✈Figure Above shows the development of turbine blade cooling since its inception. Originally it was considered sufficient to pass low pressure compressor air through the blade (single pass internal cooling) and in so doing retain its temperature below the critical level at which excessive creep would occur.
✈The requirement for greater engine power and efficiency meant that higher gas temperatures were necessary. Low pressure compressor air was no longer able to provide the amount of cooling on its own, a supplementary source of cooling was required. Research showed that, by passing high pressure compressor air through the blade as well as the low pressure air (multi-feed), a reasonable increase in the gas temperature could be achieved before blade failure was experienced.