SIMULATION OF UNSTATIONAL THERMO SHOCKED STATE GTU

Abstract

The paper proposes a method of approximate calculation of the temperature field of the turbine blade in non-stationary mode by means of CFD-modeling. The academic version of the ANSYS-Fluent software package was used as a modeling tool. The local values of the heat transfer coefficient along the contour of the blade profile were calculated in the work. Previously, the gas flow velocity in the curved interscapular channel was calculated to determine the distribution of the gas flow velocity along the convex and concave surfaces of the blade. Comparison of the data thus obtained with the result of processing the experience conducted on the turbine, shows that in the conditions of the real rotating installation, the heat transfer to the surface of the blade was approximately 2 times higher. The most probable reason for this discrepancy is the earlier beginning of the transition to the turbulent boundary layer on the surface of the blade in real conditions of high turbulence of the oncoming flow. Calculations show that in the case of a sharp change in gas temperature, the largest temperature difference in the blade occurs after a few seconds and reaches 50 ... 90% of the change in gas temperature, and in blades with thin edges - close to this value. Increasing the thickness of the edges can significantly reduce the uneven temperature in the blades with sharp changes in gas temperature. In order to identify the nature of the stress state of the blades at different modes of operation of the gas turbine unit, the temperature stresses in the blade were calculated. The calculation was performed for Mises averaged stresses  in the cross section of an unevenly heated blade. When starting the installation, the maximum force occurred 30 ... 40 seconds after the start of the rotation of the rotor almost simultaneously with the maximum temperature difference between the edges and the central part of the section. The highest stress values occurred in the region of the inlet edge, where they exceeded 680 MPa per compression. In the future, the temperature stresses decreased and even changed sign due to the cooling process of the blade, overheated when throwing the gas temperature.