Hrvatske vode
 
Pristup modeliranju prirodne konvekcije u akumulacijskim jezerima: primjer akumulacije Butoniga
Approach to modelling natural convection in reservoirs as exemplifi ed by the Butoniga reservoir

Luka Zaharija1, Davor Stipanić2, Vanja Rački3, Maja Oštrić3, Vanja Travaš1

Sažetak/Abstract: 

U kontekstu gospodarenja umjetnim akumulacijskim jezerima, prirodna konvekcija, tj. protok mase vode koji nastaje kao posljedica temperaturnog gradijenta, je posebno važan fi zikalni proces koji može značajno utjecati na proces odlučivanja i na model upravljanja akumulacija. Navedeno će se u ovom radu ilustrirati na primjeru akumulacijskog jezera Butoniga gdje prirodna konvekcija ima posebno važan značaj. U ljetnom se periodu u akumulaciji Butoniga formira termoklina te se u donjem pridnenom sloju induciraju anoksični uvjeti koji uz prisustvo mulja na dnu jezera i putem bioloških i kemijskih procesa značajno narušavaju kakvoću vode u tom području. Sve dok postoji uravnotežena temperaturna stratifi kacija, spriječeno je miješanje ovakvog anoksičnog sloja s preostalom vodom. Međutim, putem progresivnog pada srednje vrijednosti temperature zraka u ranojesenskom periodu se i gornji sloj vode hladi i započinje značajno vertikalno strujanje koje može putem prirodne konvekcije prouzročiti miješanje anoksičnog sloja i ugroziti kakvoću preostale vode u akumulaciji. Iz tog je razloga potrebno preduhitriti trenutak aktivacije vertikalnih strujanja i provesti pražnjenje akumulacije iz pridenog sloja. Donošenje odluke o trenutku pražnjenja akumulacije je vrlo složen proces koji iziskuje utemeljenje u prethodno provedenim terenskim mjerenjima i vrlo kompleksnim računalnim simulacijama. Nakon utvrđivanja najprikladnijeg vremena pražnjenja, što iziskuje opsežnu parametarsku analizu, pažnja se predaje utvrđivanju najučinkovitije dinamike pražnjenja, što je i tema ovog rada.

 

In the context of reservoir management, natural convection, i.e. volumetric flow occurring as a consequence of the temperature gradient is a particularly important physical process that can significantly influence the decision-making and reservoir management processes. This will be illustrated by the paper on the example of the Butoniga reservoir, in which natural convection plays a very significant role. In the summer period, a thermocline is formed in the Butoniga reservoir and thus anoxic conditions are induced in the lower near-bottom layer that, in the presence of mud at the reservoir bottom and through biological and chemical processes, significantly deteriorate water quality in this area. As long as there is a balanced thermal stratification, the mixing of this anoxic layer with the remaining water is prevented. However, due to a progressive decrease in the mean air temperature value in the early autumn period, the top water layer cools down and a significant vertical circulation begins, which may cause the mixing of the anoxic layer and endanger the quality of the remaining water in the reservoir through natural convection. For this reason, it is necessary to forestall the moment when vertical circulation is activated and empty the near-bottom layer of the reservoir. The decision-making regarding the moment when the reservoir should be emptied is an elaborate process that is based on the previously performed field measurements and very complex computer simulations. After the most appropriate time of the reservoir emptying is established, which requires a comprehensive parameter analysis, the attention is focused on the determination of the most efficient emptying dynamics, which is the topic of this paper.

Kategorija: 
Prethodno priopćenje / Preliminary Report
Ključne riječi/Key words: 

jezero Butoniga, ranojesensko ispuštanje, numerički model, OpenFOAM

Butoniga reservoir, early autumn discharge, numerical model, OpenFOAM

Podaci o autorima/Authors affiliations: 

1Građevinski fakultet Sveučilišta u Rijeci, Radmile Matejčić 3, 51000 Rijeka, luka.zaharija@student.uniri.hr

 

2Hidromodeling, d.o.o., Mrkopaljska 7, 51000 Rijeka

 

3VGO za slivove sjevernog Jadrana, Đure Šporera 3, 51000 Rijeka

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