THE EFFECT OF ASPECT RATIO OF ELLIPTICAL COOLING HOLES ON THERMAL CHARACTERISTICS OF GAS TURBINE BLADE

Abstract

In advanced gas turbine, the improvement of the thermal efficiency and power output is required. Among these improvements, which still getting attention considerably, increasing turbine inlet temperature that may exceed the melting point of the blade material and to avoid that internal blade cooling technique is incorporated. The common traditional cross-sectional area of the cooling channels is circular. In this paper, a modification regarding the shape of cooling hole is suggested to enhance the heat transfer between the coolant in cooling serpentine and hot gases from the combustion chamber and thus minimizing the severe temperature usually occurs in the gas turbine blade especially at first row of the rotor. The proposed shape is elliptical and to discuss different scenarios of cooling schemes, the aspect ratio of ellipse axes and the distribution of whole holes are also analyzed to figure out the best results in terms of temperature distribution, heat transferred and cooling effectiveness of each model. The three new models consist of cooling holes of (5, 6 and 7) located at the center of the curvature line of blade. Results were compared with those obtained using the model of the GE company (model-1) which is already installed in (AL-DIWANIAH GAS TURBINE POWER PLANT). It were analyzed on the basis of real data, such as geometry profile, total cooling area, and boundary conditions. Results have been discussed and it is found that model-4 is the optimum solution, because of maximum total heat transfer rate and reduction in the blade trailing edge temperature about 24% are attained in this model compared to model-1, and it is found increase number of cooling holes in the blade leads to lowers the blade trailing edge temperature, this depends on the design location of this holes on the blade surface. Meanwhile, the optimum ratio of the model-4 in the reduction of maximum temperature is (a / b = 2) by the dimensions of (a = 2 & b = 1). Steady state thermal analysis is carried out using CFD, Inconel 718 alloy selection as material and air is used as a coolant as the real condition of.