The gas turbine has an important role for the energy distribution due to its stability and flexibility. By increasing turbine inlet temperature (TIT) an increased thermal efficiency of the turbine can be achieved. The biggest limitation of the TIT is the material of the turbine components. To avoid this limitation, cooling is needed in the first stages of the turbine by air from the compressor. The downside of the cooling is the decrease of efficiency with excess of cooling air. To achieve an optimum cooling flow, the designing process is important. One major tool in the designing process is simulations by Computational Fluid Dynamics (CFD). For optimum and correct cooling design, the CFD simulations needs to accurate predict the temperature transport through the turbine. Therefore, this study focused to estimate the accuracy of different CFD methods in predicting the temperature distribution through a 1.5 stage turbine with experimental results. The CFD simulations were done by using Ansys CFX and divided into two study cases with steady RANS. One with different turbulence models; –, Wilcox – and SST – . The other with two different simulation approaches of interfaces for frame change; Mixing plane and Frozen rotor. All simulations included two configurations of swirlers clocking for interest of their differences within the turbine and validation of the CFD simulations; Passage (PA) and Leading Edge (LE) clockings. The experimental results showed a formation of gradually more uniformed temperature profile with the fluid. This could not be seen in the same extend with any of the simulations. The temperature difference between the hot and cold section with all simulations were marginally decreased in comparison of the measurements. All results with steady RANS simulations tended to over and under predict the temperatures of the hot respectively cold sections within the fluid flow through the turbine. This occurred already after the first stage guide vanes and the difference from the measurements increased after the first stage rotor. This since the steady RANS tended to under predict the mixing process through the turbine. Differences between the turbulence models were noticeable after the rotor blades, where the – turbulence model predicted most mixing of the evaluated turbulence models but badly compared to the measurements. Another outcome from this study was that the frozen rotor interface with several positions of the rotor blades did not stated better results compared to mixing plane interface for temperature distribution in axial turbines. On the other hand, one simulation of one position of the rotor with frozen rotor interface could be used to simulate an approximatively similar circumferential average temperature as the mixing plane with better convergence with the disadvantage of bigger domain. The gas turbine has an important role for the energy distribution due to its stability and flexibility. By increasing turbine inlet temperature (TIT) an increased thermal efficiency of the turbine can be achieved. The biggest limitation of the TIT is the material of the turbine components. To avoid this limitation, cooling is needed in the first stages of the turbine by air from the compressor. The downside of the cooling is the decrease of efficiency with excess of cooling air. To achieve an optimum cooling flow, the designing process is important. One major tool in the designing process is simulations by Computational Fluid Dynamics (CFD). For optimum and correct cooling design, the CFD simulations needs to accurate predict the temperature transport through the turbine. Therefore, this study focused to estimate the accuracy of different CFD methods in predicting the temperature distribution through a 1.5 stage turbine with experimental results. The CFD simulations were done by using Ansys CFX and divided into two study cases with steady RANS. One with different turbulence models; –, Wilcox – and SST – . The other with two different simulation approaches of interfaces for frame change; Mixing plane and Frozen rotor. All simulations included two configurations of swirlers clocking for interest of their differences within the turbine and validation of the CFD simulations; Passage (PA) and Leading Edge (LE) clockings. The experimental results showed a formation of gradually more uniformed temperature profile with the fluid. This could not be seen in the same extend with any of the simulations. The temperature difference between the hot and cold section with all simulations were marginally decreased in comparison of the measurements. All results with steady RANS simulations tended to over and under predict the temperatures of the hot respectively cold sections within the fluid flow through the turbine. This occurred already after the first stage guide vanes and the difference from the measurements increased after the first stage rotor. This since the steady RANS tended to under predict the mixing process through the turbine. Differences between the turbulence models were noticeable after the rotor blades, where the – turbulence model predicted most mixing of the evaluated turbulence models but badly compared to the measurements. Another outcome from this study was that the frozen rotor interface with several positions of the rotor blades did not stated better results compared to mixing plane interface for temperature distribution in axial turbines. On the other hand, one simulation of one position of the rotor with frozen rotor interface could be used to simulate an approximatively similar circumferential average temperature as the mixing plane with better convergence with the disadvantage of bigger domain. / Gasturbinen har en viktig roll i nutida och framtida energidistribution för elektricitet på grund av dess stabilitet samt flexibilitet. Genom att öka temperaturen in till turbinen ökar den termiska effektiviteten. Den största begränsning av denna temperaturökning är materialen av komponenterna i turbinen. För att kringgå detta används kylning i turbinen med luft från kompressorn. Effektiviteten kan däremot minskas vid överdriven användning av kylluft och därav är designen av kylningen viktig för optimal användning av kylluft. Ett verktyg som oftast används vid design av turbiner är simuleringar med Computational Fluid Dynamics (CFD). För att uppnå en optimal design av kylningen behöver CFD simuleringarna korrekt prediktera temperaturtransporten genom turbinen. Därför fokuserade denna studie på att uppskatta och validera olika CFD metoders förmåga att prediktera temperaturtransporten genom en 1,5 stegs axiell turbin med experimentella resultat. Stationära CFD simuleringar gjordes med RANS av olika turbulensmodeller; k – ε, Wilcox k – ω and SST k – ω. Dessutom jämfördes två olika sätt att simulera gränssnittet mellan stationära och roterande domän; Mixing plane och Frozen rotor. Samtliga simuleringsmetoder inkluderade två olika konfigurationer av virvlarepositioner; Passage (PA) och Leading edge (LE) klockningar. Experimentella resultat visade en stegvis mer enhetlig temperaturprofil med fluidflödet genom turbinen. Detta sågs dock inte i samma utsträckning i någon av simuleringarna. Temperaturskillnaden mellan de varma och kalla stråken i samtliga simuleringar minskade marginellt i jämförelse med de experimentella resultaten. Samtliga resultat med stationära RANS simuleringar tenderade att över och under prediktera temperaturen av de varma respektive kalla stråken. Detta inträffade redan efter förstastegsledskenorna, där skillnaden från de uppmätta temperaturerna ökade över första stegs rotor. Detta på grund av att mixningen i fluiden under predikterades. Skillnader mellan de olika turbulensmodellerna var synliga efter första stegs rotor där – turbulensmodell predikterade mest mixning av samtliga simuleringar av turbulensmodeller. Däremot predikterade den marginellt bättre i jämförelse med mätningarna. Andra resultat från denna studie var att gränssnittet med frozen rotor med flera positioner inte anger bättre mixning av fluiden genom rotordomänen än vad gränssnittet med mixing plane där liknande radiella temperaturprofiler fås. Däremot gav en simulering med en position av rotorn liknande resultat med radiellt fördelade temperaturer som mixing plan och skulle kunna användas för approximativa simuleringar med bättre konvergens.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:kau-68634 |
| Date | January 2018 |
| Creators | Hallbäck, Ellen |
| Publisher | Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013) |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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