Abstract
As gas turbine inlet temperature continuously increases, blade trailing edge suffers an extremely high thermal load due to the thin structure and constraint of internal convective cooling arrangements. To overcome these difficulties, pressure-side cutback, which is strengthened with multiple internal structures and land extensions, is widely used in blades to protect trailing edge from high thermal stresses. Due to the geometrical complexity and strong interactions between coolant flow and mainstream, sophisticated heat transfer and flow patterns exist in the cutback region, which presents a great challenge for the trailing edge cutback design. To understand the heat transfer and aerodynamic performance in blade with trailing edge cutback, CFD method has become an efficient tool which provides deep insights into the flow mechanisms and heat transfer characteristics in the detailed region. To accurately resolve the flow and heat transfer performance in a turbine blade with trailing edge cutback, structured grids are preferred because of higher resolution in flow/heat transfer prediction than unstructured grids, especially in boundary layers. However, for a blade with landed trailing edge cutback, few researchers tried to employ structured grids to predict aero-thermal performance due to the geometrical complexity.
In this paper, the Background-Grid Based Mapping (BGBM) method proposed in Part I of this study was adopted to generate multi-block structured grids for a gas turbine vane with landed trailing edge cutback. With the coordinate transformation strategies, multi-block structured grids for the vane with landed trailing edge cutback were generated conveniently. With the generated structured grids, flow and heat transfer performance in vane were investigated using RANS (Reynolds-Averaged Navier-Stokes) equations solutions combined with transitional turbulence model. Effects of land extensions on the heat transfer and aerodynamic performance were analyzed, as well as the effects of inflow turbulence intensity, mainstream Reynolds number and ejection rate. The results show that heat transfer coefficients on vane surface, total pressure loss coefficient and energy loss coefficient in vane are all increased with the increase of inflow turbulence intensity. However, heat transfer coefficients on cutback and trailing edge surface are not sensitive to inflow turbulence intensity. At the same inflow turbulence intensity, the aerodynamic loss in vane is decreased with increasing the Reynolds number of mainstream. The increase of ejection rate significantly increases the heat transfer coefficients on cutback surface. Compared with the vane without land extensions, heat transfer coefficients and pressure coefficients on vane surface are reduced and the heat transfer coefficients on cutback surface are increased for the vane with land extensions. In the case of Re = 2.0 × 106, the area-averaged heat transfer coefficient on landed cutback is 14.46% higher than the cutback without lands. Compared with the experimental data, predictions with structured grids based on BGBM method are more agreeable than those with unstructured grids.
