Research On The Influence Of Flow Passage Form On Aerodynamic Performance Of Large Steam Turbine Low Pressure Units

This paper mainly studies the influence of the low-pressure flow pattern of large steam turbines on the aerodynamic performance,determines the control method and control parameters suitable for the optimal flow shape of 1200mm/1500 mm ultra-long blades,and completes the choice of flow shape and advanced blade shape.Research on the influence law of aerodynamic performance of long blades.In order to study the influence of the flow shape on the aerodynamic performance of the cascade,four types of typical end wall profiles,such as equal pressure gradient,equal speed gradient,quintic curve and witozinsky urve,are designed based on the axial and axial constraints of static and dynamic blades.And the four expansion angles of 8 degrees,15 degrees,20 degrees and 25 degrees are selected to match the upper wall profile,and the numerical simulation is carried out to explore the aerodynamic performance of the blades under different end wall profiles,and comparative analysis is carried out.In this paper,the flow field of the cascade under the original line is studied.The pressure gradient and the secondary flow loss mechanism in the final cascade are analyzed.The evolution of the vortex structure in the original cascade and the root and middle of the stationary blade are captured.The velocity field characteristics at supersonic speed understand the high loss region and shock structure in the cascade.By controlling the geometric parameters of the meridian line,the control of equal speed gradient,equal pressure gradient and joint gradient can be realized,so that the radial pressure gradient in the end region of the flow field can be controlled and adjusted to optimize the internal flow field of the cascade and improve the overall aerodynamic performance.After the modification,the inlet and internal flow conditions of the cascade are improved,and the lateral pressure gradient at the top of the cascade is reduced,which improves the separation of the diffuser flow at the final stage.Compared with the original line,the total outlet pressure loss is significantly reduced while the outlet airflow angle is more evenly distributed along the leaf height,and the shock intensity at the root of the vane is reduced.With the increase of the expansion angle under the same type of end wall type,the internal pressure gradient of the cascade is fluctuated greatly,the shock intensity is obviously enhanced,and the flow is deteriorated.The results show that the choice of leaf shape has a significant effect on the cascade flow,and the post-loading leaf type and the positive-bending leaf are the main features of the leaf type in this paper.The rear loading of the airfoil reduces the length of the diffuser section and the positively curved blade facilitates the flow of low energy fluid to the middle of the cascade.The pressure distribution along the blade height after the positive bending of the blade is generally C-shaped.In addition,the positively curved blade distributes the load evenly along the blade height,and also equalizes the outlet airflow angle.Through the exploration of various aerodynamic parameters,it is found that the equal speed gradient type end wall profile has better comprehensive performance when the expansion angle is lower than 20 degrees,and the internal loss of the cascade is small.The witozinsky curve end wall profile under the large expansion angle The reaction degree distribution and the top secondary flow phenomenon can be weakened and the performance is good.Therefore,an equal pressure gradient type end wall can be selected at a small expansion angle,and a witozinsky curve should be selected under a large expansion angle.In practice,a joint design can be used to select a specific profile for a particular location to improve aerodynamic performance.