On Simulation Techniques for the Separation of Stores from Internal Installations
Simulation of store separation trajectories from inside an aircraft out through a shear layer presents serious challenges to existing experimental and analytical methodologies. In the experimental approach (wind tunnel testing), small scale models are used to minimize costs, ranging in scale factor from 1/20th to 1/5th of full size. Consequently, small physical features of the aircraft are either approximated or omitted entirely. In the case of external flow, negligible or acceptable influences are introduced, but the unsteady flow environment produced in a cavity has shown to be dependent on the size and shape of cavity and the condition of the bounding surfaces of the cavity.
Second, with regard to analytical techniques, solutions for the empty-cavity case at various flow conditions have been demonstrated; however, these solutions require several tens of computation hours on a Class VI computing machine for simple geometries. Purely analytical prediction of store separation trajectories will require even more computation hours, so that inexpensive computational fluid dynamic (CFD) trajectories are years in the future. Approximate methods have been developed to provide efficient estimates of store loads and trajectories. These “engineering methods” include mathematical expressions based on experimental data, aircraft and store dimensions, estimates of store motion damping derivatives, and the flight conditions. At the AEDC, trajectories have been predicted using an off-line version of the on-line captive trajectory support (CTS) code, for which the required loads are furnished by interpolations of a test data file. Predictions have come from the AEDC/IDL code to date, but could come from CFD codes.