Deployable fins effect on store separation dynamics

• Time-accurate URANS–6DoF DFBI framework with overset meshes and adaptive refinement for store separation with moving appendages. • Validation on the canonical WPS benchmark: steady C p maps and free-release kinematics reproduced. • Deployable fins primarily affect attitude: increased static margin and pitch/yaw damping, reduced peak angles. • Early center-of-mass trajectory largely unchanged; alignment with freestream is accelerated. • Fin deployment induces a small steady rolling moment with guidance and control implications. • Faster deployment advances benefits, but gains saturate beyond 210.6 deg/s (diminishing returns). • Robust overset strategy: prioritized interfaces + local adaptive compatibility to avoid global over-refinement. • Workflow is generalizable to other moving-appendage problems in transonic release. We present a Computational Fluid Dynamics (CFD) time–accurate Unsteady Reynolds-Averaged-Navier-Stokes (URANS) framework using a six–DoF Dynamic Fluid–Body Interaction (DFBI) solver with overset meshes and adaptive refinement to simulate the strongly coupled, nonlinear fluid–rigid–body interaction that governs store separation with moving appendages. In addition to the release itself, four deployable fins, which remain stowed during the first stage of the simulation, swing out after ejection, adding unsteady aerodynamics and further nonlinear coupling between loads and motion. To capture the multiple relative motions, the simulation employs six overset regions: one background, one store, and four fin regions. The approach is first validated on the canonical Wing–Pylon–Store (WPS) benchmark by reproducing steady C p distributions and measured free-release kinematics. It is then extended to analyze deployable fins with prescribed opening rates, assessing their effects on stability, loads, and trajectory. Results show that fins act primarily on attitude rather than on early center-of-mass motion: deployment increases static margin and pitch/yaw damping, reduces peak angles, and accelerates alignment with the freestream. The coupled response is distinctly nonlinear, with small changes in deployment law leading to noticeable differences in attitude histories. A small steady rolling moment appears, producing a gradual roll-up that must be considered in guidance and control. Increasing deployment rate advances the onset of these stabilizing effects, but benefits saturate above 210.6 deg/s. We conclude that deployable fins enhance separation safety by improving attitude stability with minimal trajectory penalty. A key contribution is the detailed meshing methodology, where adaptive refinement around moving interfaces ensures accurate, stable overset coupling without global over-refinement. The workflow is general and applicable to a wide range of moving-appendage problems.