The aim of this paper is to propose an efficient method to evaluate the Added Masses of generic shape bodies in infinite fluid or in the proximity of external walls. The Added Masses (AM) are the result of the inertial reaction of the fluid in response to an accelerated movement of a body immersed in it. The AM effects are more evident when the body density is similar to that of the surrounding fluid, as in the case of airships. In the take-off or landing phases, the proximity to the ground causes an increase in the Added Masses that must be correctly estimated to properly size the airship controls. In our method, the calculation of the Added Masses matrix is carried out by the Boundary Element Method (BEM). To verify the accuracy of the results, the study cases are based on simple shapes, whose Added Masses are well known. The analyses in infinite fluid and in the presence of a flat wall are carried out. Numerical results are compared to the theoretical values found in literature. The calculated Added Masses are intrinsically dependent on the mesh definition and the relative error, referred to the theoretical values, depends on the surface and volume discretization. In the case of interaction between geometries with complex shapes, the influence on the Added Masses is very difficult to predict without a numerical approach. The method proposed gives a good compromise in terms of quality

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The present paper is devoted to low speed aerodynamics on a 53° swept and twisted blended wing body. The geometry considered is the SACCON configuration, intensively studied in the STO-AVT 161 and 201 working groups. It includes flow control investigations aiming at reducing longitudinal as well as lateral instabilities on one hand, determination of dynamic derivatives focusing on the influence of the rotation point on the other hand. The physical analysis is based on both numerical and experimental data, including static and dynamic tests carried out in two wind tunnels at Onera-Lille. It shows that leading-edge slats are very efficient to minimize the natural pitch-down/up phenomenon occuring beyond 13° AoA for this configuration. Numerical simulations were carried out with the elsA software, solving RANS equations with the Spalart-allmaras turbulence model, for various computational grid refinements; they show a good agreement with experimental data and give insight on the flow physics. It appears that phenomena such as the re-formation of leading-edge vortices, vortex breakdown, shear layer instabilities appears to be a feature of nonslender wings. The vortical flows develop at very low angles of attack, and form close to the wing surface. A non negligible sensitivity to center of rotation location on damping derivatives in pitch have also been experimentally and numerically identified and it appears therefore important to superimpose the center of rotation and the MRP during dynamic tests and computations. Nomenclature b = Wing span [ONERA model 1.0 m] c = Chord length [0.311 m] c R = Root chord [0.690m] S = Reference area, [0.3255m 2 ] U ∞ , V = Freestream velocity q ∞ = Dynamic pressure C p = Pressure coefficient, = (p-p ∞ )/q ∞ Cx,y,z = Aerodynamic force coefficients in body axis frame (axial, side and normal) Cmx,my,mz = Aerodynamic rolling, pitching and yawing moment coefficients in body axis frame (also named Cl, Cm, Cn). Reference lengths used in scaling Cmx, Cmy and Cmz coefficients are respectively b/2, c and b/2 dt = Time step f = Frequency f* = Reduced frequency, f*=f.c/V M = Mach number MRP = Model Reference Point for expression of moments-x/c R = 0.5656 CoR = Center of Rotation -2 locations are considered: x/c R = 0.809, x/c R = 0.635 1 Engineer, ONERA-DAAP/MMHD, jean-francois.le_roy@onera.fr. 2 Phd, ONERA-DAAP/MMHD, stephane.morgand@neuf.fr. 3 Engineer, ONERA-DCSD/QSV, dominique.farcy@onera.fr. Downloaded by KUNGLIGA TEKNISKA HOGSKOLEN KTH on July 30, 2015 | http://arc.aiaa.org |

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