Abstract
Film cooling enhancement by incorporating an upstream sand-dune-shaped ramp (SDSR) to the film hole exit was numerically investigated on a flat plate under typical blowing ratios ranging from 0.5 to 1.5. Three heights of SDSRs were designed: 0.25D, 0.5D, and 0.75D. The results indicated that the upstream SDSR effectively controlled the near-wall primary flow and subsequent mutual interaction with the coolant jet, which was the main mechanism of the film cooling enhancement. First, a pair of anti-kidney vortices was formed at the trailing ridges of the SDSR, which helped suppress the kidney vortex pair due to the interaction between the coolant jet and the primary flow. Second, a weak separation and a low pressure zone were induced behind the backside of the SDSR, which caused the coolant jet to spread around the film cooling hole and improve the lateral film coverage. With respect to the baseline cylindrical film cooling holes, the effect of the upstream SDSR was distinct under different blowing ratios. Under a low blowing ratio, the upstream SDSR shortened the streetwise film layer coverage in the vicinity of the film hole centerline but increased the span-wise film layer coverage. A relatively optimal ramp height seemed to be 0.5D. Under a high blowing ratio, both the streamwise and span-wise film layer coverages improved in comparison with the baseline case. The film cooling effectiveness improved gradually with increasing ramp height.
Highlights
Film cooling techniques play an important role in the thermal protection of hot turbine engine components, such as the blade, combustor liner, and exhaust nozzle
These vortices are detrimental to film cooling because they lift the coolant jet off the protected surface and force the hot primary flow to enter beneath the coolant jet
This paper summarized a numerical study exploring the film cooling enhancement by the incorporation of an upstream sand-dune-shaped ramp (SDSR) into the film hole exit
Summary
Film cooling techniques play an important role in the thermal protection of hot turbine engine components, such as the blade, combustor liner, and exhaust nozzle. Because the cooling air for film cooling purposes is extracted from the compressor stage of the turbine engine, the use of the coolant undoubtedly results in engine performance implications. In addition to the shaped holes, researchers recently found that the upstream ramp played a role in anti-kidney vortices, which mitigated the mutual interaction between the coolant jet and the primary flow [4]. Of particular interest was the novel Barchan-dune-shaped ramp proposed by Zhou and Hu [12,13] These researchers found that the film cooling effectiveness over a test plate was significantly enhanced using the Barchan-dune-shaped ramp. At relatively high blowing ratios, the use of Barchan-dune-shaped ramps was found to be beneficial for reducing aerodynamic loss, since the unique Barchan-dune-shaped ramp design kept the coolant flow attached more firmly to the protected surface. Particular attention was given to exploring the effect of ramp height under typical blowing ratios ranging from 0.5 to 1.5
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