Numerical investigation of unsteady wave phenomena for transonic airfoil flow

Transonic flow over airfoils at high Reynolds numbers shows a high number of unsteady phenomena such as local separation regions, shock–boundary layer interaction, boundary layer transition and turbulence. Furthermore, the phenomenon of upstream moving pressure waves is observed experimentally as well as numerically under certain conditions. Generally, it is not possible to simulate correctly all transonic flow phenomena in a numerical simulation as they are of different length and time scales. However, the use of high-fidelity numerical methods and a high spatial resolution increases the range of resolved scales. This paper focuses on the numerical investigation of self-induced, unsteady pressure waves propagating over an airfoil. Weak pressure waves that are generated in the vicinity of the trailing edge propagate upstream and induce a periodic shock wave formation and motion. Although the observed phenomenon is similar to buffet, it is not separation driven and the unsteady forces are smaller. The main part of the paper is related to the comparison between experimental and numerical results, validating the used numerical method and justifying its use for the simulation of unsteady, weak pressure waves in transonic flows. Besides, a deeper insight of the complex physical mechanism leading to the observed pressure wave generation and its interaction with other flow phenomena will be provided.