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V magistrskem delu so predstavljeni rezultati simulacij turbulentnega toka v cevi s kolenom. Simulacije smo izvedli s programom za računalniško dinamiko tekočin OpenFOAM. Uporabili smo metodo velikih vrtincev, predstavili pa smo tudi osnovno idejo direktne numerične simulacije. Simulacije smo izvedli na superračunalniku Vega za tok s tremi različnimi Reynoldsovimi števili in sicer z 1400, 5600 in 10000. V simulacijah smo predpostavili, da je tok nestisljiv in da je tekočina Newtonska. Za tokove z različnimi Reynoldsovimi števili smo uporabili različno goste računske mreže. Kvaliteto mrež in točnost simulacij smo preverili s primerjavo enodimenzionalnih profilov povprečne hitrosti in fluktuacij iz naših simulacij z rezultati direktne numerične simulacije. Posebej nas je zanimal vpliv kolena na simetrijo toka za kolenom. V ta namen smo vpeljali parameter asimetrije hitrosti, ki smo ga izračunali za vse obravnavane tokove. Primerjali smo odvisnosti parametra asimetrije vzdolž cevi za vse tokove. Analogno smo naredili še s fluktuacijami hitrosti. Primerjali smo odvisnosti parametra asimetrije fluktuacij vzdolž cevi za različne tokove. Propagacijo asimetrije v toku smo nato ocenili še z vpeljavo parametrov asimetrije strižne napetosti na steni cevi in velikosti vrtinčnosti. Pokazali smo, da turbulentni tok v cevi pozabi na vpliv kolena, ko preteče približno 40 premerov cevi. V laminarnem toku, kjer koleno ustvari turbulenco, pa je ta razdalja precej daljša. In this master thesis the results of turbulent flow simulations in pipe with a bend are presented. Simulations were conducted using OpenFOAM, a code for computational fluid dynamics. We conducted large eddy simulation, however basic idea of direct numerical simulation is also presented. We simulated flows with different Reynolds numbers, namely with 1400, 5600 and 10000. We assumed incompressible flow of Newtonian fluid. We used different computational meshes for flows with different Reynolds number. Quality of meshes and accuracy of simulations was checked by comparing one dimensional profile results from our simulations with results from direct numerical simulations. We were especially interested in effect of the pipe bend on simmetry of the flow after the bend. For that reason we introduced a velocity asymmetry parameter, which we calculated for all considered flows. We compared asymmetry parameter dependency along the pipe for all flows. The same comparison was performed for the velocity fluctuations. We also compared fluctuations asymmetry parameter dependency along pipe for all flows. We then evaluated asymmetry of the flow with introduction of asymmetry parameters of wall shear stress and vorticity magnitude. Lastly we compared results of different parameters. |
