# Wind Tunnel Test on Windblown Sand Two-Phase Flow Characteristics in Arid Desert Regions
## 3 Experimental Results and Discussion
### Wind Profile in the Windblown Sand Flow Field  
To study the effect of concentration and bed surface with different particle sizes on the wind profile, Figure 10 represents wind profiles in the impurity-free wind and windblown sand flow field at three kinds of indicated wind speeds. The results show that the particle movement in the windblown sand flow field significantly reduces the wind speed below 0.3 m and has little effect on the wind speed when the height exceeds 0.3 m. The degree of influence of sand particles on the wind speed at different heights is directly related to the vertical distribution characteristics of the sand concentration shown in Figure 9. The higher the sand concentration is, the faster the wind speed decreases. In addition, at the same indicated wind speed, the degree of influence of coarse sand, fine sand and mixed sand on the wind profile increases, in turn.  
Figure 10: The wind profiles: (**a**) At the indicated wind speed of 14.74 m/s; (**b**) At the indicated wind speed of 16.68 m/s; (**c**) At the indicated wind speed of 18.61 m/s.  
To quantitatively analyze the influence of particle movement on the wind speeds at different heights, we introduce the wind speed impact value \(\Delta U_{z}\) and impact factor \(IF_{U_{z}}\), respectively. The formula is as follows:  
\[\left\{\begin{array}{l}\Delta U_{z}=U_{z(ifw)}-U_{z(ws)}\\ IF_{U_{z}}=U_{z(ws)}/U_{z(ifw)}\end{array}\right. \tag{4}\]  
where \(U_{z(ifw)}\) and \(U_{z(ws)}\) are the speeds in the impurity-free wind and windblown sand flow field at a height \(z\), respectively, in m/s.  
Figure 11 represents the impact values and impact factors of wind speeds at different heights in the windblown sand flow field. The results show that the impact factors are all less than 1, further indicating that the sand particle movement in the windblown sand flow field reduces the wind speed. The sand particle movement has more influence on the wind speed as the indicated wind speed increases, and has less impact on the wind speed as the height increases. This is because the sand concentration increases with increasing wind speed, and decreases with increasing height. From Figure 9, only a few sand particles suspend in the air flow above 0.3 m, and the sand concentration is quite low. Therefore, the reduction of the wind speed is only 0.02 m/s to 0.13 m/s. According to the impact factors at 9 different heights, the average reduction of the wind profile by coarse sand, fine sand and mixed sand is 5.2-6.4%, 7.6-10.3% and 10.8-14.6%, respectively, which may be determined by the concentration of three kinds of sand particles. In conclusion, the windblown sand flow field can be divided into the flow field inside and outside the sand particle saltation layer. Within the saltation layer, the airflow at each height is directly affected by the sand particle movement, and then the wind profile is directly related to the sand concentration distribution; while outside the saltation layer, the wind profile is basically unaffected because the sand concentration in the airflow is quite low.  
Figure 11: _Cont._  
Figure 11: The influence of particle movement on the wind speed: (**a**) At the indicated wind speed of 14.74 m/s; (**b**) At the indicated wind speed of 16.68 m/s; (**c**) At the indicated wind speed of 18.61 m/s.