Numerički proračun performansi rotora NASA 67

Žužul, Josip (2017) Numerički proračun performansi rotora NASA 67. = Numerical evaluation of the performance curve for the NASA Rotor 67. Master's thesis (Bologna) , Sveučilište u Zagrebu, Fakultet strojarstva i brodogradnje, UNSPECIFIED. Mentor: Jasak, Hrvoje.

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Abstract (Croatian)

Računalna dinamika fluida danas je neizostavni segment analize kompleksnih strujanja fluida, kako za industrijske, tako i za akademske svrhe. Kako bi se povećala primjenjivost numeričkih kodova za rješavanje širokog spektra problema moderne fizike, potrebno je razvijati nove formulacije kodova koje se potom validiraju na velikom broju testnih simulacija s poznatim detaljnim eksperimentalnim podacima. U sklopu ovog rada, testirana je nova formulacija numeričkog koda za stlačivo, turbulentno strujanje u rotirajućim turbostrojevima, implementirana u sklopu softverskog paketa foam-extend. Za probleme s izraženim transoničnim i kompresibilnim karakterom strujanja u turbostrojevima, često korišten testni primjer je aksijalni NASA Rotor 67 turboventilator zbog dostupnosti detaljnih eksperimentalnih podataka od NASA-e. Kako bi se provela numerička simulacija NASA Rotora, potrebno je prethodno izraditi 3D model NASA Rotor 67 turboventilatora, te izraditi mrežu konačnih volumena. 3D CAD model turboventilatora izrađen je u softverskom paketu SolidWorks. CAD model je temelj sljedeće faze, a to je izrada prostorno diskretizirane mreže konačnih volumena u softverskom paketu Pointwise. Zbog činjenice da NASA Rotor 67 turboventilator ima 22 rotorske lopatice, analiziran je jedan međulopatični prolaz s namjerom reduciranja računalnih resursa.Uobičajena metoda je korištenje posebnog periodičkog rubnog uvjeta koji zahtijeva konformne periodičke mreže. Kako zbog velikog uvijanja lopatice po visini, tako i zbog zahtjeva konformne mreže na periodičnim granicama, izrađena mreža je često nedovoljne kvalitete. Stoga je u svrhu izbjegavanja mreže loše kvalitete i provedbe simulacije u jednom međulopatičnom prolazu, korišteno tzv. General Grid Interface (GGI) sučelje unutar softverskog paketa foam-extend. GGI sučelje omogućava korištenje nekonformnih mreža na periodičkim granicama kako bi se prevladali problemi neadekvatne mreže u međulopatičnim prolazima.Kako bi se izradila radna karakteristika NASA Rotora na nominalnoj brzini vrtnje, potrebno je provesti veći broj numeričkih simulacija. Rezultati su prezentirani u vidu grafičkih prikaza fizikalnih veličina na različitim presjecima unutar domene. Prezentirane su i globalne karakteristike poput snage, iskoristivosti, masenog protoka i omjera totalnog tlaka.Dodatno je dan kratak pregled osnovnih principa rada turbokompresora i turboventilatora uz osvrt na ograničenja za stabilan režim rada. Prikazan je i kratak pregled čestih nestabilnosti koje se pojavljuju prilikom strujanja u turbokompresorima. Cjelokupni rad zaokružen je prikazom korištene formulacije matematičkog modela za numeričko rješavanje kompleksnih režima strujanja kao što je stlačivo, turbulentno i transonično strujanje u turbostrojevima.

Abstract

Computational Fluid Dynamics (CFD) is nowadays frequently used for the analysis of complex fluid flows for industrial and academic purposes. In order to improve and expand CFD codes which are capable of solving wide range of physical phenomena, new code formulations have to be developed and validated on a large number of test cases with comprehensive experimental data. Within this thesis, a new formulation of compressible, turbulent flow solver for rotating turbomachinery, implemented in open-source CFD package foam-extend is tested. For problems of emphasized transonic and compressible character of a flow in rotating turbomachinery, commonly used test case is a transonic NASA Rotor 67 axial-flow turbofan, due to the availability of detailed experimental data provided by National Aeronautics and Space Administration (NASA). In order to perform numerical simulations of the NASA Rotor 67, a case needs to be prepared within the preprocessing steps which include geometry and mesh generation. As a first step, geometry in terms of 3D Computer Aided Design (CAD) model is generated using a Solidworks CAD software. The created CAD model is a basis for the second step - generation of a spatially discretised grid of finite volumes, which was done using a meshing software Pointwise. Since NASA Rotor 67 turbofan has 22 equally spaced blades, only one blade passage is examined in order to reduce computational cost. This can be done by using a special, cyclic and periodic boundary condition which require identical cyclic mesh boundaries. Because of highly twisted rotor blades and cyclic boundary condition requirement, generated mesh is commonly of insufficient quality. Thus, to avoid bad mesh quality and to carry out a simulation for a single blade passage, the General Grid Interface (GGI) is used within the foam-extend CFD package. GGI allows the use of the non-conformal mesh boundaries in order to overcome grid quality issues. After successfully accomplished preprocessing steps, a number of numerical simulations is performed with the so-called "frozen rotor" approach in order to assemble a performance curve for NASA Rotor 67 turbofan at the nominal angular velocity. Results are presented in terms of graphical representations of flow field quantities at various sections of the domain. Furthermore, overall computed turbofan characteristics like power, efficiency, mass flow and total pressure ratio are also shown. Additionally, a basic working principle of turbocompressors and turbofans is presented along with the restrictions for stable operating range. Furthermore, an overview of common instabilities which occur in turbocompressors is also given. Finally, the adequate formulation of a CFD model capable of solving turbulent, transonic and compressible flow is presented.

Item Type: Thesis (Master's thesis (Bologna))
Uncontrolled Keywords: CFD; foam-extend; Transonični turboventilator; NASA Rotor 67; Generiranje mreže konačnih volumena; 3D CAD modeliranje
Keywords (Croatian): CFD; foam-extend; Transonic Turbofan; NASA Rotor 67; Mesh Generation; CAD Generation
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 12:22
Last Modified: 03 Apr 2017 12:05
URI: http://repozitorij.fsb.hr/id/eprint/7621

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