An accurate, efficient method is developed for simulating 2D unsteady viscous incompressible flows around multiple moving rigid objects in another paper. This method employs dynamical difference mesh to solve the Navier-Stokes (N-S) equations written in terms of primitive variable. There are two problems to solve: one is that the boundary conditions on given curves are imposed to computational grid points which are not coinciding with the boundary geometry; the other is that some grid points' initial variables of every time step near the objects boundary are required. In [3], a ghost cell method was used to enforce immersed boundary condition in complex geometry, which can treat both Dirichlet and Neumann boundary conditions while preserving the overall second-order accuracy of the base solver. In this paper, this ghost cell method is extended to the dynamic mesh for dealing with the internal moving boundaries. Through these approaches, the boundary conditions on an arbitrary curve are distributed to regular difference mesh points, and the initial variables can be provided to the points changing from rigid objects domain to fluid domain following time. The flow equations are solved on a difference mesh. Thus the standard N-S equations' solvers (for example, SIMPLE method) can be employed through a few modifications. So the advantages and efficiency of regular solvers are retained. The method is validated using flow past a cylinder. The flows around two cylinders which are moving relative to each other are calculated.
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