Simulations of 6-DOF Motion with a Cartesian Method

Abstract

Coupled 6-DOF/CFD trajectory predictions using an automated Cartesian method are demonstrated by simulating a GBU-31/JDAM store separating from an F/A-18C aircraft. Numerical simulations are performed at two Mach numbers near the sonic speed, and compared with flight-test telemetry and photographic-derived data. For both Mach numbers, simulation results using a sequential-static series of flow solutions are contrasted with results using a time-dependent approach. Both numerical approaches show good agreement with the flight-test data through the first 0.25 seconds of the trajectory. At later times the sequential-static and time-dependent methods diverge, after the store produces peak angular rates, however both remain close to the flight-test trajectory. A computational cost comparison for the Cartesian method is included, in terms of absolute CPU time, and relative to computing uncoupled 6-DOF trajectories through a pre-computed matrix of simulations. A detailed description of the 6-DOF method is provided in an appendix, along with verification studies confirming its numerical accuracy.

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