Large Eddy Simulation of Flow Over an Airfoil Undergoing Surging and Pitching Motions

A dynamic large eddy simulation (LES) approach is employed to study flow over an oscillating NACA 0018 airfoil with surging and pitching motions. Surging motion is studied at moderate and large advance ratios of λ=0.5 and 1.0, and a reduced frequency of k=0.0985. An airfoil at fixed incidence of 8◦ is set in a constant freestream flow at Reynolds number of ReC=300,000. LES predictions for lift force are compared to experimental results at λ=0.5 and show a good agreement. LES predictions are also made at λ=1.0 which is at the tipping point of reverse flow regime. With a large surging amplitude, there is a loss of lift during the retreating phase, and a roll up and ejection of a distinct leading-edge vortex. Pitching motion is studied at ReC=250,000 and k=0.074 with both mean and amplitude of incidence set to 10◦ . Again, LES predictions for lift force are compared with experiments. Unsteady Reynolds-averaged Navier-Stokes (URANS) predictions are also made. LES predictions show similar features in the force response as experiments while URANS lack few prominent features. In all cases, instantaneous flowfield is analyzed at different phases.