Direct numerical simulation of a flapping wing in turbulent environments

Micro-aerial vehicles (MAVs) are often designed to fly at low speeds and low altitudes, potentially experiencing strong turbulence conditions where the characteristic length-scale of the flow perturbations can be comparable to their size. Being such conditions remarkably different from those of more conventional aircraft, we still lack a thorough understanding on how atmospheric turbulence affects the aerodynamic performance of MAVs and similar devices. Here, we present a high-fidelity computational methodology to investigate low-Reynolds aerodynamic problems in the presence of a turbulent free stream with well-defined and controllable properties (e.g., homogeneity, isotropy, spectral energy distribution). First, useful indications are provided by a benchmark between the flow obtained using a synthetic turbulence generator and the fully-resolved simulation of grid-induced turbulence. Hence, focusing on bio-inspired MAVs, we characterize the case of a flapping wing impinged by fluctuations of high turbulence intensity and integral length-scale comparable to the chord, highlighting the most relevant variations in the aerodynamic response with respect to the unperturbed free-stream case.