The flow resistance of the tunnel and the boosting capacity of jetfan in the tunnel are the foundation to calculate the tunnel ventilation, they are the first ascertained parameters.
隧道的流动阻力和风机在隧道内的升压力是隧道通风计算的基础，是进行通风计算首先要确定的参数。
2
One way to increase the efficiency of a high-bypass jet engine is to turn the fan into an open rotor, a bit like returning to propellers, but using two rings of stubby counter-rotating blades.