Detailed Aerodynamic Design of the RAH-66 FANTAIL™ Using CFD

The flow field and performance of the RAH-66 FANTAIL in hover and sideward flight were analyzed using Computational Fluid Dynamic (CFD) Techniques. The results were used in the detailed design of the FANTAIL structure, blades, and transmission cooling system. A Navier-Stokes code developed at Iowa State University for ducted fans was used. This analysis solves the incompressible, laminar Navier-Stokes equations in an axisymmetric non-body fitted coordinate system to reduce problem set-up time. The fan was represented as fully-coupled, time-averaged momentum source terms in the momentum equations. This unique approach makes the code an ideal tool for the real time solution of detail design problems. Most existing CFD formulations do not have the capability to easily represent a fan installation. In this paper the predicted RAH-66 FANTAIL flow field and performance are compared with test data to validate the analysis. A discussion of some specific design issues addressed using the CFD results is also provided.