Experimental study on wake of circular cylinder over backward-facing step
|關鍵字:||圓柱;尾流;背向階梯;渦流脫離頻率;circular cylinder;wake;backward-facing step;vortex shedding frequency|
In Taiwan, one of the safety problems of many bridges is the local scour caused by flow passing around the bridge piers. Regarding engineering methods, groundsill works, gabions and other structures are usually used to protect the foundations of piers to ensure bridges safety. Because groundsill work or gabion is constructed on step, the structure can be regarded as the combination of circular cylinder and step. In the past, there were many researches about flow passing either circular cylinder or step, but few studies on the flow field of the combination of circular cylinder and step. Therefore, this experiment is conducted to study the flow field passing a circular cylinder located on a backward-facing step by using the particle image velocimetry to measure the horizontal flow fields at different layers of the wake generated by the circular cylinder. The experimental result reveals an adverse flow zone occurs in the recirculation region of step behind the cylinder. In the adverse flow zone, fluids flow toward step and faster than those on both sides of the recirculation region. Therefore, the adverse flow will become the main flow of the recirculation region. The adverse flow zone affects the wake of the circular cylinder causing a field of low velocity existing in the middle of the wake. It also results in that vortices displace laterally when flowing downstream. Furthermore, the relationship among vortex shedding frequency, height of step, and Froude number is analyzed to provide the information for the future study about the vibration of the pier and the estimation of the local scour depth.
|Appears in Collections:||Thesis|
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