EXPERIMENTAL INVESTIGATION ON VORTEX BREAKDOWN IN SPIN-UP AND SPIN-DOWN PROCESSES VIA PIV

摘要

The whole field measurements of swirling flow in spin-up and spin-down processes via PIV are presented in the paper. Investigation of the flow patterns at H/R = 1. 50 was experimentally carried out for the first time in both processes. By means of symmetry analysis, it is found that the overall flow structure in the spin-up process still keep axi-symmetric to a great extent, but deteriorated very fast in the spin-down process. The time to settle to the state of rest in the spin-down process is found to be greatly shorter than the time to achieve the steady state in the spin-up process. Temporarily oscillatory vortex breakdown was discovered during the spin-up process, although no breakdown in the steady state at the same Reynolds number is found in precious researches.