Static and Dynamic Derivatives on generic UCAV without and with leading edge control

Abstract

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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