Applications of laser doppler anemometry (LDA) to the study of some industrial two-stream mixing flow processes with streamwise vorticity

• Main Author: Hou, Yongxi.
• Other Authors: Yu, Simon Ching Man
• Format: Theses and Dissertations
• Language: English
• Published: 2008
• Subjects: DRNTU::Engineering::Aeronautical engineering; DRNTU::Engineering::Mechanical engineering::Fluid mechanics
• Online Access: http://hdl.handle.net/10356/13525
• Institution: Nanyang Technological University

Flow characteristics of a square jet with mixing tabs have been determined by a two-component laser-Doppler anemometer at a Reynolds number of 1.35 x 105. The results are complemented by flow visualization tests using Laser Induced Fluorescence (LIF) technique. Tabs of rectangular and triangular shapes at the same height to base ratio (h/b=1.3) and with their apexes leaning downstream are considered. Altogether four tabs have been used with one tab located at the center of each side wall at the exit plane. Each tab is found to produce a dominant pair of counter-rotating streamwise vortices. The combined effects of the four tabs bifurcate the jet into four "fingers" resulting in a significant increase in entrainment at the downstream locations. Strength of the streamwise vorticity generated by the rectangular tabs is higher than that of the triangular ones and decays faster with downstream distance. The implementation of the rectangular secondary tabs can effectively enhance the strength of the streamwise vorticity generated by the primary tabs. The increase in the peak vorticity strength can be found with the rectangular secondary tabs at 10° than at larger angles or without the secondary tabs. All the cases considered here showed that the streamwise vorticity dissipated within six diameters downstream of the exit plane and intense mixing took place only at one to three diameters downstream.