Sensitivity Analysis for Film Effectiveness on a Round Film Hole Embedded in a Trench Using Conjugate Heat Transfer Numerical Model

Film cooling performance is affected by many factors, for example: geometrical factors (injection angle, length-to-hole diameter ratio, surface roughness, etc.) as well as flow conditions (mass flux ratio, momentum flux ratio, turbulence intensity, etc.). In most of the film cooling literature, film effectiveness has been used as criterion to judge and/or compare between film cooling designs. Uniformity is also a critical factor, since it is determining how well the coolant spreading out downstream to protect the working surface in a gas turbine engine. Better cooling uniformity will reduce thermal stress associated with gas turbine components. A flat plate with round holes embedded in a trench is considered in this study. Although the trench may have an adverse effect on fan-shaped film hole cooling, it tremendously increases the performance of the round-hole film cooling technique in terms of film cooling effectiveness. An experimental study at CATER facility has shown that the cooling effectiveness can be retained by the addition of a trench feature while using only half a number of cooling holes. The current work is conducted based on the numerical study with a validation from in-house experimental works at CATER and the experiments from the literature. The experimental temperature distribution is captured by using Temperature Sensitive Paint and then span-wised effectiveness is calculated. The studied input parameters include flow variables (blowing ratio, BR and momentum ratio, MR) and geometrical parameters (trench-depth-to-diameter ratio, s/D and pitch-to-diameter ratio, p/D). A comparison of contributions of studied factors is investigated by using Response Surface Methodology technique. The spatially adiabatic film cooling effectiveness is selected as the primary output in the design of experimental analysis. Since the nonlinear behavior of all input factors are also of interest, three levels of each parameter will be considered. The well-know Box and Behnken design is employed to carry on this sensitivity analysis. With this method, the current study only requires 25 runs to obtain a quantified comparison of the contribution of each involved effects.