Two-Dimensional Mathematical Modelling of a Dam-Break Wave in a Narrow Steep Stream

The paper deals with hydraulic aspects of a wave, emerging as a result of a potential dam break of the upper storage reservoir of the pumpedstorage hydropower plant Kolarjev vrh. A two-dimensional depth-averaged mathematical approach was used. The upper storage reservoir and its dam failure were modelled with the mathematical model PCFLOW2D, which is based on the Cartesian coordinate numerical mesh.\ud The results of PCFLOW2D were used as the upper boundary condition for the mathematical model PCFLOW2D-ORTHOCURVE, based on the orthogonal curvilinear numerical mesh. The model PCFLOW2D-ORTHOCURVE provided a tool for the analysis of flood wave flow in a steep, narrow and geometrically diversified stream channel. The classic Manning’s equation fails to give good results for streams with steep bed\ud slopes and therefore, a different equation should be used. The application of the Rickenmann’s equation was chosen, presented in a form similar to Manning’s equation. For the purpose of the example given here, the equation was somewhat simplified and adapted to the data available. The roughness coefficient used at each calculation cell depended on the slope of that cell. The results of numerical calculations\ud were compared to measurements carried out on a physical model in the scale of 1 : 200. Regarding the complexity of the flow phenomenon a rather good correlation of maximum depth was established: only at one gauge the difference in water depth was up to 27% while at the other four it was 7% of water depth on average

Cavitation Instabilities at the Entrance Pipe of Centrifugal Pump

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Emergency gate vibration of the pipe-turbine model

The vibration behaviour of an emergency gate situated on a horizontal-shaft Kaplan turbine is studied. The analysis and transfer of the dynamic movements of the gate are quite complex. In particular the behaviour is examined of the emergency gate for the case when the power unit is disconnected from the system or there is a breakdown of the guide vane system at the moment when the maximal head and capacity are achieved. Experimental-numerical methods both in the time domain and in the frequency are employed. Natural vibrations characterize a first zone, corresponding to relatively small gate openings. As the gate opening increases, the vibration behaviour of the gate becomes increasingly dependent on the swirl pulsations in the draft tube of the turbine. Finally, the data transfer from the model to the prototype by use of the dinamic similitude law is discussed

Analiza koncentracije in usedanja suspendiranega materiala v akumulacijskih jezerih

This paper deals with the sedimentation of suspended load in the reservoirs. As an example the reservoir of the hydroelectric power plant Boštanj on the Sava River is shown. The objective of the described studies was to determine the quantity and type of deposited material in the reservoir during the selected time period. For this purpose, the mineral and chemical composition, and the concentration and the particle size of the suspended load at the intake of the water into the reservoir and at its outflow were examined. In order to determine the concentration of the suspended load, 24 water samples from the area of the intake and outflow from the reservoir were taken. At the same time the discharge of the Sava River was measured. Solid particles were removed from the water with the help of sedimentation and in the final stage of water evaporation. The results of the studies showed that the concentration of the suspended material was changing in relation to the location and the flow rate of the water. This ratio can be described with an exponential function. In suspended load composition carbonates, muscovite/illite and quartz dominatehowever, chlorite was also found, as well as small quantities of plagioclase and organic detritus. With regard to the size of the particles the examined samples are classified as silt. It was determined that the concentration of the suspended load, at the same flow rate of water, at the intake into the reservoir is larger than at the outflow. The difference is represented by the material that was sedimented in the reservoir due to the decreased speed of the water as a result of the river\u27s impoundment. A comparison of the composition of the samples from both collection sites showed that at the outflow site of the water from the reservoir there is a somewhat smaller share of carbonate grains and heavy minerals than at the intake site, and a higher content of organic detritus and clay particles can also be observed. Considering the actual discharge of water in the period between July 2006 and July 2007 and the examined ratio between the flow rate of the water and the quantity of suspended and deposited material, the total quantity of sedimented material in this period was estimated.Prispevek obravnava problem sedimentacije lebdečih plavin v akumulacijskih jezerih. Kot primer je prikazano jezero hidroelektrarne Boštanj na reki Savi. Cilj opisanih raziskav je bil ugotoviti vrsto in količino sedimentiranega materiala v jezeru v izbranem časovnem obdobju. V ta namen je bila preiskana mineralna in kemična sestava ter koncentracija in velikost suspendiranih delcev pri vtoku vode v akumulacijsko jezero in ob njenem iztoku. Za ugotovitev vsebnosti lebdečih plavin je bilo odvzetih 24 vzorcev vode z območja vtoka in iztoka vode iz akumulacijskega jezera. Istočasno je bil izmerjen pretok reke Save. Trdni delci so bili iz vode izločeni s pomočjo usedanja in v zaključni fazi izparevanja vode. Rezultati preiskav so pokazali, da se koncentracija suspendiranega materiala na posamezni lokaciji spreminja v odvisnosti od pretoka vode in jo je mogoče izraziti z eksponentno funkcijo. V sestavi lebdečih plavin se pojavljajo karbonati, muskovit/illit, kremen in klorit ter v manjši meri plagioklazi in organski detritus. Glede na velikost zrn se preiskani materiali uvrščajo med melje. Ugotovljeno je bilo, da je količina suspendiranega materiala pri enakem pretoku vode ob vtoku v akumulacijsko jezero večja kot ob iztoku. Razlika predstavlja material, ki se je v jezeru sedimentiral zaradi zmanjšane hitrosti vode kot posledice zajezitve reke. Rezultati preiskav zrnatosti so pokazali, da so se usedali predvsem delci velikosti 20 m do 100 m. Primerjava mineralne sestave vzorcevz obeh odjemnih mest je pokazala nekoliko manjši delež karbonatnih zrn in težkih mineralov ter večjo vsebnosti organskega detritusa in glinenih delcev na mestu iztoka vode iz jezera. Ob upoštevanju dejanskega pretoka vodev obdobju od julija 2006 do julija 2007 ter preiskanega razmerja med pretokom vode in količino suspendiranega in sedimentiranega materiala, je ocenjena skupna količina sedimentiranega materiala v tem času

Analiza procesa in dinamike sedimentacije suspendiranega materiala v akumulacijskih jezerih z visokimi dnevnimi oscilacijami

The river water pumped into reservoirs with high daily oscillations, e.g. at pumping hydroelectric power plants, contains different amounts of suspended load depending on the time period and the riverćs discharge. This paper presents an analysis of the suspended-load sedimentation process that is based on the interaction between the sedimentation, i.e., the settling, velocity and the motion of the water. The settling velocity of spherical particles in the presence of a buoyancy force is a function of the particle size. Laboratory investigations of the suspended material from the river-watersamples have determined the ratio between the particle size and the concentration of suspended material with respect to the river discharge, the ratio between the concentration of suspended material in the water and the discharge, and the relationship between the concentration of suspended material and the discharge of water, which is for the first time expressed as an exponential function. The motion of the water in the reservoirs with high daily oscillations is solved by the three-dimensional modeling of the liquid streams. The evaluation of the results is presented for the case of the planned Kozjak pumping hydroelectric power plant on the River Drava.V akumulacijska jezera z visokimi dnevnimi oscilacijami nivoja vode, kot na primer pri črpalnih hidroelektrarnah, se običajno črpa rečna voda, ki vsebuje različne koncentracije suspendiranega materiala glede na določena časovna obdobja in rečni pretok. Prispevek prikazuje analizo procesa sedimentacije suspendiranega materiala, ki temelji na interakciji med sedimentacijsko hitrostjo in gibanjem vode. Sedimentacijska hitrost grobozrnatih delcev je v prisotnosti sile vzgona funkcija velikosti sedimenta. S pomočjo laboratorijskih preiskav suspendiranega materiala iz vzorcev rečne vode so podane odvisnost velikosti sedimenta in koncentracije suspendiranega materiala glede na različni rečni pretok, odvisnost med koncentracijo suspendiranega materiala v vodi in pretokom v določenem časovnem obdobju ter razmerje med koncentracijo suspendiranega materiala in pretoka. Slednja odvisnost je kot novost prvič izražena z eksponentno funkcijo. Gibanje vode v rezervoarju z visokimi dnevnimi nihanji je analizirano s tridimenzionalnim modeliranjem tekočinskih tokov. Ocenitev rezultatov je prikazana na primeru načrtovane črpalne hidroelektrarne Kozjak na reki Dravi

Numerical Modeling of a Y-Bifurcator using Realizable k- e Turbulence Model

In this paper, the outhors present the results of investigation on the influence of the boundary layer mesh size to the flow variable in the numerical of realbable k- e model in order to calculate the head loss offlow through a Y-bifurcator. This bifurcator is applied for combination of urbine and pumping operation in hydro plants. Five numerical models with difierent boundary layer mesh size was created and simulated for compared to the result of measurement on a physical model. At low Reynolds number region, the pressure head different and loss coeficient varies compare to the measurement. However it becomes closer to the measurement with increasing the Reynolds number. Wall treatment give good result for simulation in low Reynolds number. The pumping mode simulations produce better result in calculating loss coeficient for all Reynolds number regions than those in turbine mode simulation

Experimental analysis of the impact of particles on the cavitating flow

The purpose of this paper is to present an analysis of the impact of solid particles on the development of cavitating flow conditions around a hydrofoil. Experimental studies have been conducted in a cavitation tunnel with three different mixtures of particles and water. We used a particle-like properties, such as are found in river water, and with increasing mass concentration. We performed measurements of torque and the relative noise in the hydrofoil. The point in the formation of vapour phase on the hydrofoil and the pronounced frequency effect were determined by measuring the relative noise. Based on the analysis the results show that the particles increase the intensity and extent of cavitation