Dvosmjerno spregnuta Euler-Eulerova simulacija nošenja snijega metodom kontrolnih volumena

Boutanios, Ziad (2018) Dvosmjerno spregnuta Euler-Eulerova simulacija nošenja snijega metodom kontrolnih volumena. = Two-way coupled Eulerian-Eulerian finite volume simulation of drifting snow. Doctoral thesis , Sveučilište u Zagrebu, Fakultet strojarstva i brodogradnje, UNSPECIFIED. Mentor: Jasak, Hrvoje.

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Abstract (Croatian)

U ovom radu prikazan je Euler-Euler dvostrano spregnut model za simuliranje nošenja snijega i strujanja s česticama niske koncentracije. Turbulentna disprezija čestica modelirana je pomoću turbulentne viskoznosti, te je razvijen novi model viskoznosti nošenih čestica. Umjesto korištenja ravnotežne formulacije koju koriste jednostrano spregnuti modeli, u ovom radu koristi se transportni model koji razrješava saltacijski sloj. Implementacija je provedena u programu foam-extend, grani programa otvorenog koda OpenFOAM R . Validacija saltacije je provedena uspoređujući rezultate s eksperimentalnim mjerenjima kontroliranog nosećeg snijega s pravim česticama snijega. Predstavljani model točno predviđa protok snijega i brzinu protoka zraka u ravnotežnim i neravnotežnim režimima u slučaju kada je raznovrsnost veličina čestica uzet u obzir. Model precjenjuje kolčinu turbulentne kinetičke energije u odnosu na eksperimentalna ispitivanja, međutim eksperimentalni podatci ne sadrže sve energetske frekvencije. Validacija suspenzije je provedena usporedbom s mjerenjima gdje je provedena kontrolirana suspenzija sedimenta. Razvijeni model točno procjenjuje kontrakciju sedimenta i profil brzine vode uzduž eksperimentalnog bazena, kao i brzinu padanja sedimenta. Osim toga, razvijeni model se pokazao boljim od jednostrano spregnutog modela baziranog na ravnotežnoj formulaciji. Nadalje, razvijeni model može koristiti nepropusni rubni uvjet umjesto perforiranog dna, što ima samo lokalni utjecaj na rezultat. Jednostruko spregnuti modeli nisu u mogućnosti koristiti nepropustan rubni uvjet. Korištene zidnih funkcija također nije preporučljivo koristiti u takvim slučajevima, jer dolazi do proizvodnje vrtložnih struktura koje su različite od onih koje se mogu naći na perforiranom dnu. Razvijeni model viskoznosti točno predviđa viskoznog smjese u usporedbi s modelima u literaturi, te pokazuje fizikalnije rezultate. Prilikom gustog nošenog snijega, predlaže se korekcija udjela volumena snijega i konstantan koeficijent od 0.1 kako bi se poboljšao Kazhikov-Smagulov model viskoznosti čestica, te promjenjiva konstanta jednaka lokalnom udjelu volumena za Carrier-Cashwell model viskoznosti. Zbog odnosa gustoće čestica i fuida, turbulencija čestica modelirana pomoću Ct modela je zanemariva i usporediva turbulenciji vode prilikom sedimentacije.

Abstract

An Eulerian-Eulerian two-way coupled model for simulating drifting snow, and solid particle-laden ows, is presented. Turbulent drag is used to account for particles turbulent dispersion. A new solid particle phase viscosity model is also developed from rst principles. The present transport model resolves the saltation layer, instead of modelling it with equilibrium formulations as in one-way coupled models. Implementation is done in foam-extend, a community-driven fork of OpenFOAM R . Validation in saltation is done against measurements from a controlled drifting snow experiment using real snow particles. The present model accurately predicts snow ux and air ow velocity in equilibrium and non-equilibrium regimes, when particle size polydispersity is considered. The model overestimates experimental measurements of turbulent kinetic energy, with concerns over the completeness of the measurements. Validation in suspension is done against measurements from a controlled sediment suspension experiment. The present model accurately predicts sediment concentration pro les, water velocity pro les, and sediment fall velocity. The present model is also shown to be superior to a one-way coupled convection-diffusion model based on an equilibrium formulation. Finally, a non-perforated boundary condition used to represent perforated bottoms is found to have a localized e ect for the present model, and unsuitable for one-way coupled models. Using wall functions in such situations is also discouraged since it would produce turbulence structures very di erent from what is observed on perforated bottoms. A resolved low Reynolds number approach is recommended instead. The present viscosity model predicts mixture viscosity accurately, and more physically than published mixture viscosity models. In the dense drifting snow regime, a volume fraction correction and multiplicative constant of 0.1 are suggested to improve the Kazhikov-Smagulov particle viscosity model, and a variable constant equal to the local phase density ratio for the Carrier-Cashwell particle viscosity model. Particle turbulent viscosity modelled with the Ct model is found negligible for drifting snow, and comparable to water turbulent viscosity for sediment, due to phase density ratio.

Item Type: Thesis (Doctoral thesis)
Uncontrolled Keywords: Euler-Euler, noseći snijeg, transport sedimenta, saltacija, suspenzija, dvostrana sprega, turbulentni otpor, strujanja s česticama niske koncentracije, viskoznost krutih čestica
Keywords (Croatian): Eulerian-Eulerian, drifting snow, sediment transport, saltation, suspension, two-way coupling, turbulent drag, particle-laden flow, solid particle phase viscosity
Subjects: TECHNICAL SCIENCE > Mechanical Engineering
Divisions: 500 Department of Energy, Power Engineering and Environment > 530 Chair of Turbomachinery
Date Deposited: 21 Nov 2018 10:12
Last Modified: 06 Dec 2018 09:59
URI: http://repozitorij.fsb.hr/id/eprint/8898

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