Abstract:
In this paper, the instability of the entropy layer over a blunt plate at a Mach number 4.5 is investigated. Direct numerical simulation (DNS) is used to compute basic flow for linear stability theory (LST). Two empirical formulas are introduced to identify the entropy-layer region and boundary-layer region. It is found that there are two generalized inflection points at a certain streamwise location in the boundary layer and entropy layer respectively. For the generalized inflection point in the entropy layer, the entropy-layer mode instabilities are studied by using the LST. The unstable region of entropy-layer disturbances is close to the leading edge, and the disturbances growth rate is very low. The evolution of entropy-layer disturbance is computed by using a DNS. The amplitude of the entropy-layer disturbance increases slowly near the leading edge, and then decreases slowly downstream. In addition, the amplitude obtained by the LST at a long distance from the leading edge is in good agreement with that of the DNS, indicating that the flow in the entropy layer has good parallelism.