风沙流中风速脉动的实验测量

Experimental Measurement of Air Flow Velocity Fluctuation of Wind-sand Flux

在风洞中测量了四种风速条件下净风与挟沙风的速度脉动,发现沙粒运动削弱了平均流速而增加了脉动流速,并且不改变流速脉动的分布规律.挟沙风的脉动速度不再像净风那样随高度增加而单调减小,而是在床面附近变化不大,接着出现极大值,随后依高度增大又趋于减小;也不像净风那样随平均风速的增大而减小,而是先增大后减小,存在极大值.

The velocity fluctuation of air flow with and without sand grain saltation is studied experimentally in a wind tunnel. The experiments were conducted with one test sand and four different stream velocities. The four velocities tested were 8.5, 11.5, (13.5,) and 22.5 m/s; measured at the centerline of the test section entrance. The mean grain diameter of the tested sand is 0.35 mm. The measurement shows that grain saltation reduces the mean velocity, while enhances fluctuation velocity of air flow, and does not change the normal probability distribution of fluctuation velocity of air flow. The fluctuation velocity of air flow with saltation, unlike that without saltation which decreases with height, keeps a constant near bed and then increases, and lastly deceases with height. The friction velocity of the air flow is larger with saltation than that without saltation.