Vehicle Aerodynamics Simulation for the Next Generation on the K Computer: Part 2 Use of Dirty CAD Data with Modified Cartesian Grid Approach

Abstract

The applicability of high-performance computing (HPC) to vehicle aerodynamics is presented using a Cartesian grid approach of computational fluid dynamics. Methodology that allows the user to avoid a large amount of manual work in preparing geometry is indispensable in HPC simulation whereas conventional methodologies require much manual work. The new frame work allowing a solver to treat 'dirty' computer-aided-design data directly was developed with a modified immersed boundary method. The efficiency of the calculation of the vehicle aerodynamics using HPC is discussed.The validation case of flow with a high Reynolds number around a sphere is presented. The preparation time for the calculation is approximately 10 minutes. The calculation time for flow computation is approximately one-tenth of that of conventional unstructured code. Results of large eddy simulation with a coarse grid differ greatly from experimental results, but there is an improvement in the prediction of the drag coefficient prediction when using 23 billion cells.A vehicle aerodynamics simulation was conducted using dirty computer-aided-design data and approximately 19 billion cells. The preparation for the calculation can be completed within a couple of hours. The calculation time for flow computation is approximately one-fifth of that of conventional unstructured code. Reasonable flow results around a vehicle were observed, and there is an improvement in the prediction of the drag coefficient prediction when using 19 billion cells. The possibility of the proposed methodology being an innovative scheme in computational fluid dynamics is shown.

Full Eulerian deformable solid‐fluid interaction scheme based on building‐cube method for large‐scale parallel computing

“…Improving the solution for cases 1 and 2 earlier using Lagrangian interpolation has been reported, but to simplify the algorithm in this research, the following interpolation methods are adopted …”

“…Improving the solution for cases 1 and 2 earlier using Lagrangian interpolation has been reported, 47 but to simplify the algorithm in this research, the following interpolation methods are adopted. 26 For the different size data exchange of case (1), we use bilinear interpolation in 2D (trilinear in 3D), which is first-order accurate, for interpolation from small cubes to large cubes. The value at the cell center q l is calculated using the cell center values q s1 , q s2 , q s3 , and q s4 in the small cubes adjacent to the large cube, as shown in Figure 7,…”

“…Recently, the building‐cube method (BCM) has been used to simulate compressible/incompressible Navier‐Stokes equations due to its ability to achieve high parallel efficiency and easily generate meshes for complex geometries with local mesh refinement. The BCM is a type of hierarchical Cartesian mesh approach in which the computational domain is divided into cubic regions called cubes (Figure ).…”

Eulerian finite volume formulation using Lagrangian marker particles for incompressible fluid–structure interaction problems

“…All the basic equations and spatial derivatives, except for the solid constitutive equation, are computed on an Eulerian mesh to avoid neighboring particle search. Although this is the same as the MPM, there are two differences between the proposed method and MPM: (a) the proposed method is formulated in a strong form that is consistent with the cell-centered finite volume fluid solver [46][47][48][49][50][51][52][53][54][55] based on a hierarchical Cartesian mesh, which is suitable for massively parallel computing; and (b) the proposed method is a monolithic FSI formulation that does not allocate moving particles in the fluid region to avoid the fluid particle redistribution problem mentioned above. To couple solid and fluid dynamics on the same Eulerian mesh, we use the incompressible mixture formulation, 56 which spatially averages the continuity equation and the equation of motion for solids and fluids, as in Sugiyama's study [34][35][36] and our previous study.…”