分叉隧道分流局部损失特性及流动特征

搭建同步满足阻力和压力相似的1/20分叉隧道通风比尺模型试验平台，并构建分叉隧道分离流动的三维CFD模型.研究分叉隧道流动特征和分流局部损失特性.结果表明：流速梯度变化和流动分离是产生主线分流局部损失的主因，而匝道分流局部损失还进一步受到流速转向的影响；主线隧道分流局部损失系数基本不受夹角的影响，而匝道分流局部损失系数在分流比小于0.5时，随着夹角的增大而增大，在分流比大于0.5时，随着夹角的增大而减小.利用试验数据修正Bassett公式，建立可准确预测夹角为5°~15°分叉隧道的分流局部损失系数计算公式，从而为分叉隧道的通风计算提供理论参考依据.

Local loss and flow characteristic of dividing flow in bifurcated tunnel

A 1/20 scale model for ventilation of bifurcated tunnel was set up in accordance with the similarity criterion of Reynolds (resistance) and Euler (pressure). The three-dimensional CFD model of separation flow at tunnel bifurcation was constructed. By combining scale model tests and CFD simulation, the local loss and flow characteristic of dividing flow at tunnel bifurcation were analyzed. It is noted that, dividing flow local losses of main tunnel are principally incurred by velocity gradient changes and flow separation between fluids and the tunnel wall, while dividing flow local losses in ramp are further affected by mainstream flow turning. As for the dividing flow local loss coefficient of the main line, it almost suffers no impacts of the included angle. Whereas for dividing flow local loss coefficient in ramp, it goes up as the included angle increases when the flow diversion ratio is smaller than 0.5, and declines with the increase of the included angle when it is greater than 0.5. Furthermore, by modifying the Bassett's expressions based on the test data, an equation was established which can be used to precisely calculate dividing flow local loss coefficients for bifurcated tunnel with any included angle within the range from 5° to 15°. The research results can provide theoretical reference for the ventilation calculation of the bifurcated tunnel.