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1

Numerical investigation of vortex wake patterns of laminar flow around two side-by-side cylinders

Nguyen Van Luc, Ho Duy Khanh

Archive of Mechanical Engineering

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2022

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LXIX, nr 3

541--565

EN

The laminar flow around two side-by-side circular cylinders was numerically investigated using a vortex-in-cell method combined with a continuous-forcing immersed boundary method. The Reynolds number (Re) of the flow was examined in the range from 40 to 200, and the distance between the cylinders varies from 1.2D to 6D, where D is the cylinder diameter. Simulation results show that the vortex wake is classified into eight patterns, such as single-bluff-body, meandering-motion, steady, deflected-in-one-direction, flip-flopping, anti-phase-synchronization, in-phase-synchronization, and phase-difference-synchronization, significantly depending on the Re, the cylinder distance, and the initial external disturbance effects. The anti-phase-synchronization, in-phase-synchronization, and phase-difference-synchronization vortex patterns can be switched at a low Re after a long time evolution of the flow. In particular, the single-bluff-body and flip-flopping vortex patterns excite the oscillation amplitude of the drag and lift coefficients exerted on the cylinders

2

Experimental study on suppression of vortex street behind perforated square cylinder

Teimourian A., Hacışevki H., Bahrami A.

Journal of Theoretical and Applied Mechanics

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2017

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Vol. 55 nr 4

1397--1408

EN

In this study, the effects of entrainment of a fluid through a perforated surface on suppression of the vortex street behind a perforated square cylinder have been studied experimentally. The wake region has been investigated in terms of coherent flow structure, time averaged properties and effectiveness of different perforations. The quantitative measurements revealed that the perforated surfaces are only effective within a width interval of y/D = ±1.0. It has been observed that in the near wake region up to approximately 1.5D downstream the wake, the shedding phenomenon has been suppressed significantly. It has been also demonstrated that velocity profiles and flow structure have been affected by different perforated surfaces and, as a result, coherent structures have been diminished considerably.

3

Badania modelowe liczby Strouhala oblodzonego cięgna mostu podwieszonego

Górski P., Pospišil S, Kuznetsov S, Tatara M., Marušić A

Budownictwo i Architektura

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2014

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Vol. 13, nr 2

201--208

PL

W artykule przedstawiono sposób i wyniki badań liczby Strouhala nieruchomego modelu oblodzonego cięgna mostu podwieszonego. Badania wykonano w tunelu aerodynamicznym z komorą klimatyczną Laboratorium Czeskiej Akademii Nauk w Telc. W komorze klimatycznej wykonano doświadczalne oblodzenie modelu cięgna o osi nachylonej pod kątem 300 do płaszczyzny poziomej. Kształt oblodzonej powierzchni zarejestrowano metodą fotogrametrii cyfrowej. Do badań w tunelu aerodynamicznym wykonano nowy model sekcyjny oblodzonego cięgna metodą druku 3D. Liczbę Strouhala wyznaczono w zakresie wartości liczby Reynoldsa od 28 do 122 na podstawie pomiaru częstości odrywania się wirów w śladzie aerodynamicznym za modelem.

EN

The paper presents the method and results of wind tunnel investigations of Strouhal number of stationary iced cable model of cable-stayed bridge. The investigations were performed in a Climatic Wind Tunnel Laboratory of the Czech Academy of Sciences in Telc. The experimental icing of the inclined cable model in the climatic chamber of the laboratory was made. The shape of the iced model was registered by a numerical photogrammetry method. For the aerodynamic tunnel investigations, the new iced cable model was made by using 3D printing method. The Strouhal number was determined within the range of the Reynolds number between 28·103 and 122·103, on the basis of the dominant vortex shedding frequency measured in the flow behind the model.

4

Pewne przypadki rezonansu wiatrowego kominów stalowych

Wichtowski B., Żurański J. A.

Inżynieria i Budownictwo

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2011

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R. 67, nr 3

154-156

PL

Na przykładzie pięciu wolno stojących kominów stalowych, przedstawiono zastosowanie środków zapobiegających drganiom kominów wywoływanym odrywaniem się wirów powietrza podczas wiatru. Omówiono zaobserwowane drgania i zastosowane środki zapobiegawcze, którymi były, z jednym wyjątkiem, turbulizatory spiralne wykonane z okrągłych prętów stalowych o średnicach 6 i 8 mm. Oceniono skuteczność przyjętych rozwiązań.

EN

The paper deals with the cross wind vibrations of five free standing steel chimneys. Such vibrations arising due to vortex shedding called as vortex excitation, are characterized by large amplitudes of chimney's top. Observed vibrations and preventive measures against them, used for those chimneys, have been presented. With one exception they were spiral.

5

Numerical analysis of controlling separation in axial cascades by excitation of periodical incoming wake

Liu F., Wang J., Wu K.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2008

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Vol. 12, No 1-2

21-34

EN

Numerical analysis has been performed of time-space structures in a large turning angle axial cascade subject to unsteady incoming wake excitation. The results have shown that intentional unsteady excitation could increase the cascade's time-averaged performance. As a result, the vortex structures corresponding to the external exciting frequency are strengthened and other disordered vortices are involved, so that the separation structures of the suction surface are translated from disorder to order. Two interaction regimes between incoming periodic wakes and separation structures are analyzed, indicating that turbulent kinetic energy can enhance momentum interchange and that wave-vortex resonance can promote rolled-up and plus-minus pairing of vortices. Based .on these, responses of separation structures from two periodic incoming wake regimes are compared. The feasibility of far-field noise reduction in ducting fans by using periodic incoming wake is considered.

6

Three-dimensional simulation of time-dependent flow behind bluff bodies

Valles B, Andersson H. I., Jenssen C. B.

International Journal of Applied Mechanics and Engineering

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2002

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Vol. 7, no 1

311-328

EN

Computer simulations of the laminar flow past three-dimensional bluff bodies are presented. The focus is on the time-dependent wake flow behind linearly tapered circular cylinders and downstream of a circular cylinder with an abrupt change in diameter. In both cases the intricate vortex shedding phenomena observed in earlier laboratory experiments are convincingly reproduced by the computer experiments. The simulations moreover provide important supplementary information not readily accessible in the laboratory.