The Influence Of The Relative Motion Of The Turbine Rotor Blade And Casing On The Heat Transfer Ang Cooling Of The Tip

In modern gas turbine,Generally speaking the tip clearance height of rotating blades can reach 2.0% of the cascade height.Due to the gap exists pressure difference on both sides,the leakage flow is usually cased in the gap,the leakage flow has a large impact on the blade tip surface.The blade tip is subjected to high-intensity thermal load caused by high temperature leakage flow.Reasonable blade tip design is great significance for improving the heat transfer performance of the tip and reducing leakage loss caused by leakage flow.In this paper,the heat transfer characteristics of the blade tip in a gas turbine and the influence of the rotor blade rotation on the heat transfer and cooling performance of the casing surface are discussed by numerical calculationFirstly,the physical model of the groove tip and casing of the three-dimensional is established,and the Realizable k-? turbulence model is selected.Using the method of constant numerical calculation to study the flow in the tip passage of the rotor when the rotor is relatively static with the casing.The streamline distribution and static pressure distribution of the flow field in the tip clearance are obtained.The effect of blow ratio on the heat transfer coefficient and cooling efficiency of the blade tip is analyzed.The results show that the heat transfer capacity of the tip is affected by the leakage vortex on the tip surface.Comparing the distribution of static pressure coefficient between the pressure surface and suction surface of the cascade,it is concluded that there is a large pressure stratification on the suction surface due to the existence of the leakage vortex.The leakage vortex forms a separation vortex at the trailing edge of the blade,which increases the static pressure coefficient of both the pressure surface and the suction surface in this area.The cooling holes on the casing can be used to spray the cooling air flow more to the tip surface,thus improving the cooling efficiency of the tip surface.Under the same geometric condition,the larger the blowing ratio is,the higher the film cooling efficiency of the tip is.Secondly,by discussing the cooling efficiency and heat transfer coefficient distribution of the blade tip during linear motion and rotational motion to study the influence of relative movement mode of rotor blade and casing on heat transfer characteristics of the blade tip.The results show that when the blow ratio is constant,the relative motion of the rotor blade and casing increases the heat transfer coefficient of the blade tip and improves the heat transfer capacity of the blade tip.When the rotor rotates,it will generate coriolis force and centrifugal force and coaxial force.These two forces have no obvious effect on the film cooling efficiencyon the tip of the blade.Finally,on the basis of rotor blade rotating,the flow field around casing and the heat transfer performance and cooling efficiency of casing surface will be discussed by changing blowing ratio,rotor speed and casing spacing.The results show that when the rotor blade is rotating,the centrifugal force acts on the fluid,so it will affect the flow of the flow field near the casing.As the rotation speed of rotor blades increased,the number of Nu on the surface of the casing was reduced,and the rotation speed increased by 100 rpm,the average value decreased by0.57%,and the cooling efficiency decreased by 0.67% on average.Because of the existence of multiple air holes on the casing surface,the blow ratio to the casing surface is very important.When the blow ratio is high,the average cooling efficiency of the casing surface is low.When the blowing ratio remains constant,the larger the hole spacing in the casing,the smaller the number of Nu on the surface,the lower the heat transfer capacity.