Advancement of Multidimentional Imaging for the Clarification of Thermofluid Phenomena

热流体动力学研究中的多维成像旨在可视化或量化速度、温度和浓度的瞬时分布。在速度测量方面，PIV （Particle Imaging velocity metry，粒子成像测速）跟踪悬浮在流动中的小颗粒，借助全息技术实现了三维速度测量。利用互相关PIV测量了湍流圆形射流的湍流时空特征，结果与热丝风速测量结果吻合较好。采用激光诱导荧光（LIF）技术和高分辨率数字图像分析技术，提出了一种同时测量喷雾中液滴速度和粒径的方法。液体温度的测量在LIF技术的应用上取得了很大的进展。一项新开发的技术，聚焦于大范围ArF激光产生的空气中氧气的LIF光谱，使测量高达5000K的温度成为可能，误差为25K。另一种测量两个波长碘LIF信号强度之比的技术允许测量高速气体射流中的温度分布。此外，利用单峰LIF技术成功地测量了微通道内流动的温度分布。在浓度测量方面，提出了一种利用PIV和LIF在多点同时测量速度和浓度的方法，并将涡度和浓度的分布进行了定量关联。将聚焦聚甲醛的LIF技术应用于高温环境下的燃油喷射反应，首次对其点火过程进行了成像。

Multidimensional imaging in the studies of thermofluid dynamics aims at visualizing or quantifying instantaneous distributions of velocity, temperature and concentration. As for velocity measurement, PIV (Particle Imaging Velocimetry) which tracks small particles suspended in the flow allowed three dimensional velocity measurement with the help of Holographic technique. A cross- correlation PIV was used to measure the temporal and spatial characteristics of turbulence in a turbulent circular jet, and the result showed a good agreement with that measured by the hot wire anemometry. A technique for the simultaneous measurement of velocity and particle size of droplets in a spray was developed which employs LIF (Laser Induced Fluorescence) technique and high resolution digital image analysis.Measurement of temperature in a fluid made a great progress which uses LIF techniques. A newly developed technique which focuses on LIF spectrum of oxygen in the air generated by a wide range ArF laser made it possible to measure the temperature as high as 5000K with an error of 25K.Another technique which measures the ratio of intensities of Iodine LIF signals at two wave lengths permitted the measurement of temperature distribution in a high speed gaseous jet. In addition, temperature distribution in the flow in a micro-channel was measured in success using the exciplex LIF technique.Regarding the concentration measurement, a method was developed which measures velocity and concentration simultaneously at multipoints using PIV and LIF, and the distributions of vorticity and concentration was correlated quantitatively. LIF technique focusing on pholmaldehyde was applied to a reacting fuel spray in a high temperature environment and the ignition process has been imaged for the first time.