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

Abstract

The flow field and performance of the RAH-66 FANTAIL^ in hover and sideward flight were::alyzed using Computational Fluid Dynamic (CFD) techniques. The m u l t s were lLFed in the detailed design of the FANTAIL structure, blades, and transmission cooling system. A Navier-Stokes code developed for ducted fans by the first author was modified and employed. This analysis solves the incompressible, laminar NavierStokes equations in a n 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. Thii unique approach makes the code an ideal tool for the solution of detail design problems in a timely manner. Mmt exkting CFD formulations d o not have the capability to easily represent a fan installation. In this paper, the predicted RAH-66 FANTAU"' flow field and performance &re c o m p a d with test data to validate the analysis. The analysis a p p e a d to accurately caphlre the nature of the FANTAIL flow fields in all conditions including the very complex vortex ring state. Performance correlations showed good agreement with the m c a $ u d trends. Overall, the demonstrated accuracy was acceptable for analyzing many detailed design issues. A brief discussion of some specific design issues addrrssed using the CFD m u l t s is also provided.

Aerodynamic simulation strategies assessment for a fenestron in hover flight

“…16). Such a suction peak has already been reported in [7]. In general, the 3D §ows are known to be challenging both for experimental sensors and numerical simulations; so, it can explain, at least partially, the discrepancies between numerical simulations and measurements.…”

“…However, this approach can be used only for axial §ight conditions and 3D effects, such as blade tip vortices, are not represented. Another way to model the §ow in the Fenestron consists in solving Navier Stokes equations on a 2D-axisymmetric shroud and by modeling the fan as a fully coupled, time-averaged momentum source term in the momentum equation [7]. While numerical predictions were in good agreement with measurements in the collector area, the pressure distribution was not accurately estimated in the blade region [7].…”

“…Another way to model the §ow in the Fenestron consists in solving Navier Stokes equations on a 2D-axisymmetric shroud and by modeling the fan as a fully coupled, time-averaged momentum source term in the momentum equation [7]. While numerical predictions were in good agreement with measurements in the collector area, the pressure distribution was not accurately estimated in the blade region [7]. Other works reported in the literature suggest to use an approach based on a 3D geometry of the shroud [8 11].…”

Detailed Aerodynamic Analysis of a Shrouded Tail Rotor Using an Unstructured Mesh Flow Solver

“…2) In the USA, the RAH-66 Comanche helicopter developed by Boeing-Sikorsky is equipped with a ducted fan designated as FANTAILÔ, 3,4) and Bell also developed a ducted tail rotor for an anti-torque system. 5) A similar shrouded tail rotor was also developed in Japan and installed on the XOH-1 helicopter.…”

“…6) Along with the development of the shrouded tail rotor systems, there have been several numerical and experimen-Ó 2004 The Japan Society for Aeronautical and Space Sciences tal researches to evaluate the aerodynamic performance of various types of shrouded tail rotors. [2][3][4][5][6][7][8][9] The aerodynamic performance of the FenestronÔ tail rotor has been studied by using two methods: a classical momentum/blade-element theory and a quasi three-dimensional method originally developed for compressor calculations. 7) Detailed aerodynamic analysis of the RAH-66 FANTAILÔ has been made by solving the incompressible laminar Navier-Stokes equations.…”