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Separation Point (separation + point)
Selected AbstractsPrediction of unsteady, separated boundary layer over a blunt body for laminar, turbulent, and transitional flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2004D. Scott Holloway Abstract The focus of this paper is to study the ability of unsteady RANS-based CFD to predict separation over a blunt body for a wide range of Reynolds numbers particularly the ability to capture laminar-to-turbulent transition. A perfect test case to demonstrate this point is the cylinder-in-crossflow for which a comparison between experimental results from the open literature and a series of unsteady simulations is made. Reynolds number based on cylinder diameter is varied from 104 to 107 (subcritical through supercritical flow). Two methods are used to account for the turbulence in the simulations: currently available eddy,viscosity models, including standard and realizable forms of the k,, model; and a newly developed eddy,viscosity model capable of resolving boundary layer transition, which is absolutely necessary for the type and range of flow under consideration. The new model does not require user input or ,empirical' fixes to force transition. For the first time in the open literature, three distinct flow regimes and the drag crisis due to the downstream shift of the separation point are predicted using an eddy,viscosity based model with transition effects. Discrepancies between experimental and computational results are discussed, and difficulties for CFD prediction are highlighted. Copyright © 2004 John Wiley & Sons, Ltd. [source] Heat transfer reduction at the separation point on a spinning sphere in mixed convectionINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2002egül Öztürk Abstract The unsteady laminar thermal boundary-layer flow over an impulsively started translating and spinning isothermal body of revolution in the case of mixed convection is investigated. Velocity components and temperature are obtained as series of functions in powers of time. The general results are applied to a spinning sphere and the development of the surface heat flux evaluated at the separation point as it advances upstream is determined. The surface heat flux evaluated at the separation point as it moves forward decreases due to the increasing magnitude and influence of the centrifugal force and it is augmented by the opposing flow and reduced by the aiding flow. Reduction of the surface heat flux at the separation point is as low as 50 per cent as compared to the heat flux at the front stagnation point. Copyright © 2002 John Wiley & Sons, Ltd. [source] Identification of Cochliobolus sativus (Spot Blotch) Isolates Expressing Differential Virulence on Barley Genotypes in SyriaJOURNAL OF PHYTOPATHOLOGY, Issue 8-9 2004M. I. E. Arabi Abstract Spot blotch, caused by Cochliobolus sativus, is a common foliar disease of barley. Information on the variability of virulence in C. sativus is essential for the production of spot-resistant barley cultivars. The virulence variability of isolates of this pathogen collected from different regions of Syria was evaluated using 10 differential barley genotypes originating from widely dispersed areas. Genotypes showed a continuous range of response from very susceptible to moderately resistant but none was immune to the disease. A cluster analysis indicated that the isolates had distinct differential virulence patterns within the three groups. A mean disease rating of 3.71 was the separation point between avirulent and virulent reactions. The data demonstrated that variation occurred in the virulence of and the resistance level to isolates and among genotypes, respectively. Isolate C41 exhibited distinct differential virulence patterns, high frequency and low variance in all genotypes. To incorporate adequate levels of resistance into future barley genotypes, disease evaluations should be made with C. sativus isolates that express the full spectrum of virulence found in Syria. [source] Pathogenic Variation among Isolates of Pyrenophora teres, the Causal Agent of Barley Net BlotchJOURNAL OF PHYTOPATHOLOGY, Issue 7-8 2003M. I. E. Arabi Abstract Isolates of Pyrenophora teres, the causal agent of net blotch of barley (Hordeum vulgare L.) has been collected from France and Syria. Their virulence spectra were evaluated using 11 barley genotypes as differential hosts. The genotypes exhibited a continuous range of response from highly susceptible to moderately resistant. A mean disease rating of 3.7 is considered as the separation point between avirulent and virulent reactions. The frequency of virulence was highest for isolates S5, R5 and S6-2 and lowest for R-ICA31 and R-HAS-6. A cluster analysis indicated that the isolates exhibited distinct differential virulence patterns and they were identified into five groups. The French isolates S5, R5 and S6-2 had a higher mean virulence and a low variance across all genotypes. None of the tested genotypes was highly resistant to all investigated isolates. [source] Separation of a sphere from a flat in the presence of couple stress fluidsLUBRICATION SCIENCE, Issue 1 2008Abdallah A. Elsharkawy Abstract A mathematical model for couple stress fluid is presented to analyse the separation flow of a fully flooded sphere from a flat under the condition of constant load. Assuming the lubricant between the sphere and the flat to contain additives, the couple stress effect, presented by the characteristic length of the additives, has been considered to account for the non-Newtonian behaviour. In addition, the effect of the sphere inertia on accelerating the separation process has been considered. Compared with the Newtonian fluid case, the results of the numerical solution indicated that the separation time increases with increasing the characteristic length of the additives. It was also found that the additive characteristic length has negligible effect on the thickness of the lubricant film at the separation point. Copyright © 2007 John Wiley & Sons, Ltd. [source] Bulk High-Impact Polystyrene Process, 1MACROMOLECULAR THEORY AND SIMULATIONS, Issue 7 2007Partitions of tert -Butyl Peroctoate, Styrene in Blends Containing Polystyrene, a Rubber Abstract In relation to the bulk high-impact polystyrene process, this work investigates the partition between phases of styrene and an initiator: tert- butyl peroctoate. A Flory-Huggins model was applied for predicting the phase separation point and the partitions of styrene and tert- butyl peroctoate. For blends of styrene, polystyrene, and a styrene-butadiene diblock copolymer, the model provides reasonable predictions of a ternary equilibrium diagram. For blends of styrene, polystyrene, polybutadiene, and tert- butyl peroctoate, the partition of tert- butyl peroctoate was measured at 25,°C. At emulated conversions of 13% or lower, equilibrium was reached after 1 h of mixing time. For the higher molar masses and conversion of 16%, equilibrium was not reached after 24 h of mixing time. To fit the equilibrium measurements, the solubility parameter of tert- butyl peroctoate was adjusted. [source] Heat transfer of combined forced and natural convection from horizontal cylinder to airHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 8 2007Kenzo Kitamura Abstract Experimental investigations have been carried out for combined convective flows of air induced around uniformly heated, horizontal cylinders. Three cases of aiding, opposing, and cross flows were examined. The experiments covered the ranges of the Reynolds and modified Rayleigh numbers of Red=50 to 900 and Rad*=5×104 to 3×106. The flow fields around the cylinders were visualized with smoke. The results showed that separation points gradually shift from those of the forced convection to the top edge of the cylinder with increasing wall heat fluxes. The local heat transfer coefficients of the cylinders were also measured. Although the local coefficients show complex variations with the forced flow velocities and the wall heat fluxes, the overall coefficients become higher than those estimated from pure forced and natural convections throughout the cases of aiding, opposing, and cross flows. Moreover, it was confirmed that the overall Nusselt numbers as well as the separation points can be predicted with the non-dimensional parameter (Grd*/NudRed2). © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(8): 474,488, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20180 [source] | ||||||||||