Research On Flow Mechanism And Shock Control Method In Transonic Turbine

Turbine is one of the important components of high-end products made by modern machinery such as aero-engine,marine gas turbine,ground heavy-duty gas turbine,marine low-speed turbocharger,etc.Its performance has a decisive role in the stability and safety of the whole machine.The technology of modern turbines is developing towards increasing the inlet temperature of turbines and reducing the number of stages.The inevitable result of the reduction of turbine stages is an increase in expansion ratio.Therefore,the development of large expansion ratio and transonic turbines is an urgent problem to be solved.However,the transonic turbine will increase the Mach number level,generate a shock phenomenon and then generate an unavoidable shock loss,which will reduce the aerodynamic performance of the turbine.In summary,research on the internal flow mechanism and shock control methods of transonic turbines is an important means to improve the aerodynamic performance of transonic turbines,and it is of great significance to guide the aerodynamic design of transonic turbines.First,the blade shape of a certain transsonic turbine is selected as the research object,and a combination of CFD numerical simulation and aerodynamic performance experiments is used to conduct an in-depth study of the internal and trailing flow conditions of the transonic turbine.The transonic turbine is obtained.Internal and trailing edge shock waves,shock wave and wake interference,shock wave and boundary layer interference distribution,etc.,provide new design ideas for the development of low shock wave loss profiles.In view of the above-mentioned flow characteristics inside the transonic turbine,through the mathematical analysis of the transonic blade curvature,a transonic blade design concept based on a mathematical polynomial model is proposed to ensure that the curvature at any point on the profile is smooth and continuous to compensate for the traditional The limitation of the leaf-type curvature adjustment further facilitates the approximation of the curvature distribution to the objective function.At the same time,the scientific validity of the mathematical model is verified by applying transonic blades.Then,a systematic and comprehensive study is conducted on the effects of transonic pharyngeal larynx position,the curvature of the posterior suction surface of the larynx larynx,the curvature of the vertebral pressure surface,and the radius of the trailing edge on the trailing edge shock.A specific method to reduce shock loss is proposed:(1)The cross-sonic turbine cascade channel in this paper uses a zoom form with an expansion ratio of 1.11,which can weaken the inner tail positive shock at the trailing edge of the cascade.Oblique shock,the overall shock intensity is reduced;(2)the blade’s suction surface throat is followed by a "buffer segment + subsequent straight blade back" to slow down the airflow velocity in front of the positive shock wave,which reduces the Mach number level,Weaken the intensity of the positive shock wave and the intensity of the oblique shock wave on the suction surface;(3)The curvature of the pressure surface of the blade is slightly increased to realize the idea of "load backward" of the blade.The strong tail expansion wave weakens the inner tail positive shock wave,but its The interference of the oblique shock and the positive shock of the outer tail cannot be ignored;(4)The intensity of the shock at the trailing edge of the airfoil decreases as the trailing edge radius decreases.The pursuit of weakening shock waves ignores cooling,structural strength and other factors.In order to explore the characteristics of the shock control method under variable operating conditions,a wide-range simulation of the blade shape is performed.A transonic turbine blade with the best aerodynamic performance can be obtained in the design conditions or a range slightly larger than the design conditions.Finally,the mechanism of shock waves in the three-dimensional space of transonic turbines is explored,and the specific method of reducing shock losses described above is applied to analyze the improvement of three-dimensional flow fields inside transonic turbines.In addition,by using the static leaf center of gravity stacking line as the rotation axis to rotate the static leaf counterclockwise,the shock condition of the trailing edge of the stationary blade and the influence of the angle of attack on the shock at the trailing edge of the moving blade were investigated.The research results are as follows:(1)By increasing the curvature of the static blade pressure surface to adjust the reaction degree distribution of the turbine stage,reducing the reaction degree below 20% of the leaf height and increasing the reaction degree above 20% of the leaf height can reduce The expansion of the airflow inside the stationary blade further reduces the shock loss at the trailing edge.Increasing the expansion of the airflow in the upper half of the moving blade causes its shock loss to increase slightly,but the overall aerodynamic efficiency of the turbine stage is increased by 0.5 percentage points;(2)Rotating the stationary blade counterclockwise,the cascade throat of the stationary blade moves forward,which increases the expansion of the airflow in the stationary blade flow path,thereby increasing the shock loss at the trailing edge,and increasing the forward attack angle of the leading edge of the moving blade,which can weaken The intensity of the shock wave at its trailing edge can cause eddy currents at the maximum thickness.