DNS of instability waves in the boundary layer of a yawed cylinder

Growth of a point source disturbance in the three-dimensional boundary layer of a yawed circular cylinder is studied using a direct numerical simulation (DNS). This study was undertaken to investigate the propagation characteristics of disturbances introduced from a point source and to find out whether the dominant instability mode is affected by the forcing frequency. Two frequencies, high and low, are studied. The cross-flow instability mode is dominant at low frequency. The instability mode is judged to be a cross-flow mode, even though typical features of viscous modes are present in the amplitude and phase profiles at high frequency. This determination is clarified and the risks of judging instability modes using only the amplitude and the phase profiles are described.