临界区系指流体的活动由层流至紊流的过渡区域。自本世纪三十年代普朗德-尼古拉兹的半经验理论发表以来,对于紊流各阻力区的流速分布和摩阻系数已做了大量的理论分析和实验研究,解决了工程上要求的流动阻力的计算问题。然而,对于临界区的研究甚少,这一方面由于临界区的雷诺数范围较窄,人们重视不够,另一方面由于临界区的流态极为复杂,对摩阻规律的制约因素较多。实验数据分散。因此,长期以来许多国家在工程上往往用层流或光滑区摩阻曲线的延伸来解决临界区的工程计算问题,但这样计算误差过大。六十年代初,苏联对四个城市煤气供应系统的流态分析指出,低压管网约有13％的管段在临界区工作。我国煤气规范组在1975年对大连造船厂家属宿舍煤气户内管的流态 Critical area refers to the fluid from the laminar flow to the turbulent transition area. Since the publication of the semi-empirical theory of Prandtl-Nicolas in the 1930s, a great deal of theoretical analysis and experimental research have been done on the flow velocity distribution and the frictional coefficient of various resistance zones in turbulent flow, which have solved the engineering requirements Flow resistance calculation problem. However, there are few studies on the critical region. On the one hand, people pay insufficient attention because of the narrow Reynolds number in the critical region. On the other hand, due to the extremely complicated flow regime in the critical region, there are many constraints on the friction law. Experimental data is scattered. Therefore, in many countries, the engineering calculation of the critical area is often solved by the extension of the laminar or smoothed area friction curve for a long time, but the calculation error is too large. In the early 1960s, the Soviet Union’s flow analysis of the gas supply systems in the four cities pointed out that about 13% of the pipe sections in the low-pressure pipe network work in the critical area. China Gas Regulatory Group in 1975 on Dalian Shipyard dormitory gas indoor pipe flow