Towards consistent hybrid overset mesh methods for rotorcraft CFD

• Published in: International journal for numerical methods in fluids Vol. 74; no. 8; pp. 543 - 576
• Main Authors: Jarkowski, M., Woodgate, M.A., Barakos, G.N., Rokicki, J.
• Format: Journal Article
• Language: English
• Published: Bognor Regis Blackwell Publishing Ltd 20-03-2014; Wiley Subscription Services, Inc
• Subjects: Accuracy; Algorithms; Central processing units; chimera method; Computational fluid dynamics; Finite element method; Fuselages; Mathematical models; overset mesh; rotor flow; rotor/fuselage; Searching
• ISSN: 0271-2091; 1097-0363
• DOI: 10.1002/fld.3861

SUMMARYThe overset mesh method chimera is popular within the rotorcraft research community, because the use of multiple, non‐matching grids make the CFD simulations of bodies in relative motion much simpler. Consequently, the relative motion between the helicopter blades and fuselage can be accurately accounted for. In this paper, the method for treating overset grids within CFD codes is presented. It is compatible with multi‐block, structured‐grid solvers. The proposed method is based on hierarchy of overset, non‐matching grids, whose cells are automatically identified as computational or non‐computational and localised with respect to all grids they overlap with. The efficiency of the method relies on the hierarchical, multi‐step approach, for the overset mesh localisation and the use of a tree search. Because of the high efficiency of the algorithm, the search for overlapping cells can be carried out on‐the‐fly, during time‐marching of the unsteady, implicit CFD solver. In addition, the algorithm is suitable for parallel execution. The method has been demonstrated for several flows, ranging from simple aerofoils to rotor‐body interaction. The paper presents and demonstrates the method and shows that it has a low CPU overhead. It also highlights the limitations of the method and suggests remedies for improvement. Copyright © 2013 John Wiley & Sons, Ltd.
A novel method for overset mesh solution localisation is presented in this paper, based on three key components: 1) The use of a pre‐localisation method to reduce the required searches for bloc‐to‐block overlaps on multi‐block structured grids. 2) A representation of the CFD mesh as a binary tree for fast point‐in‐box checks. 3) An exact arithmetics library to preserve accuracy for point co‐ordinate comparisons. The results show minimal overhead in terms of CPU time and are compared for accuracy against matching grid results or against sliding grid methods. The method was effective for a range of test cases from simple aerofoils to rotor/fuselage configurations.