90°弯道内紊流的试验研究

DEVELOPING TURBULENT FLOW IN A 90° CURVED DUCT

<正> 一、试验设备及方法 本文应用LDV测量了弯曲度R_c/D=1.69矩形弯道内的紊流。来流属于正在发展的紊流区流动,弯道的简图示于图1。流动介质为空气,入口平均流速U_a=22.8(m/s),雷诺数为5.6×10~4,Dean数为2.9×10~4,各个截面均以Z~*=0为对称面。经过校核试验,数据的对称性甚好,因此只测量半个截面。

Laser-Doppler measurements oi two orthogonal components of velocity and associated Reynolds stresses are reported for developing turbulent flow in a curved duct of 1.69 radius ratio at a Reynolds number of 5.6×104. Before 25°, the locus of maximum longitudinal mean velocity (Uθ)max moves to the inner wall, and later to the outer wall. The secondary mean velocity attains a maximun value of 0.36 of the bulk velocity at 90° plane. The maximum longitudinal fluctuation (Uθ)max is observed changeably either at the inner or at the outer wall.