Surface pressure and lagrangian coherent structure evolution on an axially accelerated delta wing

The flow field, forces, moments, and surface pressure of a NACA 0012 airfoil wing with triangular planform geometry undergoing steady and unsteady translations were measured as a model of a unmanned combat air vehicles encountering unsteady environments [1]. To characterize the evolution of the flow field structures, a Lagrangian flow field analysis including the finite-time Lyapunov exponent (FTLE) was included. Results show that axial acceleration can induce flow reattachment at high angles of attack, and FTLE can indicate the reattachment and its location as it progresses along the wing chord. At such location, the relevant change in surface pressure distribution is also observed in the experimental data, as well as correlated fluctuations in lift, drag, and pitching moment. This augmented understanding of vorticity production, reorientation, and annihilation around and in the wake of complex three-dimensional bodies may provide critical insight for effective flow-control development on vehicles unsteady environments.