Vibration induced excitation on instability waves in a Blasius flow

Here we have demonstrated that small amplitude localised vibration can artificially excite both 2D and 3D instability modes. The 2D modes was typical of Tollmien-Schlichting (TS) waves provided that the frequency of excitation lies within the unstable region of the neutral stability region obtained from linear stability theory. Further analysis of the streamwise and spanwise evolution of the instability modes identified from the temporal Fourier transform confirmed the presence of 3D oblique modes excited due to the nature of the mode shape deflection of the vibrating panel which was not uniform in the transverse direction. The effect of spanwise non-uniformity could be increased by activating the motors along the transverse direction. However, despite the higher initial forcing of the 2D TS mode from a combination of both streamwise and spanwise aligned motors, strong interaction with the 3D oblique mode led to a reduction in the growth rate of the TS wave in the farfield region.