Analysis of high frequency and transient characteristics of the flow past a circular cylinder

The high frequency and transient characteristics of the flow past a circular cylinder are experimentally measured by a high frequency particle image velocimetry (PIV) system. A circular cylinder whose diameter is 25 mm is installed in a wind tunnel with Reynolds numbers ranging from 1.19 × 10 4 to 3.4 × 10 4 . The acquisition frequency of the high frequency PIV system is 3 kHz for all tests in the present study. Based on the measurement results, the vortex parameters of the successive vortexes shedding from both the single side and bilateral sides of a circular cylinder show good similarity and repeatability at the macro-level. Besides, some high frequency and transient characteristics of the vortex parameters can be obtained by the high frequency test. The maximum dimensionless vortex strengths and the maximum dimensionless vortex radius of three successive vortexes differ from each other obviously. The deviations can reach about 28 and 10%, respectively. For the range of Reynolds numbers in the present study, the lengths of the vortex formation region are nearly equal to the diameter of the circular cylinder. The residence time of a vortex in the vortex formation region is about a vortex shedding period. The stream-wise velocity of the vortex center downstream the vortex formation region is about 0.7 times of the free stream velocity.