Pressure Fluctuation near the Limiting Characteristics in a Sonic Flow around NACA0012 Airfoil

Abstract

Pressure fluctuation for flow around an airfoil has been well studied for subsonic, transonic and supersonic flows. In this paper, the sonic flow case is studied using a NACA0012 airfoil. It is known that such a flow has a limiting characteristic line which is known to separate the supersonic region into an upstream zone(U-zone) and a downstream zone(D-zone) where the pressure waves propagate into different directions, thus it is interesting to investigate whether the pressure fluctuation also exhibits special behavior along the limiting characteristic line. From an analysis of the pressure fluctuation properties by detached eddy simulation and method of characteristics, it is found that the pressure fluctuation exhibits different behavior in these two zones, and displays interesting properties along the limiting characteristic line. The fluctuation pressure is the largest along the limiting characteristic line, while the correlation coefficient between two adjacent points is the smallest along the limiting characteristic line. Away from the limiting characteristic line, the fluctuation pressure decays. Moreover, there is a spatial variation of the pressure fluctuation across the boundary layer. This spatial variation is in the mid-frequency band in the U-zone, in the high-frequency band in the D-zone, and in the entire-frequency band along the limiting characteristics line.The special behavior of the pressure fluctuation along the limiting characteristic line revealed by this study enriches our knowledge about transonic flow.