地 点: 北京航空航天大学 流体力学研究所214

1. Title: Biofilm control and its applications

Chuanwu Xi, Ph.D ( Associate Professor of Environmental Health Sciences)

(University of Michigan School of Public Health)

Abstract:

Biofilms are aggregates of microorganisms attached on biotic or abiotic surfaces, which are ubiquitous in the natural environment, engineered systems and medical devices. Biofilms often cause a variety of issues such as corrosion of industrial pipes, deteriorated water and product quality and persistent infections, etc. In this presentation, I will discuss about mechanisms of biofilm development, several techniques we have developed in control of biofilm development, and how to apply these technologies for medical and industrial applications.

2.Title: The Study of Hot-Wire and Its Anemometers

Junde Li (Victoria University, Australia)

(Currently on leave at Tsinghua University)

Hot-wire and its anemometers have been used for turbulence measurements in air flows over many years. So far, all the verifications of the classical theoretical results of turbulence rely on the experimental results from hot-wire measurements. Hot-wire and its anemometers are still widely used today because of its high temporal resolution and reasonable spatial resolution. In using hot-wire and its anemometers for turbulence measurements, the spatial resolution and the lack of theoretical solutions for its dynamic response are two issues which have limited our ability to use it with full confidence. Here, the length to diameter ratio of the hot wire, which is directly related to its spatial resolution, is presented first using numerical results. It is found that the minimum length to diameter ratio of the hot wire depends on the materials of the hot wire and the Reynolds numbers and should not be a fixed value. The theoretical solution of the hot wire and its anemometers are then presented. It is shown that an attenuation of the hot wire exists and starts from a fairly low frequency, depending on operational parameters. It is shown that the effect of this attenuation on the measurements of second order statistics of turbulence may be small, its effect on high order structure functions can be significant. A method of correcting this hot-wire attenuation effect is proposed.