The flow field around an inclined solid emergent cylinder.

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Oral Yagci, Soheil Farazimajd, Vasileios Kitsikoudis, V.S.Ozgur Kirca

Tuesday 30 june 2015

16:45 - 17:00h at Africa (level 0)

Themes: (T) Water engineering, (ST) Experimental facilities and instrumentation

Parallel session: 7F. Engineering - Instrumentation

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The rigid cylinder-flow interaction constitutes a typical hydrodynamic problem with several field implications, which has been extensively studied by the civil engineering community. Among these topics, the rigid stem analogy is widely employed to model the flow-riparian vegetation interaction and thanks to this useful simplification, significant progress has been made in understanding this complicated phenomenon. However, it is a fact that under the effect of drag force, riparian natural vegetation elements bend and the rigid-vertical-emergent stem analogy underestimates this process. To understand the impact of bending, herein an “inclined rigid stem analogy” is investigated. According to the pertinent literature, the knowledge regarding the influence of the inclination angle on the flow field around an oblique cylinder is inadequate. From this motivation, a flume experiment was undertaken in a laboratory flume, which is 18m long, 0.5 m wide, and 0. 5 m deep. Its aim is to study the disturbance that is caused to the flow field by a 75 mm diameter oblique cylinder, streamwise oriented and placed in the middle of the flume, and investigate the effect of the inclination angle. The experiment comprises three different steady water discharges and four different inclination angles (plus the commonly studied vertical cylinder case), and each one is studied individually. For each case, spatially dense velocity measurements were conducted upstream as well as downstream of the cylinder with an Acoustic Doppler Velocimeter Profiler (Nortek Vectrino II). The measurements were obtained with 100 Hz frequency and the sampling duration was 60 seconds. The ADV was oriented to the transverse direction, and provided a 3.5 cm profile commencing from the centerline of the flume. The retrieved data were analyzed and compared in terms of mean as well as instantaneous fluctuating components. In addition, in order to understand the influence of the inclination angle on the separation that occurs at the upstream side of the cylinder, flow visualization is applied by means of Laser Sheet (Dantec). The findings clearly denote that inclination plays a crucial role on the separation process, which dictates the horseshoe vortex formation and subsequently the determination of the downstream momentum exchange.