2.2 Wind velocity measurement
The wind measurement system is composed of ”L” type pitot tube, micromanometer, hose and bracket. The pitot tube is fixed at a height of 70 cm above the central axis of the wind tunnel bottom plate, 2 m from the upwind edge of the sample trough. The micromanometer is connected with the pitot tube through a hose. During the experiment, the pressure difference between the full pressure end and the static pressure end of the pitot tube was showed by the micromanometer, and then, combining with the real-time temperature and pressure, the wind velocity was calculated. The experimental wind velocity, i.e. 70 cm high axis wind velocity are 8, 10, 12, 14 and 16 m·s-1 respectively, and the corresponding friction wind velocity (u *) are 0.34, 0.42, 0.51, 0.59 and 0.68 m·s-1respectively.