Thermal Analysis of a Film Cooling System with Normal Injection Holes Using Experimental Data

Abstract

The present study investigated temperature and thermal stress distributions in a film cooling system with normal injection cooling flow. 3D-numerical simulations using the FEM commercial code ANSYS were conducted to calculate distributions of temperature and thermal stresses. In the simulations, the surface boundary conditions used the surface heat transfer coefficients and adiabatic wall temperature which were converted from the Sherwood numbers and impermeable wall effectiveness obtained from previous mass transfer experiments. As a result, the temperature gradients, in contrast to the adiabatic wall temperature, were generated by conduction between the hot and cold regions in the film cooling system. The gradient magnitudes were about 10~20K in the y-axis (spanwise) direction and about 50~60K in the x-axis (streamwise) direction. The high thermal stresses resulting from this temperature distribution appeared in the side regions of holes. These locations were similar to those of thermal cracks in actual gas turbines. Thus, this thermal analysis can apply to a thermal design of film cooling holes to prevent or reduce thermal stresses.

Material design of a film cooling system using experimental heat transfer data

“…In other words, if an operation condition is unsuitable, local thermal cracks and structural failure may occur due to the high thermal stress. Therefore, a thermal analysis [9][10][11] and a failure analysis [12][13][14][15][16] are required for an effective thermal design.…”

“…It is necessary to estimate the stress distributions and to predict the lifetime for the cooling system due to the safety of hot components, such as combustors, vanes, and blades. In recent years, Kim et al [10] and Lee et al [11] have studied the distributions of both temperature and thermal stress that are induced by convection and conduction in a film cooling system. They found that the highest temperature and stress appear in the cooling system.…”

“…Previous studies [16,[23][24][25][26][27] have mainly focused on the material properties in a convectional cooling system. Kim et al [10] and Lee et al [11] found that thermal stresses are generated at the edges in the coating system due to thermal expansion and constraints. Among the various cooling methods, film cooling has been widely used; however, the material selection has been rarely investigated because heat transfer distributions and the wall adjacent temperature significantly depend on the operating environment.…”

“…We studied the local distributions of heat transfer, material temperature, and thermal stress in the previous studies [7][8][9][10][11][12][13][14][15][16]. In the present study, we simultaneously considered the material properties and the main stream hot gas temperature among all other factors because such factors are the most determinant factors in the beginning of a cooling system design.…”

Conjugated heat transfer and temperature distributions in a gas turbine combustion liner under base-load operation

“…Moreover, accurate prediction of conjugated heat transfer distributions on external and internal metal surfaces is also important in cooling system designs for new concept and modification. Recently, many researchers [4][5][6][7] have investigated methodologies and characteristics of the conjugated heat transfer including conduction and convection. Thus thermal analysis becomes an important issue in order to enhance the heat transfer as well as to reduce the thermal stress yielded by temperature gradients.…”