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Description:
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The inlet temperature of modern gas turbine engines has been increased to achieve higher thermal
efficiency and increased output . The blade edge regions , including the blade tip , the leading edge , and the
platform , are exposed to the most extreme heat loads , and therefore , must be adequately cooled to
maintain safety .
For the blade tip , there is tip leakage flow due to the pressure gradient across the tip . This leakage
flow not only reduces the blade aerodynamic performance , but also yields a high heat load due to the thin
boundary layer and high speed . Various tip configurations , such as plane tip , double side squealer tip , and
single suction side squealer tip , have been studied to find which one is the best configuration to reduce the
tip leakage flow and the heat load . In addition to the flow and heat transfer on the blade tip , film cooling
with various arrangements , including camber line , upstream , and two row configurations , have been
studied . Besides these cases of low inlet /outlet pressure ratio , low temperature , non -rotating , the high
inlet /outlet pressure ratio , high temperature , and rotating cases have been investigated , since they are
closer to real turbine working conditions .
The leading edge of the rotor blade experiences high heat transfer because of the stagnation flow .
Film cooling on the rotor leading edge in a 1 -1 /2 turbine stage has been numerically studied for the design
and off -design conditions . Simulations find that the increasing rotating speed shifts the stagnation line
from the pressure side , to the leading edge and the suction side , while film cooling protection moves in the
reverse direction with decreasing cooling effectiveness . Film cooling brings a high unsteady intensity of
the heat transfer coefficient , especially on the suction side . The unsteady intensity of film cooling
effectiveness is higher than that of the heat transfer coefficient .
The film cooling on the rotor platform has gained significant attention due to the usage of low -aspect
ratio and low -solidity turbine designs . Film cooling and its heat transfer are strongly influenced by the
secondary flow of the end -wall and the stator -rotor interaction . Numerical predictions have been
performed for the film cooling on the rotating platform of a whole turbine stage . The design conditions
yield a high cooling effectiveness and decrease the cooling effectiveness unsteady intensity , while the high rpm condition dramatically reduces the film cooling effectiveness . High purge flow rates provide a better
cooling protection . In addition , the impact of the turbine work process on film cooling effectiveness and
heat transfer coefficient has been investigated . The overall cooling effectiveness shows a higher value than
the adiabatic effectiveness does . |