Passive Control of the Vortex Shedding behind a Rectangular Cylinder Near a Wall
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Abstract:
지면엔 근접한 사각주 후면에서 발생하는 비정상 와류 배출은 지상 운송체, 교량, 건물 등의 항력 증가뿐 아니라, 동안정성에도 큰 영향을 미친다. 비압축성 평균 Navier-Stokes 방정식에 수정된 Keywords:
Vortex shedding
Flow Control
Vortex shedding
Strouhal number
Flow Control
Lift (data mining)
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Vortex shedding
Kármán vortex street
Potential flow
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The flow fields in vortex flow sensors with circular cylinder and trapezoidal cylinder bluff bodies are investigated respectively. Then the characteristics of two flow fields are compared by numerical simulations while the mechanism of vortex shedding is analyzed in detail. Finally, the reason, which leads to different vortex shedding frequency and effects the relationship between Reynolds number and Strouhal number, has been specified as the size of wake flow region behind bluff body where the vortex generated.
Strouhal number
Vortex shedding
Bluff
Kármán vortex street
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The physical phenomena of vortex suppression and flow patterns by deploying a very mall control cylinder in the near wake region of a main cylinder in low Reynolds numbers is studied numerically. The control diameter effect on vortex suppression and three flow patterns has been studied. The results shows the control cylinder can reduce vortex shedding frequency and suppress shedding partially or completely dependent on the diameter of control cylinder and Reynolds number. The results of a cylinder with control and without control agree with experimental and numerical studies.
Vortex shedding
Flow Control
Kármán vortex street
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A flow visualization scheme for vortex shedding flow past a circular cylinder near a wall is based on a finite difference solution to the two-dimensional Navier-Stokes equations for time-dependent incompressible viscous flows. The flow is calculated at a broad range of gap ratios for two different Reynolds numbers. The vortex shedding process is observed, and the mechanism for the vortex shedding suppression at small gap ratios is analyzed. The variations of the separation points and wake size with the gap ratio are presented. The effects of both the gap ratio and the Reynolds number on this vortex shedding flow are discussed.
Vortex shedding
Starting vortex
Hele-Shaw flow
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A version of the no-feedback-control method developed by H\"ubler and L\"uscher [Helv. Phys. Acta 62, 544 (1989)] is applied to two-dimensional open-channel flow past a plate. The control is applied in the vortex-shedding regime with the aim of reducing the effective Reynolds number, thereby suppressing the vortex shedding. It is shown that the method works well not only when the flow is globally forced but also when the forcing is restricted to the boundary-layer region.
Vortex shedding
Flow Control
Forcing (mathematics)
Kármán vortex street
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In this study, a numerical experiment of flow around a self-oscillating circular cylinder with whirling limitation was performed using the boundary element method combined with the vortex method. The flow feature of vortex shedding and the characteristics of vibration due to the fluid force were simulated about various initial setting position of circular cylinder at the Reynolds number Re=1×105, the mass ratio M=5.15, the damping factor C=0.0 and the reduced velocities Vr=1.8 and Vr=2.4. As a result of calculation, in the case of coaxial setting, the flow feature and the characteristics of cylinder vibration due to the fluid force were as same as a result of self-oscillating case, however, in the case of not coaxial setting, the frequency of cylinder's motion was changed and the flow features were changed from the twin type vortex shedding pattern to the Karman type vortex shedding pattern. It was shown that the characteristic of cylinder vibration frequency depended on both of the distance and the direction between the circular cylinder and the wall of pit.
Vortex shedding
Vortex-induced vibration
Coaxial
Kármán vortex street
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DBD (dielectric barrier discharge) plasma actuators have in recent years become increasingly attractive in studies of flow control due to their light structures and easy implementation, but the design of a series of actuators enabling drag reduction depends on many parameters (e.g., the length of the actuator, the space between actuators, and voltage applied) and remains a significant issue to address. In this study, velocities created by the DBD plasma actuators in stagnant flow obtained by the numerical model are compared with experimental results. Then, a DNS study is carried on, and spanwise oscillated DBD plasma actuators are examined to obtain a drag reduction in a fully developed turbulent channel flow. This study connects the conventional spanwise oscillated force in drag reduction studies with DBD plasma actuators. While the former is one of the most successful applications for the drag reduction, the latter is a most promising tool with its light and feasible structure.
Plasma actuator
Flow Control
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In order to investigate flow fields in vortex flow meters, we used a circular cylinder transverse in a pipe instead of a vortex -shedding bluff body. Then, time-averaged pressure distributions on the surface of the cylinder are measured, and fluctuating streamwise velocities are analyzed statistically. The contraction ratio β of a cylinder diameter to a pipe diameter varies between 0.102 and 0.510. The wall blockage of a pipe strongly influences the flow fields. Brief results are as follows. Drag coefficients and Strouhal numbers defined by the mean flow velocity are rapidly increased with β. However, the modified drag coefficients and modified Strouhal numbers, which are defined by the mean velocity through the minimum flow area in a pipe, are nearly equal to those in a two-dimensional uniform flow. Further, vortices shedding from a cylinder are aligned along the axis of a pipe.
Strouhal number
Vortex shedding
Potential flow
Water tunnel
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In this study, the flow features of vortex shedding from a self-oscillating circular cylinder and the characteristics of fluid force were examined using a vortex method simulation combined with boundary layer calculation in a uniform flow at high Reynolds number in order to investigate validity and applicability to the analysis of the flow-induced vibration problems. The calculations were performed for the parameters of the mass ratio M (=1.78, 5.15), the damping factor C (=0.0, 0.0153) and the reduced velocity Vr (=1.38-4.13) at the Reynolds number Re=1×105 based on the uniform flow velocity U and the cylinder diameter D. As a result of the calculations, two typical patterns of vortex shedding were observed, one of which is symmetric twin vortex shedding and the other is antisymmetric twin vortex shedding. It was confirmed that the calculated flow patterns and the free-oscillation motions of the cylinder, were in reasonable agreement with experimental results. The relationship between the fluid force and the resultant cylinder's displacement was investigated.
Vortex shedding
Vortex-induced vibration
Oscillation (cell signaling)
Potential flow
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