What are the factors that affect the idle speed curve of a turbine?
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There is a statement in the turbine regulations: if the starting point of the turbine’s coastdown curve is steeper than that of the normal curve, it indicates an increase in rotor wind loss (blade fouling)； A steeper end of the curve compared to a normal curve indicates increased mechanical friction. I’ve never understood this statement. I think that wind resistance and mechanical friction are present throughout the entire testing process, and both of them cause the coasting time to decrease as well as make the curve steeper. But I don’t understand why the increase caused by wind resistance appears at the beginning of the curve, while mechanical friction affects it at the end Please give me some advice!
I think it’s because within different speed ranges, the impact of blade fouling and mechanical friction on resistance has different weights