  We investigate numerically the 3-D flow around a squareback Ahmed body at
Reynolds number Re = 104. Proper Orthogonal Decomposition (POD) is applied to a
symmetry-augmented database in order to describe and model the flow dynamics.
Comparison with experiments at a higher Reynolds number in a plane section of
the near-wake at mid-height shows that the simulation captures several features
of the experimental flow, in particular the antisymmetric quasi-steady
deviation mode. 3-D POD analysis allows us to classify the different physical
processes in terms of mode contribution to the kinetic energy over the entire
domain. It is found that the dominant fluctuating mode on the entire domain
corresponds to the 3-D quasi-steady wake deviation, and that its amplitude is
well estimated from 2-D near-wake data. The next most energetic flow
fluctuations consist of vortex shedding and bubble pumping mechanisms. It is
found that the amplitude of the deviation is negatively correlated with the
intensity of the vortex shedding in the spanwise direction and the suction drag
coefficient. Finally, we find that despite the slow convergence of the
decomposition, a POD-based low-dimensional model reproduces the dynamics of the
wake deviation observed experimentally, as well as the main characteristics of
the global modes identified in the simulation.
