Abstract:
Diffused shaped holes have shown superior cooling performance over the other shapes
of holes in many situations. In the present study, numerical simulation using realizable
k-ε model with enhanced wall treatments as implemented in Ansys Fluent solver was
performed to study the effect of trench geometry made at 7-7-7 shaped hole exit on
cooling effectiveness. The predictions were generated at different depth ratios of the
trench geometry. Three different blowing ratios of M = 1.5, 3, and 5 were employed
with different depth ratios of h/D = 0.25, 0.5, and 1. Altogether nine cases were run to
generate predictions and three cases without trench, h/D = 0, at different blowing ratios
of M = 1.5, 3, and 5 were run as the baseline. All cases were maintained at density
ratio of DR = 1.5 and turbulence intensity or Tu = 0.5%.
Based on the error analyses and the comparisons performed to flow field patterns and
cooling effectiveness variations during the validation, the realizable k-ε model with
enhanced wall treatment was selected among standard k-ω, SST k-ω and realizable kε
for predictions. When compared to the baseline, not only the modified geometry
presents better cooling effectiveness according to the laterally averaged effectiveness,
but superior lateral spreading of coolant can also be observed at higher depth ratio of
trench. Maintaining higher blowing ratios at lower slot depth ratio such as h/D = 0.25
is only a waste of coolant without improvements to cooling effectiveness while higher
cooling effectiveness can be obtained by higher blowing ratios at higher trench depth
ratios. Based on the laterally averaged effectiveness, the cooling effectiveness is
improved by increasing the trench depth at all blowing ratios investigated. Based on
the lateral effectiveness variations, the coolant jet has shown a skewness at higher
blowing ratios and lower trench depth ratios while the skewness becomes invisible at
lower blowing ratios and lower trench depths. A steeper decay can be observed in
laterally averaged effectiveness at high blowing ratios (M = 5) and low slot depth ratios
(h/D = 0.25) due to the jet penetration into mainstream thereby degrading the cooling
performance.
Citation:
Sanjeeva, K.P.P. (2022). Analysis on the effect of trench geometry on film cooling effectiveness of shaped holes using rans simulation [Master's theses, University of Moratuwa]. Institutional Repository University of Moratuwa. http://dl.lib.uom.lk/handle/123/21218