报告人: Dr. Hai Li (李海博士)
01.2014 – present Postdoctoral Research, MLU Halle-Wittenberg, Halle, Germany Institute of Mechanical Process Engineering Head: Prof. Martin Sommerfeld Topic: Binary drop collision and spray drying.
09.2008 – 08.2013 Doctoral Study, TU Darmstadt, Darmstadt, Germany Institute of Fluid Mechanics and Aerodynamics Supervisor: Prof. Cameron Tropea and Dr. Ilia Roisman Thesis: Drop impact on dry surfaces with phase change
09.2006 – 06.2008 Master study, School of Aeronautical Science and Engineering, Beihang University, Beijing, China.
09.2002 – 07.2006 Bachelor Study, School of Aeronautical Science and Engineering, Beihang University, Beijing, China.
报告题目：Drop impact onto Solid Surfaces with Solidification
报告时间：2014年12月16日下午3点 ~ 5点
报告地点：新主楼C1012
报告摘要：
Airframe icing is a topic of vital importance in aviation industry because it is mainly concerned with the safe and efficient operation of aircraft under all weather conditions. Over the last 15 years the role of supercooled large droplets (SLD) in aircraft icing has received increased attention. The mechanisms of impact and solidification of SLD are still not completely understood.
The first part of the present study is an investigation of impact of a supercooled drop onto a superhydrophobic substrate. Drop impact, spreading and rebound were observed using a high-speed video system. It is found that the outcome of drop impact onto superhydrophobic substrates depends significantly on the initial drop and substrate temperatures. If both these temperatures are below the freezing point, the drop rebound is not complete. The minimum receding drop diameter was measured for various wall and drop temperatures. It was nearly linear with the dimensionless Stefan number. We have shown that at the temperature below the freezing point the icing cannot be prevented by only using superhydrophobic coatings.
The second part of this study focuses on high speed impacts of single drops with diameters ranging from 130μm to 200μm onto dry surfaces of a high velocity up to 63m/s and an inclination ranging from 0° to 75° in order to investigate the effects of oblique impact. The drop impact was recorded by shadowgraph imaging up to 1 Mfps. Six outcomes of drop impact were identified: deposition, prompt splash, corona-corona splash, corona-prompt splash, single-side splash and the aerodynamic breakup. It is found that none of the existing models for splash threshold is valid for the tested impact conditions. The mass of the secondary droplet was measured for drop impact on horizontal targets. An effective scaling parameter correlating the mass-loss coefficient was found to be a combination of the Reynolds number and the Weber number. The velocity of the splashing jets and the thickness of the spreading rim were measured at an impact velocity close to the splash threshold, and for a range of impact angles. These data deliver useful information on the characteristic properties of the secondary droplets generated by drop splash.
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