Stabilization of the Mack second mode is of great importance to control hypersonic boundary-layer transition, and the porous wall is one of the promising passive techniques. In this paper, the transition onset of a two-dimensional Mach 6 boundary layer over a flat plate with porous coating is predicted by the $e^N$ method based on the linear stability theory. The results show that the second mode instability over the smooth wall can be significantly stabilized by the porous coating. As a price, the other instabilities, mostly the lower-frequency first mode instability, are destabilized, which is more prominent over a hotter wall. Consequently, the transition onset over the porous wall is not always delayed obviously compared to the smooth wall, and even a premature transition is obtained for some porous walls, especially for a hot wall. To achieve an effective delay of transition onset over a hot wall, a sectionalized strategy is proposed in this paper. By partially using the porous wall at downstream location, the destabilization of first mode instability is relieved while the significant stabilization of second mode instability is retained for the most unstable wave, and thus the transition onset is delayed more effectively over a hot wall.

Mack第二模态的稳定对于控制高超声速边界层转变具有重要意义，而多孔壁是一种很有前途的被动技术。在本文中，二维马赫 6 边界层在具有多孔涂层的平板上的转变起始点由$e^{ñ}$基于线性稳定性理论的方法。结果表明，多孔涂层可以显着稳定光滑壁上的第二模式不稳定性。作为代价，其他不稳定性，主要是低频第一模式不稳定性，变得不稳定，这在较热的墙壁上更为突出。因此，与光滑壁相比，多孔壁上的过渡开始并不总是明显延迟，甚至对于一些多孔壁，尤其是热壁，会出现过早的过渡。为了有效延迟热壁上的过渡开始，本文提出了一种分段策略。通过部分使用下游位置的多孔壁，