Three Unstructured Computational Fluid Dynamics Studies on Generic Unmanned Combat Aerial Vehicle

Abstract

Three independent studies from the United States (NASA), Sweden (Swedish Defense Research Agency), and Australia (Defense Science and Technology Organization) are analyzed to assess the state of current unstructured grid computational fluid dynamic tools and practices for predicting the complex static and dynamic aerodynamic and stability characteristics of a generic 53-deg swept, round-leading-edge uninhabited combat air vehicle configuration, called SACCON (which stands for "stability and control configuration"). NASA exercised the USM3D tetrahedral cell-centered flow solver, while the Swedish Defense Research Agency and the Defense Science and Technology Organization applied the Swedish Defense Research Agency/EDGE general-cell vertex-based solver. The authors primarily employ tbe Reynolds-averaged Navier-Stokes assumption, with a limited assessment of the EDGE detached eddy simulation extension, to explore sensitivities to grids and turbulence models. Correlations with experimental data are provided for force and moments, surface pressure, and off-body flow measurements. The vortical flowfield over SACCON proved extremely difflcult to model adequately. As a general rule, the prospect of obtaining reasonable correlations of SACCON pitching moment characteristics with the Reynolds-averaged Navier-Stokes formulation is not promising, even for static cases. However, dynamic pitch oscillation results seem to produce a promising characterization of shapes for the lift and pitching moment hysteresis curves. Future studies of this configuration should include more investigation with higher-fidelity turbulence models such as detached eddy simulation. b C," or CM f k log(r/rO) MRP Nomenclature wing span, 1.54 m lift coefficient, lift/<jr^5"f pitching moment coefficient, pitching moment/^-^SrefC'ref pressure coefficient reference chord, 0.479 m wing root chord, 1.06 m sinusoidal oscillation frequency about pitch, roll, or yaw axis, Hz. wind-tunnel test reduced frequency. order of magnitude drop in solution residual (e.g., -4 means a four orders of magnitude drop) freestream Mach number, 0.144 moment reference point for pitching moment, 0.600 m from apex .Tormalm@foi.se. *Senior Scientist, Flight Systems, Air Vehicles Division; Stefan. Schmidt@dsto.defence.gov.au. Ne = number of tirne steps per oscillation cycle, 2;r/(A-• ht*) p = static pressure. Pa Re"ef = Reynolds number based on Cfef, 1.6 X 10R RP = rotational reference point for pitch and yaw oscillation. 0.855 m from apex ratel, rate2 = primai-y and secondai7 VGRID viscous stretching factors [see Eq. (1)] 5fef = reference area, 0.77 ms/LE = fractional distance from wing apex along wing leading edge r = temperature, K Ai = physical time step, s Ar* = characteristic time step. Ai • U^/c^^f U^ = freestreatn velocity, 50 m/s X, y, z = niodel coordinates, m Cü = angle of attack, ÜQ ± Aa, deg OÍ0 = nominal angle of attack for pitch oscillation, deg ß = angle of sideslip, deg Aa = range of pitch oscillation about body axis, ± deg i5,-i-i = VGRID viscous grid spacing norma...

Numerical Assessment of Leading- and Trailing-Edge Control on a Swept Lambda Wing

“…To meet this challenge, a NATO Science and Technology Organization (STO) task group was formed in 2011: Applied Vehicle Technology (AVT)-201, titled "Extended Assessment of Reliable Stability and Control Prediction Methods for NATO Air Vehicles." This group directly follows the successful work by AVT-113 [1][2][3][4][5][6][7] and AVT-161 [8][9][10][11][12][13][14][15][16][17] on basic aerodynamics, both static and dynamic, for generic delta wings, as well as a lambda wing planform. A blended-wingbody model was developed within the AVT-161 task group and was named the stability and control configuration, or SACCON.…”

Static and dynamic numerical simulations of a generic UCAV configuration with and without control devices

“…14 The objectives and strategy of the research group are described by Cummings and Schütte. 15 A detailed description of the flow physics and evaluation of the S&C prediction capabilities of the SACCON configuration is given by Schütte et al 16 and Frink et al 17 In the follow on program within the NATO STO/AVT-201 Task Group on "Extended Stability and Control Prediction Methods for NATO Air Vehicles" 18,19 the SACCON UCAV configuration has been modified and trailing edge control devices have been implemented. A description of the model configurations and experimental results from the wind tunnel tests are presented for the low speed tests by Huber et al 20 and Vicroy et al 21 and for the high speed investigations by Rein et al 22 In this paper the prediction capabilities of high fidelity, Reynolds-averaged Navier-Stokes based CFD methods of the flow field and aerodynamic behavior of the SACCON configuration with control devices will be shown.…”

Flow Control and High-Lift Performance for Flying-Wing Unmanned Combat Air Vehicle Configurations by inserting slots

“…A disadvantage, however, is that as the angle of attack is increased, the leading edge vortices become detached and experience a forward migration to the outboard section of the wing. The intensity of this forward migration of flow to the outer panels of the vehicle grow significantly in high angles of attack regime [4].…”