Evaluation of Isolated Fuselage and Rotor-fuselage Interaction Using Cfd

The US Army Aeroflightdynamics Directorate (AFDD), the French Office National d’Etudes et de Recherches Aérospatiales (ONERA) and the Georgia Institute of Technology (GIT) are working under the United States/France Memorandum of Agreement on Helicopter Aeromechanics to study rotorcraft aeromechanics issues of interest to both nations. As a task under this agreement, a comparative study of the Dauphin 365N helicopter has been undertaken to analyze the capabilities and weaknesses of state-of-the-art computational fluid dynamics (CFD) codes, with the aim of fuselage performance prediction and investigation of rotor-fuselage interaction. Three CFD flow solvers applied on three meshes provide similar results in terms of pressure coefficient. Force predictions vary somewhat. This paper presents details on the grid sensitivity and the low Mach number preconditioning influence. The importance of taking into account the wind tunnel strut and the rotor hub is shown. The pressure coefficients along top and bottom centerlines of the fuselage are in good agreement with the experiment except in the area aft of the hub. There remains a discrepancy between the computed forces and the experimental data due in part to modelling inaccuracies. Rotorfuselage interactions are performed using uniform and non-uniform actuator disk models in order to simulate the rotor downwash. NOTATIONS Drag CD S = : drag force coefficient, m 0.5 p V 2 Reference frame: Ω Ω Presented at the American Helicopter Society 60 Annual Forum, Baltimore, MD, June 7-10, 2004. Copyright © 2004 by the American Helicopter Society International, Inc. All rights reserved. Side CS S = : side force coefficient, m 0.5 pΩ VΩ 2 Lift CL S = : lift force coefficient, m 0.5 pΩ VΩ 2 p − pΩ CP = : pressure coefficient 0.5 pΩ VΩ 2 200CT/Δ : rotor thrust Re : Reynolds number S : rotor disk area, m VΩ : freestream velocity, m/s a : pitch angle, degrees ∞ : sideslip angle, degrees ∞ : Low Mach number preconditioning parameter pΩ : freestream fluid density