His sudden entrance took everyone by surprise.

他的突然出场使所有人都感到意外。

The sudden entrance of the icy air through the broken window changed the particles of water into snow.

窗户被打破以后，冷风突然涌进大厅，湿热的空气中的水汽于是就凝成了雪花。

The non-symmetric refracted flow is possible to correspond to the non-symmetric entrance condition of upstream cross before sudden expansion section, and also to the symmetric entrance condition.

这种非对称折冲流动可能与上游突扩前断面非对称入口条件相对应，也可能与上游突扩前断面对称入口条件相对应。