Laser doppler anemometer for turbulent and multiphase flows

点击翻译按钮获取中文摘要

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.