| With the rapid development of science and technology,the performance of gas turbine is gradually improved.The working efficiency of gas turbine is the key index to judge its performance.Increasing the inlet working fluid temperature can improve the efficiency of gas turbine.However,the inlet temperature has far exceeded the maximum temperature that turbine blade materials can bear,so there are many cooling methods,and film cooling is one of them.When the turbine is doing work,film cooling is used to protect the first stage rotor and stator blades,but the cooling fluid will inevitably affect the mainstream flow.The high-speed rotation of the rotor blade determines that this motion is highly unsteady,and this unsteady characteristic will aggravate the complexity of the flow field in the dynamic-static interference.The transport of upstream stator wake is one of the key factors leading to unsteady flow.The wake makes the free flow have unstable speed and temperature,which in turn affects the distribution of cooling flow field in the lower moving blade channel and the heat transfer on the surface of moving blade.Therefore,it is of great significance to explore the unsteady wake for the design and improvement of blade cooling system.In this paper,the numerical simulation method is used to investigate the influence of the wake of the stationary blade with air-cooled structure on the flow field and heat transfer of the lower moving blade,and to establish a reference for the optimal design of the turbine.Commercial CFX software and k-ω turbulence model are used for unsteady numerical simulation.Firstly,the influence of the wake of the stationary blade on the heat transfer and flow characteristics of the moving blade under the dynamic-static interference is studied.From the temperature field and vorticity field,the action law of the wake on the surface of the lower moving blade is obtained.The results show that the wake on the suction side develops and declines earlier than that on the pressure side,and the wake in adjacent cycles will influence each other.The wake on the pressure side in the previous cycle will affect the wake on the suction side in the next cycle.Under the wake effect,the distribution of heat transfer coefficient on the pressure surface is more uniform than that on the suction surface.The axial positions of the peak heat transfer coefficients at the top,middle and root sections are different.The heat transfer coefficients of the three blade heights are larger at the leading edge,and decrease after passing through the leading edge.The second peak heat transfer occurs between the stagnation area of the suction surface and the stop line of the trailing edge,and the interaction between the tip leakage vortex and the wake will promote the heat transfer.Near the leading edge,the wake completely reacted with the leading edge channel vortex at 3/4T,and after that,the wake was not enough to overcome the channel vortex,and the vortex volume in the channel increased.Secondly,the heat transfer law of stationary blade wake to moving blade under the influence of rotating speed,mass-flow ratio and mainstream turbulence is explored,and the mechanism is analyzed.The influence of wake on the cooling efficiency,temperature,heat transfer coefficient and Nusselt number of the rotor blade surface is analyzed from the heat transfer point of view.From the point of view of flow characteristics,the distribution of cross-section vorticity of moving blade,Q criterion in moving blade channel,the distribution of vorticity at the interface between rotor and stator,and the change of turbulent kinetic energy on the surface of moving blade with time are discussed.The results show that when the rotating speed is between 7500 rpm and8000rpm,the convective heat transfer effect on the rotor blade surface increases with the increasing of rotating speed,and the vorticity in the channel is generated from the blade root to the blade tip.When the rotating speed is between 8000 rpm and 8500 rpm,with the increase of rotating speed,the inhibition of wake on vortex pair decreases,and the vorticity in the channel increases,and it is concentrated in the middle part of the blade,which makes the heat transfer effect worse.The mass-flow ratio is between 2.1% and 2.7%.With the increase of mass-flow ratio,the effect of wake on cooling fluid is enhanced,the cooling efficiency is improved,the vorticity in the moving blade channel increases,and the heat transfer effect decreases.The mass-flow ratio is between 2.7% and 3.1%.With the increase of mass-flow ratio,the cooling efficiency decreases,the vorticity decreases and the heat transfer coefficient increases.Under the condition of 1%mainstream turbulence,the mixing of mainstream and cooling gas is weak,the strength of the opposite vortex pair in the moving blade channel is weak,and the heat transfer coefficient is large.Under the condition of 5% mainstream turbulence,the surface disturbance of the moving blade is severe,the vorticity has a strong effect on the strength,the wake has a weak effect,and the heat transfer coefficient is small.Under the condition of 10% mainstream turbulence,the mainstream turbulence is large,which is not conducive to the full mixing of mainstream and cooling gas.The vortex pair in the moving blade channel is weak,the vortex suppression effect of the wake is enhanced,and the heat transfer coefficient is large.Finally,nine orthogonal simulation schemes with three factors and three levels are established,and the influence of the three factors on the average cooling efficiency of the lower moving blade surface is compared and analyzed,and the best cooling scheme is determined.The results show that the primary and secondary relationship of the three factors on the surface cooling efficiency of moving blades is: mass-flow ratio > rotating speed > mainstream turbulence.The joint action of influencing factors will affect the flow state in the moving blade channel.Therefore,reasonable parameter setting is very helpful to improve the aerodynamic performance of gas turbine. |
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