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Vortex Shedding Control Using a Permeable Plate Located Around the Separation Point of a Circular Cylinder

The flow downstream of a plain cylinder with attached permeable plates having various porosity ratios was investigated experimentally using both Particle Image Velocimetry (PIV) and dye visualization techniques to control the vortex shedding around the circular cylinder. The diameter of the cylinder and length to diameter ratio of the plate were kept constant as d= 50 mm and L/d=1.0, respectively. The porosity ratio, β which can be defined as the ratio of open area to the whole body surface area was taken as β=0.4, 0.5, 0.6, 0.7 and 0.8 (permeable plates). The study was performed considering deep water flow conditions and depth-averaged free stream velocity was taken constant as U = 95.2mm/s which corresponded to a Reynolds number of Red = 5000 based on the cylinder diameter. The results of a plain cylinder were compared with the results of cylinder with permeable plates in order to understand the control effect. Both qualitative and quantitative results revealed that the plates are effective on the unsteady flow structure downstream of the cylinder, i.e. the vortex formation length was increased, turbulent statistics was reduced and both width and length of the wake were changed by usage of permeable plates attached around the separation point of the cylinder.Copyright

Determınatıon of Atomızatıon Characterıstıcs of a Dıesel Injector

Atomization of liquid fuels is very important topic for combustion studies since it enhances air/ fuel mixing process and therefore ensures perfect combustion. With today’s common diesel injectors, fuel is directly injected into the combustion chamber with extremely high pressures which exceed 1300 bar in order to obtain perfect atomization. However, these high injection pressures unfortunately create some problems in the injection system such as cavitation erosion which may lead to mechanical failure. Introducing of air into the injector prior to combustion will increase fuel atomization, provide more complete combustion, enhance fuel economy and results in lower engine emissions. The aim of this study is to investigate atomization behaviour of a newly introduced diesel engine which mixes air and fuel prior to combustion chamber.

Suppression of Vortex Shedding Downstream of a Circular Cylinder Using Permeable Cylinders in Shallow Water

The characteristics of the flow around a 50mm circular cylinder surrounded by a permeable outer cylinder were investigated by Particle Image Velocimetry (PIV) and flow visualization techniques in order to control the unsteady flow structure downstream of the cylinder in shallow water. The effect of outer permeable cylinder with a porosity of β = 0.4 on the flow control was studied using five different diameters; D = 60, 70, 80, 90, 100mm. Depth-averaged free stream velocity was kept constant as U = 170mm/s corresponding to a Reynolds number of Re = 8500 and the water height was adjusted to hw = 25mm throughout the study. The results clearly showed that the outer permeable cylinder significantly affects the flow structure of the inner cylinder. It was found that by the existence of outer cylinder, the frequency of unsteady vortex shedding is reduced, vortex formation region is elongated and fluctuations are attenuated which are good indications of effective flow control. Owing to the results, optimum parameters were defined and suggested for the suppression of vortex-induced vibrations on bluff bodies.Copyright

The Passive Control of Unsteady Flow Structure Downstream of a Circular Cylinder in Shallow Water

In the present study, it was aimed to suppress the vortex shedding occurred in the near wake of a circular cylinder (inner cylinder) by perforated cylinder (outer cylinder) in shallow water flow. The inner cylinder (Di) and outer cylinder (Do) have fixed diameters, such as Di = 50 mm and Do = 100 mm, respectively. The effect of porosity, β, was examined using four different porosity ratios, 0.3, 0.5, 0.6 and 0.8. In order to investigate the effect of arc angle of outer cylinder, α, four different arc angles, α = 360°, 180°, 150° and 120° were used. The experiments were implemented in a recirculating water channel using the particle image velocimetry, PIV technique. The depth-averaged free-stream velocity was kept constant as U∞ = 100 mm/s which corresponded to a Reynolds number of Re = 5000 based on the inner cylinder diameter. The results demonstrated that the suppression of vortex shedding is substantially achieved by perforated outer cylinder for arc angle of α = 360° at β = 0.6. Turbulence Kinetic Energy statistics show that porosity, β, is highly effective on the flow structure. In comparison with the values obtained from the case of the bare cylinder, at porosity β = 0.6, turbulence characteristics are reduced by %80. Also, the point, which the values of maximum TKE, shift to a farther downstream compared to the case of bare cylinder.Copyright