Simulacije turbulentnega prenosa toplote ob greti foliji z metodo velikih vrtincev

Kren, Jan (author), Tiselj, Iztok (mentor), Mikuž, Blaž (co-mentor)

Na Odseku za reaktorsko tehniko Inštituta Jožef Stefan se postavlja nov eksperiment v Laboratoriju za termohidravliko večfaznih tokov (THELMA). Namen eksperimenta je študija temperaturnih fluktuacij na greti kovinski foliji, ki je hlajena s turbulentnim tokom. Načrtovanje eksperimenta temelji na numeričnih simulacijah, v katerih smo analizirali vpliv različnih aproksimacij na temperaturne fluktuacije na greti foliji. To delo opisuje rezultate simulacij. Tok in prenos toplote v novem eksperimentu smo napovedali s simulacijami z metodo velikih vrtincev (ang. Large Eddy Simulation) s pomočjo računalniškega programa OpenFOAM. Prevajanja toplote v foliji nismo modelirali. Folijo smo opisali z idealiziranim robnim pogojem konstantnega toplotnega toka. Simulacije so predpostavljale nestisljiv, polno razvit turbulentni tok Newtonske tekočine z Reynoldsovim številom 10000. V prvih simulacijah je bila dodana temperatura kot pasivni skalar, torej brez povratne zanke na enačbo za ohranitev gibalne količine. Drugi del simulacij pa je upošteval spreminjanje viskoznosti vode s temperaturo ter vzgonske sile. Določili smo ustrezno toplotno moč folije v eksperimentu ter moč, pri kateri je mogoče zanemariti vpliv temperature na materialne lastnosti vode. Posebej nas je zanimala porazdelitev temperature na vroči foliji v turbulentnem režimu. Z analizo koherentnih termičnih struktur v simulacijah smo uspeli določiti potrebno resolucijo in frekvenco visokohitrostne termične kamere pri danemu Reynoldsovemu in Prandtlovemu številu. V zaključku je predstavljena kratka primerjava naših simulacij s preliminarnimi meritvami temperaturnih fluktuacij na greti foliji.

• Language: Slovenian
• Keywords: računska dinamika tekočin, metoda velikih vrtincev, turbulenten tok, prenos toplote, enofazni tok, OpenFOAM
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FMF - Faculty of Mathematics and Physics
• Year: 2020
• PID: 20.500.12556/RUL-119285
• COBISS.SI-ID: 27398915
• Publication date in RUL: 06.09.2020

Secondary language

• Language: English
• Title: Large Eddy Simulations of turbulent heat transfer near heated foil

Abstract

At Reactor Engineering Division of Jožef Stefan Institute a new experiment is being designed in the THELMA laboratory to study temperature fluctuations at the heated foil cooled by turbulent flow. Detailed design of the experiment is based on Computational Fluid Dynamics (CFD) studies which are described in the present work. The flow and heat transfer in the new experiment predicted with a wall-resolved Large Eddy Simulation (LES) using a wall-adapting local eddy-viscosity (WALE) model in OpenFOAM computer code. Foil was modeled with approximation of the constant heat flux. Simulations assumed incompressible, fully developed turbulent flow of Newtonian fluids with Reynolds number of 10000. In the first part of the study, heat transfer has been included to the study using temperature as a passive scalar, so there is no feedback loop on mass and momentum conservation equation. The second part of the simulations took into account the influence of the temperature on the water viscosity and density. We have identified the power of the foil in the experiment and the maximum foil temperatures at which the water temperature can be described with the passive scalar approximation. The most relevant result of our simulations were temperature fluctuations on the foil. With observation and analysis of coherent thermal structures in simulations we have predicted the required resolution and frequency needed by thermographic high-speed camera at given Reynolds and Prandtl numbers. In the Conclusions we present the comparison of our simulations with the preliminary measurements.

• Keywords: Computational Fluid Dynamics, Large Eddy Simulation, Heat Transfer, Turbulent Flow, single phase flow, OpenFOAM