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Numerical simulations of flow over stationary deposit
Chára, Zdeněk; Vlasák, Pavel; Kysela, Bohuš; Konfršt, Jiří
2014 - anglický
The paper deals with a water flow in a horizontal, circular pipe of inner diameter 40 mm with a stationary deposit. The deposit was formed by spheres of diameter d=6 mm. The thickness of the deposit was about two sphere diameters. The flow was experimentally studied by the PIV method and COMSOL Multiphysics 4.4 was used as tool for numerical simulations as well. Two approaches were used to create the stationary deposit. In the first one was the deposit was replaced by a rough wall with different values of the roughness parameter ks. In the second case the deposit was created from the identical spherical particles. The results of the simulations and the experimental data are compared.
Klíčová slova:
stationary deposit; PIV method; numerical simulations
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Numerical simulations of flow over stationary deposit
The paper deals with a water flow in a horizontal, circular pipe of inner diameter 40 mm with a stationary deposit. The deposit was formed by spheres of diameter d=6 mm. The thickness of the deposit ...
Stationary- and sliding beds in pipe flows of settling slurry
Matoušek, Václav; Krupička, Jan; Chára, Zdeněk
2014 - anglický
Investigations are discussed on the effect of stationary- and sliding beds on a behavior of settling slurry flows. Results are presented of our recent experiments with two fractions of ballotini in a 100-mm-pipe loop. Experimental work contained measurements of concentration profiles and velocity profiles. The experimental results for flows with stationary deposits are compared with predictions using our formulae for solids transport and bed friction in layered flows. CFD simulations are included to validate the velocityprofile measurements and to verify the bed roughness predictions in the flows with stationary beds. Furthermore, the measured velocity profiles are compared to profiles predicted using the log law of the wall with boundary shear velocities determined from the linear distribution of shear stress across the pipe flow. The approach is successful in the flow below the upper wall of the pipe but fails above the top of the deposit where the stress distribution is different as verified by the CFD simulation. The concept of the linear-distribution of shear stress is well applicable in flows with sliding beds. An example is given of a solution for a partially-stratified flow with sliding bed using the 1-D Stress- Distribution based Model.
Klíčová slova:
experiment; hydraulic transport; concentration profile; velocity profile; sheet flow
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Stationary- and sliding beds in pipe flows of settling slurry
Investigations are discussed on the effect of stationary- and sliding beds on a behavior of settling slurry flows. Results are presented of our recent experiments with two fractions of ballotini in a ...
Long-term hydroecological monitoring in the Krkonoše Mts
Tesař, Miroslav; Šír, Miloslav
2013 - anglický
The cloud and fog water deposition proved to be important delivery mechanism for both water and pollutants in mountainous headwater regions. A fogwater study has been conducted in the Krkonoše Mts. since 1999 till the present time. The sampling site for the observation and evaluation occult precipitation in the Western region was established in the Modrý potok basin (1010–1554 m a.s.l., 2.62 km2) at the highest point of the watershed (passive cloud and fog water collector) while the bulk precipitation and throughfall samplers were installed near to the closure profile of the basin. Rain gauges are evenly situated at six altitudes of the watershed (from 1020 to 1365 m a. s. l.). In the Eastern region the both passive and active collectors were installed close to the Labská bouda chalet (1325 m a.s.l). The active collector (Eigenbrodt, Germany) is operated automatically by the PWD-11 sensor (Vaisala, Finland). Collected samples were stored in polyethylene bottles and transported as soon as possible to the laboratories of the Czech Geological Survey and Geological Institute of ASCR to the chemical analyses. The results for 1999–2011 will be presented in this article. A wide range of concentrations were encountered, most typically exceeding concentrations occurring in rain (so-called enrichment factors were evaluated) and the estimated wet deposition of the most important chemical compounds were calculated and compared with respect to weighted means of bulk precipitation collected in the open area. Based on the model predictions and on the water balance of the forest canopy the annual occult precipitation total for the Krkonoše Mts. was estimated by 20–25 % of the annual falling precipitation total. The research is supported by the Czech Science Foundation (205/09/1918).
Klíčová slova:
occult precipitation; cloud and fog water deposition; water chemistry
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Long-term hydroecological monitoring in the Krkonoše Mts
The cloud and fog water deposition proved to be important delivery mechanism for both water and pollutants in mountainous headwater regions. A fogwater study has been conducted in the Krkonoše Mts. ...
Spinnability of PEO solutions with respect to their aging
Zelenková, Jana; Peer, Petra; Filip, Petr
2013 - anglický
Non - negligible portion of pol ymer commodity suffers from ageing that participates in sometimes significant changes of products attributes. Rheology represents a useful tool for a description of this process. The aim of this contribution is to evaluate possible ageing of PEO solution ( polyethylen e oxide ( M w =300,000 g/mol) dissolved in water at 10 wt.% concentration) based both on rheological characterization and on quality of electrospun fibres. Rheological measurements in steady shear and oscillatory modes were carried out using a rota tional rheometer MCR 501 (Anton Paar, Austria) equipped with the concentric cylinders geometry. The electrospinning measurements were executed with the help of a proposed laboratory device. The tip - to - collector distance attained 20 cm, applied voltage rang ed from 20 to 30 kV. The obtained electrospun fibres were analysed using a scanning electron microscope (VEGA 3, Tescan, Czech Republic). Both types of measurements were carried out in the period of several months during which the solution studied was plac ed in a dark and tempered box (25°C). The measurements indicate no ageing impact on rheological characteristics or quality of electrospun fibres. This guarantees more or less the identical quality of non - woven textiles prepared from PEO solutions regardles s of time period during which the solutions are deposited.
Klíčová slova:
polyethylene oxide (PEO); ageing; electrospinning; rheological properties
Dokument je dostupný na externích webových stránkách.
Spinnability of PEO solutions with respect to their aging
Non - negligible portion of pol ymer commodity suffers from ageing that participates in sometimes significant changes of products attributes. Rheology represents a useful tool for a description of ...
Coarse-grained particles conveying along a pipe bed
Vlasák, Pavel; Chára, Zdeněk; Konfršt, Jiří; Kysela, Bohuš
2013 - anglický
The paper describes the results of a flow visualisation of model coarse-grained fully stratified particle-water mixtures. Investigation was focussed on study of the particle behaviour and carrier liquid and conveyed particles local velocities. Glass balls and washed graded pebble gravel of mean diameter of 6 mm were conveyed by water in a horizontal smooth pipe loop with a transparent pipe viewing section of inner diameter 40 mm. Particle movement along the pipe invert and particulate stationary bed, created by two layers of spherical particles of the same size as the conveyed particles, was studied. The effect of stationary bed on local velocity values of the carrier liquid and conveyed particles were determined. It was conducted that the maximum liquid velocity is significantly shifted from pipe centre to a higher position in the flow pattern with stationary bed.
Klíčová slova:
coarse-grained slurry; flow structure; visualisation; liquid local velocity; particle velocity; rychlost; částice
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Coarse-grained particles conveying along a pipe bed
The paper describes the results of a flow visualisation of model coarse-grained fully stratified particle-water mixtures. Investigation was focussed on study of the particle behaviour and carrier ...
Early warning system for flash floods in the Krkonoše Mts
Tesař, Miroslav; Šír, Miloslav
2013 - anglický
The present contribution describes a sophisticated local warning system (LWS) for detection of local flash floods that is built in the Krkonoše Mts. in the upper of the Úpa river with the closing profile at Horní Maršov (573–1602 m a.s.l., 81.70 km2). This system is based on the new knowledge of the discontinuous character of water transport in an unsaturated zone and involves: (i) instrumentation: (1) stream gauge monitoring stations with data transfer to the internet, (2) monitoring stations (equipped by rain gauge, air and soil thermometers, soil water tensiometers and soil moisture meters) with data transfer to the internet, (ii) software: (1) the internal software of the stream gauge and monitoring stations for the measurement, storage and transfer the data to the dispatching centre, (2) software of a central data repository, (3) software for data transmission in the internet browser, (3) software for the forecasting of flood risk and sending flood alert, (iii) dispatching centre: (1) operating of the data repository, (2) forecasting of the water level for the each of connected stream gauge station, (3) sending flood alert, (iv) handbooks and user’s Guides: (1) hydrological and soil surveying, (2) LWS design, (3) operation and maintenance of the LWS, (v) complete projection documentation of the LWS, (vi) installation of the LWS in a catchment, (vii) testing and routine operation of the LWS. The described LWS is supported by the Technology Agency of the Czech Republic (Project TA02021451).
Klíčová slova:
early warning system; flash flood; surface and soil water monitoring
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Early warning system for flash floods in the Krkonoše Mts
The present contribution describes a sophisticated local warning system (LWS) for detection of local flash floods that is built in the Krkonoše Mts. in the upper of the Úpa river with the closing ...
Improvements of saltation model
Kharlamova, Irina; Vlasák, Pavel
2013 - anglický
The present paper introduces a new model of a bed-load transport. The model simulates a particle motion in the channel with turbulent flow and rough bed. The effects of mutual interaction of conveyed particles with carrier liquid, with bed particles, and also with other conveyed particles are taken into account. The model predicts average saltation characteristics, e.g. saltation length and height, particles distribution in vertical direction, and mass rate of conveyed particles per unit area of channel bed.
Klíčová slova:
částice; modely
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Improvements of saltation model
The present paper introduces a new model of a bed-load transport. The model simulates a particle motion in the channel with turbulent flow and rough bed. The effects of mutual interaction of conveyed ...
Saltation of sand in vicinity of cylindrical column
Kharlamova, Irina; Kharlamov, Alexander; Vlasák, Pavel
2013 - anglický
The paper presents a model of sand sediment transport in water stre am in vicinity of a high cylindrical col umn. It is assumed that an averaged turbulent flow is horizontally layered in vicinity of the cylinder. In ea ch layer the flow around the cylinder is modelled as a potential flow generated by a vertical dipole line. Flow in viscous sub-layer on the surface of the cylinder is neglected. The presented flow model is approximate; however it is simple for use. Trajectories of saltating particles near the cylinder were calculated. Further investigation of such flow will allow a determination of zones where solid particles will collide with the column. That might be useful for prevention of its damage or destruction
Klíčová slova:
saltation of sand; flow around cylinder; logarithmic profile; dipole line; averaged turbulent flow
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Saltation of sand in vicinity of cylindrical column
The paper presents a model of sand sediment transport in water stre am in vicinity of a high cylindrical col umn. It is assumed that an averaged turbulent flow is horizontally layered in ...
Extreme runoffs from the Modrý důl basin in the vegetation season
Šír, Miloslav; Tesař, Miroslav; Dvořák, Igor
2013 - anglický
The main objective of the present article is to advance understanding of the complex role of various vegetation cover in extreme runoff formation in the Modrý potok basin. This watershed (1010–1554 m a.s.l., 2.62 km2) is situated in the northern part of the Czech Republic in the eastern part of the Krkonoše Mts. The soil types are the mountainous Podzole and Lithosol with a thin humic layer on crystalline bedrock. Monitoring stations with data transfer to the internet are installed on several localities differing in the type of vegetation cover (in the grassland and dwarf pine above the forest margin, in the growth of mature spruce forest, and in the grassland below the spruce forest). The discharge at the closing profile is continuously recorded. Meteorological data are collected at a station close to the Výrovka chalet (1360 m a.s.l.): year-round precipitation, solar radiation, wind speed and direction, air and soil temperatures and soil moisture. The long-term monitoring of the water balance of the headwater catchment Modrý potok and its soil water regime was evaluated taking into account the discontinuous character of water transport in an unsaturated zone. Extreme runoffs in a vegetation season are caused by these factors: (1) oversaturation of the soil profile, (2) water repellency of the soil surface, (3) gravitationally destabilized flow of water in the soil profile, (4) extreme rainfall. The typical combinations are (1) and (3) – gravitationally destabilized flow of water can be caused even by a small rainfall under the oversaturation, (2) and (4) – long-term drought can cause the water repellency of the soil surface and the extreme rainfall. The research is supported by the Czech Science Foundation (205/09/1918) and by the Technology Agency of CR (TA02021451).
Klíčová slova:
surface runoff formation; headwater catchment; water balance; soil water monitoring
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Extreme runoffs from the Modrý důl basin in the vegetation season
The main objective of the present article is to advance understanding of the complex role of various vegetation cover in extreme runoff formation in the Modrý potok basin. This watershed (1010–1554 ...
Oblique collisions of non-rotating spherical particles with a wall
Chára, Zdeněk; Vlasák, Pavel; Kysela, Bohuš
2013 - anglický
In the present paper non-rotating particle-wall collisions were experimentally investigated. By means of the PIV method a velocity field around falling spheres was analyzed. It was shown that the wake behind the particle which approached a bed in non-normal direction was asymmetrical and after the impact the wake passed the particle only along one side. This non-symmetrical velocity field resulted in additional forces which pushed the particle to an opposite direction than was the direction of the particle motion just after the impact.
Klíčová slova:
wake; particle trajectory; velocity field
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Oblique collisions of non-rotating spherical particles with a wall
In the present paper non-rotating particle-wall collisions were experimentally investigated. By means of the PIV method a velocity field around falling spheres was analyzed. It was shown that the ...
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