Flow control downstream of a circular cylinder by a permeable cylinder in deep water

The flow characteristics of a circular cylinder surrounded by an outer permeable cylinder were experimentally investigated using Particle Image Velocimetry Technique in deep water flow. In order to consider the effects of diameter and porosity of the outer cylinder on flow structures of the inner cylinder, five different outer cylinder diameters (D=37.5, 52.5, 60, 75 and 90 mm) and eight different porosities (?= 0.4, 0.5, 0.6, 0.65, 0.7, 0.75, 0.8 and 0.85) were selected. During the experiments, the diameter of inner cylinder was kept constant as d=30 mm. The depth-averaged free-stream velocity was adjusted as U=0.156 m/s, which corresponds to the Reynolds number of Re=5000 based on the inner cylinder diameter. It has been concluded that both the outer permeable cylinder diameter and the porosity have important influences on the attenuation of vortex shedding in the wake region. The presence of outer permeable cylinder decreases the magnitude of Reynolds shear stress and turbulent kinetic energy compared to the bare cylinder case. Moreover, the spectral analysis of vortex shedding frequency has revealed that the dominant frequency of vortex shedding downstream of the cylinder arrangement also reduces substantially due to the weakened Karman shear layer instability. © 2014 Techno-Press, Ltd

Passive control of circular cylinder wake in shallow flow

The control of vortex shedding of a circular cylinder in shallow water using a splitter plate located in the downstream of the circular cylinder was studied by employing particle image velocimetry (PIV) technique. Experiments were carried out in a water channel having a test section of 8000 mm × 1000 mm × 750 mm dimensions at a Reynolds number of 6250. The length of the splitter plate (L) was varied within the range of 0.5 ? L/D ? 2 with an increment of 0.5. The plate was submerged into water at different height ratios (hp/hw) such as 0.25, 0.5, 0.75 and 1.0. Mean velocity vector field, corresponding vorticity contours, streamline topologies and turbulent quantities were calculated using 300 instantaneous velocity vector field measured by PIV. As the ratio of hp/hw increases, the effect of the splitter plate on the suppression of the vortex shedding increases. Flow characteristics and examination of spectra indicate that Karman vortex shedding is attenuated pronouncedly for the cases of L/D ? 1 and hp/hw ? 0.75. The transverse Reynolds normal stress is more effective on the attenuation of turbulent kinetic energy than the streamwise Reynolds normal stress. The value of peak transverse Reynolds normal stress is reduced to 90% of that of the bare cylinder at most. © 2012 Elsevier Ltd. All rights reserved.National Council for Scientific Research: 105M267The authors would like to acknowledge the financial support of the Scientific and Technological Research Council of Turkey for funding under Contract No. 105M267

Comparative mineralization of basic red 18 with electrochemical advanced oxidation processes

In this study, the role of electrochemical oxidation processes, including the electro-Fenton, the electro-persulfate (PS), and the electro/FeII/PS processes, in the removal of Basic Red 18 (BR18) from aqueous solutions was investigated. It was found that the electro-PS process successfully removes colour, but after 5 h, it produced only 75 % mineralization. In the same conditions, more effective mineralization was achieved by the electro/FeII/PS process than by the electro-Fenton method. At pH levels of 3.0 and 5.7, very effective mineralization results were produced by the electro/FeII/PS process. Moreover, the maximum mineralization current efficiency values were obtained by the electro/FeII/PS process. The mineralization efficiency of the electro/FeII/PS process was determined to be 97 % under the following conditions: BR18 initial dye concentration of 100 mg L-1, pH of 5.7, contact time of 5 h, PS concentration of 10 mM, Fe2+ concentration of 0.2 mM, and a sodium sulfate concentration of 0.05 M. © 2018 Serbian Chemical Society. All rights reserved

Flow control behind a circular cylinder via a porous cylinder in deep water

DANTEC DYNAMICS GmbH;KAMAX Holding;LENAM s.r.o.;MIT s.r.o.;SPECION s.r.o.7th International Conference on Experimental Fluid Mechanics 2012, EFM 2012 --20 November 2012 through 23 November 2012 -- Hradec Kralove --In this present work, the effects of surrounding outer porous cylinder on vortex structure downstream of a circular inner cylinder are investigated experimentally in deep water flow. The porosity of outer cylinder were selected as ß = 0.4, 0.5, 0.6, 0.65, 0.7, 0.75, 0.8 and 0.85. Porosity is defined as the ratio of the gap area on the body to the whole body surface area. The ratio of outer cylinder diameter to inner cylinder diameter, Do/D i was selected as 2.0, i.e. the inner cylinder diameter is D i = 30 mm where the outer cylinder diameter is Do = 60 mm. All experiments were carried out above a platform. The water height between the base of the platform and the free surface was adjusted as 340 mm. Free stream velocity is U = 156 mm/s, which corresponds to the Reynolds number of Re i = 5,000 based on the inner cylinder diameter. It has been observed that the outer porous cylinders have influence on the attenuation of vortex shedding in the wake region for all porosities. The turbulent intensity of the flow is reduced at least 45% by the presence of outer porous cylinder compared to the bare cylinder case. The porosities ß = 0.4 and 0.5 are most suitable cases to control the flow downstream of the circular cylinder. © Owned by the authors, published by EDP Sciences, 2013

Evaluation of energetic-exergetic and sustainability parameters of biodiesel fuels produced from palm oil and opium poppy oil as alternative fuels in diesel engines

In present study, the energetic and exergetic performances of a diesel engine fueled with conventional diesel and various biodiesel fuels were investigated experimentally. Energetic and exergetic performance parameters of the engine fueled with neat diesel, neat opium poppy and neat palm biodiesel fuels were calculated and compared with each other. Moreover, the sustainability analysis was carried out in the study. The findings of this study indicated that the energetic and exergetic performance parameters were profoundly affected by the engine speed and the fuel type. Both the thermal and exergetic efficiencies were the highest at the engine speed of 1600 rpm for all tested fuels. At this engine speed, the lowest thermal efficiency of the engine occurred with palm biodiesel as 34.92%, while the highest thermal efficiency value was 35.85% with diesel fuel. The exergy efficiencies of corresponding fuel types ranged from 32.50% to 33.64% for palm biodiesel and diesel fuels, respectively. In addition, the difference between the exergy efficiencies of diesel fuel and opium poppy biodiesel fuel was about 0.90%. Both the energy and exergy efficiencies diminished with the increment of engine speed higher than 1600 rpm for all fuel types. The maximum values of sustainability index for all fuel types were obtained at the engine speed of 1600 rpm. The best exergetically-sustainable fuel was the diesel fuel followed by the opium poppy biodiesel fuel. According to the results, opium poppy biodiesel might replace with the conventional diesel fuel due to the similarity of energetic and exergetic performance parameters. © 201

Flow control behind a circular cylinder via a porous cylinder in deep water

In this present work, the effects of surrounding outer porous cylinder on vortex structure downstream of a circular inner cylinder are investigated experimentally in deep water flow. The porosity of outer cylinder were selected as β = 0.4, 0.5, 0.6, 0.65, 0.7, 0.75, 0.8 and 0.85. Porosity is defined as the ratio of the gap area on the body to the whole body surface area. The ratio of outer cylinder diameter to inner cylinder diameter, Do/Di was selected as 2.0, i.e. the inner cylinder diameter is Di = 30 mm where the outer cylinder diameter is Do = 60 mm. All experiments were carried out above a platform. The water height between the base of the platform and the free surface was adjusted as 340 mm. Free stream velocity is U = 156 mm/s, which corresponds to the Reynolds number of Rei = 5,000 based on the inner cylinder diameter. It has been observed that the outer porous cylinders have influence on the attenuation of vortex shedding in the wake region for all porosities. The turbulent intensity of the flow is reduced at least 45% by the presence of outer porous cylinder compared to the bare cylinder case. The porosities β = 0.4 and 0.5 are most suitable cases to control the flow downstream of the circular cylinder

Direct liquefaction of high-sulfur coals: Effects of the catalyst, the solvent, and the mineral matter

WOS: 000178122100005Two low-rank coals with high sulfur contents (Gediz subbituminous coal: 7.6 wt % S:dry basis. Cayirhan lignite: 5.7 wt%, S:dry basis.) were subjected to hydroliquefaction. Liquefaction conditions included dry or solvent mediated runs under pressurized hydrogen without added catalyst or with the impregnated catalyst precursor ammonium heptamolybdate AHM). Gediz coal having higher sulfur content gave 90% conversion in the absence of catalyst and solvent. Maximum conversion (98%) and maximum oil + gas yield (70%) from this coal were obtained by impregnating AHM onto coal and carrying out liquefaction in H-2/tetralin system at 450 degreesC for 30 min. Under the same conditions, Cayirhan lignite gave 85% conversion and 70.5% oil + gas yield. The superior hydrodesulfurization effect of impregnated AHM on the oil fraction when used in the absence of solvent (less than 0.1% S in lignite's oil and less than 1% S in subbituminous coal's oil following one-stage hydrogenation) is a promising finding of this work. AHM was found to be much more effective in liquefaction of Cayirhan lignite and this has been ascribed to the well-dispersion of AHM throughout this lignite's structure via a cation-exchange mechanism through oxygen functionalities. Strong evidence for the catalytic effect of clay minerals in coal structure on char-forming reactions during liquefaction was observed by making use of liquefaction reactions of demineralized coal samples. It was also observed that tetralin had a retarding effect on the condensation and subsequent cross-linking reactions