Detailed comparison between DNS and wind tunnel experiment for an airfoil at Re $=$ 20,000 with a view towards control

The reduction in size and weight of electronic devices in recent years has enabled the use of small flying devices that operate at Re \textless 1.5 x 10$^{\mathrm{5}}$ for a variety of applications. At these low Re, the boundary layer often separates before the trailing edge, even at low angles of attack, leading to aerodynamic behaviors that are not predicted by classical inviscid theories. There is currently no comprehensive database of airfoil data in this Re regime, where the sensitivity of the boundary layer behavior to small disturbances in the free stream often leads to discrepancies between results generated in different facilities. Here we provide experimental results generated in a wind tunnel with a low turbulence intensity for a NACA 65(1)-412 airfoil at Re $=$ 2 x 10$^{\mathrm{4}}$. Several unexpected phenomena are observed in force balance results and explanations are proposed based on PIV flow visualization. Qualitative and quantitative comparisons are made with results from a DNS code using higher-order discontinuous Galerkin methods. Internal acoustic forcing at locations dictated by Lagrangian Coherent Structure behavior is explored as a potential closed loop flow control strategy.