Aerodynamic Load Maps of Bluff-Body Combinations in Incompressible Flow

Prior work showed high-resolution maps of aerodynamic load coefficients for various geometric shapes, as well as parametric variations on canonical models. The problem of obtaining predictions on new shapes using generalized interpolations and combinations of canonical shapes, is explored in this paper. Two cases are considered. The first is that of an engine container used as a helicopter slung load. Full scale flight data provide the dynamics, so that the effects of different uncertainties and simplifications are examined. The progression is from interpolated Fourier coefficient data on an approximate, canonical shape, to dynamic simulation at different levels of fidelity. The second case is one of predicting the aerodynamic load map of a complex practical shape — a road vehicle used as a slung load, starting by combining data on canonical shapes. In both cases, this paper presents predictions using approximations; the future work expects to present wind tunnel results on a scale model of the engine container, and on an actual combination of canonical shapes. The cylinder approximation gives a good prediction of the flight test dynamics history and divergence speed. Adding a drag estimate for the tethers achieves good correlation with the flight test trail angle behavior, with some error apparent at the highest speed. However, this error underpredicts drag, which may be the effect of support structure including flat-plate baffles, not yet modeled. In the second case, a weighted combination of Fourier coefficients for a cylinder and a rectangular prism, gives a good representation of the drag and side force coefficient maps for a HumVee model; correlation of the yawing moment is less accurate.