Computations of an aero engine gas turbine combustor liner temperature using computational fluid dynamics and conjugate heat transfer methodology

In combustion chambers, gas temperatures occurring due to combustion are higher compared to the melting point of the combustor liner material. So during the combustor design various types of cooling procedures are used to keep the hot gases away from the liner. Nevertheless hot spots may occur over the liner as a result of unsteady behavior of the turbulent reacting flow. To locate the hot spots, the most reliable method is performing rig tests. However when the accessibility issues and the cost of the experimental study is considered, rig testing cannot be used intensively during the design process. Therefore Computational Fluid Dynamics (CFD) with Conjugate Heat Transfer (CHT) approach is utilized for liner temperature prediction. In this thesis study, it is aimed that liner temperatures of the combustor of a turbojet and a turboshaft engine are computed using CFD employing CHT. Firstly, a non-reacting, non-isothermal flow problem in a double pipe heat exchanger - which has less computational costs - is carried out as a preliminary study to investigate the physical and numerical CFD parameters. The wall temperature of the liner dividing the hot gas and cool air streams is calculated by two dimensional CFD analyses with CHT method and empirical correlations. The results obtained from Reynolds Averaged Navier-Stokes (RANS) based CFD analyses and the empirical correlations are well agreed. In addition, a turbulence model study is performed to determine an appropriate one for the CHT cases. Consequently the Realizable k-ɛ turbulence model is opted due to low computational cost and robustness. After that, turbojet engine combustor is analyzed for the atmospheric and the full load flight condition. For the atmospheric condition, the predicted and measured temperature values are compared and it is observed that the Hybrid Eddy Break Up (HEBU) combustion model and Realizable k-ɛ turbulence model produce results that are in more agreement with the measurements. For the full load flight condition, which has higher inlet temperature and operating pressure; higher wall temperatures than the ones computed for the atmospheric condition are observed as expected. It is known that flame characteristics can vary according to the operating conditions. To this respect, the highest temperature regions over the liner are observed in the dilution zone of the combustion chamber for the atmospheric condition and in the secondary zone for the full load flight condition. The highest wall temperature values for the atmospheric and the full load flight conditions are calculated as 1260 K and 1470 K respectively. Finally, the flame characteristics inside the turboshaft engine combustor which is straight-through flow are examined and liner temperatures are predicted. It is observed that the liner is cooled down to acceptable levels by the holes placed on the inner and outer sides. Since there are no cooling holes in the dilution zone, the hot combustion products, having temperature values about 1600 K, reside quite close to the wall. Therefore metal temperature values as high as 1420 K are seen in this region of the combustor.