NUMERICAL INVESTIGATION OF THE EVOLUTION OF TWO-DIMENSIONAL T-S WAVES ON AN ANISOTROPIC COMPLIANT WALL

As inspired by the flexible characteristics of the feathers of birds, the influence of an anisotropic compliant wall on the spatial evolution of the T-S wave in the subsonic boundary layer flow is studied numerically in this article. First of all, the numerical results are in good agreement with that predicted by the linear stability theory and also the numerical results obtained by others. This demonstrates the reliability of the cell-centered finite difference method with high-order accuracy, which is adopted in this article. After that, a part of the rigid wall is replaced with an anisotropic compliant wall. The obtained results show that the compliant wall is able to reduce or even remove the unstable growth region of the T-S wave, i.e., suppress the amplitude growth of the T-S wave. Thus, the compliant wall has the potential to delay laminar-turbulent transition. The deformation of the compliant wall not only has components corresponding to the T-S wave waveform, but also the wall vibration with longer wavelength and same frequency compared to the T-S wave, which is caused by the leading edge of the compliant wall. The parameter study shows that with increased damping, the wall vibration by the leading edge is weakened. An increase in the rigidity, tension or elastic coefficient of the compliant wall will result in the wall stiffer and thus lead to smaller deformation. The greater the incline angle of the supporting lever arm, the stiffer the compliant wall. The increase of any of the above parameters will lead to a reduction in the suppression effect of the compliant wall on the T-S wave. When the flow direction is reversed, the suppression effect is also weakened. This research is aimed to reveal some of the mysteries of bird's efficient flying, and provides new ideas for passive flow control to reduce drag.