Store Trajectory Response to Unsteady Weapons Bay Flowfields

Abstract

It has long been suspected that the inherently unsteady flow inside and immediately around an internal weapons bay may cause a difference in the trajectory of a store released from the bay depending on the time of release. Computational studies of this have indicated that there may be a trajectory divergence with time of release, but not enough to represent a danger to the aircraft. There have also been recent test incidents that have suggested that the effect of unsteadi ness may be important and in fact may cause departure of the store from the predicted trajectory. An investigation of the effect of unsteady weapons bay flowfields on the trajectory of released stores, and specifically on the deviation of the trajectories depending on the time of release, is the purpose of this study. Computational prediction of the trajectory using a computational fluid dynamics (CFD) flow solution coupled with a six degree -of -freedom (6DOF) trajectory solution should provide a technique which is properly scaled, repeatable, accurate, and includes the time -accurate unsteady effects. The computational toolset will first be demonstrated on a set of test data for which trajectory deviation with time of release has been shown. After the too l has been demonstrated, a parametric study will be performed to assess the sensitivity of the trajectory deviation to various store separation parameters, including store mass properties, ejection characteristics, flow characteristics, and weapons bay geo metry. Two additional tasks were also performed as part of this effort. The development and testing of rapid approximate methods for the investigation of time -dependant trajectories is performed, and a technique for the accurate simulation of the time av erage of an unsteady flowfield using steady simulation techniques is also developed and tested .