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Drag Reduction (drag + reduction)
Selected AbstractsLaminar Drag Reduction in Hydrophobic MicrochannelsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 6 2009P.-F. Hao Abstract The apparent slip effects of laminar water flow in smooth hydrophobic microchannels and patterned hydrophobic microchannels were investigated. A series of experiments were performed to demonstrate the drag reductions for laminar water flow in hydrophobic microchannels. These microchannels were fabricated from silicon wafers using photolithography and were coated with hydrophobic octadecyltrichlorosilane (OTS). To generate a larger drag reduction, the patterned hydrophobic microchannels were fabricated to allow the liquid to flow over a region of trapped air in the cavity between the microridges. With the geometrical dimensions used, pressure drop reductions ranging from 10 to 30,% were found in the smooth microchannels and patterned microchannels. The pressure drop reduction was shown to increase with increasing microridge spacing and decreasing microchannel width. Using micro-particle image velocimetry (PIV), we measured an apparent slip velocity at the wall of approximately 8,% of the centerline velocity, yielding a slip length of approximately 2,,m in the smooth hydrophobic microchannel. Theoretically, the analytical solution derived for three-dimensional flow in a rectangular duct is presented to predict the slip velocity and slip length at the wall based on the pressure drop measurement. These results are in agreement with the experimental data obtained using micro-PIV. [source] Experimental investigation of turbulent boundary layer flow with surfactant additives using PIV and PDAHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 2 2005Wang Dezhong Abstract Drag reduction of turbulent water flow with surfactant (CTAC) additives was experimentally investigated. By using PIV and PDA measurements, the spatial velocity distribution of surfactant solution flow was clarified in a two-dimensional water channel. With an increasing Reynolds number, it was found that drag reduction of surfactant solution flow is enhanced within the region of drag reduction. However, in the region of post drag reduction, the drag-reducing coefficient approaches one without surfactant when Reynolds number is increased. In the near-wall region, velocity profiles of the drag-reducing fluid are similar to, but not the same as, the laminar profiles of the Newtonian fluid. When compared to the case of water flow without surfactant, the velocity contour lines of the drag-reducing fluid run approximately parallel to the wall. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(2): 99,107, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20047 [source] Drag reduction by flow separation control on a car after bodyINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2009Mathieu Rouméas Abstract New development constraints prompted by new pollutant emissions and fuel consumption standards (Corporate Average Economy Fuel) require that automobile manufacturers develop new flow control devices capable of reducing the aerodynamic drag of motor vehicles. The solutions envisaged must have a negligible impact on the vehicle geometry. In this context, flow control by continuous suction is seen as a promising alternative. The control configurations identified during a previous 2D numerical analysis are adapted for this purpose and are tested on a 3D geometry. A local suction system located on the upper part of the rear window is capable of eliminating the rear window separation on simplified fastback car geometry. Aerodynamic drag reductions close to 17% have been obtained. Copyright © 2008 John Wiley & Sons, Ltd. [source] Experimental investigation of turbulent boundary layer flow with surfactant additives using PIV and PDAHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 2 2005Wang Dezhong Abstract Drag reduction of turbulent water flow with surfactant (CTAC) additives was experimentally investigated. By using PIV and PDA measurements, the spatial velocity distribution of surfactant solution flow was clarified in a two-dimensional water channel. With an increasing Reynolds number, it was found that drag reduction of surfactant solution flow is enhanced within the region of drag reduction. However, in the region of post drag reduction, the drag-reducing coefficient approaches one without surfactant when Reynolds number is increased. In the near-wall region, velocity profiles of the drag-reducing fluid are similar to, but not the same as, the laminar profiles of the Newtonian fluid. When compared to the case of water flow without surfactant, the velocity contour lines of the drag-reducing fluid run approximately parallel to the wall. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(2): 99,107, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20047 [source] Use of TLC-FID and GC-MS/FID to examine the effects of migratory state, diet and captivity on preen wax composition in White-throated Sparrows Zonotrichia albicollisIBIS, Issue 4 2010RAYMOND H. THOMAS Preen wax is important for plumage maintenance and other functions. Its chemical composition is complex, and separating and quantifying its components, commonly by gas chromatography (GC), can be challenging. We present a simple analytical system consisting of thin-layer chromatography/flame ionization detection (TLC-FID) using a solvent system of 100% toluene to analyse the complex compound classes present in preen wax. We used GC and TLC-FID to investigate the effects of migratory status, diet and captivity on the preen wax composition of White-throated Sparrows Zonotrichia albicollis, and to measure the quantity of preen wax on the head, primary and tail feathers. White-throated Sparrows produced preen wax containing only monoesters regardless of migratory state. The monoesters contained several isomers consisting of homologous series of fatty alcohols (C10,C20) and fatty acids (C13,C19) esterified together in different combinations to form monoesters with total carbon numbers ranging from C23 to C38. Weighted average monoester carbon number was greater in captive birds than in wild birds and was greater in captives fed a formulated diet enriched with sesame oil than in birds fed the same diet enriched with fish oil. Captivity and migratory state also affected the complexity of the mixture of monoesters. There was significantly more preen wax on head feathers compared with primary and tail feathers. We suggest that among its many functions, preen wax may play a role in drag reduction by affecting the physical properties of feathers, and/or the fluid flow at their surfaces. [source] Experimental research on drag reduction by polymer additives in a turbulent pipe flowTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2002Shao Xueming Abstract In order to investigate the effects of injection position on drag reduction as well as further the effects of polymer additives on turbulent structures, LDA measurements of turbulent pipe flows were conducted. The results show that the amount of drag reduction grows with the increase of the Reynolds number, and injecting the polymer at the centre of pipe is more effective than at the wall. Due to the addition of polymer solution, the axial, radial r.m.s. velocity fluctuations and Reynolds stress decrease over the entire pipe cross-section, the time auto-correlation coefficients of axial and radial velocity fluctuation at the centre of pipe decay more slowly, the number of spectrum peaks is decreased, and the peak shifts towards lower wave numbers. The results also reveal that, due to the addition of polymer solution, the large-scale vortices are enhanced and small-scale vortices are suppressed. On a effectué des mesures par anémométrie laser Doppler d'écoulements turbulents dans des conduites afin d'étudier l'effet de la position de l'injection et l'effet de l'ajout d'additifs à base de polymères sur la réduction de traînée. Les résultats montrent que la réduction de traînée augmente avec le nombre de Reynolds et qu'il est plus efficace d'injecter le polymère au centre de la conduite qu'à la paroi. Du fait de l'ajout d'une solution de polymères, les fluctuations de vitesse efficace radiale et axiale et la contrainte de Reynolds diminuent sur toute la section transversale de la conduite, les coefficients d'auto-corrélation de temps de la fluctuation de vitesse efficace radiale et axiale au centre de la conduite décroissent plus lentement, le nombre de pics du spectre diminue et les pics tendent à avoir un nombre d'ondes moins grand. Les résultats montrent également que, grâce à l'ajout de la solution de polymères, les tourbillons de grande échelle sont plus nombreux tandis que les tourbillons de petite eéhelle disparaissent. [source] Computational Fluid Dynamics and Digital Particle Image Velocimetry Study of the Flow Through an Optimized Micro-axial Blood PumpARTIFICIAL ORGANS, Issue 5 2006Michael Triep Abstract:, A detailed knowledge of the flow field in a blood pump is indispensable in order to increase the efficiency of the pump and to reduce the shear-induced hemolysis. Thus, three different impeller designs were developed and tested by means of computational fluid dynamics (CFD) and digital particle image velocimetry (DPIV). The results show a good agreement of CFD and DPIV data. An optimization of the impeller could be achieved by following the concept of turbulent drag reduction for the axisymmetric center body. [source] Laminar Drag Reduction in Hydrophobic MicrochannelsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 6 2009P.-F. Hao Abstract The apparent slip effects of laminar water flow in smooth hydrophobic microchannels and patterned hydrophobic microchannels were investigated. A series of experiments were performed to demonstrate the drag reductions for laminar water flow in hydrophobic microchannels. These microchannels were fabricated from silicon wafers using photolithography and were coated with hydrophobic octadecyltrichlorosilane (OTS). To generate a larger drag reduction, the patterned hydrophobic microchannels were fabricated to allow the liquid to flow over a region of trapped air in the cavity between the microridges. With the geometrical dimensions used, pressure drop reductions ranging from 10 to 30,% were found in the smooth microchannels and patterned microchannels. The pressure drop reduction was shown to increase with increasing microridge spacing and decreasing microchannel width. Using micro-particle image velocimetry (PIV), we measured an apparent slip velocity at the wall of approximately 8,% of the centerline velocity, yielding a slip length of approximately 2,,m in the smooth hydrophobic microchannel. Theoretically, the analytical solution derived for three-dimensional flow in a rectangular duct is presented to predict the slip velocity and slip length at the wall based on the pressure drop measurement. These results are in agreement with the experimental data obtained using micro-PIV. [source] Drag reduction by flow separation control on a car after bodyINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2009Mathieu Rouméas Abstract New development constraints prompted by new pollutant emissions and fuel consumption standards (Corporate Average Economy Fuel) require that automobile manufacturers develop new flow control devices capable of reducing the aerodynamic drag of motor vehicles. The solutions envisaged must have a negligible impact on the vehicle geometry. In this context, flow control by continuous suction is seen as a promising alternative. The control configurations identified during a previous 2D numerical analysis are adapted for this purpose and are tested on a 3D geometry. A local suction system located on the upper part of the rear window is capable of eliminating the rear window separation on simplified fastback car geometry. Aerodynamic drag reductions close to 17% have been obtained. Copyright © 2008 John Wiley & Sons, Ltd. [source] Laminar Drag Reduction in Hydrophobic MicrochannelsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 6 2009P.-F. Hao Abstract The apparent slip effects of laminar water flow in smooth hydrophobic microchannels and patterned hydrophobic microchannels were investigated. A series of experiments were performed to demonstrate the drag reductions for laminar water flow in hydrophobic microchannels. These microchannels were fabricated from silicon wafers using photolithography and were coated with hydrophobic octadecyltrichlorosilane (OTS). To generate a larger drag reduction, the patterned hydrophobic microchannels were fabricated to allow the liquid to flow over a region of trapped air in the cavity between the microridges. With the geometrical dimensions used, pressure drop reductions ranging from 10 to 30,% were found in the smooth microchannels and patterned microchannels. The pressure drop reduction was shown to increase with increasing microridge spacing and decreasing microchannel width. Using micro-particle image velocimetry (PIV), we measured an apparent slip velocity at the wall of approximately 8,% of the centerline velocity, yielding a slip length of approximately 2,,m in the smooth hydrophobic microchannel. Theoretically, the analytical solution derived for three-dimensional flow in a rectangular duct is presented to predict the slip velocity and slip length at the wall based on the pressure drop measurement. These results are in agreement with the experimental data obtained using micro-PIV. [source] | |||||||||||||