One of the important parameters that aff ects the gas turbine blades fi lm cooling is the behavior of the main fl ow. Due to
the blade rotation, a periodical frequency is moving through the main fl ow. In this study, a numerical simulation is used
to investigate the eff ect of the bulk fl ow pulsations on fi lm cooling. The study is carried out on a fl at plate surface with a
simple cylindrical hole inclined by 30o with the direction of the main fl ow stream. The study is carried out at blowing ratios
of 0.5, 1.0, and 2.0. The free stream Strouhal number ranged from 0 to about 0.49, and the coolant Strouhal number ranged
from 0 to 4.1 compared to 0.2–6.0 for the operating turbine range. The free stream is represented by a sinusoidal profi le
with pulsation velocity amplitude in the free stream of ± 20% of the time-averaged free stream velocity. The realizable k–ε
model is used to solve the momentum equation. A comparison with previous experimental studies is presented to verify
the numerical model. The results show that the pulsating fl ow has a signifi cant eff ect on the fi lm cooling performance for
pulsating frequency higher than 35 Hz. For pulsating frequency higher than 35 Hz, at blowing ratio 0.5, as the pulsating
frequency increases, the fi lm cooling eff ectiveness decreases while at blowing ratio 2.0, the fi lm cooling eff ectiveness increases
with increasing pulsating frequency. The reduction in the overall-time averaged fi lm cooling eff ectiveness at pulsating
frequency 75 Hz with blowing ratio equal to 0.5 is about 49.7% of the fi lm cooling at zero pulsating frequency, while the
increase in it at the pulsating frequency 75 Hz with blowing ratio equal to 2 is about 108%. |
