顺流向正弦脉动风作用下矩形柱体的空气动力学特征

在正弦脉动风作用下，采用三维大涡模拟(3D LES)研究了截面宽高比为5∶1矩形柱体的非定常空气动力学特性。对比均匀流作用下柱体表面压力系数的风洞试验值与数值计算结果，二者吻合很好，验证了3D LES的计算精度。首先分析了来流波长对柱体表面平均再附长度的影响，发现当来流波长处于(0.25~5)λ_s0(λ_s0为自然涡脱的波长)范围时，平均再附长度随来流波长的增加而增加。而当来流为长波脉动(波长不小于5 λ_s0)时，平均再附长度与均匀流下基本一致。在短波脉动(波长不大于0.25λ_s0)来流作用下，平均再附长度与来流波长无关，但明显较长波来流的短。柱体表面平均压力系数受脉动风的影响与平均再附长度的变化一致，再附长度的减小引起平均压力系数曲线的斜率、最大吸力和分离点平均压力系数均有所增大。另一方面，柱体表面脉动压力系数随来流波长的增加而减小，对于短波(波长小于0.5 λ_s0)脉动来流，表面脉动压力系数与驻点脉动压力系数的比值与来流条件无关。此外，当来流波长处于(0.375~1.33)λs0范围时，尾流的漩涡脱落频率刚好等于来流脉动频率的一半，即出现了顺流向正弦脉动流作用下漩涡脱落的锁定现象。

Aerodynamic characteristics of a rectangular cylinder in streamwise sinusoidal flow

3D LES approaches were applied to study the unsteady behavior of a rectangular 5∶1 (width-height ratio) cylinder due to sinusoidal oscillating flow. The pressure distributions on conditions of uniform flow were compared between experimental and numerical results, and the numerical ones agreed well with experimental ones. The effects of oscillating wave length on the mean reattachment length were studied. On condition that the wave length is in the range (0.25~5) λ_s0 (λ_s0 is wave length of natural vortex shedding), the mean reattachment length increases with increasing wave length. However, insensitivities of mean reattachment length are observed at high wave length conditions (λ≥5 λ_s0). In addition, the mean reattachment length of flow with low wave length (λ≤0.25 λ_s0) is significantly lower than those with high wave length. The mean pressure changes in accordance with mean reattachment length, a decrease in the latter can cause an earlier recovery of the former and the suction peak to increase. On the other hand, the fluctuating pressures decrease with increasing wave length of oscillating flow. For flow with wave length below 0.5 λ_s0, the shape of normalized (by the value at the stagnation point) fluctuating pressures along the side surfaces is independent of wave length. If the wave length is in the range (0.375~1.33) λ_s0, the wake vortex shedding frequencies are half of the oscillating frequencies, which is known as the lock-on phenomenon.