Tightly Coupled CFD/6-DoF Solver for Store Separation Simulation

Store separation from aircraft remains a critical aspect of flight safety and weapon system integration, particularly in modern configurations involving internal weapon bays. Traditional quasi-steady aerodynamic approaches, based on precomputed look-up tables and weak CFD/6DoF coupling, are effective for analyzing releases of underwing stores but have proven to be inadequate for capturing the highly unsteady and nonlinear aerodynamic phenomena present in cavity flows. These flows are dominated by strong longitudinal pressure gradients, broadband noise, and tonal oscillations known as Rossiter modes, all of which can significantly influence store trajectories and potentially lead to unsafe separations. To overcome these fundamental limitations, the present work develops a tightly coupled CFD/6DoF simulation methodology capable of resolving transient aerodynamic fields and dynamic store motion simultaneously, thereby enabling accurate prediction of store trajectories within unsteady flow environments such as weapon bays. The methodology is designed with particular emphasis on industrial applicability and seamless integration into established certification workflows. The developed methodology integrates three different rigid body dynamics solvers: RBD, RJS and SSTP. RBD is coded from scratch and optimized for a strong CFD/6DoF coupling; RJS and SSTP are proprietary softwares currently employed in industrial workflows. The coupling strategy employs overset meshing to accommodate complex relative motions between store and aircraft. A validation of the developed methodology was conducted using a test case which is typically employed for store separation studies, then simulations of releases from an internal weapon bay using three different configurations, are presented. The results demonstrated to be accurate regardless of the employed 6DoF solver, proving the methodology to be consistent and robust. The simulations of releases from a weapon bay confirmed the importance of the ERU for safe separation, while the inclusion of spoilers is shown to alter the aerodynamic forces and moments acting on the store with findings that align with established experimental and numerical literature on cavity flow control mechanisms. Beyond validation activities, this work contributes to understanding unsteady cavity aerodynamics and the dynamic response of stores during release. The tightly coupled approach captures the time-varying aerodynamic loads that quasi-steady or weakly coupled methods struggle to resolve. Concluding recommendations for future development include improving CFD results by employing more accurate turbulence models such as DES or IDDES, designing and testing an hybrid workflow which allows to switch to a quasi-steady computation to reduce computational cost, and to improve the RBD solver as well as MATLAB library loading times to minimize simulation overhead.