Comparative Study of Aerodynamic Interference During Aft Dispense of Munitions

Based on forthcoming USAF needs, an investigation was launched to further the understanding of aft dispense of munitions in a high-speed environment. A computational fluid dynamics (CFD) study was performed followed by a wind tunnel experiment. The study consisted of a strut-mounted cone simulating a parent vehicle and a sting mounted cone-cylinder store situated directly behind the cone. The CFD modeled the test objects inside a supersonic wind tunnel in which the experiments took place. The CFD study consisted of evaluating a new strut designed to reduce asymmetry in the airflow aft of the cone. The CFD study also included predictions of axial loads acting on the store in various locations behind the cone. The experimental study consisted of implementing the new strut and introducing a miniature load cell for comparison to CFD load predictions. The CFD study indicated the newly designed strut lengthened the cone's base region by 27% and reduced transverse forces acting on the store by as much as 50% in two of the three locations evaluated. The experimental studies were successful in obtaining axial force coefficients that matched the CFD trend and were typically within 30% of the magnitudes. It was concluded that the load cell was generally adequate in measuring the axial loading on the store though its accuracy is less than that of a typical wind tunnel balance. The error trends indicate that the polymer store introduces the least amount of statistical error making it the most accurate representation of the results. Significant sources of error include transverse vibrations and axial buffeting observed in the wind tunnel tests.