Large-eddy simulation of the compressible flows around a wavy-axis square cylinder

Abstract

The compressible flows past a wavy-axis square cylinder are numerically carried out by means of the large-eddy simulation technique for two different free-stream Mach numbers (M∞=0.71 and 0.85), which are less than the critical Mach number Mcr (≈0.9). The Reynolds number based on the side-length of the wavy-axis square cylinder is chosen as 4×105. For comparison, the compressible flows around the corresponding normal square cylinder are also calculated. The control effects and mechanisms are systematically analyzed. Comparing the wavy-axis square cylinder with a normal square cylinder for M∞=0.71 and 0.85, about 23.5% and 8.1% drag reductions are acquired, respectively, and the fluctuating forces are suppressed significantly. Based on the analysis of drag decomposition, when M∞<Mcr, the drag reduction related to vortex force prevails over that relevant to compressible effect. Moreover, the wavy-axis square cylinder can also provide the effective control for type C moving shock. The effective drag reduction and suppression of fluctuating force obtained by the wavy-axis square cylinder are closely associated with the higher base-pressure and lower turbulent fluctuations in the near wake, which can be achieved by the strengthened compressibility and waviness effect of shear-layer. However, when M∞ approaches Mcr, the effective flow control from the wavy-axis square cylinder is attenuated due to the competition between strengthened compressibility and the waviness effect of the shear-layer.