Investigation On Convective And Conjugate Heat Transfer Characteristics Of Cooling Structures In Gas Turbine Thin-Wall Blade

Gas turbine is the key power equipment for aeronautical propulsion and efficient use of fossil fuels,and more advanced/efficient turbine cooling design is one of the key technologies.Thin-wall turbine blade is widely considered to be a potential blade cooling structure,since it can reduce the thermal resistance between hot gas and coolant and increases the heat exchange efficiency.In the present study,we focused on unique geometries of Thin –wall cooling blades and extracted the key issues of the internal cooling and film cooling.The heat transfer and flow mechanisms of these typical structures are studied by means of experimental and numerical methods.In the present study,the convective and conjugate heat transfer characteristics of an impingement array with a short impingement distance and the narrow pinfin array were investigated.The short impingement distance reduces the massflow rate of the upstream jet rows and intensifies the crossflow effect.The heat transfer performance of an inclined impingement array(≤40°)is quite similar to that of a normal impingement array.A new correlation in predicting the heat transfer coefficient of an impingement array with low impingement distance was proposed and validated.A new variable is raised to evaluate the cooling uniformity of impingment array.Decreasing the target wall thickness results in increasing overall cooling efficiency and decreasing temperature uniformity.There also exists a certain point,beyond which increasing the coolant mass flow rate leads to a marginal increase of cooling efficiency.The thermal performance of film cooling with varied length-to-diameter ratio was investigated experimentally and numerically under flat-plate and cascade conditions.It was found that the extremely short L/D hole accelerates the dissipation of kidney vortex and significantly increases the film effectiveness,the short L/D hole strengthens the kidney vortex and decreases the film effectiveness,and the long L/D hole weakens the kidney vortex and increase the film effectiveness.The flow mechanism is that the extremely short L/D hole has a high in-hole turbulence intensity that accelerates the dissipation of kidney vortex,the short L/D hole megers the in-hole kidney vortex with the mainstream K-H shear vortex to form the mainstream kidney vortex,and the K-H shear vortex evolves into the mainstream kidney vortex for the long hole.Based on the heat transfer and fluid dynamics of cylindrical hole,a method was proposed to optimize fan-shaped holes with a short L/D by changing the hole entrance shape and expanding the hole exit area.The optimized short L/D fan-shaped holes were validated to produce high overall heat transfer performance.Combining internal cooling and film cooling work,the convective heat transfer performance of impingement-effusion double wall structure was investigated.The effets of wall thickness and injection dierection were quantitatively illustrated in terms of adiabatic film effectiveness and heat transfer coefficient.For forward injection,reducing the effusion plate thickness promotes the jet lift-off and intensifies the boundary layer disturbance,which results in decreasing adiabatic film effectiveness and heat transfer coefficient.For backward injection,it intensifies the jet-crossflow interaction and suppresses the jet lift-off,leading to increased adiabatic film effectiveness,slightly increased heat transfer coefficient,and decreased net heat flux reduction.Furthermore,the cooling contributions of impingement-only,film-only,pinfin,and impingement-film strucutres to the impingement-pinfin-effusion unit were quantitatively evaluated through conjugate heat transfer measurements.It was pointed out that,from a view of conjugate heat transfer,decreasing the wall thickness favorably increases the overall cooling efficiency of double wall cooling structures.It was also pointed out that the double wall cooling structure should be investigated with conjugate heat transfer method.The results of the present study provide the foundation for the efficient cooling design of turbine blades for the next generation of gas turbines.