Applied Mechanics and Materials Vols. 444-445

Abstract: The lattice Boltzmann method (LBM) is considered as an alternative scheme to the standard Navier-Stokes approach. To simulate the high Reynolds number turbulence, several approaches based on LBM have been proposed. Among them, 5 approaches including the direct numerical simulation, dynamic subgrid scale model, inertial range consistent subgrid model, very large eddy simulation and entropic lattice Boltzmann method are discussed in detail. Features including improvements and shortcomings of each approach are presented. Whats more, application prospects of these approaches in high Reynolds number turbulence simulations are pointed out.

Abstract: This paper aimed to investigate the multi-objective optimization method of supercritical airfoil. To achieve the optimal design of supercritical airfoil Rae2822, an improved NSGA-2 (Nondominated Sorting Genetic Algorithm) method was utilized, while the cross-operator and adaptive-variation operator were introduced to improve the convergence speed of the algorithm. During the optimization, the airfoil parametric modeling was achieved based on the Bezier-Bernstein method, and the objective function was obtained through solving the N-S equations. Considering the parallel computation characteristics of the algorithm, the computation was conducted in large-scale Linux computer system to reduce the solving time. Optimization results showed that the undominate solution with high quality obtained through the NSGA-2 method distributed evenly, which provided the designer a wider choosing space. It was also showed that the multi-objective optimization method presented in this paper was feasible and reliable.

Abstract: In this paper, the fluid and structure model are fully coupled and put into FSI solver to calculate simultaneously to predict vortex-induced vibration. Multiple iterative calculations are needed in each time step and the fluid and structure model perform the next step calculation until satisfy the requirement of accuracy, which is different from conventional method used to simulate VIV. The present results agree well with the experimental results of other researchers.

Abstract: This work focuses on the effects of the particle shape factor and blockage ratio on the friction coefficient and drag coefficient of the drop-shaped particle for Reynolds number ranging from 10^-2 to 10² when the particle is settling under gravity. Comparison with the results of a circular particle has also been presented. It has been shown that the particle friction coefficient keeps constant when Reynolds number is below 1, and increases as Reynolds number increasing when Reynolds number is greater than 1. Furthermore, results have also shown that both the friction coefficient and drag coefficient of the circular particle are smaller than those of the drop-shaped one when Reynolds number is below about 30 while bigger than those of drop-shaped one when Reynolds number is larger than 30.

Abstract: The present article describes the combination of the correlation based transition model of Menter et al. with the Detached Eddy Simulation (DES) and Delayed Detached Eddy Simulation (DDES) methodology. The interaction between transition model and DES or DDES method was investigated by T3A test case. The grid sensitivity of the combined methodology is discussed and the resolution is given. Then, the simulation of flow over foil of medium thick at stall angle was performed. The combined methodology produce results that have better agreement with experiment comparing to RANS transition model or fully turbulent DES/DDES alone. And the DDES based combined model shows a better agreement with experiment in the simulation of trailing edge separation comparing to DES based combined model.

Abstract: Thanks to the recent development of tools such as CUDA and OpenCL it has become possible to fully utilize Graphical Processing Units (GPUs) for scientific computing. OpenCL promises huge savings in parallel code development and optimization efforts due to it is not restricted to a specific architecture. We have developed an OpenCL-based acceleration framework on GPU for numerical simulations of incompressible flows using incompressible Smoothed Particle Hydrodynamics (ISPH). In order to assess the performance of the GPU implementation presented in the present work, a comparison was made against the implementation of the same ISPH in CPU using OpenCL.

Abstract: In wind tunnel tests, the size of the test model is generally much less than the real aircraft, which makes that the Re number during the test is an order of magnitude smaller than the flight Re number. The fixed transition is an important means to improve the test Re number. In the paper, the transition turbulence modelis used to simulate the flow characteristics of the test model (Re=1.5×10⁶), flight model (Re=12×10⁶) and fixed transition model. It is shows that the drag coefficient of the transition model increases and the lift coefficient decreases to compare with the test model and flight model. Compared with the flight model, the turbulent velocity profile of transition model in layer boundary is inadequate, its relative Re number is smaller, so the further amend in the aerodynamic characteristics need to be made.

Abstract: By using the FINE software developed by NUMECA Company, the hydraulic performance of the impeller of a centrifugal pump with spatial guide vanes was numerically simulated. The S-A turbulent model was used to numerically calculate the three-dimensional flow field in the centrifugal pump under three different conditions. The flow analysis shows that the pressure gradient on the vane surface gradually reduces with the increasing of the flow rate; the position of axial vortex between vanes has nothing to do with the flow rate; the tangential flow gradient in the flow passage decreases with the increasing of the flow rate. Compared with the test results, it is obvious that this numerical simulation can accurately predicate the complicated three-dimensional flow and the hydraulic performance of the pump.

Abstract: A lattice Boltzmann method (LBM) with single-relaxation time and on-site boundary condition is used for the simulation of viscous flow in a three-dimensional (3D) lid-driven cavity. Firstly, this algorithm is validated by compared with the benchmark experiments for a standard cavity, and then the results of a cubic cavity with different inflow angles are presented. Steady results presented are for the inflow angle of and, and the Reynolds number is selected as 500. It is found that for viscous flow under moderate Reynolds number, there exists a primary vortex near the center and a secondly vortex at the lower right corner on each slice when, namely in a standard 3D lid-driven cavity, which cant be found when. So it can be thought that the flow pattern in a 3D lid-driven cavity depends not only on the Reynolds number but also the inflow angle.

Abstract: In this paper the ability of the Lattice Boltzmann Method (LBM) is investigated for simulating acoustic problems, especially for the propagation of acoustic waves in a wall bounded region. To treat the wall boundary conditions, a non-equilibrium extrapolation scheme for the LBM is adopted. LBM is next applied to simulate the complex aerodynamic noise generated from a square cylinder. In order to efficiently suppress the disturbances at the computational boundaries, the improved absorbing boundary condition (IABC) is developed in this paper. To validate the flow and acoustic solution of a square cylinder, comparisons between the present LBM and the previous studies are carried out. It is demonstrated that the LBM can efficiently simulate the noise generated from a square cylinder.