Gas turbine design has been characterized over the years by a continuous increase of the maximum cycle temperature, justified by a corresponding increase of cycle efficiency and power output. In such way turbine components heat load management has become a compulsory activity and then, a reliable procedure to evaluate the blades and vanes metal temperatures, is, nowadays, a crucial aspect for a safe components design. This two part work presents a three-dimensional conjugate heat transfer procedure developed in the framework of an internal research project of GE Oil & Gas. The procedure, applied to the first rotor blade of the MS5002E gas turbine, consists in a decoupled analysis in which the internal cooling system was modeled by an in-house one dimensional thermo-fluid network solver, the external heat loads and pressure distribution have been evaluated through 3D CFD and the heat conduction in the solid is carried out through a 3D FEM solution. The second part of this work is focused on the improvement of external heat loads prediction through the use of a full featured geometry of the blade. In particular a detailed representation of the rim seal is accounted for as well as the actual geometry of the squealer tip. A new set of conjugate results is compared with temperature obtained by metallographic analysis, pointing out the relevant effect of the actual endwall contour on the metal temperature distribution at low spans of the blade.
Due to the stringent cooling requirements of novel aeroengines combustor liners, a comprehensive understanding of the phenomena concerning the interaction of hot gases with typical coolant jets plays a major role in the design of efficient cooling systems. In this work an aerodynamic analysis of the effusion cooling system of an aero-engine combustor liner was performed; the aim was the definition of a correlation for the discharge coefficient (CD) of the single effusion hole. The data was taken from a set of CFD RANS simulations, in which the behavior of the effusion cooling system was investigated over a wide range of thermo fluid-dynamics conditions. In some of these tests, the influence on the effusion flow of an additional air bleeding port was taken in account, making possible to analyze its effects on effusion holes CD. An in depth analysis of the numerical data set has pointed out the opportunity of an efficient reduction through the ratio of the annulus and the hole Reynolds numbers: the dependence of the discharge coefficients from this parameter is roughly linear. The correlation was included in an in-house one dimensional thermo-fluid network solver and its results were compared with CFD data. An overall good agreement of pressure and mass flow rates distributions was observed. The main source of inaccuracy was observed in the case of relevant air bleed mass flow rates, due to the inherent three-dimensional behavior of the flow close to bleed opening. An additional comparison with experimental data was performed in order to improve the confidence in the accuracy of the correlation: within the validity range of pressure ratio in which the correlation is defined (> 1.02), this comparison pointed out a good reliability in the prediction of discharge coefficients. An approach to model air bleeding was then proposed, with the assessment of its impact on liner wall temperature prediction.
Gas turbine design has been characterized over the years by a continuous increase of the maximum cycle temperature, justified by a corresponding increase of cycle efficiency and power output. In such way turbine components heat load management has become a compulsory activity and then, a reliable procedure to evaluate the blades and vanes metal temperatures, is, nowadays, a crucial aspect for a safe components design. This two part work presents a three-dimensional conjugate heat transfer procedure developed in the framework of an internal research project of GE Oil & Gas. The procedure, applied to the first rotor blade of the MS5002E gas turbine, consists of a conjugate heat transfer analysis in which the internal cooling system was modeled by an in-house one dimensional thermo-fluid network solver, the external heat loads and pressure distribution have been evaluated through 3D CFD and the heat conduction in the solid is carried out through a 3D FEM solution. The first part of this work is focused on the description of the procedures in terms of set up of the equivalent fluid network model of internal cooling system and its tuning through experimental measurements of blade flow function. A first computation of blade metal temperature was obtained by coupling with CFD computations carried out on a de-featured geometry of the blade. Achieved results are compared with the data of a metallographic analysis performed on a blade operated on an actual engine. Some discrepancies are observed between datasets, suggesting the necessity to improve the models, mainly from the CFD side.
One of the most critical parameters in the design process of cooled hot gas components, is the Back Flow Margin (BFM). This dimensionless parameter quantifies the margin to hot gas ingestion through a cooled component wall. A correct evaluation of this parameter is crucial in order to avoid component failure. In presence of combustion chambers that exhibit low pressure losses, BFM becomes one of the most restrictive requirements in the thermal design of cooled components. In this work, a conceptual BFM assessment of the first nozzle of an HP gas turbine is described. The component is subject to the highest thermal load; complex cooling systems are required to ensure an acceptable metal temperature and to match life time requirement. Due to manufacturing tolerances and fluid dynamic uncertainties, hot gas ingestion events are possible also for a nozzle that exhibits BFM higher than zero in nominal conditions, even if with a low probability. Here, the cooling scheme of the nozzle is modeled using an in-house fluid network tool that allows a quick and accurate computation of the equivalent cooling scheme and thus the occurrence of hot gas ingestion, corresponding to a negative flow rate in one of the cooling sub-models. However, as the probability of hot gas ingestion is rather small, an accurate estimation of this event based on the standard Monte Carlo method requires a huge number of runs. A more efficient estimation of this probability can be obtained using stochastic expansion methods, such as the Polynomial Chaos Expansion. Pseudospectral approximations based on either a tensor-product expansion or the Sparse Pseudospectral Approximation Method (SPAM) are used, in order to estimate the probability of hot gas ingestion and the sensitivity to random parameters. The results are compared with those coming from Monte Carlo method, showing the superior accuracy of the stochastic expansion methods.
This paper reports the results of an experimental campaign involving heat transfer measurements on the target surface of an impingement jet array. Test were performed with the help of an open loop wind tunnel test rig, housing a model of the cooling system. The model general layout consists of an impingement channel, designed as a straight duct with rectangular section. A side of the channel is a steel impingement plate, while the opposite side acts as the impingement target surface and is composed of an electrically heated Inconel sheet supported by a thin steel plate. The coolant flow is provided by a plenum located upstream the impingement plate. The combined use of an inverter controlled electric fan and four rotary vanes vacuum pumps allows air circulation inside the model. Convective heat transfer coefficient on the impingement target surface is evaluated through a steady-state technique. The temperature of the target surface is measured through IR thermography: the outer side of the target surface is painted with a high-emissivity black coating and is observed by an IR camera; the inner temperature is then obtained through a simple finite difference model of the target plate. In the present work, different impingement layouts were tested (3 ≤ Sx/d ≤ 10, 3 ≤ Sy/d ≤ 20, 2.5 ≤ H/d ≤ 3.33) for different values of jet Reynolds number (2000 ≤ Rej ≤ 19000). Heat transfer results show a good agreement with the existing correlations, thus providing a validation for the adopted measurement technique, and extend the investigation to holes pitch values outside from correlations.
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