No (235)
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Experimental investigation of Magnus force acting on smooth sphere at high Reynolds numbers
Kharlamov, Alexander; Chára, Zdeněk; Vlasák, Pavel
2008 - English
The paper describes the results of experimental research dealing with rotating smooth spherical particles moving quasi-steadily in calm water. The motion of the particles was recorded by a digital video camera. The kinematics of the particles motion was analyzed numerically. The dimensionless Magnus force coefficient, the Reynolds number Re and spin parameter Γ (ratio of peripheral sphere velocity and translational velocity) were evaluated from the time series of the particle coordinates and its angle of rotation. The Magnus force was determined as a function of the Reynolds number and spin parameter for 3000 < Re < 42000 and 0.1 < Γ <7. The results were compared with results from literature and overall data were fitted by a simple function valid for 0.5 < Re < 140000 and 0.1 < Γ <10. Článek popisuje výsledky pokusů s rotující hladkou kulovou částicí při kvazi-stabilním pohybu v klidné vodě. Pohyb částice byl zaznamenán digitální videokamerou a kinematické parametry pohybu částice numericky analyzovány. Bezrozměrný součinitel Magnusovy síly, Reynoldsovo číslo a spin parametr Γ (poměr obvodové rychlosti rotující částice a její translační rychlosti) byly vyhodnoceny z časových řad souřadnic a úhlů rotace částice. Magnusova síla byla určena v závislosti na Reynoldsově čísle a spin parametru pro oblast 3000 < Re < 42000 a 0,1 < Γ <7. Výsledky byly porovnány s literárními údaji a data byly aproximovány jednoduchou funkcí platnou pro oblast 0,5 < Re < 140000 a 0,1 < Γ <10.
Keywords:
Magnus force; smooth spherical particle; particle rotation; Reynolds numbers; experimental investigation
Available at various institutes of the ASCR
Experimental investigation of Magnus force acting on smooth sphere at high Reynolds numbers
The paper describes the results of experimental research dealing with rotating smooth spherical particles moving quasi-steadily in calm water. The motion of the particles was recorded by a digital ...
Soil water dynamics in the Šumava Mts. and in the Krkonoše Mts. in August 2002
Tesař, Miroslav; Krejča, M.; Polívka, Jiří; Šír, Miloslav
2008 - English
The soil water movement during extreme rain is analysed in the Doupě and Kout catchment (Šumava Mts, Southern Bohemia) and in the Modrý Důl catchment (Krkonoše Mts., Northern Bohemia). Two cyclones, which moved from Hungary to Poland, caused extreme rainfall and subsequent extreme runoff in August, 2002. Precipitation, air and soil temperature, and tensiometric pressure were recorded in catchments. The analysis showed that the huge rain amount in August 2002 exceeded the retention capacity of the catchment covered by mature spruce forest and dwarf pine forest (Modrý Důl), dead forest and herb undergrowth (Kout), clearing covered by herbs (Doupě). It means that the plant cover played a negligible role in the runoff generation. The soil cover was not able to prevent the country from catastrophic runoff because its retention capacity is rather low (60 – 90 mm). V článku je analyzován pohyb vody v půdě při extrémních deštích v povodích Doupě a Kout (Šumava, Jižní Čechy) a v povodí Modrý potok (Krkonoše, Severní Čechy). Dvě cyklóny, které se přesouvaly z Maďarska směrem k Polsku, způsobily extrémní srážky a následné extrémní odtoky v srpnu 2002. V povodích jsou zaznamenávány srážky, teploty vzduchu a půdy a tenzometrické tlaky. Analýza ukázala, že vysoký srážkový úhrn v srpnu 2002 přesáhl retenční kapacitu povodí krytého dospělým smrkovým lesem a klečí (Modrý Důl), mrtvým lesem a bylinným podrostem (Kout) a porostem bylin na pasece (Doupě). To znamená, že vegetační kryt hrál zanedbatelnou roli při formování odtoku. V důsledku poměrně nízké retenční kapacity (60 – 90 mm) nebyl půdní kryt schopen zabránit katastrofickému odtoku.
Keywords:
mountain hydrology; extreme rain; soil-water movement
Available at various institutes of the ASCR
Soil water dynamics in the Šumava Mts. and in the Krkonoše Mts. in August 2002
The soil water movement during extreme rain is analysed in the Doupě and Kout catchment (Šumava Mts, Southern Bohemia) and in the Modrý Důl catchment (Krkonoše Mts., Northern Bohemia). Two cyclones, ...
Runoff formation in Senotín: a revitalised sub-mountain headwater area
Tesař, Miroslav; Syrovátka, O.; Lichner, Ľ.
2008 - English
The purpose of the Senotín pilot project (1993–2000) was to determine methods of revitalisation of a sub-mountain headwater area (0.38 km2) in the Novobystřická Vysočina Highlands (610–725 m a. s. l.). Seven underground clay shields stopped pipe drainage, and four balks prevented surface and subsurface runoff. These adaptations improved the water retention capacity of the whole catchment, as demonstrated by the formation of runoff in the revitalised area. A typical rainstorm (amount 15 mm, duration 5.6 hours, max. intensity 1.8 mm/20 minutes) and consequent runoff was analysed, along with the role of soil in runoff retardation and water retention. The time course of the contributing area was also quantified. The contributing area was formed in the surface soil layer with a thickness of about 40 cm. Runoff retardation lasted two hours after the rain began. Retention reached 98% of the total rainfall. Runoff lasted for 85 hours. Účelem projektu Senotín (1993–2000) bylo nalézt metody revitalizace podhorské pramenné oblasti (0,38 km2) v Novobystřické pahorkatině (610–725 m n. m.). Bylo vystavěno sedm podzemních jílových stěn, které přerušily trubní drenáž. Čtyři meze zabraňují povrchovému a podpovrchovému odtoku. Tyto terénní úpravy zlepšily vodní retenční kapacitu celého povodí, což je demonstrováno na příkladu formování odtoku z přívalového deště. Bylo analyzováno formování odtoku z deště o úhrnu 15 mm, trvání 5,6 hodin a maximální intenzitě 1,8 mm za 20 minut. Byl stanoven časový průběh retence vody v povodí a průběh velikosti zdrojové plochy. Zdrojová plocha se vytvořila v povrchové půdní vrstvě o mocnosti asi 40 cm. Retardace odtoku trvala asi 2 hodiny po začátku deště. Retence vody v povodí dosáhla 98 % srážkového úhrnu. Odtoková vlna trvala 85 hodin.
Keywords:
headwater area; landscape revitalisation; runoff formation
Available at various institutes of the ASCR
Runoff formation in Senotín: a revitalised sub-mountain headwater area
The purpose of the Senotín pilot project (1993–2000) was to determine methods of revitalisation of a sub-mountain headwater area (0.38 km2) in the Novobystřická Vysočina Highlands (610–725 m a. s. ...
Small Icing Wind Tunnel
Horák, V.; Hoření, Bohumír; Rozehnal, D.; Svoboda, E.
2007 - English
The paper deals with a small icing wind tunnel realized at the Department of Aerospace and Rocket Technologies in conjunction with the aircraft icing simulation project. There are presented some results of the airfoil ice accretion prediction and various resulting ice shapes from icing wind tunnel. Appropriate consideration is given to the ice shape geometry measurement either.
Keywords:
aircraft icing; icing wind tunnel; ice accretion
Available at various institutes of the ASCR
Small Icing Wind Tunnel
The paper deals with a small icing wind tunnel realized at the Department of Aerospace and Rocket Technologies in conjunction with the aircraft icing simulation project. There are presented some ...
Influence of reactive extrusion process on rheological properties of metallocene polypropylenes
Pivokonský, Radek; Zatloukal, M.; Filip, Petr; Tzoganakis, C.
2007 - English
Constitutive equations represent a powerful tool for analysis and description of linear and branched polymer materials (even for polydisperse ones). Predictive/fitting capabilities of three constitutive models (eXtended Pom-Pom, PTT-XPP, and modified Leonov models) were examined using four standard industrial PE materials (two linear and two branched). All the materials were tested in both shear and uniaxial extensional flows (steady and transient). Constitutive equations represent a powerful tool for analysis and description of linear and branched polymer materials (even for polydisperse ones). Predictive/fitting capabilities of three constitutive models (eXtended Pom-Pom, PTT-XPP, and modified Leonov models) were examined using four standard industrial PE materials (two linear and two branched). All the materials were tested in both shear and uniaxial extensional flows (steady and transient). Advantages/disadvantages of the individual models to the individual types of materials are discussed and experimentally documented. Konstituční rovnice představují účinný nástroj pro analýzu a popis lineárních a rozvětvených polymerních materiálů. Jsou porovnány možnosti popisu a predikce tří konstitučních rovnic (XPP, PTT-XPP a modifikovaného Leonovova modelu) při aplikaci na čtyři standartní PE materiály (dva lineární a dva rozvětvené). Testování proběhlo jak ve smykovém tak v elongačním toku. Jsou diskutovány výhody a nevýhody jednotlivých modelů.
Keywords:
constitutive equations; polymer melts; shear flow; elongational flow
Available at various institutes of the ASCR
Influence of reactive extrusion process on rheological properties of metallocene polypropylenes
Constitutive equations represent a powerful tool for analysis and description of linear and branched polymer materials (even for polydisperse ones). Predictive/fitting capabilities of three ...
Magnus and Drag Forces Acting on Golf Ball
Kharlamov, Alexander; Chára, Zdeněk; Vlasák, Pavel
2007 - English
The paper describes the results of experiments with a rotating golf ball moving quasi-steadily in calm water. The motion of the ball was recorded on a digital video camera. The Cartesian coordinates and the angle of rotation of the ball were determined from the records of motion. The dimensionless drag force coefficient, Magnus force coefficient and translational and rotational Reynolds numbers were calculated from the time series of the ball coordinates and the angle of rotation for each recorded frame. The calculated data were averaged over rectangular cells on experimental domain on the plane of translational and rotational Reynolds numbers, i.e. 1.2 104 < Re < 1.6 104 and 3.8 103 < Reω < 2.7 104. The coefficients were presented in tabulated form.
Keywords:
golf ball; Magnus force; drag force; particle rotation
Available at various institutes of the ASCR
Magnus and Drag Forces Acting on Golf Ball
The paper describes the results of experiments with a rotating golf ball moving quasi-steadily in calm water. The motion of the ball was recorded on a digital video camera. The Cartesian coordinates ...
Project: Transition to turbulence modeling
Horák, V.; Hoření, Bohumír
2007 - English
The project is focused on the transition from laminar to turbulent flow modelling. Developed code will be formulated in such a way to enable an effective parallel processing.
Keywords:
laminar-turbulent transition; turbulence modelling
Available at various institutes of the ASCR
Project: Transition to turbulence modeling
The project is focused on the transition from laminar to turbulent flow modelling. Developed code will be formulated in such a way to enable an effective parallel processing.
Influence of plants on heat balance and entropy exchange
Šír, Miloslav; Weger, J.; Tesař, Miroslav; Lichner, Ľ.
2007 - English
The aim of this study is to quantify the synergy between the vegetation cover, solar radiation, air temperature and soil moisture. Heat balance, potential and actual transpiration, and net entropy exchange at three localities under different plant cover was studied in order to determine crucial factors determining phytomass productivity in cold climatic areas of Bohemian Forest. The phytomass productivity can be quantified by the entropy exchange associated with the latent heat flux. Water shortage is a crucial factor determining phytomass productivity in dry and warm seasons in cold climatic conditions of Czech mountains. Cílem této studie je kvantifikovat synergii mezi vegetačním krytem, slunečním zářením, teplotou vzduchu a vlhkostí půdy. Pro určení rozhodujících faktorů určujících produkci fytomasy v chladné klimatické oblasti Šumavy byla ve třech lokalitách s různým vegetačním krytem zkoumána tepelná bilance, potenciální a aktuální transpirace a výměna entropie. Produkce fytomasy může být kvantifikována produkcí entropie spojenou s tokem latentního tepla. V chladných klimatických podmínkách českých hor je nedostatek vody rozhodující faktor určující produkci fytomasy v suchých a teplých obdobích.
Keywords:
plant transpiration; phytomass productivity; heat balance; entropy exchange; short rotation coppices
Available at various institutes of the ASCR
Influence of plants on heat balance and entropy exchange
The aim of this study is to quantify the synergy between the vegetation cover, solar radiation, air temperature and soil moisture. Heat balance, potential and actual transpiration, and net entropy ...
On the characterisation of the Vočadlo fluids using a back extrusion technique
Filip, Petr; David, Jiří; Pivokonský, Radek
2007 - English
Back extrusion represents one of the cheapest and time-saving experimental methods how to determine rheological characteristics of the fluids studied. This method is based on plunging of a circular rod into an axisymmetrically located circular cup containing the experimental sample. Formerly this method was successfully applied to power-law, Bingham and Herschel-Bulkley fluids. The aim of this contribution is to present a sufficiently simple user-friendly procedure how to determine the individual rheological parameters appearing in the Vočadlo model (sometimes called Robertson-Stiff one) - yield stress, consistency parameter and flow behaviour index. Metoda zpětné extruse se řadí k levnějším a časově úspornějším metodám, pomocí kterých lze vyhodnotit parametry vybraných reologických modelů jako např. mocninného či Herschelova-Bulkleyho. Tento příspěvek se zabývá určením hodnot parametrů pro Vočadlův model.
Keywords:
Back extrusion; Viscosity; Vocadlo model; Robertson-Stiff model
Available at various institutes of the ASCR
On the characterisation of the Vočadlo fluids using a back extrusion technique
Back extrusion represents one of the cheapest and time-saving experimental methods how to determine rheological characteristics of the fluids studied. This method is based on plunging of a circular ...
Investigation of particle size distribution in s-l system measured by image analysis
Kysela, Bohuš; Ditl, P.
2006 - English
An experimental method enabling to investigate of PSD (Particle Size Distribution) changes vs. time during processes with suspensions. Experimentální metoda umožňující sledování casových změn v distribučním rozdělení v s-l systémech např. při rozpouštění.
Keywords:
laser visualization; dissolution; image analysis; particle distribution
Available at various institutes of the ASCR
Investigation of particle size distribution in s-l system measured by image analysis
An experimental method enabling to investigate of PSD (Particle Size Distribution) changes vs. time during processes with suspensions....
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