Numerical Study on the Stability of Hypersonic Wake Flow over Blunt Body and Global Stability Analysis

Abstract

The structural instabilities of base flow in hypersonic wake flow over sphere are investigated by numerical simulation in this paper. Numerical simulation method is second-order accuracy NND scheme in spatial direction and Second-order Runge-Kutta scheme in temporal direction. Wakes flow of sphere at M∞=2, Re=1.71E+6(based on the sphere radius) and at M∞=6, Re=1.71E+6 are simulated. Stable solutions are obtained and there are a primary separation and a secondary separation zone in flow over sphere at M∞=2 and M∞=6. Later, without any arbitrary disturbance imposed, the structural instability still occurs after a certain critical time. The evolving process of the structure of flow over sphere is a periodic behavior in the forepart, but it evolves into a non-periodic behavior after a critical time at M∞=2. In the period time, the topological structures of the flow field over sphere and their evolving process at M∞=6 are similar to that of M∞=2, but there is non-periodic behavior observed at M∞=6 in spite of long calculation time. In the case of sphere, the results by global stability theory, numerical results and results of power spectrum are compared each other. The global stability analysis method can give a good prediction result. This study result indicates that the present numerical simulation method and global stability analysis method can be used for the study of the stability of base flow and confirms that hypersonic flow at the base is also instability.