EXPERIMENTAL INVESTIGATION OF AIR-COOLED TURBINE BLADESnIN TURBOJET ENGINE IX - EVALUATION OF THE DURABILITY OF NONCRITICAL ROTOR BLADES IN ENGINE OPERATION

摘要

An investigation is being conducted to evaluate the durability of promising blade configurations of air-cooled rotor blades in a modified turbojet engine and to obtain some insight regarding the effect of vibration, large chordwise temperature gradients, creep, oxidation, heat-treatment, and method of fabrication on the life and the durability of blade configurations made of noncritical materials. The results obtained with 12 blades fabricated from noncritical materials are pre¬sented. These blades comprised five basically different structural or cooling configurations or both. Two of the configurations were modified at the leading and trailing edges to provide film cooling of the blades and thus decrease the chordwise temperature gradients at the possible expense of strength. Three of the configurations had no leading- or trailing-edge modifications and consequently had large chordwise tem-perature gradients.nThe investigation of these blade configurations consisted in operating the blades over a range of continuous engine speeds from 4000 to 11,500 rpm and cooling-air flows per blade from 15 to 5 percent of the combustion-gas flow per blade. The blades which could withstand the continuous speed operation were subjected to a more severe test that consisted of alternate cycles of 5 minutes at idle speed (4000 rpm) and 15 minutes at rated engine speed (11,500 rpm) with 15 seconds allowed for acceleration or deceleration. At rated engine speed the effective gas temperature was maintained at 1450° F. This temperature corresponds to a turbine-inlet temperature of approximately 1670° F. The cooling-air flow per blade for the cyclic' test was maintained at a constant value of 5 percent of the combustion-gas flow per blade at rated engine speed.