Jie Wu

Bio: Jie Wu is an academic researcher from Nanjing University of Aeronautics and Astronautics. The author has contributed to research in topics: Lattice Boltzmann methods & Finite volume method. The author has an hindex of 22, co-authored 72 publications receiving 1229 citations. Previous affiliations of Jie Wu include Shenyang Aerospace University.

Development of Lattice Boltzmann Flux Solver for Simulation of Incompressible Flows

Abstract: A lattice Boltzmann flux solver (LBFS) is presented in this work for simulation of incompressible viscous and inviscid flows. The new solver is based on Chapman-Enskog expansion analysis, which is the bridge to link Navier-Stokes (N-S) equations and lattice Boltzmann equation (LBE). The macroscopic differential equations are discretized by the finite volume method, where the flux at the cell interface is evaluated by local reconstruction of lattice Boltzmann solution from macroscopic flow variables at cell centers. The new solver removes the drawbacks of conventional lattice Boltzmann method such as limitation to uniform mesh, tie-up of mesh spacing and time interval, limitation to viscous flows. LBFS is validated by its application to simulate the viscous decaying vortex flow, the driven cavity flow, the viscous flow past a circular cylinder, and the inviscid flow past a circular cylinder. The obtained numerical results compare very well with available data in the literature, which show that LBFS has the second order of accuracy in space, and can be well applied to viscous and inviscid flow problems with non-uniform mesh and curved boundary.

Numerical study on the power extraction performance of a flapping foil with a flexible tail

Abstract: The numerical study on the power extraction performance of a flapping foil with a flexible tail is performed in this work. A NACA0015 airfoil is arranged in a two-dimensional laminar flow and imposed with a synchronous harmonic plunge and pitch rotary motion. A flat plate that is attached to the trailing edge of the foil is utilized to model a tail, and so they are viewed as a whole for the purpose of power extraction. In addition, the tail either is rigid or can deform due to the exerted hydrodynamic forces. To implement numerical simulations, an immersed boundary-lattice Boltzmann method is employed. At a Reynolds number of 1100 and the position of the pitching axis at third chord, the influences of the mass and flexibility of the tail as well as the frequency of motion on the power extraction are systematically examined. It is found that compared to the foil with a rigid tail, the efficiency of power extraction for the foil with a deformable tail can be improved. Based on the numerical analysis, it is indicated that the enhanced plunging component of the power extraction, which is caused by the increased lift force, directly contributes to the efficiency improvement. Since a flexible tail with medium and high masses is not beneficial to the efficiency improvement, a flexible tail with low mass together with high flexibility is recommended in the flapping foil based power extraction system.

Flow control of a circular cylinder by using an attached flexible filament

Abstract: The flow control of a circular cylinder by using a flexible filament has been numerically investigated in this work. The cylinder is either fixed or elastically mounted, and the filament is attached to the base of the cylinder. Its leading end is fixed and its trailing end is free to flap. To execute the numerical simulation and deal with the fluid-structure interaction (FSI) of the filament as well, an improved immersed boundary-lattice Boltzmann method (IB-LBM) is presented. As compared to the conventional IB-LBM for handling the FSI of a filament, the current method can incorporate the mass effect of the filament and no user-defined spring parameter is needed to calculate the interaction force on the filament. After validating the employed method, the effects of the filament on the flow control of the cylinder are systematically examined by varying the bending coefficient (Kb) and length (L) of the filament. The laminar flow with a Reynolds number of 150 is considered in this study. Based on the numeri...

A Ghost-Cell Immersed Boundary Method for Flow in Complex Geometry

Abstract: An efficient ghost-cell immersed boundary method (GCIBM) for simulating turbulent flows in complex geometries is presented. A boundary condition is enforced through a ghost cell method. The reconstruction procedure allows systematic development of numerical schemes for treating the immersed boundary while preserving the overall second-order accuracy of the base solver. Both Dirichlet and Neumann boundary conditions can be treated. The current ghost cell treatment is both suitable for staggered and non-staggered Cartesian grids. The accuracy of the current method is validated using flow past a circular cylinder and large eddy simulation of turbulent flow over a wavy surface. Numerical results are compared with experimental data and boundary-fitted grid results. The method is further extended to an existing ocean model (MITGCM) to simulate geophysical flow over a three-dimensional bump. The method is easily implemented as evidenced by our use of several existing codes.

Space-time finite element techniques for computation of fluid-structure interactions

Abstract: We describe the space–time finite element techniques we developed for computation of fluid–structure interaction (FSI) problems. Among these techniques are the deforming-spatial-domain/stabilized space–time (DSD/SST) formulation and its special version, and the mesh update methods, including the solid-extension mesh moving technique (SEMMT). Also among these techniques are the block-iterative, quasi-direct and direct coupling methods for the solution of the fully discretized, coupled fluid and structural mechanics equations. We present some test computations for the mesh moving techniques described. We also present numerical examples where the fluid is governed by the Navier– Stokes equations of incompressible flows and the structure is governed by the membrane and cable equations. Overall, we demonstrate that the techniques we have developed have increased the scope and accuracy of the methods used in computation of FSI problems. � 2005 Elsevier B.V. All rights reserved.

Numerical simulations of 3D flows with moving contact lines

Abstract: Computational methods have been extended recently to allow for the presence of moving contact lines in simulated two-phase flows. The predictive capability offered by these methods is potentially large, joining theoretical and experimental methods. Several challenges rather unique to this area need to be overcome, however, notably regarding the conditions near a moving contact line and the very large separation of length scales in these flows. We first summarize the main models for moving contact lines and follow with an overview of computational methods that includes direct continuum approaches and macroscale models that resolve only the large-scale flow by modeling the effects of the conditions near the contact line using theory. Results are presented for contact-line motion on ideal as well as patterned and grooved surfaces and for extensions to account for complexities such as thermocapillarity and phase change.

A visual study of the flow structures behind a heaving and pitching finite-span wing

Abstract: The three-dimensional structure of the flow behind a heaving and pitching finite-span wing is investigated using dye flow visualization at a Reynolds number of 164. Phase-locked image sequences, which are obtained from two orthogonal views, are combined to create a set of composite images that give an overall sense of the three-dimensional structure of the flow. A model of the vortex system behind the wing is constructed from the image sequences. Variations of the Strouhal number, pitch amplitude and heave/pitch phase angle are qualitatively shown to affect the structure of the wake.