This paper presents two different numerical methods to predict the thermal load of a convection-cooled gas-turbine blade under realistic operating temperature conditions. The subject of the investigation is a gas-turbine rotor blade equipped with an academic convection-cooling system and investigated at a cascade test-rig. It consists of three cooling channels, which are connected outside the blade, so allowing cooling air temperature measurements. Both methods use FE models to obtain the temperature distribution of the solid blade. The difference between these methods lies in the generation of the heat transfer coefficients along the cooling channel walls which serve as a boundary condition for the FE model. One method, referred to as the FEM1D method, uses empirical one-dimensional correlations known from the available literature. The other method, the FEM2D method, uses three-dimensional CFD simulations to obtain two-dimensional heat transfer coefficient distributions. The numerical results are compared to each other as well as to experimental data, so that the benefits and limitations of each method can be shown and validated. Overall, this paper provides an evaluation of the different methods which are used to predict temperature distributions in convection-cooled gas-turbines with regard to accuracy, numerical cost and the limitations of each method. The temperature profiles obtained in all methods generally show good agreement with the experiments. However, the more detailed methods produce more accurate results by causing higher numerical costs.
This paper presents developing secondary flow and heat transfer measurements in a ribbed cooling channel. Experiments are carried out for Reynolds number ranging from 25,000–140,000. Regionally averaged local heat transfer measurements are conducted using heated copper segments. Flow measurements are carried out using a miniature five-hole pressure probe and presented for cross sections at intervals of 1.8 hydraulic diameters dh in flow direction. Results are compared to numerical simulations using explicit algebraic Reynolds stress and turbulent heat transfer models. The paper focuses on the entrance region where secondary flow structure has not emerged yet. The findings show that the well-known secondary flow structure of the crossed rib configuration, consisting of one large single rotating secondary flow, is not established until approximately 6–7 dh in main flow direction. Instead two opposed vortices are identified which dominate the flow characteristics and provide an increase in heat transfer of up to 15–20% when compared to the periodically developed flow condition. Thus, for the first time to the author’s knowledge, the paper describes in detail the developing secondary flow in a crossed rib arrangement and links it to the heat transfer distribution observed. In summary, this paper stresses the importance of the developing flow region for the design process in convection cooled gas turbines, especially for short channels of high pressure blades and vanes, as it has a significant effect on cooling channel heat transfer performance.
This paper presents different numerical methods to predict the thermal load of a convection cooled gas turbine blade under realistic operating temperature conditions. The subject of the investigation is a gas turbine rotor blade which is equipped with a state-of-the-art convection cooling system. Firstly, two FEM based methods are introduced. One method, referred to as FEM1D method, uses empirical correlations from the open literature to obtain one dimensional heat transfer coefficients along one flow line inside the cooling channels while in the hot gas path a three dimensional CFD simulation is used. The second method (FEM2D) uses three dimensional CFD simulations to obtain two dimensional heat transfer coefficient distributions for both, the inner cooling channels and the hot gas path. The results from both numerical methods are compared with each other and are validated with experimental data, quantifying also their accuracy limits. In total this paper gives an evaluation of two different FEM methods to predict temperature distribution in convection cooled gas turbines. Their accuracy, numerical cost and limitations are evaluated. It turns out that the temperature profiles gained by both methods are generally in good agreement with the experiments. However, while causing higher numerical costs the more detailed FEM2D method achieves more accurate results.
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