对流体机械内液滴与叶片的碰撞过程和冲击力的研究

几乎各类流体机械内都存在着液滴与叶片碰撞的现象。利用液滴与叶片的碰撞，可制造喷雾、减少工艺设备或冲洗叶片积灰结垢；但是，液滴与叶片的碰撞，也会造成流体机械的气动性能明显下降和恶化，还可能造成叶片磨损。本项目拟通过实验和数值模拟方法，着重进行三个方面工作：首先，通过采用PIV、高速摄影技术和转子遥测技术，实验观察和定量分析液滴与叶片碰撞后，二次液滴在叶片通道内的时空分布规律，探索液滴碰撞所导致流体机械气动性能下降的机理；其次，采用压电薄膜三维力传感器，测量液滴的切向和垂直碰撞速度分量的变化对液滴和叶片碰撞的三维冲击力的时频域特征的影响，以及该冲击过程的统计特征；最后，对液滴与旋转圆盘碰撞后的二次液滴的时空变化规律和特点进行实验测量，并通过数理统计归纳分析，建立液滴与叶片的碰撞飞溅模型。本项目可加深对流体机械内部气液两相流场相互作用机理的认识，为数值计算流体机械内的气液两相流场奠定基础。

The impact of drops on blades can be observed in almost all kinds of turbomachinery. On the one hand, such impact can be used to generate spray, cut down some equipment in process flows and wash ash or tar on the blade. On the other hand, it may result in pressure and efficiency drops of turbomachinery, or even lead to blade erosion. The proposed investigations are to be conducted focusing on the following three aspects. First, the temporal and spatial distributions of the secondary droplets of impact drops in the blade passages are to be recorded and quantitatively analyzed using a particle image velocimeter(PIV), a high-speed camera and a wireless telemetry system for rotary machine,to explore into the mechanisms for the deterioration of aerodynamic performance of turbomchinery. Second, the time evolution of the shock forces of the impact drop is to be measured, and its influence is to be analyzed on the characteristics and variation in temporal and spatial spectrums due to the changes in tangential and normal components of the drop impact velocity, by using a three-axis sensing head made of polyvinylidene difluoride (PVDF) piezoelectric film. The statistic features of the impact forces are also to be presented. Finally, the temporal and spatial distributions of the secondary droplets of the drop impacting on a rotating disk are to be measured. On the basis of statistics of the secondary droplet, a splashing model on drops impacting on blades is to be developed. The present proposal is to get insight into the two phase flow field with respect to the interference between airflow and drops. It will also prepare the ground for the computation and optimization of the air-liquid two-phase flow fields in turbomachinery.