Coupled CFD and Rigid Body Dynamics Modeling of a Spinning Body with Flow Control

Abstract

This paper describes a computational study undertaken to model the flight trajectories of a spinning projectile both with and with out aerodynamics flow control. The flow control is achieved through synthetic jets and the trajectories are computed using a coupled computational fluid dynamics (CFD)/rigid body dynamics (RBD) technique. A timeaccurate Navier-Stokes computational technique has been used to obtain numerical solutions for the unsteady jet-interaction flow field for a spinning projectile at subsonic speeds. Initial velocity of Mach = 0.39 is considered. Numerical solutions have been obtained using Reynolds-Averaged Navier-Stokes (RANS) and hybrid RANS/Large Eddy Simulation (LES) turbulence models. Unsteady numerical results obtained from the coupled method show the show the effect of the jet activation on the flow field, on the aerodynamic coefficients, the flight path of the projectile, and the resulting divert authority. I. Introduction he prediction of aerodynamic coefficients for projectile configurations is essential in assessing the performance of new designs. Accurate determination of aerodynamics is critical to the low-cost development of new advanced guided projectiles, rockets, missiles, and smart munitions. Fins, canards, and jets can be used to provide control for maneuvering projectiles and missiles. The flow fields associated with these control mechanisms for the Army weapons are complex involving three-dimensional (3-D) shock-boundary layer interactions, jet-interaction with the free stream flow, and highly viscous dominated separated flow regions 1-3 . The jet interference can extend over significant portions of the projectile and must be modeled correctly. For missiles, jet thrusters have been studied over a number of years to provide high-speed aerodynamic control. These thrusters interact with the surrounding flow field and the resulting jet interaction flow field again is complex. Recently, several studies have shown that tiny synthetic unsteady jets can significantly alter the flow field and pressure distributions for airfoils and cylinders. 4-6 These synthetic jets are active control devices with zero net mass flux and are intended to produce the desired control of the flow field through momentum effects. Many parameters such as jet location, jet velocity, and actuator frequency can affect the flow control phenomenon. Smith and Glezer 4 have conducted an excellent study of the flow control by synthetic jets to provide increased fundamental understanding of the flow physics. Amitay et al. 5 experimentally investigated flow separation control on a cylinder using synthetic jet actuators. Their work showed that the interaction of the synthetic jet with the free stream flow resulted in a virtual modification of the body shape and significantly increased the lift force as a result of the flow reattachment. Aerodynamic flow control over an unconventional airfoil has also been demonstrated by Amitay et al. 6 to enhance post stall performance using actuators operating at frequencies higher than the characteristic frequency of the airfoil. The synthetic jets are also being investigated for possible applications to improve heat transfer, drag reduction, and enhance mixing 7 in combustors etc. The present analysis involves these synthetic jets for projectile aerodynamic control. The emphasis in the present research is to provide insight into the interaction of these unsteady jets with the free stream flow and to determine the feasibility of these jets for aerodynamic control of a subsonic spinning projectile. In addition, the objective was to accomplish through coupled CFD and RBD methods.