Highpressure gas venting through pipeline belongs to unsteady flow,undergoing three flow states i.e.choked flow (supercritical flow),critical flow and subcritical flow.

• 高压天然气通过管路放空属非稳定流动，放空过程要经历壅塞流（超临界流）、临界流、亚音速流三种状态。放空管路的特征对气体流动的影响极大，其摩阻作用不容忽视。