Computational Fluid Dynamics Study for Drag Reduction of an Airborne Surveillance Gimbal

This article describes the drag minimization of an existing gimbal assembly mounted to an airplane, scanning a sight for surveillance purposes. The aerodynamics problem has been numerically investigated using a Commercial Computational Fluid Dynamics software Fluent 19.2 by solving Unsteady Reynolds-Averaged Navier Stokes equations. For the existing surveillance system, the given flight operational conditions were analyzed based on International Standard Atmosphere where the flow obtained is incompressible turbulent flow. A validation and verification study on a three-dimensional sphere simulation was conducted at two Reynolds numbers of 1×106 and 1.5644×106 using two different turbulence models, the SST k- $\omega$ and the realizable k- $\varepsilon$ . The drag and lift forces and flow separation angle were compared with literature. Based on the flow simulation setup of the sphere, the existing gimbal was simulated for Reynolds number of 1.5644×106 comparing both turbulence models. Large zone of vorticity, low-pressure wake, separation and vortex shedding were clearly observed introducing huge drag. Two force design changes were suggested which are changing the gimbal orientation and optimizing the gimbal geometry. The simulation results described in this study have illustrated the capability of both turbulence models. The results obtained agreed really well when compared computationally and experimentally. Improvements of almost 60% were obtained by the two suggested solutions where the optimized gimbal showed higher improvement percentage.