绕细长旋成体非对称涡非定常性的实验研究

Experimental investigation of asymmetry vortex unsteadiness over slender cylinders

详细地给出了尖锥头和椭球头细长旋成体大迎角绕流非对称侧向力的时均值和脉动值的实验结果,特别是检测了侧向力低频大振幅分量的脉动特性。实验结果表明,在迎角0°～40°范围内时均升力系数和阻力系数实验结果和由横流理论预测的结果基本一致,时均侧力系数存在的迎角范围及其最大值尖锥头明显大于椭球头旋成体。由侧力瞬时值的时间过程表明,细长体大迎角绕流非对称背涡具有明显的非定常特征(即使在中等迎角30°～40°情况下,绕流就表现为非定常的),反映在侧力系数过程线上是一个非周期的随机过程,由不同频率和振幅的分量组成。其中,低频大振幅分量由分离涡核的振动引起,中等频率分量由类似于Karman涡的脱落引起,高频小振幅分量主要由分离剪切层中的小尺度湍涡(eddies)和来流湍流度引起。实验还发现,虽然随迎角的增加,低频分量的振幅不断增大,但主频基本保持不变,对于尖锥体约1.0Hz,对于椭球体约2.0Hz。

The asymmetry side-force mean values and fluctuating-values of cone and elliptic slender cylinders are given in detail. The low-frequency-and-high-amplitude fluctuating characteristics of side-forces are emphasized. The experimental results indicate that mean lift-coefficent and drag-co-efficent are in agreement with prediction of cross-flow theory basically. As far as existing-force' s incidence range and maximum side-force are concerned, those of cone slender cylinder are evidently larger than those of elliptic slender cylinder is very evident, even at incidence of 30?~ 40? in terms of time-history of side-force instantaneous value which is a nonperiodic stochastic process. For the nonperiodic stochastic process, it is concluded for low-frequency-and-large-amplitude component arising from the vibration of vortex core, moderate-frequency component being similar with that of karman-vortex shedding and high-frequency-and-small-amplitude component be led to by small-scale eddies of seperated shear layer and coming-flow turbulence level. The experimental result also indicates that with incidence increasing, low-frequency component's amplitude increases, but it is almost constant for primary frequency which is 1 .OHz for cone slender cylinder and 2 .OHz for elliptic