Abstract:
Due to a relative high thermal efficiency, the gas turbine engine has wide ranging applications in various industries today. The aerospace and power generation sectors are probably the best known. One method of increasing the thermal efficiency of a gas turbine engine is to increase the turbine inlet temperature. This increase in temperature will result in an additional thermal load being placed on the turbine blades and in particular the nozzle guide vanes. The higher temperature gradients will increase the thermal stresses. In order to prevent failure of blades due to thermal stresses, it is important to accurately determine the magnitude of the stresses during the design phase of an engine. The accuracy of the thermal stresses mainly depends on two issues. The first is the determination of the heat transfer from the fluid to the blade and then secondly the prediction of the thermal stresses in the blade as a result of the thermal loading. In this study the flow and heat transfer problem is approached through the use of computational fluid dynamics (CFD). The principal focus is to predict the heat transfer and thermal stresses for steady state cases for both cooled and uncooled nozzle guide vanes through numerical modelling techniques. From the literature, two studies have been identified for which experimental data was available. These case studies can therefore be used to evaluate the accuracy of using CFD to simulate the thermal loading on the blades. One study focused only on solving heat transfer whilst the other included thermal stress modelling. The same methodology is then applied to a three-dimensional application in which flow and heat transfer was solved for a nozzle guide vane of a commercial gas turbine engine. The accuracy of results varied with the choice of turbulence model but was, generally within ten percent of experimental data. It was shown that the accurate determination of the heat transfer to the blade is the key element to accurately determine the thermal stresses.
