ENHANCED FILM COOLING EFFECTIVENESS USING TURBULENCE PROMOTER IN COOLING HOLE

The film cooling is investigated experimentally and numerically for gas turbine blade cooling. Film cooling performance is vital for safe operation of the blades. By calculating the film cooling effectiveness, the effect of wall roughness through a turbulence promoter inside the cooling hole is evaluated. A turbulence promoter of aspect ratio <i>K</i> &#61; <i>L/h</i> from 6 to 14, varying pitch <i>L</i> with constant height <i>h</i>, is introduced. Blowing ratio range from <i>M</i> &#61; 0.5 to 2 and fixed mainstream Reynolds number, Re &#61; 2.0 &times; 10⁵ is tested. Smooth cooling hole and flat plate surface with angle of 35&deg; is set up in a wind tunnel to compare the results and validate the CFD approach assessing the turbulence models <i>k-&epsilon;</i> renormalized group theory (RNG) and Reynolds stress model (RSM). A swirl flow develops inside the cooling hole due to installing the turbulence promoter. The coolant discharge is modified in turbulence parameters improving momentum and heat transfer rates compared to the normal case. This has an impact on the film cooling performance. The results indicate film cooling effectiveness and surface protection enhancement, obtained for the best aspect ratio and blowing ratio. Coolant wall roughness may be used to improve the design of coolant hole and to reduce the number of orifices needed for safe gas turbine blades.