A Collision Detection Approach To Chimera Grid Assembly for High Fidelity Simulations of Turbofan Noise George Zagaris * Daniel J. Bodony † Mark D. Brandyberry ‡ Michael T.Campbell § Eric Shaffer ¶ Jonathan B. Freund k University of Illinois at Urbana-Champaign, IL, 61801, USA A key advantage of Chimera meshes is their suitability for high fidelity moving grid simulations. However, an inherent requirement and challenge is the need to establish the inter-grid communication with minimal user intervention in an efficient manner, a process called grid assembly. This paper presents a method for grid assembly that is based on collision detection. The primary benefits of this approach are that (1) it requires user-intervention only at the problem setup stage, and (2) the method is applicable to both structured and unstructured grids. Numerical results are presented for a 2-D linear cascade model of a fan-rotor system at realistic flow conditions as well as several other configurations to verify the present approach. I. Introduction T he Chimera meshing approach simplifies the problem definition and solution strategy for the analysis of complex geometry systems. 1, 2 In this approach, different grids are used to model different portions of the domain and interpolation links the solution from one grid to another. Both structured and unstructured grids may comprise the total grid system, though historically only one type is used for a given problem. For systems involving moving parts, such as the rotor-stator system of interest here, the Chimera ap- proach naturally allows one to discretize the moving and non-moving portions separately, alleviating any remeshing requirement. In the rotor-stator context a subset of the more general Chimera approaches is the sliding interface method wherein two adjacent grids share a common boundary and pass data through it via interpolation. For tonal problems one can couple the sliding interface with a chorochronic (space-time) buffer, 3 though this is not applicable to broadband predictions. One drawback of the sliding interface is that it requires unstructured grids description or structured grids that are significantly constrained to allow for both a common planar boundary and the blade geometries. In either situation a high-fidelity simulation is difficult. The sliding interface method is also not transferable to other situations. The approach followed here builds upon the key advantage of Chimera approach; namely its suitability for high-fidelity moving grid simulations. 4–7 However, an inherent requirement and challenge for such dynamic Chimera approaches is the capability to establish the needed communication between grids in an automated and efficient manner as part of the solution process. This requirement is generally known as the grid assembly step and is the primary focus of this paper. There are several grid assembly codes currently available. Overflow 8 and Beggar 9 have internal overset grid assembly capability. However, this capability is not easily accessible to third party flow-solvers. PEGA- SUS 10, 11 has been successfully incorporated within a loosely integrated simulation framework and applied to moving grid simulations, 12, 13 although information is shared between the fluid solver and PEGASUS * Research Programmer, Computational Science and Engineering at UIUC and IllinoisRocstar LLC. AIAA Member. † Assistant Professor, Department of Aerospace Engineering, UIUC. Senior AIAA Member. ‡ Chief Operating Officer. IllinoisRocstar LLC. § Principal Research Programmer, Computational Science and Engineering at UIUC and IllinoisRocstar LLC. ¶ Research Scientist. Computational Science and Engineering at UIUC and IllinoisRocstar LLC. k Associate Professor, Department of Mechanical Science and Department of Aerospace Engineering at UIUC. Senior AIAA Member. 1 of 12 American Institute of Aeronautics and Astronautics