scholarly journals Atmospheric Kármán Vortex Shedding from Jeju Island, East China Sea: A Numerical Study*

2015 ◽  
Vol 144 (1) ◽  
pp. 139-148 ◽  
Author(s):  
Junshi Ito ◽  
Hiroshi Niino
Keyword(s):  
Vortex Shedding ◽  
Bluff Body ◽  
Numerical Study ◽  
Jeju Island ◽  
Cloud Formation ◽  
Surface Drag ◽  
Convective Boundary ◽  
Sensitivity Experiment ◽  
Karman Vortex ◽  
Cloud Patterns

Abstract A mesoscale atmospheric numerical model is used to simulate two cases of Kármán vortex shedding in the lee of Jeju Island, South Korea, in the winter of 2013. Observed cloud patterns associated with the Kármán vortex shedding are successfully reproduced. When the winter monsoon flows out from the Eurasian continent, a convective mixed layer develops through the supply of heat and moisture from the relatively warm Yellow Sea and encounters Jeju Island and dynamical conditions favorable for the formation of lee vortices are realized. Vortices that form behind the island induce updrafts to trigger cloud formation at the top of the convective boundary layer. A sensitivity experiment in which surface drag on the island is eliminated demonstrates that the formation mechanism of the atmospheric Kármán vortex shedding is different from that behind a bluff body in classical fluid mechanics.

scholarly journals Design and Analysis of A Vortex Induced Vibration Based Oscillating Free Stream Energy Converter

2021 ◽  
pp. 112-117
Author(s):  
Ratan Kumar Das ◽  
Muhammad Taharat Galib
Keyword(s):  
Vortex Shedding ◽  
Large Scale ◽  
Bluff Body ◽  
Free Stream ◽  
Theoretical Formula ◽  
Pendulum Motion ◽  
Ansys Fluent ◽  
Vortex Induced Vibration ◽  
Karman Vortex ◽  
Lock In

The Kármán Vortex Shedding is one of the special types of vortex that is generated from asymmetric flow separation. For many years engineers tried to suppress the vortex shedding as it brings unnecessary motion to the static members inside the flow field. A converter model is designed and studied to harness the energy associated with this vortex shedding and convert it into usable form rather than suppressing it. It is a bluff body placed on the free stream incurring vortex-induced vibration and giving out a swinging pendulum motion. This motion is utilized to produce electricity. The model is analyzed on the free stream of water and conversion efficiency of 8.9% is achieved. A theoretical formula is derived regarding the force acting on the bluff body during the motion. Various parameters such as aspect ratio, flow velocity, lock-in delay, frequency of oscillation, etc. as well as their relations are studied by simulating the model in ANSYS FLUENT 18.1 for different configurations. From the simulated results it is obvious that as the lift force on the bluff body increases, more power generation is possible. Also, the experimental results paved the way for further study for practical large-scale implementation of the converter.

What is the Role of the Stagnation Region in Karman Vortex Shedding?

2011 ◽  
Vol 18 (3) ◽  
pp. 361-370 ◽  
Author(s):  
Grzegorz Pankanin
Keyword(s):  
Vortex Shedding ◽  
Bluff Body ◽  
Flow Visualisation ◽  
Information Channel ◽  
Hot Wire ◽  
Stagnation Region ◽  
Karman Vortex ◽  
Experimental Findings ◽  
The Relationship

What is the Role of the Stagnation Region in Karman Vortex Shedding?This paper is devoted to the problem of the appearance of a stagnation region during Karman vortex shedding. This particular phenomenon has been addressed by G. Birkhoff in his model of vortices generation. Experimental results obtained by various research methods confirm the existence of a stagnation region. The properties of this stagnation region have been described based on experimental findings involving flow visualisation and hot-wire anemometry. Special attention has been paid to the relationship between the existence of a slit in the bluff body and the size of the stagnation region. The slit takes over the role of the stagnation region as an information channel for generating vortices.

A Numerical Study of Flow Patterns, Drag and Lift for Low Reynolds Number Flow Past Tandem Cylinders of Various Shapes

2017 ◽  
Author(s):  
Yidan Song ◽  
Rui Zhu ◽  
Terrence Simon ◽  
Gongnan Xie
Keyword(s):  
Vortex Shedding ◽  
Bluff Body ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Bluff Bodies ◽  
Distance Ratio ◽  
Reynolds Number Flow ◽  
Drag And Lift ◽  
Lift And Drag ◽  
Center Distance

The flow over two different shaped bluff bodies in tandem arrangement was numerically investigated by using the finite volume method with Computational Fluid Dynamics (CFD) techniques. The shape of the downstream main bluff body is a right circular cylinder, with shape unchanged, while the shape of the upstream bluff body varies between: circle, triangle, square, ellipse and cylindrical half-shell. The hydraulic diameters of both front and rear bluff bodies are equal. The analysis is carried out for Reynolds numbers of 100, 300 and 500, and center-to-center distance ratios, L/D, of 1.5, 2, 3, 4.5 and 6. Flow characteristics in terms of the lift and drag coefficients and Strouhal number are analyzed and the vortex shedding patterns around the bluff bodies are described. The influence of the shape of the fore cylinder on the flow characteristics is the innovation point of this paper. It is concluded that the center-to-center distance ratio, L/D, and the shape of the upstream bluff body have important effects on the drag and lift coefficients, vortex shedding frequencies from the two bluff bodies, and flowfield characteristics.

scholarly journals Numerical study of bio-convection flow of magneto-cross nanofluid containing gyrotactic microorganisms with activation energy

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Qiu-Hong Shi ◽  
Aamir Hamid ◽  
M. Ijaz Khan ◽  
R. Naveen Kumar ◽  
R. J. Punith Gowda ◽  
...  
Keyword(s):  
Radiation Effects ◽  
Numerical Study ◽  
Source Parameters ◽  
Lewis Number ◽  
Convective Boundary Condition ◽  
Convection Flow ◽  
Convective Boundary ◽  
Similarity Transformations ◽  
Cross Nanoliquid ◽  
Source Sink

AbstractIn this study, a mathematical model is developed to scrutinize the transient magnetic flow of Cross nanoliquid past a stretching sheet with thermal radiation effects. Binary chemical reactions and heat source/sink effects along with convective boundary condition are also taken into the consideration. Appropriate similarity transformations are utilized to transform partial differential equations (PDE’s) into ordinary ones and then numerically tackled by shooting method. The impacts of different emerging parameters on the thermal, concentration, velocity, and micro-rotation profiles are incorporated and discussed in detail by means of graphs. Results reveal that, the escalation in magnetic parameter and Rayleigh number slowdowns the velocity and momentum of the fluid. The increase in Biot number, radiation and heat sink/source parameters upsurges the thermal boundary but, converse trend is seen for escalating Prandtl number. The density number of motile microorganisms acts as a growing function of bioconvection Lewis number and declining function of bioconvection Peclet number.

Numerical study of the flow over the modified simple frigate shape

2020 ◽  
pp. 095441002097775
Author(s):  
Tong Li ◽  
Yibin Wang ◽  
Ning Zhao
Keyword(s):  
Bluff Body ◽  
Recirculation Zone ◽  
Numerical Study ◽  
Reference Value ◽  
Flow Fields ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Simulation Results

The simple frigate shape (SFS) as defined by The Technical Co-operative Program (TTCP), is a simplified model of the frigate, which helps to investigate the basic flow fields of a frigate. In this paper, the flow fields of the different modified SFS models, consisting of a bluff body superstructure and the deck, were numerically studied. A parametric study was conducted by varying both the superstructure length L and width B to investigate the recirculation zone behind the hangar. The size and the position of the recirculation zones were compared between different models. The numerical simulation results show that the size and the location of the recirculation zone are significantly affected by the superstructure length and width. The results obtained by Reynolds-averaged Navier-Stokes method were also compared well with both the time averaged Improved Delayed Detached-Eddy Simulation results and the experimental data. In addition, by varying the model size and inflow velocity, various flow fields were numerically studied, which indicated that the changing of Reynolds number has tiny effect on the variation of the dimensionless size of the recirculation zone. The results in this study have certain reference value for the design of the frigate superstructure.

An experimental and numerical study of the resonant flow between a hull and a wall

2021 ◽  
Vol 930 ◽  
Author(s):  
I.A. Milne ◽  
O. Kimmoun ◽  
J.M.R. Graham ◽  
B. Molin
Keyword(s):  
Vortex Shedding ◽  
Particle Image ◽  
Numerical Study ◽  
Numerical Models ◽  
Vertical Wall ◽  
Liquefied Natural Gas ◽  
Narrow Gap ◽  
Image Velocimetry ◽  
High Degree ◽  
Wave Induced

The wave-induced resonant flow in a narrow gap between a stationary hull and a vertical wall is studied experimentally and numerically. Vortex shedding from the sharp bilge edge of the hull gives rise to a quadratically damped free surface response in the gap, where the damping coefficient is approximately independent of wave steepness and frequency. Particle image velocimetry and direct numerical simulations were used to characterise the shedding dynamics and explore the influence of discretisation in the measurements and computations. Secondary separation was identified as a particular feature which occurred at the hull bilge in these gap flows. This can result in the generation of a system with multiple vortical regions and asymmetries between the inflow and outflow. The shedding dynamics was found to exhibit a high degree of invariance to the amplitude in the gap and the spanwise position of the barge. The new measurements and the evaluation of numerical models of varying fidelity can assist in informing offshore operations such as the side by side offloading from floating liquefied natural gas facilities.

Aerodynamics of a two-dimensional bluff body with the cross-section of a train

2020 ◽  
Vol 23 (12) ◽  
pp. 2679-2693 ◽  
Author(s):  
Huan Li ◽  
Xuhui He ◽  
Hanfeng Wang ◽  
Si Peng ◽  
Shuwei Zhou ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Large Amplitude ◽  
High Speed ◽  
Bluff Body ◽  
Mean Amplitude ◽  
Two Dimensional ◽  
Aerodynamic Forces ◽  
Moderate Reynolds Number ◽  
Amplitude Mode

Experiments on the aerodynamics of a two-dimensional bluff body simplified from a China high-speed train in crosswinds were carried out in a wind tunnel. Effects of wind angle of attack α varying in [−20°, 20°] were investigated at a moderate Reynolds number Re = 9.35 × 104 (based on the height of the model). Four typical behaviors of aerodynamics were identified. These behaviors are attributed to the flow structure around the upper and lower halves of the model changing from full to intermittent reattachment, and to full separation with a variation in α. An alternate transition phenomenon, characterized by an alteration between large- and small-amplitude aerodynamic fluctuations, was detected. The frequency of this alteration is about 1/10 of the predominant vortex shedding. In the intervals of the large-amplitude behavior, aerodynamic forces fluctuate periodically with a strong span-wise coherence, which are caused by the anti-symmetric vortex shedding along the stream-wise direction. On the contrary, the aerodynamic forces fluctuating at small amplitudes correspond to a weak span-wise coherence, which are ascribed to the symmetric vortex shedding from the upper and lower halves of the model. Generally, the mean amplitude of the large-amplitude mode is 3 times larger than that of the small one. Finally, the effects of Reynolds number were examined within Re = [9.35 × 104, 2.49 × 105]. Strong Reynolds number dependence was observed on the model with two rounded upper corners.

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