Numerical Investigation of Aerodynamic Effects of Geometry and Sensor Distance on a Spherical Projectile

The present study investigates the flow around two tandem spheres and their aerodynamic optimization. In a systematic view, the downstream sphere is regarded as the projectile and the upstream sphere is the sensor. The aim of this study is to find the most appropriate configuration with lowest drag force. Therefore, the results of the effects of the center-to-center (CC) distance of the spheres, and the reduction of the sensor’s diameter were investigated in 15 different cases. The results show that as the distance between the spheres decreases, the drag force of the spheres decreases too; reduction in the sensor’s diameter would increase the projectile’s drag while decreasing the sensor’s drag. The highest effects on drag reduction were induced by constant distance between spheres and a change in sensor’s diameter. Consequently, in the last stage of the study, the adjoint solution of the FLUENT software was used to reduce the drag of the whole set through optimization of the sensor frontal hemisphere. However, due to systematic limitations, only the shape of the forepart of the sensor can be changed. Since the sphere is a bluff body, efficient options are needed for the adjoint optimization algorithm and it’s worth noting that the optimized shape in each case is different from other cases. The highest drag reduction happened in the case with a CC distance of 2.5 m and sensor diameter of 0.75 m. Furthermore, the case with CC distance of 1m and sensor diameter of 0.25 is the only case after optimization in which simultaneously the drag force of both spheres has been reduced.