Numerical study on compressible flow around a circular cylinder in proximity to the wall

Abstract

In the present study, the compressible flow around a circular cylinder in proximity to the wall is investigated. By using direct numerical simulation approach, the flow behavior with the Reynolds number 100 and the Mach numbers 0.1 - 0.6 are examined. The numerical result shows that the compressibility effect would enhance the flow stability, whereas the strength of shedding vortices, the shedding frequency, and the fluctuation of aerodynamic force are reduced by increasing the Mach number. Through the examination of signed enstrophy and shear steepness in the cylinder boundary layer, it is found that the vortices shedding from the free-stream side and the wall side are concurrently inhibited by the wall when the cylinder is fully embedded in the wall boundary layer, and the strength of the wall-side vortices is relatively weaker. This imbalance would be intensified when the cylinder gets closer to the wall, and thus a reduction in the shedding frequency is produced. Based on this effect of wall proximity on frequency, the flow behavior is divided into three regimes, i.e., high-frequency, low-frequency, and completely suppression regimes. Finally, from the observation of mean forces, the trend of mean drag and lift force coefficients with regard to the Mach number and gap ratio is described as the scaling behavior in terms of two piecewise functions.