MEASUREMENTS OF THERMALLY STRATIFIED PIPE-FLOW USING IMAGE-PROCESSINGTECHNIQUES

The cross-correlation technique and Laser Induced Fluorescence (LIF) h ave been adopted to measure the time-dependent and two-dimensional vel ocity and temperature fields of a stably thermal-stratified pipe flow. One thousand instantaneous and simultaneous velocity and temperature maps were obtained at overall Richardson number Ri=0 and 2.5, from whi ch two-dimensional vorticity, Reynolds stress and turbulent heat flux vector were evaluated. The quasi-periodic inclined vortices (which con nected to the 'crest') were revealed from successive instantaneous map s and temporal variation of vorticity and temperature. It has been rec ognized that these vortices are associated with the 'crest' and 'valle y' in the roll-up motion.