沙尘大气物理约束方程研究

基于风沙两相流的相互作用和气块质量变化的观点,推导出了闭合的沙尘大气物理约束方程组.理想状况下对之分析发现:沙尘大气密度比同体积洁净大气大,一定程度上会减缓气块的运动速度;沙尘与空气间的速度差异会使得细粒子处于高流速区,而粗粒子位于低流速区;温度差异会使得沙尘在上升运动中充当热源,下沉运动中充当冷源,从而加强对流;沙尘大气质量定容热容会在等压面上诱发新的温度梯度,促进沙尘云边界处的夹卷;沙尘大气气体常数会在等温面上诱发新的气压梯度,促进沙尘云边界处的夹卷;质量变化会对气块密度、速度和温度造成较大影响.总之,沙尘云要比基于被动标量的方程组模拟结果更高大、内部对流更强、边界处夹卷更活跃、水平运动更迟缓.

Study of physical constraint equation of sand-dust atmosphere

The closed physical constraint equations of sand-dust atmosphere are established based on both the interaction of wind-blown-sand two-phase flows and the mass change. Ideal analysis of the equations shows the following findings: (1) the density of the sand-dust atmosphere is bigger than that of the pure atmosphere, which will reduce the velocities of air parcels of the former to some extent; (2) velocity difference between sand-dust particles and air can make the fine particles located in a high-speed region and the coarse particles located in a low-speed region; (3) temperature difference between sand-dust particles and air can make the particles tend to enhance convection through acting as a heat source in updraft and a cold source in downdraft; (4) the constant-volume mass-specific heat capacity of the sand-dust atmosphere can give rise to the generation of new temperature gradient on an isobaric surface and then enhance the entrainment at the boundary of a sand-dust cloud; (5) the gas constant of the sand-dust atmosphere can lead to the generation of new pressure gradient on an isothermal surface and also enhance the entrainment at the boundary of a sand-dust cloud; (6) mass change can largely affect density, velocity and temperature of the sand-dust atmosphere. In brief, compared with the sand-dust cloud given by equations based on passive scalar, the real sand-dust cloud is high and great. Besides this, its inner convection and its entrainment at the boundary are active, and its horizontal motion is slow.