| Sažetak | Kavitacija je prirodna pojava pare u struji kapljevine do koje dolazi zbog lokalnog pada tlaka, uzrokovanog efektima strujanja. Ona je štetna pojava koja narušava strukturu struje fluida, uzrokuje buku i vibracije, a može uzrokovati i oštećenja na strojnim elemen- tima. Zbog toga je od izrazitog interesa proučavanje nastanka, te predvidanje kavitacije, radi suzbijanja mogućih neugodnih posljedica. Sa modernim napredkom tehnologije, u tu svrhu se danas sve više koristi Računalna Dinamika Fluida (RDF).
Ovaj rad objašnjava moderno poimanje nastanka kavitacije, te predstavlja matematičke modele koji opisuju ponašanje pare i kapljevine u kavitirajućim strujama. Uz to, prikazuje načine na koji se ti modeli primjenjuju u RDF-u, te pojednostavljenja modela koja se moraju uzeti u obzir.
U sklopu rada su obavljene simulacije u foam-extend i OpenFOAM programskim pake- tima, u svrhu validacije kavitacijskih modela. Cilj rada je bio usporediti Schnerr-Sauer kavitacijski model, odnosno implementaciju istog u OpenFOAM-u, sa eksperimentalnim rezultatima.
U tu svrhu su izvedene dvije računalne mreže. Prva je 2D mreža u kojoj je prikazano NACA009 krilo s podrezanim izlaznim bridom i korištena je za 2D simulacije strujanja. Druga je 3D mreža u kojoj je prikazano Delft Twist 11 krilo, te je korištena za potpune 3D simulacije strujanja.
Tijekom rada je obavljeno sveukupno 12 simulacija, od toga 8 na 2D mreži i 4 na 3D mreži. Za svaku pojedinu brzinu strujanja odradile su se 4 simulacije. Simuli- rano je strujanje sa pojavom kavitacije i bez nje, te za svaki slučaj jedno strujanje sa modeliranjem turbulencije, te bez turbulencije. Rezultati simulacija su usporedeni sa eksperimantalnim rezultatima iz drugih radova.
Na kraju rada je dan osvrt na valjanost rezultata i trenutno stanje RDF istraživanja na području kavitacije. |
| Sažetak (engleski) | Cavitation is a natural occurrence of vapor in a flow of liquid, caused by a local drop in pressure. It is a harmful occurrence that disrupts the flow, causes noise and vibrations, and can even inflict structural damage to machine elements. For these reasons, the study of cavitation inception is of particular interest, as is the ability to anticipate cavitation and facilitate the design of engineering devices to avoid the harmful side effects. Thanks to the modern advancements in technology, today, Computational Fluid Dynamics (CFD), is being applied in cavitation research.
This thesis explains the current understanding of cavitation inception and presents the mathematical models that describe the behavior of the vapor and liquid phase in cavitating flows. In addition it shows the methods and simplifications, with which those models are used in CFD.
In the scope of this thesis, simulations were performed using foam-extend and OpenFOAM software packages, with the purpose of validating the cavitation models. The goal of the thesis was to compare the OpenFOAM implementation of the Schnerr-Sauer cavitation model with experimental results.
With that in mind, 2 reference geometries were selected. The first is a 2D mesh in which the NACA009 Truncated Hydrofoil is situated, and it was used for the 2D flow simulations. The second is a 3D geometry in which the Delft Twist 11 Hydrofoil is situated, and it was used for 3D flow simulations.
In this study, a total of 12 simulations was performed. Out of those, 8 were on the 2D mesh, and 4 on the 3D mesh. For each inlet velocity, 4 simulations were performed. Both cavitating and non-cavitating flow was simulated, and for each experimental setup, one simulation with turbulence modeling and one without. The results were compared to experimental research results.
At the end of the thesis, a brief review of the results and the current state of CFD cavitation research was given. |
