Zbyněk Zachoval

The Influence of Roughness on the Discharge Coefficient of a Broad-Crested Weir

The Influence of Roughness on the Discharge Coefficient of a Broad-Crested Weir The use of environmentally-friendly materials in hydraulic engineering (e.g. the stone lining of weirs at levees) calls for the more accurate estimation of the discharge coefficient for broad-crested weirs with a rough crest surface. However, in the available literature sources the discharge coefficient of broad-crested weirs is usually expressed for a smooth crest. The authors of this paper have summarized the theoretical knowledge related to the effect of weir crest surface roughness on the discharge coefficient. The method of determination of the head-discharge relation for broad-crested weirs with a rough crest surface is proposed based on known discharge coefficient values for smooth surfaces and on the roughness parameters of the weir. For selected scenarios the theoretical results were compared with experimental research carried out at the Laboratory of Water Management Research, Faculty of Civil Engineering (FCE), Brno University of Technology (BUT). Vliv Drsnosti na Velikost Součinitele Průtoku u Přelivu se Širokou Korunou Používání přírodě blízkých materiálů ve vodním hospodářství (např. kamenná opevnění povrchu přelivů v ochranných hrázích) vyvolává požadavek přesnějšího stanovení součinitele průtoku pro přelivy se širokou a hydraulicky drsnou korunou. V dostupných literárních pramenech je součinitel průtoku přelivů se širokou korunou obvykle vyjádřen pouze pro hladký povrch koruny přelivu. Autoři článku shrnuli teoretické poznatky týkající se vlivu drsnosti povrchu koruny přelivu na součinitel průtoku a navrhli metodu pro stanovení způsobu hydraulického výpočtu konzumční křivky přepadu přes přeliv se širokou a drsnou korunou. Postup vychází ze znalosti součinitele průtoku přelivu s hladkou korunou a charakteristik drsnosti. Pro vybrané scénáře byly teoreticky vypočítané hodnoty porovnány s výsledky experimentálního výzkumu uskutečněného v Laboratoři vodohospodářského výzkumu Ústavu vodních staveb, Fakulty stavební, Vysokého učení technického v Brně.

Shape of the nappe during free overfall from a rectangular channel with zero bed slope

Abstract The paper deals with selected procedures used to calculate the shape of compact nappe during free overfall from a smooth horizontal channel with rectangular cross section. Calculated and measured water surface and velocity conditions in the end section, the level of water surface upstream in front of the end section and the shape of the compact part of an overfall nappe are described for a particular compared case.

Incipient motion of coarse uniform gravel

ABSTRACT The influence of several parameters on the incipient motion of gravels has been carefully examined from theoretical and experimental standpoints. The effect of the longitudinal bed slope is significant and well described with existing methods. This analysis shows that the effects of the grain Reynolds number and relative submergence are negligible for turbulent flows over hydraulically rough boundaries. Laboratory experiments for homogeneous gravels on a plane bed provided detailed measurements of both mean flow velocity and velocity fluctuations for the analysis of the lift and drag coefficients. This analysis of the lift and drag coefficients enables a better evaluation of the Shields parameter for incipient motion as a function of the angle of repose . The theoretical developments presented in this paper are corroborated by the results of our laboratory experiments as well as many others available in the literature.

Discharge coefficient of a rectangular sharp-edged broad-crested weir

Abstract This paper is concerned with the determination of the relationship for the calculation of the discharge coefficient at free overflow over a rectangular sharp-edged broad-crested weir without lateral contraction. The determination was made on the basis of new measurement in a range of the relative thickness of the weir from 0.12 to 0.30 and newly in a large range of relative height of the weir extremely from 0.24 to 6.8 which greatly expands the application possibilities of low weirs. In addition, the effects of friction and surface tension on the value of the discharge coefficient were evaluated as well as the effect of the relative thickness of the weir. The new equation for discharge coefficient, expressed using the relative height of the weir, was subjected to verification made by an independent laboratory which confirmed its accuracy.

Discharge Coefficient of a Trapezoidal Broad-Crested Side Weir for Low Approach Froude Numbers

AbstractEven though broad-crested side weirs have been subjected to numerous studies, guidance for discharge coefficient determination for broad-crested side weirs still has not been clearly given. Experimental research was carried out to describe the flow conditions in front of a trapezoidal broad-crested side weir at low Froude numbers in the approach channel for various combinations of inflow and overflow discharges. Three side weir variants with different oblique angles were studied. Flow characteristics at the side weir were analyzed and assessed based on the results obtained from extensive measurements performed on a hydraulic model. The empirical relation between the coefficient of obliqueness, the angle of side weir obliqueness, and Froude numbers upstream and downstream of the weir was derived.

Flow characteristics at trapezoidal broad-crested side weir

Abstract Broad-crested side weirs have been the subject of numerous hydraulic studies; however, the flow field at the weir crest and in front of the weir in the approach channel still has not been fully described. Also, the discharge coefficient of broad-crested side weirs, whether slightly inclined towards the stream or lateral, still has yet to be clearly determined. Experimental research was carried out to describe the flow characteristics at low Froude numbers in the approach flow channel for various combinations of in- and overflow discharges. Three side weir types with different oblique angles were studied. Their flow characteristics and discharge coefficients were analyzed and assessed based on the results obtained from extensive measurements performed on a hydraulic model. The empirical relation between the angle of side weir obliqueness, Froude numbers in the up- and downstream channels, and the coefficient of obliqueness was derived.

Zone of flow separation at the upstream edge of a rectangular broad-crested weir / Oblast odtržení proudu na návodní hraně pravoúhlého přelivu se širokou korunou

The paper deals with the determination of the basic characteristics of flow at the crest of a rectangular broad-crested weir and in detail with the characteristics of flow separation at the upstream edge of the weir crest. The determination of the characteristics is made on the basis of measurement of the water surface level, the pressure head and the velocity field using the Particle Image Velocimetry method. The characteristics are expressed dimensionless in relation to the energy overflow head and the critical depth. Článek pojednává o stanovení základních charakteristik proudu na široké koruně pravoúhlého přelivu a detailně o charakteristikách odtržení proudu za návodní hranou koruny přelivu. Charakteristiky jsou stanoveny na základě měření úrovně hladiny, tlakové výšky a rychlostního pole metodou Particle Image Velocimetry. Charakteristiky jsou vyjádřeny bezrozměrně ve vztahu k energetické přepadové výšce a kritické hloubce.

Earth-Fill Dam Monitored by EIS Method during Application of Nutrient Aqueous Solution used in BioSealing Method

The paper gives short information about the results of monitoring the electrical properties of an earth-fill dam during the application of a nutrient aqueous solution used in the method BioSealing. Monitoring is carried out using a Z-meter device when applying the method of electrical impedance spectrometry and, in some cases, is part of a system of monitoring seepage through the earth-fill dam of the water reservoir by its administrator. Information about the changes that take place in the body of the dam during the movement of the water level in the reservoir or after the influence of weather changes or human activity are given through the monitored changes in the electrical parameters of the soil of the dam with time.