analysis are studied for both circular and lobed jet orifices for a range of Reynolds number from 1000 to 72000. The pseudopotential Shan/Chen model Lattice Boltzmann Method is applied to study the small density ratio at low Reynold’s number and low Weber number liquid jet breakup of the water/silicon oil multiphase fluid. Multiphase jet flow simulations at high Reynold’s number and high Weber number are performed by utilizing OpenFOAM and predicted results are compared with results of documented experimental measurements

Vortex-Induced Vibration of Circular Cylinders Using Multi-Block Immersed Boundary-Lattice Boltzmann Method

Despite decades of research, vortex-induced vibration (VIV) of circular cylinders is still a topic of strong interest in fluid mechanics, as it is of great importance in many engineering disciplines, such as bridges, nuclear reactors and high-rise buildings. In order to provide an in-depth understanding of complex fluid-structure interaction during VIV, this thesis considers the following physical scenarios using an in-house code developed based on immersed boundary-lattice Boltzmann method (IB-LBM). First, a system with two fixed cylinders with an intermediate centre-to-centre spacing is considered. It is found that the frequency component of the force on each individual cylinder changes from a single value to multiple ones, then to a large number of discrete ones and eventually to a broadband continuous spectrum, as the alignment angle increases. Second, the vibration of a cylinder may occur due to fluid-structure interaction, and thus the free motion is investigated using the results from the corresponding forced oscillation. It is shown that when a cylinder is in periodic free motion, its motion will remain the same if the combined mass-damping parameter remains unchanged and the variations of body mass and stiffness follow a particular pattern. Here, the damping ratio is redefined using the motion frequency of the body instead of the commonly adopted natural frequency of the body. Third, large-eddy simulation as turbulence model is implemented in the computer code and multi grids are adopted in IB-LBM to improve computation efficiency and accuracy. Turbulent flow is then studied. The results show that the effect of the Reynolds number on the well-known three response branches at different reduced velocities, or initial, upper and lower branches, is significant. When Reynolds number is fixed, at its lower range calculated, there are only initial and upper branches, and at higher range, there are only upper and lower branches

A Numerical Study on the Deformation of Liquid-Filled Capsules with Elastic Membranes in Simple Shear Flow

Ph.DDOCTOR OF PHILOSOPH

Local Domain-Free Discretization Method and Its Combination with Immersed Boundary Method for Simulation of Fluid Flows

Ph.DDOCTOR OF PHILOSOPH