Investigation On Aerodynamic Design Method Of Megawatts Variable Geometry Turbine With Wide Operating Conditions

Gas turbines are applied to more and more equipment because of their superior performance,as the application scenarios become more complex,the requirements for their working condition adjustment performance are gradually increasing,and variable cycle engines using variable geometry turbine technology can achieve these performance requirements.At present,the working conditions of variable geometry turbines studied at home and abroad are concentrated in the range of small rotation angles,there is almost no research on the coupling selection rules of the end wall parameters,airfoil parameters and shaft parameters of variable geometry turbines spanning the entire flow range,and the turbines studied are mainly used in medium and large gas turbines such as aeroengines and ship gas turbines,while there are relatively few studies on variable geometry turbines for small gas turbines.Therefore,studying the design method of the variable geometry turbine in the small-sized megawatt-class gas turbine can lay a technical foundation for the design and adjustment of the megawatt-class gas turbine in wide operating conditions.First of all,using self-programming combined with numerical simulation software to generate the data set of the research object,and based on the support vector machine model,the proxy model of flow rate and airflow angle is constructed,comparing the predicted results of the surrogate model with the numerical simulation results,it is found that the surrogate model can accurately predict the relationship between the guide vane installation angle and the cascade flow and guide vane outlet airflow angle;the variable geometry turbine cascade with a consistency greater than 1 has a wider flow adjustment range and a more stable outlet angle adjustment performance.Secondly,combined with the geometrical characteristics of the spherical end wall of the small-sized turbine,the modified design of the spherical end wall of the studied power turbine was completed,and the full working condition adjustment of the adjustable guide vane was realized,preliminary study of the radial balance equation in the spherical end wall,and try to get the blade twist law applicable to the spherical flow channel,the selection rules of the parameters of the adjustable guide vane shaft under the geometric constraints of the spherical end wall are studied.The results show that the smaller the forward angle of the spherical end wall,the smaller the flow loss,and the blades with orthogonal design can also reduce the loss;the spherical end wall medium circulation blade is actually an equal α blade;increasing the coverage of the shaft of the cascade and reducing the consistency of the cascade can reduce the leakage area of the gap.Finally,based on the modified turbine with a spherical end wall,its wide-range regulation performance from the minimum flow rate to the maximum flow rate is studied,and on the basis of the original geometry,the model of the rotating shaft and part of the gap is added to study the influence of the part of the gap in the spherical end wall of the blade on the performance of the turbine during the rotation of the blade.The research shows that when the cascade is opened,the existence of the gap will increase the flow rate and shaft torque,and it will be the opposite when the cascade is closed,and the variation range of the two is mainly affected by the width of the gap;the existence of the gap will increase the loss in the guide vane,and the increase of the loss is mainly affected by the consistency of the shaft;the larger the projected area of the gap,the greater the flow effect brought by the gap.The design method of the spherical end wall and the selection rules of the shaft parameters obtained in this paper can provide a certain reference for the optimal design of small gas turbines under wide operating conditions.