Small-Caliber Exterior Ballistics: Aerodynamic Coefficients Determination by CFD
Véronique DE BRIEY will publicly defend his thesis entitled "Small-Caliber Exterior Ballistics: Aerodynamic Coefficients Determination by CFD".
The models used to calculate small-caliber projectile trajectories are often only drag-based, given the presumed short ranges and the assumed small variation of the aerodynamic parameters in flight. Depending on the type of application, "field" calibrations are then performed to compensate for the observed deviations. However, with the new small-caliber applications and the inherent increased challenges, these simplified methods do not yield satisfactory results anymore in terms of accuracy and attitude upon impact.
In the first part, next to reviewing existing trajectography models, we discuss their implementation in our own trajectory program VTraj, developed in LabVIEW. The six degrees of freedom (6 DoF) model allows to compute the flight of any symmetrical or asymmetrical projectile (spin- or fin- stabilized). Its parameters include a complete set of static and dynamic contributions, including Magnus and pitch damping forces \& moments. This model allows the analysis of all translation and angular motions of the projectile's body. The models give good agreement with published results on standard reference projectiles for the trajectory parameters.
In part two, we focus on the methodology to capture the static and dynamic aerodynamic coefficients by steady and unsteady RANS methods for subsonic, transonic and supersonic flight conditions.
Accurate resolution of the flow in the boundary layer and in the wake of the projectile proved to be of utmost importance for the correct determination of the coefficients. The coefficient extraction methods are assessed with published results for canonical shapes and good agreement is achieved. The results highlight the strong dependency of the pitch damping coefficient on the reduced pitch frequency which varies along the flight path.
Rigid Body Dynamics (RBD) as well as Computational Fluid Dynamics (CFD) are finally combined in order to evaluate the behavior of specific small-caliber applications: non-lethal projectiles operating in the low subsonic domain, long-range projectiles with focus on transonic domain crossing, and asymmetric configuration are studied. The resolution of the dynamic flow around the projectile and the prediction of stability upon impact are confronted with experimental results and the match is very promising. The research also gives new insight into the diverse phenomena at hand in the transonic domain, or for projectiles with mass unbalance, and the change they impart on static and dynamic stability characteristics.
The defense will take place on July 05 at 03:00 pm and is accessible to all via Lifesize