Computational fluid dynamics-modelling of a multi-stage transonic axial-flow compressor.

Nel, Philip (2017-12)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: This research originates from commercial interest in the numerical modelling of transonic axial compressors. The Darmstadt R-1/S-1 and NASA Stage-37 transonic stages are used as validation test cases using commercial (ANSYS® CFX®) and open-source (MULTALL-open) CFD software. Various turbulence models, including a transition model, are tested. The structure parameter of the SST γReθ model is calibrated to reduce over-predicted shock-induced boundary layer separation and to predict the correct separation behaviour on the Darmstadt stator. At the operating point, the numerical and experimental stage pressure ratio and efficiency for NASA Stage-37 differ by 0.8% and 0.3%, respectively (1.8% and 1.5% for the Darmstadt test case). Aspects of a specific multi-stage compressor, such as the effects of fillets and surface roughness are investigated. It was found that at certain shaft speeds, fillets restrained hub corner stall. Blade surface roughness has a greater effect on overall performance than endwall roughness due to for example, the outward migration of a thickened suction side boundary layer, which mixes with the tip leakage flow. The difference between transient and steady-state results is investigated. Inaccurate treatment of flow features at the mixing plane of a steady-state model gains significance in the modelling of multi-stage compressors. The mixing plane approximation leads to reduced hub corner stall at some blade rows and reduced entropy production by the tip clearance flow. Lastly, the ability of the MULTALL-open turbomachinery design suite of programs to be used for transonic axial compressor performance prediction is investigated. Good estimates could be obtained. The accuracy with which MULTALL resolves typical flow features of transonic axial compressors such as the tip clearance flow features, is found to be promising. It is concluded that MULTALL can be used for transonic axial compressor performance prediction.

AFRIKAANSE OPSOMMING: Hierdie navorsing ontstaan uit kommersiële belangstelling in die numeriese modelering van transsoniese aksiaalvloei kompressors. Die Darmstadt R-1/S-1 en NASA Stage-37 transsoniese kompressor stadiums word gebruik as toetsgevalle vir kommersiële (ANSYS® CFX®) en oopbron (MULTALL-open) berekeningsvloeimeganika sagteware. Verskillende turbulensie modelle word getoets, insluitende ’n turbulensie-oorgangsmodel. Die struktuur parameter van die SST - γReθ turbulensie model is gekalibreer om oorgeskatte skok-geïnduseerde grenslaag skeiding te verminder en om die korrekte wegbrekingsgedrag op die Darmstadt stator te voorspel. By die ontwerpspunt verskil die numeriese en eksperimentele drukverhouding en benuttingsgraad van die NASA Stage-37 toetsgeval met 0.8% en 0.3%, onderskeidelik (1.8% en 1.5% vir die Darmstadt toetsgeval). Aspekte van ’n spesifieke multi-stadium kompressor, soos die effekte van vulradiusse en oppervlakgrofheid word ondersoek. Daar is gevind dat by sekere as-snelhede, vulradiusse die naafhoek wegbreking verminder. Die grofheid van die lem se oppervlak het ’n groter effek op die algehele verrigting as die grofheid van die rand a.g.v. bv.; die uitwaartse migrasie van ’n verdikte grenslaag aan die laagdruk kant van die lem, wat met die lekvloei van die lempunt meng. Die verskil in resultate tussen tyd afhanklike en bestendigte modelle word ondersoek. Onakkurate hantering van die vloei kenmerke by die meng-tussenvlak van die bestendige model, word uitgelig in die modellering van multi-stadium kompressors. Die meng-tussenvlak benadering lei tot verminderde naafhoek wegbreking by party lemrye en verminderde entropie produksie by die lekvloei van die lempunt. Laastens word die vermoë van die MULTALL turbo masjienerie ontwerpsprogramme vir die gebruik van transoniese aksiaalvloei kompressor verrigtingsvoorspelling ondersoek. Goeie skattings kon verkry word. Die akkuraatheid waarmee MULTALL tipiese vloei eienskappe van transsoniese aksiaalvloei kompressors soos die lekvloei by die lempunt oplos, is belowend. Daarmee word afgelei dat MULTALL gebruik kan word vir die voorspelling van die verrigting van transsoniese aksiaalvloei kompressors.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107297
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