学术报告
Pressure PIV: A Novel Optics-Based Pressure Measurement Technique
Xiaofeng Liu （刘霄峰）
Department of Mechanical Engineering，Johns Hopkins University，USA

报告摘要：
Motivated by the fact that there was a lack of an appropriate means for measurement of the instantaneous spatial pressure field in fluid dynamics research, a novel system and technique capable of performing such a measurement in a non-intrusive manner in turbulent flow fields was developed (Liu and Katz, Exp Fluids 2006, Phys. Fluids 2008, JFM 2013). Originally utilizing four-exposure PIV, i.e., two 2K´2K CCD cameras and dual-head perpendicularly polarized Nd:Yag lasers, and later on a time-resolved version with a high-speed camera and a high repetition rate laser, the system measures the distribution of material acceleration by comparing the velocity of the same group of particles at different time, and then integrates to obtain the pressure field. In order to minimize the error in the pressure field measurement, an efficient algorithm featuring virtual boundary omni-directional integration over the entire flow field was introduced and the corresponding code was developed. This code can accommodate general boundary shapes, e.g. lifting surfaces, corners, etc. With this system, the instantaneous velocity, material acceleration, and pressure field can be measured simultaneously.
Validation of the technique includes several feasibility studies and accuracy assessments, using synthetic images of vortex and stagnation point flows as well as a DNS (direct numeral simulation) database of forced isotropic turbulence. Validation tests on a turbulent 2D open cavity flow indicate that the spatial pressure measurements are in full-agreement with the independent cavitation inception index measurements.
In addition to the principles, procedures and development history, in this presentation I will also show example applications of the pressure measurement technique in unsteady fluid dynamics, acoustics and turbulence research. A focus of future research is on the development of a time-resolved 3D velocity measurement technique which couples tomographic PIV together with the extension of the current pressure measurement technique to 3D. As will be discussed, this opens up the prospect of direct measurement of all components of the fluctuating pressure-strain rate tensor in turbulent flows for the first time.

刘霄峰简介：
刘霄峰博士是约翰霍普金斯大学机械工程系兼职研究员。曾任该系博士后研究员、助理研究员。美国圣母大学航空工程博士，北京航空航天大学空气动力学学士和硕士。曾在中国运载火箭技术研究院国际合作处任项目经理，从事外星发射服务的技术协调和支持工作。之后调入清华大学工程力学系，担任流体力学实验室讲师。刘霄峰博士是美国物理学会会员，美国机械工程师学会会员，并于2013年10月当选为美国航空航天学会副会士。刘霄峰博士的研究专长包括实验流体动力学，高升力空气动力学，湍流剪切层流动，尾迹流，涡动力学，空泡现象，流固耦合，流体声学，蒸发换热，图像处理，以及以光学测量为基础的空间压力场全场测量技术的开发和应用。
时间：2014年3月21日上午08:30-10:00
地点：蒙民伟科技大楼北楼N-412室
主办：清华大学航院流体力学研究所   
欢迎各位老师同学参加！

清华大学航天航空学院工程力学系流体力学研究所
Institute of Fluid Mechanics，Department of Engineering Mechanics
School of Aerospace, Tsinghua University, Beijing 100084, P. R. China