Flow Field Investigations on the Effect of Rib Placement in a Cooling Channel With Film-Cooling

Martin Kunze, Konrad Vogeler

abstract:

This paper presents experimental investigations on flat plate film-cooling in combination with a ribbed cooling channel. The effect of rib placement on the film- cooling injection and the channel flow field was studied. The velocity fields were measured using optical, non-intrusive laser measurement techniques as LDA (Laser- Doppler-Anemometry) and PIV (Particle-Image-Velocimetry). The cooling channel has a rectangular-shaped cross section with an aspect ratio of AR 2:1. It is equipped with 12 transverse ribs (ϕ = 90°, e/Dh = 0.078, Pr/e = 10). In the center rib segment, three film holes with a hole diameter of D = 5mm ( α = 35°, L/D = 7, Ph/D = 3) are placed. The dimensionless rib-to-film hole position s/D is varied from 4.5 to 10.5. The investigations are conducted at isothermal conditions for a variation of the coolant Reynolds number Rec,Dh from 10000 up to 60000 and for three hole blowing rates M = 0.5, 0.75 and 1.0.
The experimental results for the film-cooling injection showed only small influence of the rib placement on the flow field. Due to different coolant-to-main flow pressure ratios for each hole, a non-uniform share of coolant mass flow occurs. Intense streamwise mixing and decay of the turbulence in the film jet was observed within the first 10 hole diameter in streamwise. Enhancement of the turbulence intensity inside the jet core was found with increasing coolant Reynolds numbers.
Considering the flow field inside the internal cooling channel, significant influence of the rib position was found which is most pronounced at low Reynolds number (Rec,Dh = 10000) and high blowing ratios (M = 1.0). The effect becomes significantly smaller when the Reynolds number is increased. This is mainly attributed to the strongly increasing channel mass flow which equals to a decreasing suction ratio SR = uh/um of the holes. For the purpose of validation, particular experimental results are compared to numerical simulations using the commercial solver Ansys CFXTM and the shear stress turbulence model (SST). The entire fluid domain was modelled with a block-structured approach. Measured velocity, total pressure and turbulence profiles are imposed at the inlet of the main flow and cooling channel as boundary conditions.

reference:

Martin Kunze, Konrad Vogeler
"Flow Field Investigations on the Effect of Rib Placement in a Cooling Channel With Film-Cooling"
ASME Paper GT2013-94096, 58th ASME Turbo Expo, San Antonio TX, USA, June 3rd-7th, 2013.