Generation of Aerodynamic Coefficients Using Time-Accurate CFD and Virtual FLy-Out Simulations

This paper describes a multidisciplinary computational study undertaken to compute the unsteady free-flight aerodynamics of spinning and finned projectiles. Advanced computational fluid dynamics (CFD), rigid body dynamics (RBD), and flight control systems have been successfully coupled on high performance computing platforms for "Virtual Fly-Outs" of munitions. Time-accurate CFD has been performed to compute the unsteady aerodynamics of spinning projectiles and coupled CFD/RBD methods have been used to compute the unsteady aerodynamics associated with the free flight of a finned projectile at supersonic speeds using an advanced scalable unstructured flow solver on a highly parallel Linux Cluster. A method to efficiently generate a complete aerodynamic description for projectile flight dynamic modeling is described. At the core of the method is an unsteady, time accurate CFD simulation that is tightly coupled to a RBD projectile flight dynamic simulation. A set of short time snippets of simulated projectile motion at different Mach numbers is computed and employed as baseline data. For each time snippet, aerodynamic forces and moments and the full rigid body state vector of the projectile are known. With time synchronized air loads and state vector information, aerodynamic coefficients can be estimated with a simple fitting procedure. By inspecting the condition number of the fitting matrix, it is straight forward to assess the suitability of the time history data to predict a selected set of aerodynamic coefficients. The technique is exercised on a fin stabilized projectile with good results.