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Simplified Numerical Approach for the Prediction of Aerodynamic Forces on Grid Fins

Grid fins are unconventional control devices used for aerodynamic control of various types of missiles. Low hinge moment requirement and superior packaging potential make grid fins attractive alternatives to conventional planar fins. Unlike missiles with planar fins, widely accepted preliminary design tools for missiles with grid fins are not available. As an alternative, aerodynamic forces and moments are obtained through full computational fluid dynamics solutions. However, generating an aerodynamic force and moment database in the preliminary design stage using full computational fluid dynamics solutions takes too much time due to the complex geometry of grid fins and the corresponding mesh requirements. In this study, the unit grid fin concept, which is a small representative portion of a grid fin, is introduced for the efficient prediction of flows around missiles with grid fin controls. The study is conducted at Mach numbers of 0.7, 1.2, and 2.5 in an angle-of-attack range between 0 and 15deg. First, the validation of the proposed technique is done for side fins in the + configuration, for which there are available experimental data. Then, the idea is applied for the simulation of the more common x configuration. It is shown that, although requiring much less computational resources and time as compared to a full computational fluid dynamics solution, the unit grid fin approach can provide acceptable results for preliminary design. The body interference correction turns out to be critical in the performance of the proposed method, and the deficiency of a simple potential flow-based approach is demonstrated.