Razvoj in eksperimentalna validacija tri-razsežnega numeričnega modela za napovedovanje značilnosti plinsko fokusiranih mikro-curkov

Kovačič, Krištof (author), Gregorc, Jurij (mentor), Šarler, Božidar (comentor)

V magistrskem delu smo zasnovali tri-razsežni numerični model za napovedovanje dvo-faznih tokov, ki nastanejo pri plinsko fokusiranih mikro-curkih voda-zrak. Uporabljena je formulacija mešanice za popis nestisljivega, newtonskega toka vode in fokusirnega zraka, ki vključuje k-? SST turbulenčni model zaradi zagotavljanja numerične stabilnosti. Postopek numeričnega reševanja temelji na metodi kontrolnih volumnov z metodo volumna tekočine, ki vključuje geometrijsko rekonstrukcijo stične površine. Z ustrezno izbranimi robnimi in začetnimi pogoji takšen model omogoča natančno, ponovljivo, od računske mreže neodvisno in stabilno numerično simulacijo tlačnih in hitrostnih polj. Numerični model smo validirali z rezultati meritev na vertikalni, navzdol postavljeni konfiguraciji šobe. Razvili smo namenski računalniški program za analizo karakterističnih parametrov mikro-curkov iz eksperimentalno dobljenih videoposnetkov in numeričnih animacij. Reynolds-ovi števili za zrak in vodo v numeričnih simulacijah sta v območju 1009–2421 in 48–104, Weber-ovo število pa 0,57–3,0. Identične oblike mikro-curkov so pri enaki kombinaciji volumskih pretokov zraka in vode opazne tako pri eksperimentalnih videoposnetkih kot tudi pri numeričnih animacijah. Zasnovan model dobro napove povprečne in lokalne premere mikrocurka. Analizirali smo tudi časovni potek razpada curka, na katerega vplivajo nestabilnosti. Preverili smo, kako se kinetična energija prenaša s plina na kapljevino in opazili mesta z lokalno povišanimi vrednostmi kinetične energije zraka.

• Language: Slovenian
• Keywords: mikro-curek, tokovno fokusiranje, numerični model, video analiza, premer, nestabilnosti, validacija
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FS - Faculty of Mechanical Engineering
• Place of publishing: Ljubljana
• Publisher: [K. Kovačič]
• Year: 2022
• Number of pages: XXVI, 100 str.
• PID: 20.500.12556/RUL-139611
• UDC: 004.942:519.876.5(043.2)
• COBISS.SI-ID: 120792835
• Publication date in RUL: 06.09.2022

KOVAČIČ, Krištof, 2022, Razvoj in eksperimentalna validacija tri-razsežnega numeričnega modela za napovedovanje značilnosti plinsko fokusiranih mikro-curkov [online]. Master’s thesis. Ljubljana : K. Kovačič. [Accessed 14 April 2025]. Retrieved from: https://repozitorij.uni-lj.si/IzpisGradiva.php?lang=eng&id=139611

Secondary language

• Language: English
• Title: Development and experimental validation of a 3D numerical model for prediction of gas-focused micro-jets characteristics

Abstract

In the Master thesis, we designed a three-dimensional numerical model for predicting twophase flows that occur in gas-focused micro-jets of water-air. A mixture formulation is used to describe the incompressible, Newtonian flow of water and focusing air, including a k-ω SST turbulence model to ensure numerical stability. The numerical solution procedure is based on the finite volume method with the volume of fluid method, which includes the geometric reconstruction of the free surface. With appropriately chosen boundary and initial conditions, such a model enables accurate, reproducible, mesh-independent and stable numerical simulation of pressure and velocity fields. The numerical model is validated with the results of measurements on a vertical, downward-positioned nozzle configuration. We have developed a dedicated computer program to analyse the characteristic parameters of micro-jets from experimentally obtained videos and numerical animations. The Reynolds numbers of air and water in the numerical simulations are in the range 1009–2421 and 48–104, and the Weber number 0.57–3.0. Identical shapes of micro-jets are observed in experimental videos and also in numerical animations for the same combination of air and water volumetric flow rates. The model predicts well the average and local diameters of the micro-jet. We have also analysed the temporal development of the jet breakup due to instabilities. We have checked how the kinetic energy is transferred from the gas to the liquid and noticed spots with locally increased values of the kinetic energy of the air.

• Keywords: micro-jet, flow focusing, numerical model, video analysis, diameter, instability, validation