Abstract
The influence of the expansion corner on pressure fluctuation is an important subject in supersonic flow around high-speed vehicles. Past studies have clarified how the expansion corner alters the root-mean-square of the fluctuating pressure coefficient (Cprms) and the power spectral density (PSD) without considering how these fluctuating properties are related to compressible waves. In this paper, we use characteristics to determine the direction of wave propagation and identified three zones—U-zone, M-zone and D-zone—within which both Cprms and PSD are likely to display different behaviors across the boundary layer. The U-zone is upstream of the characteristic line of the second family and passing through the corner. The D-zone is downstream of the characteristic line of the first family and passing through the corner. The middle zone lies between the U-zone and D-zone. The results of Cprms and PSD at different layers within the boundary layer are obtained using numerical computation through a Detached Eddy Simulation (DES). It is found that in the U-zone and D-zone, both Cprms and PSD are the same in different layers within the boundary layer. In the M-zone, however, both Cprms and PSD may vary in different layers and this variation occurs in the high-frequency band upstream of the corner and mid-frequency band downstream of the corner. A feedback mechanism is tentatively used to explain the difference of spatial distribution of fluctuation properties inside the M-zone.
Highlights
The fluctuating pressure acting on the surface of the vehicle induces structural vibration, which may cause damage to the aircraft structure and a strong noise environment that affects the normal operation of airborne instruments, including the reliability and safety of weapons and equipment [1]
In the M-zone, both Cprms and power spectral density (PSD) may vary in different layers and this variation occurs in the high-frequency band upstream of the corner and mid-frequency band downstream of the corner
We use characteristics to determine the direction of wave propagation and identify three different zones — U-zone, M-zone and D-zone. These zones are bound by the characteristic lines of the first and second families and start from the expansion corner
Summary
The fluctuating pressure acting on the surface of the vehicle induces structural vibration, which may cause damage to the aircraft structure and a strong noise environment that affects the normal operation of airborne instruments, including the reliability and safety of weapons and equipment [1]. We consider pressure fluctuations due to expansion corners, which are typical geometric configurations that change the local flow properties, leading to the formation of a complex fluctuating environment [6] This topic has received a number of studies. Roberson [6] based on the experimental data on the wall, and they found the relationship between the Cprms and the local Mach number of the separated flow caused by several expansion corners (cone-cylinder, back step, etc.). The surface pressure fluctuations of subsonic turbulent flow downstream of small expansion corners were found to be normally distributed through the expansion process but were severely attenuated [9].
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