Influence of Cooling Flow Rate Variation on Gas Turbine Blade Temperature Distributions

Abstract

Temperature and flow rate of combustion gases and cooling stream are essential conditions for blade integrity in gas turbines. Since the combustion products pass directly to the first stage of blades high thermal stresses can develop, so the temperature field in the blade material must be controlled to avoid damage and/or reduction of blade useful life. This paper discusses an investigation on the influence of cooling airflow reduction on blade life. The flow rate reduction under consideration may be due to malfunctions of the compressor such like deposits or partial blockage in the blade ducts. It has been reported that air discharge from the compressor can be reduced up to 15% of the nominal rate due to deposits related with impurities contained in the environment. In this work an evaluation of the effect of reducing the cooling airflow rate on the temperature distribution on the blades surface is attempted. The flow stream that surrounds the blade together with the cooling airflow in the blade interior channels were characterized in the laboratory. Fields of temperature on the blade surface were obtained using the temperature sensitive paint technique, TSP. Thermocouple measurements were used for punctual temperatures as a reference. The results showed the regions of possible thermal stresses concentration as a function of cooling airflow rate variations. Additionally, the problem was resolved computationally in conjugate mode, considering both fluid streams external and internal plus heat conduction at the interior of the blade material. The computer model is used to simulate other conditions not addressed in the experiment. The paper discusses the comparison of numerical to experimental results and discusses the methodology for further work.