Controlling the vortex shedding phenomenon behind the cylinder with rotary controllers

نوع: Type: thesis

مقطع: Segment: PHD

عنوان: Title: Controlling the vortex shedding phenomenon behind the cylinder with rotary controllers

ارائه دهنده: Provider: Masoud Najafi

اساتید راهنما: Supervisors: DR Mohsen Goodarzi

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: DR Mohamad Saeed Aghighi, DR Hosein Ahmadi kia, DR Farzad Veysi

زمان و تاریخ ارائه: Time and date of presentation: March, 3 , 2023 at 11 AM

مکان ارائه: Place of presentation: Seminar 2

چکیده: Abstract: After several decades of labor by engineers and scientists, fluid dynamics around objects with a wide cross-section and methods of reducing fluid forces and vortex shedding-induced vibrations around them is still a dynamic field of research. Due to resonance, structures are typically destroyed by the vortex shedding-induced vibrations behind them, making it expensive and sometimes impossible to fix the resulting defects. Important practical examples in dealing with vortex shedding include heat exchangers, chimneys, marine structures, and tall structures and power lines. This thesis aims to investigate the effect of two rotating controllers on vortex shedding behind a cylinder with a square cross-section at 0 and 45-degree encounter angles to the main flow and the ability to limit the range of aerodynamic fluctuation forces arising from vortex shedding on the cylinder in laminar and turbulent flow at Reynolds numbers of 150 and 24,000. Ansys Fluent was used for analyzing flow field and aerodynamic forces on the cylinder. The results showed that in a cylinder with 0-degree encounter angle in laminar flow, applying this method in certain spatial coordinates, can completely suppresses vortex shedding in the entire flow field and reducing the drag coefficient of the cylinder and controllers. However, despite eliminating the effects of vortex shedding on the cylinder and controllers in certain spatial coordinates in the cylinder with the 45-degree encounter angle, this method cannot completely suppresses vortex shedding. The results indicate that in the cylinder with 45-degree encounter angle, vortex shedding is completely stopped at higher rotational speeds for the controllers. Analysis of vortex shedding pattern and flow field, showed that the controllers create three general regimes in the flow field. In the second regime, vortex shedding is completely stopped in the entire flow field. In the third regime, vortex shedding is completely stopped between the cylinder and controllers but continues after the controllers. An important finding is that depending on the positioning of controllers in any spatial coordinate in laminar flow, the induced fluctuating forces to the cylinder and controllers are harmonic or periodic. In turbulent flow for the cylinder with a 0-degree encounter angle, the controllers in certain spatial coordinates make the flow quasi-laminar while reducing the cylinder's root mean square fluctuation of lift and drag coefficient by a maximum of 90% and making them periodic or harmonic. However, it could not completely stop vortex shedding in the flow field. For the cylinder with the 45-degree encounter angle in turbulent flow, the controllers could only reduce the root mean square fluctuation of lift coefficient by a maximum of 63%

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