Suppression of Secondary Flows in a Turbine Nozzle with Controlled Stacking Shape and Exit Circulation by 3D Inverse Design Method

For the axial turbine stage, the design of circulation RVθ distribution between the nozzle and blade has an important effect on the stage performance, because it determines the work distribution in the blade, the stage reaction and the twisting shape of the blade.  This paper describes the new method of full 3D inverse design method in which the blade geometry can be determined by specified distributions of circulation (RVθ) and blade thickness.  In this 3D inverse design method, span wise work distribution of the turbine stage is controlled specifying the RVθ distribution of the nozzle exit.  In this design procedure RVθ distribution at the nozzle exit and 3D stacking condition are both controlled by 3d inverse design so as to suppress the nozzle secondary flows effectively.  The desirable RVθ distribution and 3d stacking shape with were obtained by the 3D inverse method were confirmed by Dawes 3D Navier-Stokes analysis.  The results shows that the secondary loss is reduced when the design RVθ at the mid span is set larger compared to that near the end wall.  In addition to the control of the RVθ distribution, 3D stacking shape is very simple compared to a conventional bowed type stacking. Moreover when this stacking shape is used, span wise distribution of work does not change from the design condition unlike the case of conventional bowed shape stacking shape.  The results of single stage performance the conducted using an air turbine facility show an improvement in efficiency compared to the 2d design stage and prove viability of the 3d inverse design of axial turbine blades.

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