Numerical Study Of Droplet Impact Dynamics On Power Transmission Lines

The safe and stable operation of the power system is one of the key components of a country’s industrial and daily life.As the facility that traverses the largest geographic area in the power system and is most severely affected by the natural environment and climate,the overhead power transmission lines are always inevitably affected by various natural disasters.Among them,ice and snow disasters may cause severe icing of a large number of transmission lines,which may further cause breaking of transmission lines and falling transmission tower,even outage of the regional power system.It is one of the serious natural disasters that the power system must deal with.Currently,the ice melting technology of transmission lines in China is at the world’s leading level and has played a very good role in the national power system’s resistance to ice and snow disasters.However,at the same time,there is a lack of theories and technologies related to the anti-icing property of transmission lines.In fact,the application of anti-icing technology on transmission lines can directly reduce the impact of ice and snow disasters and the pressure of ice melting work,thus the prospects are very good.However,the current anti-icing technologies(such as anti-icing coatings,etc.)are not sufficiently effective,and research breakthroughs in related theories and technical methods are still pending.The study of this problem can provide theoretical support for the optimal design of transmission line anti-icing technology,and has important theoretical significance and practical application value.The research idea of this thesis is to introduce the recently developed many-body dissipative particle dynamics(MDPD)into the fundamental research of transmission lines and establish a set of application framework of MDPD by programming and develop a software for numerical simulation with the purpose of providing new ideas for the research of anti-icing property of transmission lines,and put effort on exploring a new method for relevant fundamental research.The proposed MDPD application framework is used to unveil the dynamics in the process of droplet impact on the transmission line and provide theoretical support for the optimal design of the anti-icing performance of the transmission line.The main research contents and results of this thesis are as follows:(1)For the first time,this particle-based numerical simulation method was introduced in the field of power system transmission line anti-icing research,and a set of MDPD application framework was proposed and established,based on which the application framework was completed through programming,and numerical simulation research was successfully carried out on the dynamic characteristics involved in droplet impact on transmission lines.(2)Through the numerical simulation study of the droplet impact on conventional insulated transmission lines,it is found that for hydrophilic insulated transmission lines,the larger the initial impact velocity is,the larger the spreading diameter will be,and the retraction is more likely to happen;however,for hydrophobic transmission lines,whatever the initial impact velocity,the retraction of contact line can always happen.Four typical wrapping modes are discovered through further analysis: non-reaching,over-reaching,merging,and reaching-retracting wrapping modes.The happening of these wrapping modes depends on the size of the transmission lines,wettability,and the initial impact velocity.The research in this thesis elucidates these relations.(3)The simulation research on droplet impact on transmission lines with different wettability shows that the post-impact morphology also depends on the surface wettability of the transmission lines,for hydrophilic surfaces,the droplet can merge into a smaller droplet and drip off,but for hydrophobic surfaces and superhydrophobic surfaces,the droplet can finally be split into two smaller droplets and then drip off.(4)The simulation research on droplet impact on superhydrophobic transmission lines shows the non-dimensional spreading diameter(NSD)increases along with the increase of initial impact velocity,and under the same initial impact velocity,the NSD can increase along with the increase of the size of the transmission lines;however,the wrapping angle of a droplet to the transmission lines increases with the increase of initial impact velocity,then decrease with the increase of initial impact velocity.Four detachment modes can be found from the analysis of simulation results: bouncing,dripping,partial sticking,and full sticking,their distribution depends on the initial impact velocity and the size of the transmission lines.Further analysis discovered that the contact time of the droplet with the transmission lines is related with the detachment modes,for bouncing mode,the contact time is in line with the initial impact velocity,but for dripping mode,the contact will decrease with the increase of initial impact velocity.“waiting time” and “shrinking time” phenomena were also found in the simulation;the splashing angle is also related with the size of transmission lines,as the bigger the size is,the large the angle will be.(5)The simulation of droplet impact on stripe-patterned heterogeneous insulated transmission lines shows that in the process of droplet spreading,the hydrophilic stripes can facilitate the spreading of droplet while the hydrophobic ones can impede it,but in the process of retracting,the hydrophilic stripes will stick the contact line while the hydrophobic ones facilitate the retraction.(6)The simulation research on droplet impact on stranded transmission lines shows that the wettability of this kind of transmission line can affect the droplet remaining on the surfaces significantly.Further analysis shows that the grooves formed by the neighbouring strands can guide the spreading and retracting of the droplet contact line;and the guiding effect depends on the number of strands.For a stranded transmission line,if the pitch is short,the droplet tends to spread around the axial direction while if the pitch is long,the droplet will tend to spread along the axial direction.Also,the droplet can bounce off from the transmission lines with superhydrophobic surfaces,and the longer the pitch is,the longer the contact time will be.Based on the research in this thesis,the main novelties can be found in three aspects:first,explore a new method(the MDPD application framework)and provide a research tool for the study on the anti-icing property of power transmission lines.Second,find out some new phenomena and conclude some new understandings based on the simulation of droplet impact on insulated and stranded power transmission lines.Third,this thesis focuses on the theoretical and fundamental study of anti-icing transmission lines,comprehensive studies have been carried out on homogeneous cylindrical insulated transmission lines,heterogeneous cylindrical insulated transmission lines(stripe-patterned)and stranded transmission lines with different wettability,plenty of simulation results have been gained,and rules are concluded.The research idea and results have high academic values for further research of transmission lines with anti-icing property.