Keywords: unstructured mesh, navier-stokes, time accuracy, deforming mesh, adaptive remeshing.

Problems of industrial and academic relevance frequently involve flows around geometries which change with time. In both the military and civilian aircraft industries, the simulation of flows involving multiple bodies in relative motion is of great interest e.g. the release of stores from aircraft or formation flying, such as air refuelling. Manoeuvering aircraft not only experience geometry changes, through the deployment of control surfaces, but also through aeroelastic effects, which may change the aerodynamic characteristics significantly. Such problems may involve motion that is essentially known a--priori or motion that is directly coupled with the flow field and dynamics of the problem. Problems may be well approximated by simulating the geometry changes as the movement of two or more rigid bodies, while others will require significant deformation of components. Such transient flows provide additional computational difficulties, as the mesh must be modified during the computation process, to accommodate the changes in the geometry.

Unstructured mesh based methods have proved to be very effective for the solution of problems involving high speed compressible flows. The principal advantages of this approach are well known and centre, mainly, on the observation that it provides a powerful tool for the discretisation of domains of complex shape. An additional feature is that adaptive mesh procedures can be readily implemented, allowing the solution quality to be enhanced [1]. For problems involving large deformation of components, which cannot be broken down into smaller entities in relative motion, the approach employed here involves the use of a single, consistent, unstructured mesh for each time step [2]. With time, this mesh will need to be adapted, to allow for the changing geometry in the solution. In order to achieve a solution, in an acceptable time scale, parallel implementation of the complete solution procedure has to be ensured. In this paper, we will consider the parallelisation of a basic unstructured mesh solver for aerospace engineering applications. We will also present the outline of the various geometric partitioning approaches we developed to enable us to address the computational demands of the mesh generator. Furthermore, a parallel implementation of the mesh adaptation required to ensure the validity of the meshes for unsteady flow in the presence of moving boundary components is also presented. Various examples are used to show the efficiency and the predictive capability of the complete method.

[1]

J. Peraire, M. Vahdati, K. Morgan, O.C. Zienkiewicz, "Adaptive remeshing for compressible flow simulations", J. Comput. Phys., 72, 449-466, 1987.

[2]

O. Hassan, E.J. Probert, K. Morgan, N.P. Weatherill, "Unsteady flow simulation using unstructured meshes", Computer Methods for Applied Mechanical Engineering, 189, 1247-1275, 2000. doi:10.1016/S0045-7825(99)00376-X

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