Laser doppler anemometer for turbulent and multiphase flows

工业和/或环境应用中遇到的大多数流动都是湍流，也就是说，它们的特征是与速度场中明显随机的小尺度波动相关的混合程度增强。湍流有许多重要的实际应用，包括增加表面摩阻和增加壁面换热速率。除了湍流之外，流动还可能表现出额外的复杂性来源，如与外表面分离，从而产生速度降低的尾流区和可能的回流流。其他流动可能涉及多个相，如液体中的气体或蒸汽气泡和固体颗粒。随着流动复杂性的增加，使用计算机模型预测流动特征变得越来越困难。实验研究被用来提高我们对复杂流动的理解，通常的长期目标是能够为工程应用预测它们。测量复杂湍流中的速度场是一个特殊的挑战。为了捕捉速度场的小尺度波动，用于测量速度场的仪器必须具有瞬时速度场的多分量分辨率。完成这一任务的一个研究工具是激光多普勒风速仪(LDA)系统。该设备使用多束激光来有效地测量流动中的局部速度。目前的研究拨款将升级萨斯喀彻温省大学现有的LDA系统的处理器，然后将用于研究广泛的基本和应用流动，包括：粗糙表面上的湍流边界层；壁面喷流；横流中短堆积后的复杂尾流；泰勒气泡在液体中上升；下落的环形胶片。

Most flows encountered in industrial and/or environmental applications are turbulent, which is to say that they are characterised by enhanced levels of mixing associated with apparently random small-scale fluctuations in the velocity field.  Turbulence has many important practical applications including increased skin friction drag and increased wall heat transfer rates.  In addition to turbulence, flows can exhibit additional sources of complexity, such as flow separation  from an exterior surface, which then creates a wake region of reduced velocity and possible recirculating flow.  Other flows can involve multiple phases, such as gas or vapour bubbles and solid particles in a liquid.  As the flow complexity increases, the prediction of flow feaures using computer models becomes increasingly more difficult. Experimental studies are used to improve our understanding of  complex flows, often with the long term goal of being able to predict them for engineering applications.  Measurement of the velocity field in complex turbulent flows presents a special challenge.  In order to capture the small-scale fluctuations of the velocity field, the instrument used to measure the velocity field must be capable of multi-component resolution of the instantaneous velocity field.  One research tool that accomplishes this task is a laser doppler anemometer (or LDA) system.  This equipment uses multiple laser beams to effectively measure the local velocity in a flow.  The present research grant will upgrade the processor of an exisitng LDA system at the University of Saskatchewan, which will then be used to study a wide range of fundamental and applied flows including: a turbulent boundary layer on a rough surface; a wall jet; the complex wake behind a short stack in a cross-flow; Taylor bubbles rising in a liquid; falling annular films.