Implications of Day Temperature for a High-Pressure-Turbine Blade's Low-Cycle-Fatigue Life Consumption

H IGH-PERFORMANCE aircraft used in modern aviation, especially for military purposes, are complex in design and are required to operate under severe stresses and temperatures [1]. Thus, designer and users of these aircraft continually seek greater reliability, increased availability, enhanced performance, improved safety, and low life-cycle costs. Any extensions of the life expectations of aeroengines directly lower the life-cycle cost and depend upon the types of mission undertaken, operating conditions experienced, and rate of in-service engine deterioration. Significant adverse effects of in-service aeroengine deterioration have been already established by earlier investigations [2–4]. However, as the result of a comprehensive literature review, it was realized that in addition to aeroengine deterioration, the condition of incoming airstream is also expected to have significant effects on an aeroengine’s overall performance. In a country such as Pakistan, variation of day temperature over the year (i.e., from 0 to 50 C) significantly alters the condition of the incoming airstream. Any change in day temperature affects the quality of the incoming airstream for aeroengine operation as well as that of the air surrounding the air vehicles, thereby affecting the performance of both by altering atmospheric and aerodynamic characteristics [5]. As a result, an aeroengine will seek a different steady operating point, thereby resulting in a variation of the high-pressure spool speed (HS) for providing the same thrust to keep the aircraft’s performance invariant. Any rise in the HS results in greater low-cycle-fatigue (LCF) damage for the hot-end components and thereby higher engine life-cycle costs. Possessing a better knowledge of the impacts of day temperature upon the LCF life consumption of an aeroengine’s hot-end components helps the users to take wiser management decisions. Hence, this investigation was undertaken. There are many components in an aeroengine, but its performance is highly sensitive to changes in only a few. Among these, the highpressure turbine (HPT) blades are the most sensitive components, because they are subjected to both the highest rotating speeds and gas temperatures [2], and so they were selected for the present investigation.