Blok-spregnuti algoritam za dvo-jednadžbene modele turbulencije

master's thesis

• Title (english): Block-Coupled Solution Algorithms for 2-equation Turbulence Models
• Author: Robert Keser
• Mentor: Hrvoje Jasak (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2016-03-25, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering; Process Energy Engineering
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Basic Technical Sciences; Fluid Mechanics

Abstract

Korištenje modernih implictno spregnutih algoritama za povezivanje jednadžbi brzine i tlaka dovelo je do znatno brže konvergencije rješenja u usporedbi s tradicionalnim odvojenim algoritmima. Prilikom simulacije turbulentnih strujanja spregnutim rješavačima brzine i tlaka konvergenciju rješenja često ograničava odvojeno rješavanje jednadžbi modela turbulencije, stoga se u ovom radu razmatra implicitno sprezanje dvojednadžbenih modela turbulencije.
Prije implementacije implicitno spregnutih dvojednadžbenih modela turbulencije, nužno je provesti linearizaciju nelinearnih izvorskih i ponorskih članova te analizu stabilnosti i pozitivnosti produkata linearizacije. Prikazuju se linearizacija i implementacija dvojednadžbenih modela turbulencije k-epsilon i k-omega SST unutar foam-extend (OpenFOAM-ova inačica koju razvija zajednica) softverskog paketa.
Validacija implementiranih modela turbulencija provodi se na dva poznata slučaja strujanja za koja su dostupna eksperimentalna mjerenja: odvojeno nestlačivo strujanje oko NACA 4412 aeroprofila pri maksimalnom uzgonu te nestlačivo strujanje u kanalu s naglim proširenjem. Validacija k-omega SST modela turbulencije provodi se na oba slučaja strujanja, dok se k-epsilon model validira samo na strujanju unutar kanala.
Također se uspoređuju performanse implementiranih implicitno spregnutih modela s odgovarajućim postojećim odvojenim inačicama modela turbulencija. Slično kao i prilikom validacije, usporeba k-omega SST modela provodi se na oba slučaja strujanja, dok se k-epsilon model uspoređuje samo na slučaju strujanja unutar kanala.

Abstract (english)

Modern implicitly coupled pressure–velocity algorithms introduced a considerable increase in the convergence rates when compared with segregated algorithms. Although, segregated treatment of turbulence model equations often limits such algorithms from reaching their full potential. Hence, implicit coupling of two-equation turbulence models is investigated.
In order to implement the implicitly coupled turbulence models in the block-matrix framework, it is necessary to linearise the non-linear source and sink terms. The linearised sources and sinks also need to undergo the stability and boundedness analysis. Linearisation and implementation of two-equation turbulence models, k-epsilon and k-omega SST, in foam-extend (the community-driven fork f the OpenFOAM) software is presented.
Validation of implemented turbulence models is performed. The two validation cases are: a separated flow past a NACA 4412 airfoil at maximum lift and an incompressible turbulent flow over a backward facing step. Validation of the implicitly coupled k-omega SST model is performed for both cases, whereas validation of the implicitly coupled k-epsilon model is performed only for the backward facing step case.
Finally, performance of implemented turbulence models is compared with existing segregated models. Benchmarking is performed on the two validation cases. Similarly as for the validation, both implemented turbulence models are benchmarked on the backward facing step case and only the k-omega SST is benchmarked on the NACA 4412 case.

• Keywords: CFD; OpenFOAM; foam-extend; modeliranje turbulencije; k-epsilon; k-omega SST; blok-matrica; implicitno sprezanje; linearizacija; validacija; mjerenje performansi
• Keywords (english): CFD; OpenFOAM; foam-extend; turbulence modelling; k-epsilon; k-omega SST; block-matrix; implicit coupling; linearisation; validation; benchmarking
• Language: croatian
• URN:NBN: urn:nbn:hr:235:410634
• Study programme: Title: Mechanical Engineering; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra inženjer/inženjerka strojarstva (magistar/magistra inženjer/inženjerka strojarstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2019-05-28 10:19:49