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CivilComp Proceedings
ISSN 17593433 CCP: 90
PROCEEDINGS OF THE FIRST INTERNATIONAL CONFERENCE ON PARALLEL, DISTRIBUTED AND GRID COMPUTING FOR ENGINEERING Edited by:
Paper 45
Parallel Computational Fluid Dynamics: Not without its Challenges T.N. Croft, D. Carswell, M. Cross, D. McBride, S. Rolland, A.K. Slone and A.J. Williams
Centre for Civil and Computational Engineering, School of Engineering, Swansea University, United Kingdom T.N. Croft, D. Carswell, M. Cross, D. McBride, S. Rolland, A.K. Slone, A.J. Williams, "Parallel Computational Fluid Dynamics: Not without its Challenges", in , (Editors), "Proceedings of the First International Conference on Parallel, Distributed and Grid Computing for Engineering", CivilComp Press, Stirlingshire, UK, Paper 45, 2009. doi:10.4203/ccp.90.45
Keywords: computational fluid dynamics, parallel computing, scalability, rotating mesh.
Summary
Computational fluid dynamics (CFD) has advanced over the last thirty years to the point whereby simulations with million node meshes modelling complex geometries with a comprehensive suite of physics is now commonplace. Moreover, code parallelisation strategies based upon domain, (more precisely, mesh) partitioning are now well established to the point where commercial CFD software tools all include parallel capabilities, which run scalably on parallel computing systems with adequate communications speeds. These approaches were enabled through the emergence of:
The mesh partitioning approach to CFD code parallelisation implicitly assumes that the compute load at each element of control volume is identical, and where this is the case codes scale well. However, there are a range of physical flow phenomena where the compute load cannot be guaranteed to be uniform across the mesh, and it is under these conditions that scalability might become significantly limited. Flows through domains with rotating machinery have presented a range of challenges to the CFD community over the last decade or so. There are two key complexities introduced by rotating machinery  the introduction of momentum into the flow field at specific locations, and the loading of the flow on the rotating structure as well as the details of the flow interacting with it. In the paper we consider the three conventional ways to capture the impact of rotating machinery on flows:
In this paper attention is then focussed upon a straightforward strategy to enable the multiple reference frame approach to run in parallel. In the scheme the element adjacencies change on the interface between parts of the mesh influenced by different reference frames. In order for this technique to run in parallel there is a need to extend the communication schedules so that all data associated with near interface geometry is available on all processors. Although this is safe in computational terms, it is also potentially expensive unless the number of elements bounding the rotating surface is small compared to the overall mesh size. All the above strategies have been implemented within the CFD module of the multiphysics code PHYSICA, which employs a fully unstructured mesh of any mix of elements up to and including hexahedra together with conventional finite volume solution procedures for multicomponent multiphase free surface reacting flows. The code has been parallelised using a conventional mesh partitioning approach employing the JOSTLE partition tool and the CAPLIB message passing library. Using the above CFD technology the rotating equipment modelling strategies referred to above are all evaluated with regard to their parallel scalability. They are all shown to be surprisingly scalable in parallel, so long as the ratio of the number of elements bounding the rotating reference frame is small compared to the total mesh size. purchase the fulltext of this paper (price £20)
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