| The impact of raindrops on the soil surface plays an important role in the occurrence and development of splash erosion,and its physical characteristics are very important to further study the mechanism of splash erosion.At present,there are many kinds of instruments that can directly observe raindrops,but most of them assume the shape of raindrops and have large errors in the measurement of raindrop terminal velocity,which leads to the relatively lag in the theoretical research and calculation of erosion dynamics.In this study,a series of work was carried out by using the particle imaging transient measurement visualization instrument of planar array electrical coupling element developed by our team,the instrument through to the raindrops in the process of rainfall for instantaneous sampling image,combined with image noise removal,sketch raindrops,raindrops matching method,realized the raindrops in the process of rainfall and continuous dynamic monitoring in real time.The instrument was used to study the physical characteristics of raindrops under natural rainfall and simulated rainfall conditions,and the splashing erosion characteristics under different rainfall conditions were analyzed by combining the splashing erosion disk.This paper mainly focuses on different types of natural rainfall and simulated rainfall with different intensities,studies the physical characteristics of raindrops from parameters such as raindrop size distribution,raindrop terminal velocity and raindrop kinetic energy,and analyzes the influence of raindrop physical characteristics parameters on splashing erosion,so as to promote the study of raindrop erosion in the splashing erosion process.The main conclusions of this paper are as follows:1.Understand the physical characteristics of raindrops in natural rainfall.（1）The raindrops with a diameter of less than 1 mm were the main contributors to the number concentration of raindrops of the two types of rainfall,and the contribution rate to stratiform rainfall was greater than that to convective rainfall.The raindrops with diameters greater than 1 mm and less than 2 mm were the main contributors to the rainfall intensity of the two types of rainfall,and the contribution rate to the rainfall intensity of stratiform was also greater than that of convective rainfall.In the relationship between the number concentration and average diameter of rain drops and rainfall intensity,the increasing trend of the number concentration and average diameter of rain drops in stratiforms decreases gradually with the increase of rainfall intensity.The mean diameter of rain drops in convectives is similar to its changing trend,while the number concentration of rain drops increases linearly with the increase of rainfall intensity.（2）The distribution range of end velocity of convective rainfall is larger than that of stratiform rainfall,and the average end velocity of stratiform rainfall and convective rainfall is 3.00 and 3.37 m s-1,respectively.Among them,raindrops with terminal velocity of about 4.20 m s-1accounted for the largest proportion.With the increase of raindrop diameter,the increasing trend of the end velocity of stratiform raindrops slows down and tends to be stable,while the increasing trend of the end velocity of convective raindrops is similar to a linear increase.（3）According to the distribution of raindrop kinetic energy in natural rainfall,raindrops with diameters greater than 1 mm and less than 2 mm contribute more to the kinetic energy of stratiform rainfall.The raindrops with diameters greater than 2 mm and less than 3 mm contribute more to the kinetic energy of convective rainfall.The main factor affecting the kinetic energy of rain drops in stratiform and convective is the diameter of raindrops,which increases with the increase of rainfall intensity,showing a power function and a linear function,respectively.2.Understand the physical characteristics of simulated raindrops.（1）The raindrops with diameter less than 1 mm were the main contributors to the number concentration of raindrops in different intensity simulated rainfall,and the raindrops increased with the increase of rainfall intensity.The raindrops with diameters greater than 1 mm and less than 2 mm were the main contributors to the rainfall intensity of simulated rainfall with different intensities,which also increased with the increase of rainfall intensity.The number concentration of raindrops increases linearly with the increase of rainfall intensity,while the mean diameter of raindrops decreases.（2）Under the simulated rainfall conditions of different intensities,the raindrops with terminal velocity of about 4.20 m s-1accounted for a large proportion.The relationship between raindrop diameter and terminal velocity can be expressed by power function,and when the raindrop diameter is small rain 0.50 mm,the magnitude of the fitting raindrop terminal velocity is similar.（3）From the distribution of raindrop kinetic energy in simulated rainfall,it can be seen that raindrops with diameters greater than 1 mm and less than 2 mm are the main contributors to the kinetic energy of raindrops in simulated rainfall from 50-90 mm h-1.According to the analysis of the relationship between the raindrop kinetic energy,the size distribution of raindrops and the terminal velocity of raindrops,the main influencing factor of the raindrop kinetic energy is the number concentration of raindrops.The kinetic energy of raindrops increases linearly with the increase of rainfall intensity.3.The influence of the physical characteristics of raindrops in natural rainfall on the splash erosion rate was investigated.（1）The relationship between rainfall intensity and kinetic energy of natural rainfall has obvious influence on the relationship between rainfall intensity and splash erosion rate.（2）There is no significant function relationship between the splash rate and the number concentration of raindrops;The splash erosion rate increases with the increase of the average diameter and terminal velocity of raindrops,and the amplitude increases,which can be expressed by power function equation.（3）On the spatter erosion rate of natural rainfall can be seen that the spatter erosion rate increases with the increase of erosive force parameters,and the increase range also increases,which can be expressed by exponential function equation.Among them,the raindrop kinetic energy is the most closely related to the spatter erosion rate of erosional force parameter.4.The influence of the physical characteristics of raindrops on the splash erosion rate of simulated rainfall was investigated.（1）The accumulated splash erosion increased with the increase of rainfall intensity,but the increasing range decreased gradually.The greater the rainfall intensity,the greater the splash erosion rate in the same period.The relationship between rainfall intensity and kinetic energy of simulated rainfall has obvious influence on the relationship between rainfall intensity and splash erosion rate.（2）The relationship between splash rate and raindrop number concentration can be expressed by a power function equation,showing an overall increasing trend.However,with the increase of the average diameter and terminal velocity of raindrops,the overall decreasing trend can be expressed by an exponential function equation.（3）The relationship between splash erosion rate and erosive force can be expressed by linear function equation.The raindrop pressure is the most closely related erosive force parameter to the splash erosion rate. |
PDF Full Text Request