A Validation of FlightStream for Store-Separation Modeling
Matthew S. Campbell · 2024
Store-separation modeling is a critically important topic in the realm of aerodynamics simulation. Some very strange events have been occurred when a store is released from a pylon, including airframe strikes, stores that might be live fused, going along non-intuitive trajectories, and in some cases not going anywhere at all for uncomfortably long times. Hundreds of stores await flight testing and ultimately certification in part because the CFD studies required to ensure that these bizarre behaviors and unanticipated outcomes do not occur for a full complement of flight conditions. While CFD solvers can generally resolve the complex proximity flows involved in flow separation events, classical approaches to aerodynamics harness potential flow and the mature development of boundary layer theory to capture loads far more efficiently than CFD solvers. The classical aerodynamics solver used in this work is FlightStream®. The flow solver makes use of rings of surface vorticity on an unstructured surface mesh covering the outer mold line of the aircraft plus store to predict aerodynamic forces with attached flow. Vorticity is shed from the geometry to calculate aerodynamic loads. The solver has both inviscid and viscous coupling models which can be used for analysis and the appropriate solver can be chosen according to the requirements. For separated regions, a base flow can be marked and modeled using the classical aerodynamics solver. These models are at a design study level of fidelity at a minimum, computationally efficient, and suitable for reliable flight simulation studies with appropriate complementary validation studies. This paper seeks to validate the capability of a classical panel-type aerodynamics solver to capture accurate pressure distributions, aerodynamic loads, and trajectory data of an external store in a separation event for a generic wing-pylon-store configuration at low sub-sonic speed. The proximity interaction of the store and pylon in a steady-state simulation will be investigated by comparing the pressure distribution from the classical aerodynamics approach along the store to data from an equivalent setup in FLUENT. If the aerodynamic parameters of critical interest can be developed using classical aerodynamics, the process of certifying stores for flight testing can be dramatically sped up. Loads and trajectory of the store separation event will be captured in an unsteady simulation using the embedded 6dof solver and the aerodynamic loads along the trajectory are compared to data obtained with a FLUENT dynamic mesh simulation. The validation of the separation event in the simulation is crucial as loads and trajectories cannot be unaccounted for in proposed flight tests. For example, a significant pitch-up could jeopardize the aircraft. Preliminary results show a strong correlation in the trends of pressure distributions along the store at various angular positions, confirming that proximity interaction is being captured with reasonable accuracy by classical aerodynamics solver. A demonstration of the 6dof with the store and in a simplified mass drop where aerodynamics is not considered. The work to be completed for the paper includes configuring the FLUENT dynamic mesh simulation and comparing these results to the classical aerodynamic solver loads.