To protect the gas turbine blades suffering from the hot gas by adapting the film cooling technology
a novel film cooling geometry with an upstream ramp is proposed in view of the requirement for further increasing adiabatic film cooling effectiveness and decreasing expense of coolant. The performance of film cooling with upstream ramps is numerically investigated with k-ε turbulence model. The effects of arrangement for four different ramps
including the undivided ramp
the ramp divided in the lateral sides
the ramp divided in several positions and the ramp divided in the center
on flow structures are analyzed. The adiabatic film cooling effectiveness and heat transfer coefficient of these four film cooling geometries are compared. The results show that the intensity of entrainment is sensitive to the length of ramp and is independent on the ramp arrangements. Different vortex structures are induced due to the different arrangement for ramps. The ramp divided in the center region generates a pair of vortexes which rotates in the opposite direction with the kidney vortexes
and this pair of vortexes contributes to the lateral spreading of coolant
which increases the film cooling performance. The ramp divided on both sides generates a pair of vortexes which rotates in the same direction with the kidney vortexes
and this pair of vortexes lifts off the coolant further
which increases the film cooling performance. The highest adiabatic film cooling effectiveness in the spanwise direction and the highest NHFR(net heat flux reduction)are observed in the case of the ramp divided in the center.
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references
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