Heat Transfer And Aerodynamic Characteristics Of Film Cooling Under Turbine Flow Condition

Film cooling is one of the most important cooling technologies of modern gas turbine. As the load of a single turbine stage increases, the pressure gradient and the turning angle of turbine flow increases. Thus makes the interaction between film cooling jet and turbine main flow becomes more and more significant.The film cooling performance in turbine environment differs from that in the flat plate condition. Wall curvature and streamwise pressure gradient are two important characteristics of the turbine main flow. The present study conducted a serious of experimental, theoretical and numerical research on the effect of wall curvature and pressure gradient on film cooling heat transfer and aerodynamiccharacteristics and reveal the interaction mechanism of the cooling jet and the turbine flow. Based on these effects, a curvature and pressure gradient modification method on film cooling effectiveness is developed.Pressure sensitive paint(PSP) is the main measurement technique in the present study, and a system error analysis is conducted. The system error consists of the heat and mass transfer analogy error and the multiple mass transfer error. Film cooling is a convection dominatingphenomena and the heat and mass transfer analogy holds well. The random error is less than 10% for the most of the cases in the present study.The research on the effect of wall curvature and pressure gradient on film cooling effectiveness shows that these two turbine characteristics effect the blowing off of the film cooling jet and the streamwise dissipation and spanwise diffusion of the coolant. For simple angle cylindrical hole, there is a determinant point that when the momentum ratio is smaller than the certain value, film cooling effectiveness is highest on concave wall and the rank is opposite when the momentum ratio is larger than the value. The value increases with stronger favorable pressure gradient and ranges from 0.55 to 0.75 in the present research. For compound angle hole, the cooling effectiveness is always the highest on convex wall. While for shaped film cooling hole, the cooling performance is worse on both curved wall than flat wall.Based on film cooling effectiveness results, blowing off parameter, streamwise dissipation parameter and spanwise diffusion parameter is used in the curvature and pressure gradient modification method on film cooling effectiveness which is available for simple angle film cooling, compound angle film cooling and shaped hole film cooling. The error of the modification method is less than 10% for most cases in the valid range. Cascade film cooling experiments are also conducted to validate the modification method in the actual turbine film cooling prediction.For the aerodynamic characteristics of film cooling, the effect of momentum supplement of the coolant jet with large blowing ratios is significant when pressure loss coefficient is investigated. Kinetic loss coefficient considering the kinetic energy of the coolant jet is a proper parameter to investigate the aerodynamic loss of film cooling. The kinetic loss coefficient increases with blowing ratio and favorable pressure gradient decreases the loss coefficient. The kinetic loss coefficient of compound angle film cooling is much higher than the axial hole.