Application of Various Turbulence Models to Investigate the Aerodynamic Performance of a NASA Dual Control Missile

Abstract

This paper contains an investigation on the ability of some of the current turbulence models to predict viscous effects in supersonic Mach number regimes. In most cases these turbulence models have been derived and validated in traditional subsonic to transonic Mach number regimes and their application to supersonic and hypersonic regimes is assumed valid without a proper recourse to understanding the wider implications of viscous flow field at high Mach numbers. In such flow regimes, such characteristics as the strong shock interactions with control surfaces and evolving vortices present in the flow, or other large entropy gradients brought about by the fore body or other fin surfaces produce non trivial challenges for the turbulence models. This study was aimed at interrogating the strength of the turbulence models to model such physics. The Applied Vehicle Technology (AVT) Panel Group 082 of the Research Technology Organisation (RTO) selected a dual control NASA missile to investigate the capabilities of Computational Fluid Dynamics (CFD) to predict the flow field and performance characteristics of complex shaped projectiles at high Mach numbers. There are two types of difficulties that are encountered when computing such problems. The first type are geometry based, and are related to the shape of the nose and fore body, number and types of strakes or forward control mechanisms, fin geometry deployment, and shape and design of the cowls and intakes. The second type of difficulties deal with flow complexities such as the heat transfer (M>4) implications; the vortices shed from the fore body and other control surfaces; the interaction of these vortices with the body structures, the free stream, and each other; the base flow interaction with the free stream; the boundary layer development; and, in the case of supersonic flows, the shock boundary layer interactions. Air breathing missiles with intakes or missiles with jet controlled guidance systems add to the flow complexities. The purpose of this study as a whole was to investigate the capability of the turbulence models to accurately perform CFD simulations of the flow past the NASA dual control missile at two angles of attack, alpha = 6 and 24°. The group had used both structured and unstructured type grids to identify any strengths or advantages of a particular method. The evolution of the vortex formed by the front fins was of particular interest as the fore body vortices will undoubtedly interact very strongly with the forward strakes at higher angles of attack and affect the controllability of the projectile. Also, the flow deflected by the forward strakes will subsequently impinge upon the aft control surfaces, which could possibly lead to control failure if the missile was not designed appropriately.