Van Holsbeke, Cedric

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Ghent University Academic Bibliography

The use of a castellated mesh for resistancecalculations of upper airwaysCedric Van HolsbekeSupervisor(s): Pascal Verdonck, Peter Van RansbeeckI. INTRODUCTIONNowadays, Computational Fluid Dynamics(CFD) is accepted as an important tool for ana-lyzing treatments for respiratory diseases. Pre-vious studies showed that, in sleep apnea pa-tients, the change in upper airway resistanceafter mandibular repositioning correlates verywell with the clinical outcome [1]. A full au-tomatic system based on open source softwarewould help the acceptance of CFD in clini-cal practice. The problem is that regular au-tomatic mesh generators can not guarantee themesh quality as skewness problems can be si-tuated at the boundaries. When using castella-ted meshes, the quality is always good as thismesh does not follow the boundary perfectly(figure 1(a)), however this means that geome-trical errors are introduced compared to regular(snapped) meshes (figure 1(b)). In this study,CFD calculations are performed using the opensource CFD code OpenFOAM (OpenCFD Ltd,UK) in order to test if castellated meshes aresuited for resistance calculations of upper air-ways.II. MATERIALS AND METHODSAn upper airway is segmented from compu-ted tomography scans, from the hard palate tothe vocal cords. The open source SnappyHex-Mesh (OpenCFD Ltd, UK) is used for the ge-neration of a castellated mesh and a snappedmesh. As a verification, a tetrahedral grid is—————————————————–C. Van Holsbeke is affiliated to the Department ofMechanical Engineering, Faculty of Applied Engi-neering Sciences, University College Ghent(a)Castellated mesh (b)Regular meshFigure 1. Meshescreated using a validated commercial mesh ge-nerator TGrid 5.0.6 (Ansys, Lebanon, USA).All meshes contain about 1.000.000 cells. Cal-culations are performed laminar and second or-der discretization algorithms are chosen.III. RESULTSThe difference in resistance between theTGrid mesh and the snapped SnappyHexMeshmesh is only 0.4%. However, the differencebetween the results of these meshes and the ca-stellated mesh is 10%.IV. CONCLUSIONSCastellated meshes are not suitable for resis-tance calculations of upper airways. The intro-duced errors at the boundaries are too big inthese complex geometries. However, snappedmeshing with SnappyHexMesh shows to be apromising tool in further research.REFERENCES[1] J.W. De Backer, O.M. Vanderveken, W.G. Vos,A. Devolder, S.L. Verhulst, J.A. Verbraecken,P.M. Parizel, M.J. Braem, P.H. Van de Heyning,and W.A. De Backer, “Functional imaging usingcomputational fluid dynamics to predict treat-ment success of mandibular advancement devicesin sleep-disordered breathing,” Journal of Biome-chanics, vol. 40, no. 16, pp. 3708–3714, 2007.

The use of a castellated mesh for resistance calculations of upper airways

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The use of a castellated mesh for resistance calculations of upper airways

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