The Influence of Humidity on the Creep Life of a High Pressure Gas Turbine Blade: Part II—Case Study

Abstract

The determination of the rate of heat transfer from the turbine blade in a cross flow is important in hot section gas turbine life assessment. For design purposes, the rate of heat transfer is normally fixed by semi-empirical correlations. These correlations require knowledge of fluid properties which depend on temperature. For gases these properties are normally available only for the dry state, thus the possible effect of the water vapour content has been overlooked. Many gas turbines operate in environments in which air humidity is very low and therefore has little influence on gas turbine performance. However humidity becomes more important in hot, humid climates where there are large variations in ambient absolute humidity, especially in hot and humid climates. The aim of this paper is to investigate and present the effect of humidity at different operating conditions on the turbine blade coolant heat transfer and blade creep life. The effect of humidity was considered only on the air coolant side. he The heat transfer coefficient on the hot side was calculated for dry hot gas. This avoided the balancing effect of each other (heat transfer coefficient coolant side and hot side). The WAR at each operating point is quantified based on the ambient temperature and the relative humidity (0%–100%). Results showed that with increasing WAR the blade inlet coolant temperature reduced along the blade span. The blade metal temperature at each section was reduced as WAR increased, which in turn increased the blade creep life. The increase in WAR increased the specific heat of the coolant and increased the heat transfer capacity of the coolant air flow. Different operating points were also evaluated at different WAR and Tamb to identify the effect of WAR on the creep life. The results showed that an increase in WAR increased the blade creep life. The creep life of the blade at each section of interest was obtained as a function of the blade section stress and the blade metal section temperature using the LMP approach.

Probabilistic Life Assessment of Gas Turbine Blade Alloys under Creep

“…According to the results, an increase in WAR from 0 to 0.08 percentages causes creep life to increase from 4000 to 6000 hours. Also proposed method results have been compared with FEM results which gathered form literature review [25] and it shows that it has good…”

“…Some researchers have studied the influence of humidity changes in temperature variations and studied temperature variations in creep life indirectly. [25] Also, they have not considered uncertainties in the service condition. This study aims to propose a new method of creep life estimation method considering humidity directly with the entrance of humidity factor to classical LMP method.…”

“…Temperature and mechanical stress distribution across the length of blade span were collected from FE analysis gathered from the literature review as there is not any published experimental creep data considering different humidity percentages. Figure 5 shows FE analysis of GT blade (metal temperature and mechanical stress distributions at different humidity which is used as entrance data in this study [25]. Also Larson-Miller parameter is obtained from LMP versus mechanical stress diagram which is given in Figure 6.…”

Hot Corrosion Damage Modelling in Aero Engines based on Performance and Flight Mission Analysis

“…Mohamed et al [16] correlated power demand with HPT blade creep life through the effect of TET on the Creep Factor. Eshati et al [17] studied the effect of humidity on the remaining creep life of HPT blades under a range of TETs by considering the change in heat transfer to the blade due to the water presence in the flow and they identified that a higher Water to Air Ratio (WAR) is beneficial to creep life. Hanumanthan et al [18] estimated the operational severity factor of HPT blades for different take-off and climb derates, as well as ambient temperature.…”

“…If only one representative flight mission or the average flight mission is available for an engine type of a fleet, then Eq. ( 16) converts to (17):…”