Investigation Of Quasi Three-dimensional Aerodynamic Design Method For Long Blade Of Low-pressure Turbine

Energy conservation and emission reduction has been the trend nowadays, which putsforward higher aerodynamic performance requirements for steam turbine. As the mostimportant part of steam turbine, blade plays the key role in the conversion from energy towork. The efficiency of steam turbine largely depend on the blade design. In this paper,aerodynamic design method for turbine long blade is investigated systematically, and theblade design of three stages of steam turbine has been accomplished. S2meridianthrough-flow design and controlled vortex modeling are achieved by compiling thecomputing program by Fortran. Several flow patterns which are used in the program havealso been discussed. The last stage blades are modeled according to two design schemeswhich differ in the flow pattern. Afterwards the aerodynamic performance comparison of thetwo design schemes can be checked by CFD software.For S2meridian through-flow design, streamline curvature method are adopted to writeS2stream surface computing program which includes the flow velocity, mass and streamlineiterations. The streamline distribution on S2surface can be calculated by the program after acertain triangle of airflow circulation distribution form is given and calculation stations areset between cascade gaps. Obviously, different triangle of airflow will lead to the differenceof S2meridian through-flow. After analyzing the several commonly used kinds of flowpattern, two design schemes with different triangle of airflow distribution can be used in thispaper. Uniform circulation control is used for the last stage of steam turbine in scheme1, andcontrolled-vortex pattern is used for the same stage in scheme2. Besides, uniformcirculation control is also used for the other two stages in both schemes.In the controlled-vortex design program, the unknown coordinate of blade profilecan be calculated. Then each camber line of the blade can be drawn out with obtainedcoordinate r, z,. Thickness distribution is loaded on the camber line and front and trailing edges are modified. The three-dimensional shape of the blade is generated after bladeprofiles on different cross-sections are accumulated. The last stage blades which are got fromthe two schemes are imported to Numeca software for three-dimensional calculation. Theresults show that scheme1has a higher efficiency of about4.5%than scheme2, and theflow field of scheme1is more reasonable and well-distributed.Based on the above work, an aerodynamic design system for steam turbine long bladehas been built. Blade design can be quickly completed in the case that a reasonable flowpattern is given, which is of great significance to turbine factories..