Receptivity of a Hypersonic Blunt Cone: Role of Disturbances in Entropy Layer
Bingbing Wan, Caihong Su, Jianqiang Chen
Abstract
The boundary-layer receptivity of the second mode to a slow acoustic wave is investigated using direct numerical simulation for a Mach 6 flow over a blunt cone with the nose radius of 5.08 mm. The mean flow behind the shock can be divided into three layers: outer layer, entropy layer, and boundary layer. With the forcing of an acoustic wave, the excited disturbances at downstream locations close to the nose include the fast mode in the boundary layer and the disturbances in the entropy layer and outer layer. Direct numerical simulations show that the disturbance in the entropy layer actually plays a key role in exciting the second mode. The whole process of receptivity is found to follow a three-stage route. In the first stage, the fast mode is excited in the boundary layer. Although it has a dominant amplitude initially, it experiences a significant decay. In the second stage, it is overtaken by the disturbance in the entropy layer. In the third stage, the latter enters the boundary layer and excites the second mode near the lower branch, which is due to a different mechanism of synchronism.