This work deals with the CFD analysis of flow in the middle stage of the radial-flow multistage pump operating in turbine regime. The pump specific speed nq is equal to 23. Two complete stages are analysed with fully unsteady simulation to avoid the influence of boundary conditions and the position of rotor and stator parts on the results. The ANSYS CFX commercial CFD package is used to solve the three-dimensional Reynolds-averaged Navier-Stokes equations using Menter's SST turbulence model. and Obsahuje seznam literatury
Článek seznamuje čtenáře s CFD výpočty prováděnými pro potřeby Oddělení chemických laserů Fyzikálního ústavu AV ČR. Simulace nízkotlakého nadzvukového proudění plynných směsí slouží pro design nadzvukových směšovacích trysek, které tvoří část dutiny chemického laseru COIL. Velmi náročné výpočty chemicky reagujícího proudění slouží jako doplněk experimentální diagnostiky, ověřování reakčních mechanismů a optimalizace provozních podmínek laseru. Výpočty jsou prováděny na uživatelském výpočetním serveru Luna komerčním CFD softwaru. V první části článku je uvedena matematická formulace modelu, okrajových podmínek, použité aproximace. V druhé části článku jsou uvedeny tři příklady konkrétních numerických simulací., Vít Jirásek., and Obsahuje seznam literatury
This paper deals with studying of two topics – measuring of velocity profile deformation behind a over-flooded construction and modelling of this velocity profile deformation by computational fluid dynamics (CFD). Numerical simulations with an unsteady RANS models - Standard k-ε, Realizable k-ε, Standard k-ω and Reynolds stress models (ANSYS Fluent v.18) and experimental measurements in a laboratory flume (using ADV) were performed. Results of both approaches showed and affirmed presence of velocity profile deformation behind the obstacle, but some discrepancies between the measured and simulated values were also observed. With increasing distance from the obstacle, the differences between the simulation and the measured data increase and the results of the numerical models are no longer usable.
CFD simulation is aimed on the two-stage pump operation modeling in the pump and turbine regime. The flow analysis will be focused on the proper angle of wicket gates attack and on the separation localization. This investigation should bring the geometry modifications that will increase the hydraulic efficiency. The computational model was created in preprocessor GAMBIT and software Fluent will be used for the finite computation.
Gyrodactylus salaris Malmberg, 1957 is a major pathogen of wild Salmo salar L. parr populations in Norway, and its delimitation from non-pathogenic species is important. The present study was undertaken to test the power of chaetotaxy to differentiate between three populations belonging to both the same and different clades (as stated by mtDNA) of G. salaris, in addition to three different species of gyrodactylids (G. salaris, G. thymalli and G. caledoniensis). The gyrodactylids were processed for chaetotaxy in situ and a maximum of 50 specimens per collection site were used to construct a generalised map over the sensilla. The sensilla were found in all populations to be symmetrically distributed around the median longitudinal axis, according to a formula of 7 dorsal (34 sensilla) and 8 ventral (44 sensilla) clusters on each side of the median line. The three Norwegian populations of G. salaris were found identical, as were the population of G. thymalli. The specimens of G. caledoniensis from Scotland, however, were found to differ from the Norwegian species G. salaris and G. thymalli by the position of one sensillum in two of the clusters. A comparison of the sensillum pattern of laboratory maintained G. salaris (River Lierelva) with results obtained ten years earlier, questions the temporal stability of the chaetotaxy pattern. The present results indicate that chaetotaxy can be used to discriminate between certain Gyrodactylus spp. but not generally.
A comparison has been made between the chaetotaxy of the gyrodactylid monogeneans Macrogyrodactylus clarii Gussev, 1961 and M. congolensis (Prudhoe, 1957) Yamaguti, 1963 from the gills and skin, respectively, of the catfish Clarias gariepinus (Burchell) from the river Nile in Egypt. Bilaterally arranged argentophilic structures on the surface of these parasites are presumed to be sensilla and are more abundant in M. clarii than in M. congolensis especially on the ventral surface (124 vs. 66). In both species these sensilla are concentrated on the head lobes and in the pharyngeal region, but there are features of the sensilla patterns that can be used to distinguish the two species. Comparison is made with sensilla patterns of other gyrodactylids. A system of cells and dendritic processes, most probably part of the nervous system, also has an affinity for silver in the two species. There are no previous records of extensive argentophilic elements in the nervous systems of monogeneans.
Variables of gas exchange of flag leaves and grain yield potentials of five representative winter wheat (Triticum aestivum L.) cultivars varied greatly across different development stages under the same management and irrigation. The cultivars with high yield potential had higher net photosynthetic rate (PN), PPFD (photosynthetic photon flux density) saturated photosynthetic rate (Psat), stomatal conductance (gs), and maximum apparent quantum yield of CO2 fixation (Φm,app) than those with low grain yield, but their dark respiration rate (RD) and compensation irradiance (Ic) were remarkably lower. Compared with overall increase of yield potential of 71 % from low yield cultivars to high yield ones, PN, Psat, Φm,app, and gs were 13, 19, 57, and 32 % higher, respectively; but RD and Ic decreased by 19 and 76 %, respectively. Such difference was evidently large during anthesis stage (e.g., PN by 33 %), which indicated that this period could be the best for assisting further selection for better cultivars. However, transpiration rate (E) and water use efficiency (WUE) differed only little. At different development stages, especially at anthesis, PN and Psat were positively correlated with Φm,app, gs, and yield potential, and negatively correlated with RD and Ic. Thus the high-yield-potential winter wheat cultivars possess many better characters in photosynthesis and associated parameters than the low-yield cultivars. and G. M. Jiang ... [et al.].
Human society needs still more intensive exploitation of all kinds of
transportation facilities. This need has already lasted for several decades and will be much more imperative in future. Mobility is one of the basic requirements for survival, besides the energy and food resources, health care and security. The requirements on transportation systems concern not only the quantitative and qualitative aspects of transportation activities, but still more also the aspects of their reliability and safety. This concerns not only the transported subjects or goods but also the environment.
The losses caused by failures of transportation activities reach even now a very high level and if not limited by systematic research and preventive activity, they will reach quite a tremendous level soon.
However, practically all the conternporary transportation vehicles, trains, ships and planes and also all the transportation systems need, for their proper operation, the interaction with human beings, which drive them, controls them or uses them and maintains them.
In spite of the fact that significant progress was made in recent years as concerns the transportation systems automation, the fully automatic transportation systam in use is still foreseen in the considerably far future.
Analyzing the reliability and safety of transportation, one finds that the activity of a human being is the weakest point. The technical reliability of almost all transportation tools has improved quite a lot in the past years; however, the human subject interacting with them has not changed too much, as for his/her reliability and safety of the respective necessary interaction.
Therefore there is a vital necessity to improve it and the possibilities how to implement it will stay more and more in the focus of our interest.
In this paper an overview of the related problems is made, the challenges for further research and development in this area are discussed and the outline of a vision, with respect to human interaction reliability, of optimized transportation systems is presented.