凹半球降落伞模型在加速和定常流中的流场观测

 在北京航空学院水槽中,用氢泡法对绕凹半球模型流动进行了研究。模型前后流速分布是用氢泡时间线测量的,它与在起动开始时由无旋流理论估算值接近,但当起动旋涡变大以后,在尾流中流速差别变大。在模型后部诱导出较大的反流速席。所以由无旋估计的虚质量只在开始时是可用的,并且在起动涡变大时,虚质量应更大。 在定常流中,在模型前有时形成一个大旋涡,这个旋涡是非定常的并且可能引起侧向力和伞的非定常运动。模型上适当开孔可减小甚至消除此旋涡。

EXPERIMENTAL INVESTIGATION ON RIGID HOLLOW HEMISPHERICAL PARACHUTE MODEL IN ACCELERATING AND STEADY FLOW

The flow around hollow hemisphere models was investigated in. water channel at B. I. A. A. by hydrogen bubble technique. The flow velocity distribution both in front of and behind the model was measured by hydrogen bubble time lines. It is closed to the values estimated by the irrotational flow theory for the flow right after the start. As the starting vortex grew larger, the flow in the wake is quite, different, A large reversed flow is induced behind the model. Hence, the apparent mass estimated by irrota-tional flow can only be at the beginning. It should be much larger as the starting vortex becomes larger.Sometimes a large vortex in front of model may be formed in the steady flow as shown on plate 3. This vortex is unstable and may cause side force and unstable motion to a parachute. This vortex can be reduced and even be eliminated by holes suitably placed on the model.