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Title:Numerični model robnih elementov za nestacionarne turbulentne tokove
Authors:Lupše, Janez (Author)
Škerget, Leopold (Mentor) More about this mentor... New window
Ravnik, Jure (Co-mentor)
Files:.pdf DR_Lupse_Janez_2013.pdf (27,34 MB)
 
Language:Slovenian
Work type:Dissertation (m)
Typology:2.08 - Doctoral Dissertation
Organization:FS - Faculty of Mechanical Engineering
Abstract:V doktorski disertaciji obravnavamo razvoj numeričnega algoritma za reševanje turbulentnih tokov, osnovanega izključno na metodi robnih elementov (MRE). Rešujemo Navier-Stokesov sistem enačb, zapisan v hitrostno-vrtinčnem zapisu. Sestavljen je iz enačb kinematike toka, s katerimi poiščemo neznane vrednosti vrtinčnega polja na robu območja reševanja in neznane vrednosti hitrostnega polja v območju, ter enačb kinetike vrtinčnosti, temperature in modelov turbulence. Enačba, s katero poiščemo vrednosti vrtinčnega polja na robu območja, je diskretizirana s standardno, enoobmočno MRE, vse ostale enačbe pa so zapisane v diskretni obliki s pomočjo MRE s podobmočji, kar omogoča velike prihranke pri računalniškem spominu. Ker je v večini realnih primerov turbulentnih tokov nepraktično ali celo nemogoče direktno reševati Navier-Stokesov sistem enačb, ga poenostavimo. V delu obravnavamo predvsem poenostavitev vodilnih enačb s pomočjo Reynoldsovega povprečenja (RANS). Z ohranitvijo lokalnega časovnega odvoda prenosnih spremenljivk časovno povprečenje omejimo na določen časovni interval ter tako dobimo neastacionarne-RANS enačbe (URANS). Razviti algoritem smo preverili na testnih primerih, katerih analitične rešitve poznamo. Naslednji korak je bil preračun laminarnih tokov, kjer smo izračunali tok v kanalu, tok v gnani kotanji in naravno konvekcijo v zaprti kotanji. Na koncu smo izračunali še vrsto turbulentnih tokov: turbulentni tok v kanalu, turbulentni tok preko stopnice v kanalu, turbulentni tok v kanalu s periodičnimi zožitvami in tok v kanalu s kvadratno oviro. Z naštetimi primeri smo potrdili pravilnost razvitega numeričnega algoritma in implementacije modelov turbulence, tako za časovno povprečene kot tudi nestacionarne izračune turbulentnega toka.
Keywords:metoda robnih elementov, hitrostno vrtinčen zapis, Reynoldsovo povprečene enačbe, modeli turbulence, nestacionarni tok, računalniška dinamika tekočin
Year of publishing:2012
Publisher:J. Lupše]
Source:[Maribor
UDC:532.527:519.61/.64(043.3)
COBISS_ID:266064640 Link is opened in a new window
NUK URN:URN:SI:UM:DK:FPT67B65
Views:1653
Downloads:104
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Categories:KTFMB - FS
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Secondary language

Language:English
Title:NUMERICAL MODEL OF NON-STATIONARY TURBULENT FLOWS BY BOUNDARY ELEMENT METHOD
Abstract:This work focuses on a development of the numerical algorithm for solving turbulent flows, based solely on the boundary element method. The Navier-Stokes system of equations is solved in velocity-vorticity form. This formulation is comprised of kinematics equations for unknown boundary vorticity field values and unknown domain velocity values, and kinetics equations for vorticity field, temperature field and turbulence models. Kinematics equation for unknown boundary vorticity values is discretized by the standard, single-domain boundary element method. All other equations are written in discrete form by sub-domain boundary element method, since this approach leads to large savings in computer memory and CPU time. Since it is for most cases of turbulent flows impractical or even impossible to solve the Navier-Stokes system directly, it has to be simplified. In this work, we are focusing mostly on simplification of governing equations by Reynolds averaging (RANS). With conservation of local time derivative of transport variables, time average is limited on single time interval, what leads to so called unsteady RANS (URANS). The developed algorithm was tested on various test cases with known analytical solutions. Furthermore it was used to calculate laminar flows, such as channel flow, driven cavity flow and natural convection in closed cavity. Finally we calculated various turbulent flows; turbulent channel flow, turbulent flow over backward facing step, turbulent flow over periodic hills channel and turbulent flow in a channel with square obstacle. Results from simulations confirmed the validity of the developed numerical algorithm and implementation of turbulence models for stationary and non-stationary turbulent flows.
Keywords:boundary element method, velocity-vorticity, Reynolds averaged equations, turbulence models, non-stationary flow, computational fluid dynamics


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