Blade Faults in Gas Turbines

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Gas turbines are often exposed to ingestion of particles suspended in the air such as dust, ash, salt, ice, water droplets, and sand particles during operation. These particles are the most important factor that cause blade fault in all types of gas turbines. The most common types of blade fault are fouling, erosion, tip clearance increase, water ingestion, and foreign object damage (FOD) [1]. Most of mentioned cases cause roughness over the blade surfaces that deteriorate the gas turbine performance. Different numerical methods were used to solve the gas turbine cascade flow field in recent years. In most of these studies, the quasi-three dimensional Navier-Stokes analysis is used. On the other hand, in some studies the flow fields were experimentally tested. Sheets of sandpaper with different equivalent sand-grain roughness heights have been used by researchers to produce roughness on surface of gas turbine blades placed in a wind tunnel and applying flow conditions of their case. 1.1 Experimental work Yun et al. [2] used sheets of sandpapers with equivalent sand-grain roughness heights of 106 and 400 micrometers. The performance tests have been conducted in a low speed, single-stage, axial flow turbine having roughened blades. They showed that for blades with roughnesses of the fully rough regime (400 ), the normalized efficiency decreases by 11 percent for stator vanes and 8 percent for rotor blades. For blades having a roughness in the transitionally rough regime (106
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