Application of a Conjugate Fluid Flow and Heat Transfer Method in the Thermal Design Process of a Convection-Cooled Turbine Nozzle Vane

Abstract

High cycle efficiencies and high power-weight ratios are two major requirements for the economic operation of present day gas turbines. These requirements lead to extremely high turbine inlet temperatures and adjusted pressure ratios. The permissible hot gas temperature is limited by the material temperature of the vane. Intensive cooling is required to guarantee an economically acceptable life span of the components which are in contact with the hot gas. Convection cooling in blades and vanes has been a common cooling technique for decades. However, the optimization of the cooling configuration is still a great challenge in the thermal design process. One objective in the thermal design process is a general reduction of the temperatures in the vane material, especially in regions with high thermal loads, e.g. the leading edge. Another goal is to create a more equal temperature distribution in the vane walls. This will lead to a reduction in the thermal stress and strain. The aim of research is to minimize the supply of cooling fluid taking the physical restrictions mentioned above into consideration. Therefore, a new numerical procedure for CFD in combination with an FEM stress analysis represents a valuable tool for the thermal design of turbine vanes, minimizing the experimental effort. This paper demonstrates the application of a new numerical method for the conjugate calculation of internal and external fluid flows and the heat transfer in and through the vane walls in a thermal design process of a convection cooled turbine guide vane. The advantage of this approach is the prediction of fluid flow properties and wall temperatures without requiring information on additional heat transfer conditions or temperature distributions at the external surfaces of the vane. This is a great advantage because the data desired are unknown or not available in the design process of new cooled blades or vanes. Another advantage is the fact that the interactions of fluid flow and heat transfer are taken into account by the conjugate calculation. After a short description of the conjugate fluid flow and heat transfer method, results for the two-dimensional aerodynamic and thermal investigation of a convection cooled, high-pressure turbine nozzle guide vane are presented. The highly accurate determination of the temperature distribution is essential for the correct calculation of thermal stress and strain. The comparison of numerical and experimental results demonstrates the performance of the code since the differences in the surface temperature distributions are less than 2%. On basis of the numerical results for the original cooling configuration, two more configurations were designed and investigated using the conjugate method. It can be shown that surface temperature peaks can be reduced and a more equal temperature distribution in the vane material can be reached. This also has consequences for the thermal stress and strain in the vane walls as shown by an FEM stress and strain analysis.