Ispitivanje inačica poboljšanih funkcija zida u simulaciji turbulentnog strujanja

Šutalo, Filip (2017) Ispitivanje inačica poboljšanih funkcija zida u simulaciji turbulentnog strujanja. = Evaluation of variants of enhanced wall treatment wall function in turbulent flow simulations. Master's thesis (Bologna) , Sveučilište u Zagrebu, Fakultet strojarstva i brodogradnje, UNSPECIFIED. Mentor: Jasak, Hrvoje.

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Abstract (Croatian)

Ovaj rad prikazuje implementaciju i rezultate simulacija za zidne funkcije za modele turbulencije s dvije transportne jednadžbe. Fokus je na ispitivanju zidnih funkcija primjerenih u uvjetima neravnotežnog turbulentnog graničnog sloja za koje standardne zidne funkcije izvedene iz zakona zida nisu prikladne. Iako se rad primarno fokusira na zidne funkcije, za dublje razumijevanje problema nužno je poznavati principe o modeliranju turbulencije. Iz tog razloga, istaknuti su osnovni koncepti pri izvodenju zakona zida. Izrazito važno svojstvo, koje definira postupanje s rubnim uvjetima na zidu, je asimptotska konzistentnost modela turbulencije, koja je ukratko pojašnjena. Generalna metodologija specificiranja rubnih uvjeta na zidu je objašnjena, te su dani izvodi matematičkih izraza za svaku metodu. Tretman rubnih uvjeta na zidu za k − ω SST model temeljen na izrazu za neravnotežni turbulentni granični sloj [1] izveden je detaljno i vodi k zaključku da uključivanjem konvektivnih članova u izraze može dovesti do poboljšanja u točnosti. Prikazane zidne funkcije, ugradene su u foam-extend i usporedeni sa standardnim zidnim funkcijama za dva slučaja: opstrujavanje NACA4412 aeroprofila i opstrujavanje rotacijskog elipsoida. Zaključeno je da odredeni tretmani rubnih uvjeta na zidu nude prednost nad trenutačno korištenima u foam-extendu, no i da je potrebna daljnja analiza utjecaja gradijenta tlaka i konvektivnih članova.

Abstract

This work presents several treatments of the wall boundary conditions for RANS turbulence models. The focus is the investigation of wall functions suitable for non-equilibrium conditions where the standard wall functions derived from the law-of-the-wall are known to fail. Although the thesis focuses on wall treatments, for deeper understanding of the problem, knowledge of turbulence modelling is essential. Therefore some key concepts are outlined through a derivation of the law-of-the-wall. Also, analytical solutions for the k − ε and k − ω SST model for near-wall regions are given. A property, which defines the treatment of the wall boundary condition, is the asymptotic consistency of turbulence model which is briefly discussed. A general methodology for specifying the wall boundary condition is explained and expressions for each method are presented in detail. Wall treatment for the k − ω SST model based on pressure sensitised law-of-the-wall [1] is derived in detail and leads to a conclusion that including the convective terms in expressions could improve accuracy. The wall treatments are implemented in foam-extend and compared with standard wall func- tions on two test cases: flow past the NACA4412 aerofoil and the 6:1 prolate spheroid. A conclusion is reached that certain wall treatments offer an advantage over standard ones implemented in foam-extend, although it is emphasised that further investigation on the effects of pressure gradient and convective terms should be conducted.

Item Type:	Thesis (Master's thesis (Bologna))
Uncontrolled Keywords:	CFD; foam-extend;modeliranje turbulencije;k − ε zidne funkcije;k − ω SST tretman rubnih uvjeta na zidu; NACA4412; rotacijski elipsoid
Keywords (Croatian):	CFD;foam-extend;turbulence modelling;k − ε wall functions;k − ω SST wall;treatments;NACA4412;prolate spheroid
Subjects:	TECHNICAL SCIENCE > Mechanical Engineering > process energy engineering
Divisions:	500 Department of Energy, Power Engineering and Environment > 530 Chair of Turbomachinery
Date Deposited:	27 Mar 2017 08:58
Last Modified:	03 Apr 2017 12:04
URI:	http://repozitorij.fsb.hr/id/eprint/7620

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