Study On Film Cooling Effectiveness With Injection From Sister Holes

Gas turbinesare widely used in a wide variety of industrial applications,includingthe aviation and electricity generation.It has been proven that the thermal efficiencyand power output increases along with the elevatation of turbine inlet temperature,which is far higher than the melting point of the blade material. As a consequence, itis significant to accurately estimate the film cooling efficiency in the designing ofturbine blades. There are many factors influencing film cooling，of which the factorof the hole shape is especially outstanding. Although the use of complexspecial-shaped holes improves the film cooling efficiency effectively, cylinder holeshave still broad applications, due to the limitation of the processing technique and thecost. Therefore, it is one of the most important issues to find a kind of hole shapewhich not only increases the film cooling efficiency but also easily to be processed.In this present work, the CFD commercial software Fluent is used to investigatethe film cooling efficiency in different sister holes angles and different holeshape,such as sister holes and one inlet double outlet hole. To solve the Navier-Stokes equations based on the Realizablek turbulence mode, governing equationsof the model are discretized by control volume method, and SIMPLE algorithm isintroduced to simplify the program during the discretization.Simulation results show that: sister holes improve film cooling effectivenessmainly through the interaction of vortex from secondary and vortex from main hole,pulling jet center which has been raised to the crosswise direction, damage the vortexpair, change the lift force to transverse tensile, maintaining flow adhesion andimprove the transverse distribution of coolant. Compared to other special-hole shapes,sister holes are easy to processe and they plays a significant role n actual production,as it is advantageous to increase the film cooling efficiency in contrast to cylinderholes. Along with increased of the blow ratio,the difference is more obviousindifferent angle sister holes. Considering the cooling efficiency of both near and far hole area region we conclude that sister holes best angle is30°. The down streamextension and lateral coverage area are bigger than other two kind of angles.By comparison between the condition of30°sister holes and one inlet doubleoutlet hole，its result shows that: the film cooling effectiveness of sister holes ishigher than one inlet double outlet hole on the main flow direction near by the holeregion, and advantages are highlighted with the increasing of blowing ratio. But in thecase of earlier wall attachment jet, due to the Momentum loss caused by the mix ofThe jet and the main stream, the far from the hole region cooling effectiveness ofsister hole is worse.on laterally direction near by the hole region,the gas film ofsister holes is more uniform, far from the hole because of the velocity difference ofthe main hole and jet hole the gas film offset to other side lead to one side of plate’effectiveness better than another side. Through comprehensive comparison we canknow that under low blowing ratio one inlet double outlet is the first choice and in thecase of high blowing ratio sister holes have obvious advantages.