The continuous increase of turbine inlet temperature (TIT) has presented a great challenge for high pressure gas turbine blade design due to sophisticated heat transfer and film cooling characteristics in high temperature environment. Up to present, TIT of the modern gas turbine engine has been far exceeding the melting point of blade material. If the aero-thermal performance of a blade has not been well understood, the service life will be shortened and operating safety will be affected, significantly. In the first stage of high pressure gas turbine, blade trailing edge suffers extremely high thermal load due to thin structure and limitation of internal convective cooling. To cool the trailing edge region, one method is to have a pressure side cutback, which supplies the coolant through a connected slot and is strengthened with multiple internal structures in coolant passage. To further strengthen the trailing edge cutback, lands are commonly adopted in the coolant slot and extend to the downstream cutback region (i.e. landed trailing edge cutback). Evidences have shown that the landed trailing edge cutback has the advantages of reduced total pressure loss and improved structural integrity compared to the conventional cutback configuration (without lands). As a result, in modern gas turbines, the landed trailing edge cutback is very popular in industrial practice because of excellent heat transfer and aerodynamic performance. However, most of the previous research focused on the heat transfer and film cooling effect in the modeled blade trailing edge cutback. A few researchers experimentally investigated the film cooling effect on the blade trailing edge with land extensions. There is still a lack of understanding on the specific influence mechanism of land extensions on flow and heat transfer characteristics of the trailing edge region in gas turbine blade.

In this study, the background-grids based mapping (BGBM) method presented in Part I of this work was adopted to generate the multi-block structured meshes for blade with landed trailing edge cutback. With the coordinate transformation strategy, the mesh generation process for the trailing edge cutback with land extensions in cascade was simplified. Using the RANS (Reynolds-Averaged Navier-Stokes) equations solutions combined with transitional turbulence model SST Gamma-Theta, the flow and heat transfer performance in a gas turbine blade with landed trailing edge cutback was numerically investigated. At three inflow turbulence intensities, three mainstream Reynolds numbers and three coolant injection rates, heat transfer coefficient distributions and aerodynamic losses in a blade with landed trailing-edge cutback were compared to those without land extensions. With the existing experimental data, the reliability of numerical methods was validated at a range of operation conditions. The results show that heat transfer coefficients on blade surface are gradually increased with the increase of inflow turbulence intensity. However, heat transfer coefficients on trailing edge cutback are not sensitive to the variations of inflow turbulence intensity. The energy loss coefficient and total pressure loss coefficient in blade with lands are both increased with the increase of inflow turbulence intensity. With the same inflow turbulence intensity, the aerodynamic loss in blade is reduced with increasing the mainstream Reynolds number. For the blade with lands, the increase of ejection rate has little influence on the heat transfer coefficient distributions on blade surface. However, the increase of ejection rate significantly increases the heat transfer coefficients on blade trailing edge cutback. As the ejection rate reaches 2.4-2.6%, the blade has a relatively low flow loss and high heat transfer performance. Compared with the blade without land extensions, heat transfer coefficients and pressure coefficients on blade surface are reduced, and the heat transfer coefficients on the cutback surface are increased in the blade with land extensions.


Background-Grid Based Mapping Approach to Film Cooling Meshing: Part II \u2014 Applications in Vane With Landed Trailing-Edge Cutback

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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