Commercial aero-engines may operate in dust-laden environments, such as taking off and landing on desert ground or flying through volcano dust cloud, and foreign particles frequently deposit at hot surface and film hole-exits, which results in partial blockage of film holes, clog of cooling air, reduction in cooling effect, and could induce catastrophic damage. This problem has not been well solved up to now. This paper presents an experimental investigation on two surface deposition models (deposition limited to upstream of hole with a peak height of 1.5 diameter of hole called D1.5, and downstream forming a trench with a peak height of 1.0 diameter of hole, called D1) and two blockage models (leading edge of hole LB, and trailing edge TB), as well as two combined models D1.5-LB, and D1-TB. The experiments are conducted in a low speed water tunnel using Planar Laser Induced Fluorescence (PLIF) technique. Through this experiment, the following interesting phenomena, which were not reported in previous literatures, are reveled: 1) The effect of blockage ratio at leading edge on cooling performance of combined D1.5-LB is opposite to individual LB, i.e. in the case of combined D1.5-LB, a higher blockage ratio corresponds to a lower cooling effectiveness; whereas, for individual LB, the cooling effectiveness increases with the blockage ratios in the tested range. 2) At all blowing ratios, the cooling performances of combined D1.5-LB are better than that of perfect model D0-B0 (without deposition and blockage). At all blockage ratios tested in this experiment, in the case of combined D1.5-LB, a higher blowing ratio corresponds to a higher cooling effectiveness and a lager film coverage length. 3) At lower blockage ratios of 0.1 and 0.3, the overall-averaged cooling effectiveness of combined D1-TB is higher than that of perfect model D0-B0. At large blockage ratio 0.5, the blockage effect is dominant, and the averaged cooling effectiveness of combined model D1-TB is lower than that of D0-B0. In the case of individual deposition model D1-B0, although the lateral-averaged film cooling effectiveness is augmented, the area of film cooling is reduced.
This paper presents an experimental investigation on the overall cooling performances of two endwall specimens, one is a simple film cooling, the other is a laminated structure with pin-fins and impingement holes, but has the same cover board of the simple film cooling endwall. The two specimens are made of stainless steel with a real size of a gas turbine endwall. The experiments were carried out in a large temperature ratio (TR) of mainstream to cooling air (TR = 2.47), which is close to real operation conditions of modern gas turbines. The surface temperatures were measured by an infrared thermal imaging system (ITIS) at three blowing ratios (BRs = 0.63, 1.02, 2.04). The overall effectiveness of the two specimens was analyzed and compared. Through the analysis and comparisons, some interesting phenomena are discovered: 1) In general, as like as the previous studies of endwall cooling, the laminated endwall specimen can provide a higher cooling effectiveness averaged over the entire area than the simple film cooling specimen; 2) However, if we want to get more exact designs, the combination of the two structures may be better. Because of at low BR = 0.63, the simple endwall specimen can locally demonstrate a better cooling effect in an elliptic region of the endwall; 3) At high BR = 2.04, the design strategy of the simple endwall specimen can also locally be used in a triangle region. The exact designs can not only increase overall cooling effect, but also reduce the weight of whole endwalls.
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