Boundary layer and near wake measurements of a two-dimensional airfoil with background-oriented schlieren method

This paper demonstrates the capability of the background-oriented schlieren technique as a new method for measuring time-resolved shear layer characteristics on a two-dimensional airfoil in a blow-down type pressurized wind tunnel. The experiments were performed on a NACA 0018 airfoil in the unsteady transonic wind tunnel located at the Aerospace Research Center, the Ohio State University. In addition, an analytical model utilizing the temperature law of the wall and a two-dimensional computational fluid dynamics simulation were compared with the experimental optical measurements to understand the flow field. The boundary layer, near wake, and stagnation streamline of the airfoil are characterized by the optical method. The effects of heat transfer and viscous dissipation on the measured density gradient are also examined. The agreement in the boundary layer and wake profiles among the analytical, computational, and experimental methods demonstrates that this optical method can be useful to study forced and free shear layers in similar scenarios.